Article

Big Bang 6Li nucleosynthesis studied deep underground (LUNA collaboration)

January 2017
Astroparticle Physics 89

DOI:10.1016/j.astropartphys.2017.01.007

Authors:

Michael Anders

M. Aliotta

University of Edinburgh

Show all 37 authorsHide

The correct prediction of the abundances of the light nuclides produced during the epoch of Big Bang Nucleosynthesis (BBN) is one of the main topics of modern cosmology. For many of the nuclear reactions that are relevant for this epoch, direct experimental cross section data are available, ushering the so-called “age of precision”. The present work addresses an exception to this current status: the ²H(α, γ)⁶Li reaction that controls ⁶Li production in the Big Bang. Recent controversial observations of ⁶Li in metal-poor stars have heightened the interest in understanding primordial ⁶Li production. If confirmed, these observations would lead to a second cosmological lithium problem, in addition to the well-known ⁷Li problem. In the present work, the direct experimental cross section data on ²H(α, γ)⁶Li in the BBN energy range are reported. The measurement has been performed deep underground at the LUNA (Laboratory for Underground Nuclear Astrophysics) 400 kV accelerator in the Laboratori Nazionali del Gran Sasso, Italy. The cross section has been directly measured at the energies of interest for Big Bang Nucleosynthesis for the first time, at 80, 93, 120, and 133 keV. Based on the new data, the ²H(α, γ)⁶Li thermonuclear reaction rate has been derived. Our rate is even lower than previously reported, thus increasing the discrepancy between predicted Big Bang ⁶Li abundance and the amount of primordial ⁶Li inferred from observations.

LUNA: Status and Prospects

Preprint

Jul 2017

The essential ingredients of nuclear astrophysics are the thermonuclear reactions which shape the life and death of stars and which are responsible for the synthesis of the chemical elements in the Universe. Deep underground in the Gran Sasso Laboratory the cross sections of the key reactions responsible for the hydrogen burning in stars have been measured with two accelerators of 50 and 400 kV voltage right down to the energies of astrophysical interest. As a matter of fact, the main advantage of the underground laboratory is the reduction of the background. Such a reduction has allowed, for the first time, to measure relevant cross sections at the Gamow energy. The qualifying features of underground nuclear astrophysics are exhaustively reviewed before discussing the current LUNA program which is mainly devoted to the study of the Big-Bang nucleosynthesis and of the synthesis of the light elements in AGB stars and classical novae. The main results obtained during the study of reactions relevant to the Sun are also reviewed and their influence on our understanding of the properties of the neutrino, of the Sun and of the Universe itself is discussed. Finally, the future of LUNA during the next decade is outlined. It will be mainly focused on the study of the nuclear burning stages after hydrogen burning: helium and carbon burning. All this will be accomplished thanks to a new 3.5 MV accelerator able to deliver high current beams of proton, helium and carbon which will start running under Gran Sasso in 2019. In particular, we will discuss the first phase of the scientific case of the 3.5 MV accelerator focused on the study of

^{12}

C+

^{12}

C and of the two reactions which generate free neutrons inside stars:

^{13}

\alpha

,n)

^{16}

O and

^{22}

Ne(

\alpha

,n)

^{25}

Mg.

The d --a Radiative Capture Process Reaction Rate with Three-Body Forces

Article

Feb 2023

Nuclear reaction theory, such as deuteron-alpha radiative capture, has been an essential part of developing nuclear physics. This reaction is the only process that leads to the production of 6 Li. The deuteron-alpha radiative capture reaction has been investigated under the framework of Effective Field Theory, up to next to leading order (NLO). In this study, alpha particles were considered structureless and the Coulomb effects were assumed as a Coulomb correction for E 1 and E 2 electric multipole transitions, up to NLO. By inserting three-body forces, the scattering amplitude was computed at the initial state of the deuteron-alpha P-wave for the sum of both multipole transitions E 1 and E 2. Two of the low-energy photonuclear observables, including the astrophysical S-factor and reaction rate of deuteron-alpha radiative capture reaction, are calculated. The calculated photonuclear observables are in satisfactory agreement with the other theoretical methods and the available experimental data, with energies relevant to Big-Bang Nucleosynthesis.

The d-α Radiative Capture Process Reaction Rate with Three-Body Forces

Article

Dec 2022

Nuclear reaction theory, such as deuteron-alpha radiative capture, has been an essential part of developing nuclear physics. This reaction is the only process that leads to the production of 6Li. The deuteron-alpha radiative capture reaction has been investigated under the framework of Effective Field Theory, up to next to leading order (NLO). In this study, alpha particles were considered structureless and the Coulomb effects were assumed as a Coulomb correction for E1 and E2 electric multipole transitions, up to NLO. By inserting three-body forces, the scattering amplitude was computed at the initial state of the deuteron-alpha P-wave for the sum of both multipole transitions E1 and E2. Two of the low-energy photonuclear observables, including the astrophysical S-factor and reaction rate of deuteron-alpha radiative capture reaction, are calculated. The calculated photonuclear observables are in satisfactory agreement with the other theoretical methods and the available experimental data, with energies relevant to Big-Bang Nucleosynthesis.

Li-6 Breakup and Formation at Astrophysical Energies

Article

Feb 2021

The main components of nuclear fusion processes that occur in stars are the radiative capture and its inverse reaction, during helium transforms into heavier elements. The deuteron-alpha radiative capture and the reactions are studied using Effective Field Theory (EFT). The scattering amplitude for the initial P-wave states of deuteron-alpha for the sum of and transition are found, up to next to leading order(NLO). Furthermore, the photodisintegration rate of the reaction is calculated. The obtained results are in good agreement with the available experimental data and those of other theoretical models, at astrophysical energies.

Determination of the asymptotic normalization coefficient (nuclear vertex constant) for α + d →6Li from the new direct measured d(α,γ)6Li data and its implication for extrapolating the d(α,γ)6Li astrophysical S factor at Big Bang energies

Article

Jan 2019

The results of the analysis of the new experimental astrophysical S factors [Formula: see text] [D. Trezzi et al., Astropart. Phys. 89, 57 (2017)] and those measured earlier [R. G. Robertson et al., Phys. Rev. Lett. 47, 1867 (1981)] for the nuclear-astrophysical [Formula: see text] reaction directly measured at extremely low energies [Formula: see text], which is derived within the modified two-body potential method, are presented. New estimates and their uncertainties have been obtained for values of the asymptotic normalization coefficient for [Formula: see text] and for the direct astrophysical [Formula: see text] factors at Big Bang energies.

LUNA: Status and prospects

Article

Jul 2017
PROG PART NUCL PHYS

The essential ingredients of nuclear astrophysics are the thermonuclear reactions which shape the life and death of stars and which are responsible for the synthesis of the chemical elements in the Universe. Deep underground in the Gran Sasso Laboratory the cross sections of the key reactions responsible for the hydrogen burning in stars have been measured with two accelerators of 50 and 400 kV voltage right down to the energies of astrophysical interest. As a matter of fact, the main advantage of the underground laboratory is the reduction of the background. Such a reduction has allowed, for the first time, to measure relevant cross sections at the Gamow energy. The qualifying features of underground nuclear astrophysics are exhaustively reviewed before discussing the current LUNA program which is mainly devoted to the study of the Big-Bang nucleosynthesis and of the synthesis of the light elements in AGB stars and classical novae. The main results obtained during the study of reactions relevant to the Sun are also reviewed and their influence on our understanding of the properties of the neutrino, of the Sun and of the Universe itself is discussed. Finally, the future of LUNA during the next decade is outlined. It will be mainly focused on the study of the nuclear burning stages after hydrogen burning: helium and carbon burning. All this will be accomplished thanks to a new 3.5 MV accelerator able to deliver high current beams of proton, helium and carbon which will start running under Gran Sasso in 2019. In particular, we will discuss the first phase of the scientific program with the 3.5 MV accelerator. Such a program will be focused on the study of

^{12}

C+

^{12}

C and of the two reactions which generate free neutrons inside stars:

^{13}

\alpha

,n)

^{16}

O and

^{22}

Ne(

\alpha

,n)

^{25}

Mg.

New results for the astrophysical S-factor and reaction rate of radiative 3He4He capture

Article

Full-text available

Jun 2017

In the frame of modified potential cluster model based on the classification of orbital states by Young diagrams and revised interaction potential parameters for the bound states of 7Be in 3He4He cluster model with forbidden states the astrophysical S-factor for the radiative capture reaction has been calculated from the 10 keV. Obtained results S(23 keV) = 0.561 keV b reproduce the latest experimental data at 23 keV. Calculated and parametrized reaction rate is compared to some results known in the range of temperatures from 0.05 to 5 T9.

Detailed study of the astrophysical direct capture reaction Li 6 ( p , γ ) Be 7 in a potential model approach

Article

Full-text available

Dec 2023

The astrophysical S factor and reaction rates of the direct capture process Li6(p,γ)Be7 are estimated within a two-body single-channel potential model approach. Nuclear potentials of the Gaussian form in the P3/22 and P1/22 waves are adjusted to reproduce the binding energies and the empirical values of the asymptotic normalization coefficients (ANC) for the Be7(3/2−) ground and Be7(1/2−) excited bound states, respectively. The parameters of the potential in the most important S1/22 scattering channel were fitted to reproduce the empirical phase shifts from the literature and the low-energy astrophysical S factor of the LUNA Collaboration. The obtained results for the astrophysical S factor and the reaction rates are in very good agreement with available experimental data sets. The numerical estimates reproduce not only the absolute values, but also the energy dependence of the S factor and the temperature dependence of the reaction rates of the LUNA Collaboration. The estimated Li/H7 primordial abundance ratio of (4.67±0.04)×10−10 is consistent with recent big bang nucleosynthesis result of (4.72±0.72)×10−10 after the Planck telescope observation.

Theoretical calculation of nuclear reactions of interest for Big Bang Nucleosynthesis

Preprint

Dec 2020

Alex Gnech

Standard Big Bang Nucleosynthesis (BBN) predicts the abundances of the light elements in the early universe. Even if the overall agreement with the experimental data is good, still some discrepancies exist on the relic abundances of

{}^7

Li and

{}^6

Li. In order to exclude or confirm these scenarios, the BBN model needs precise input parameters, in particular the cross-sections of the BBN nuclear reaction network. However, the suppression of the cross-sections due to the Coulomb barrier makes the measurement very difficult and so affected by large systematic errors. Therefore, reliable theoretical calculations result fundamental in order to reduce the uncertainties. In this work we present a theoretical study of two nuclear reactions connected to

{}^6

Li abundance and recently the

\alpha

\rightarrow

{}^6

Li +

\gamma

and the p+

{}^6

\rightarrow

{}^7

Be+

\gamma

radiative captures. For the first reaction we use a so-called ab-initio approach in which we solve the full six-body problem by using realistic nuclear potentials to describe the nucleon interactions. In particular we concentrate on the calculation and characterization of the final state of the reaction, the

{}^6

Li ground state, focusing on the electromagnetic static structure and the quantities relevant from the astrophysical point of view such as the asymptotic normalization coefficient. For doing this we use the Hyperspherical Harmonic approach developed by the Pisa group providing for the first time the possibility of using this approach beyond A = 4 nuclear systems. The second reaction is instead studied by using a two-body cluster approach where the proton and

{}^6

Li are considered as structureless particles. The angular distribution of the emitted photon obtained in this work were used by the LUNA Collaboration to determine the efficiency of the detector used in the measurement of the reaction.

\gamma

-ray Spectroscopy of

^{85}

Se Produced in

^{232}

Th Fission

Article

Jan 2020

On Introducing Charge-Symmetry-Breaking Terms to Nuclear Energy Density Functionals

Article

Jan 2020

The Charge-Symmetry-Breaking (CSB) character of the nucleon–nucleon interaction is well-established. This work presents two different ways of introducing such effects into a nuclear Energy Density Functional (EDF). CSB terms are either coming from the effective theory expansion or are derived from electromagnetic mixing of rho0 and omega mesons. These terms are then introduced to Skyrme and Quark–Meson-Coupling EDFs, respectively.

Measurement of the

\gamma

Decay from the Energy Region of the Pygmy Dipole States Excited in the

^{208}

(p,p'\gamma )

Reaction at CCB

Article

Jan 2020

The muon intensity in the Felsenkeller shallow underground laboratory

Preprint

Full-text available

Apr 2019

The muon intensity and angular distribution in the shallow-underground laboratory Felsenkeller in Dresden, Germany have been studied using a portable muon detector based on the close cathode chamber design. Data has been taken at four positions in Felsenkeller tunnels VIII and IX, where a new 5 MV underground ion accelerator is being installed, and in addition at four positions in Felsenkeller tunnel IV, which hosts a low-radioactivity counting facility. At each of the eight positions studied, seven different orientations of the detector were used to compile a map of the upper hemisphere with 0.85{\deg} angular resolution. The muon intensity is found to be suppressed by a factor of 40 due to the 45 m thick rock overburden, corresponding to 140 meters water equivalent. The angular data are matched by two different simulations taking into account the known geodetic features of the terrain: First, simply by determining the cutoff energy using the projected slant depth in rock and the known muon energy spectrum, and second, in a Geant4 simulation propagating the muons through a column of rock equal to the known slant depth. The present data are instrumental for studying muon-induced effects at these depths and also in the planning of an active veto for accelerator-based underground nuclear astrophysics experiments.

Direct measurement of nuclear cross-section of astrophysical interest: Results and perspectives

Article

Full-text available

Mar 2018
INT J MOD PHYS A

Stellar evolution and nucleosynthesis are interconnected by a wide network of nuclear reactions: the study of such connection is usually known as nuclear astrophysics. The main task of this discipline is the determination of nuclear cross-section and hence of the reaction rate in different scenarios, i.e. from the synthesis of a few very light isotopes just after the Big Bang to the heavy element production in the violent explosive end of massive stars. The experimental determination of reaction cross-section at the astrophysical relevant energies is extremely difficult, sometime impossible, due to the Coulomb repulsion between the interacting nuclei which turns out in cross-section values down to the fbar level. To overcome these obstacles, several experimental approaches have been developed and the adopted techniques can be roughly divided into two categories, i.e. direct and indirect methods. In this review paper, the general problem of nuclear astrophysics is introduced and discussed from the point of view of experimental approach. We focus on direct methods and in particular on the features of low-background experiments performed at underground laboratory facilities. The present knowledge of reactions involved in the Big Bang and stellar hydrogen-burning scenarios is discussed as well as the ongoing projects aiming to investigate mainly the helium- and carbon-burning phases. Worldwide, a new generation of experiment in the MeV range is in the design phase or at the very first steps and decisive progresses are expected to come in the next years.

Cosmological lithium problem solution in accelerator experiment

Article

Jan 2025
Russ Phys J

G.N. Dudkin

The cosmological lithium problem is a serious problem for understanding the early Universe, which casts doubt on the Big Bang nucleosynthesis (BBN) model. The problem is that the data on the abundance of 6Li and 7Li elements obtained from astronomic observations and in the BBN model are too different, based on the data on all nuclear reactions in which these elements produce (or destroy). Astronomy continues to improve the optical instrumentation in order to achieve better resolution and efficiency. In nuclear physics, cross sections of all reactions resulting in the lithium nucleus production (or destruction) are being clarified. This work presents a brief review of related theoretical calculations and experimental data. Experimental results are presented in the laboratory coordinate system for 3H(3He, γ)6Li reaction at an energy of 38 keV, first obtained using the Hall ion accelerator in National Research Tomsk Polytechnic University, Tomsk, Russia. S-factor calculated for 3H(3He, γ)6Li S = 0.15 ± 0.03 keV·b reaction is inconsistent either with approximation of the experimental data obtained at high energies, or theoretical calculations. It is also inconsistent with assumptions about a new physics hidden in this reaction. Our work discusses the possibility of solving the cosmological lithium problem via reactions with light neutron clusters.

Novel approach to infer the H 2 ( p , γ ) He 3 angular distribution: Experimental results and comparison with theoretical calculations

Article

Sep 2024

The D(p,γ)He3 reaction, where ‘D’ denotes ‘H2’, is of primary importance in cosmology and nuclear physics since it offers a unique opportunity to test predictions based on the description of nuclear interactions. We present a novel approach to extract the angular distribution of the photons emitted by the D(p,γ)He3 reaction inferred from the shape of the experimental γ spectra. The measurement was performed in the Gran Sasso Laboratories by the LUNA collaboration. By using a HPGe detector faced to an extended deuterium gas target, it was possible to derive the angular distribution in the 30–280 keV kinetic energy range and to compare the results with recent ab initio predictions.

Laboratory for Underground Nuclear Astrophysics

Article

Full-text available

Jun 2024

Denise Piatti

Nuclear reactions shape the life and death of stars and they produce most of the chemical elements in the Universe. The cross section, at the energy of the Gamow peak, is a crucial ingredient to improve our knowledge on stellar and Universe chemical evolution. Its low value at stellar energies prevent direct measurements in earth-based laboratories. In recent years low energy data significantly improved thanks to underground facilities, pioneered by the Laboratory for Underground Nuclear Astrophysycs (LUNA). LUNA started its activity in 1991 with a 50 kV electrostatic accelerator installed under Gran Sasso, which is a natural shield against cosmic rays ensuring a ultra low background environment. LUNA early activity was dedicated to reactions relevant to the Sun, and then, thanks to the installation of a new accelerator (LUNA400), it focused on the study of the Big Bang Nucleosynthesis (BBN) and of the CNO, NeNa and MgAl cycles. LUNA is now facing the next steps, helium and carbon burning, thanks to the new 3.5MV accelerator, which has just started its activity at the Bellotti Facility of LNGS. The accelerator provides hydrogen, helium and carbon beams, allowing to study the reactions that shape both the evolution of massive stars to their final fate and the synthesis of most of the elements in the Universe.

Study of the 7Be(d,3He)6Li* reaction at 5 MeV/u

Article

Full-text available

Apr 2024
PHYS LETT B

The measurement of the 7Be(𝑑,3He)6Li* transfer cross section at 5 MeV/u is carried out. The population of the 2.186 MeV excited state of 6 Li in this reaction channel is observed for the first time. The experimental angular distributions have been analyzed in the finite range DWBA and coupled-channel frameworks. The effect of the 7Be(𝑑,3He)6Li reaction on both the 6Li and 7Li abundances are investigated at the relevant big-bang nucleosynthesis energies. The excitation function is calculated by TALYS and normalized to the experimental data. The 𝑆 factor of the (𝑑,3 He) channel from the present work is about 50% lower than existing data at nearby energies. At big-bang energies, the 𝑆 factor is about three orders of magnitude smaller than that of the (𝑑, 𝑝)channel. The (𝑑,3He) reaction rate is found to have a less than 0.1% effect on the 6,7 Li abundances.

ЯДЕРНАЯ СТРУКТУРА И ДИНАМИКА СИСТЕМЫ

{}^{\textbf{4}}

He +

{}^{\textbf{2}}

H В МИКРОСКОПИЧЕСКОМ КЛАСТЕРНОМ ПОДХОДЕ

Article

Mar 2023

А. С. Соловьев

Шестинуклонная ядерная система

{}^{4}\textrm{He}+^{2}

H исследуется в рамках микроскопического кластерного подхода, сформулированного в осцилляторном представлении. Вычисляются полный и парциальные астрофизические S -факторы радиационного захвата

{}^{2}

(\alpha,\gamma)^{6}

Li, фазы упругого рассеяния

{}^{2}

(\alpha,\alpha)^{2}

H и основные свойства ядра

{}^{6}

Li. Полученные результаты находятся в хорошем согласии с доступными экспериментальными данными.

Nuclear Physics Mid Term Plan at LNGS

Article

Full-text available

Mar 2024

The Istituto Nazionale di Fisica Nucleare—Laboratori Nazionali del Gran Sasso (LNGS) is one of the largest underground physics laboratory, a very peculiar environment suited for experiments in Astroparticle Physics, Nuclear Physics and Fundamental Symmetries. The newly established Bellotti Ion Beam facility represents a major advance in the possibilities of studying nuclear processes in an underground environment. A workshop was organized at LNGS in the framework of the Nuclear Physics Mid Term Plan in Italy, an initiative of the Nuclear Physics Division of the Instituto Nazionale di Fisica Nucleare to discuss the opportunities that will be possible to study in the near future by employing state-of-the-art detection systems. In this report, a detailed discussion of the outcome of the workshop is presented.

To the Nature of Dark Matter

Article

Nov 2023

G.N. Dudkin

Effects of three-nucleon forces in the d(α, γ ) 6 Li reaction

Article

Jul 2023
PRAMANA-J PHYS

Nuclear reaction theory is important, especially at low energies, as are predictions of the characteristics of the heaviest nuclei, including processes for laboratory synthesis, and realistic prediction of many theoretical models of nuclear reaction. The deuteron–alpha radiative capture process is important in the evolution of nuclear physics processes. This reaction is one of the most important processes that happens in stars when helium is transformed into heavier elements. The

d(\alpha ,\gamma )^6

Li reaction has been studied using effective field theory (EFT), up to next to leading order (NLO). The effects of three-body forces and Coulomb interaction between charged particles were examined assuming that

\alpha

-particles had no structure. The scattering amplitude is calculated for the sum of the multipole transitions

E_1

and

E_2

at the starting state of the deuteron–

\alpha

P-wave. The reported findings are consistent with the experimental data and previous theoretical computations, with energy relevant to Big-Bang Nucleosynthesis (BBN).

Nuclear Structure and Dynamics of the \boldsymbol{{}^{4}\mbox{He}+^{2}}H System within a Microscopic Cluster Approach

Article

Apr 2023

A. S. Solovyev

Measuring the cross section of the N 15 ( α , γ ) 19 F reaction using a single-fluid bubble chamber

Article

Mar 2023

N15(α,γ)19F is believed to be the primary means of stellar nucleosynthesis of fluorine. Here, we present the use of a single-fluid bubble chamber to measure the cross section of the time-inverse photodissociation reaction. The method benefits from a luminosity increase of several orders of magnitude due to the use of a thicker liquid target—when compared to thin films or gas targets—and from the reciprocity theorem. We discuss the results of an experiment at the Thomas Jefferson National Accelerator Facility, where the cross section of the photodisintegration process F19(γ, α)N15 was measured by bombarding a superheated fluid of C3F8 with bremsstrahlung γ rays produced by impinging a 4–5.5 MeV electron beam on a Cu radiator. From the photodissociation yield the cross section was extracted by performing a convolution with a Monte Carlo–generated γ-ray beam spectrum. The measurement produced a cross section that was then time inverted using the reciprocity theorem. The cross section for the N15(α,γ)F19 reaction was determined down to a value in the range of hundreds of picobarns. With further improvements of the experimental setup the technique could potentially push cross section measurements down to the single picobarn range.

Measuring the cross section of the

^{15}

\alpha

\gamma

)

^{19}

F reaction using a single-fluid bubble chamber

Preprint

Full-text available

Feb 2023

{15}N(\alpha,\gamma)^{19}

F is believed to be the primary means of stellar nucleosynthesis of fluorine. Here we present the use of a single-fluid bubble chamber to measure the cross section of the time-inverse photo-dissociation reaction. The method benefits from a luminosity increase of several orders of magnitude due to the use of a thicker liquid target -- when compared to thin films or gas targets -- and from the reciprocity theorem. We discuss the results of an experiment at the Thomas Jefferson National Accelerator Facility, where the cross section of the photodisintegration process

^{19}F(\gamma, \alpha)^{15}

N was measured by bombarding a superheated fluid of C

_3F_8

with bremsstrahlung

\gamma

-rays produced by impinging a 4 - 5.5 MeV electron beam on a Cu radiator. From the photodissociation yield the cross section was extracted by performing a convolution with a Monte Carlo-generated

\gamma

-ray beam spectrum. The measurement produced a cross section that was then time inverted using the reciprocity theorem. The cross section for the

^{15}N(\alpha,\gamma)^{19}$F reaction was determined down to a value in the range of hundreds of picobarns. With further improvements of the experimental setup the technique could potentially push cross section measurements down to the single picobarn range.

Elastic, inelastic, and one-neutron transfer angular distributions of Li 6 + Sn 120 at energies near the Coulomb barrier

Article

Jul 2022

The elastic scattering, first 2+ and 3− target inelastic excitation and one neutron pickup angular distributions for the Li6+Sn120 reaction have been measured for three bombarding energies (19, 24, and 27 MeV). Data have been analyzed through coupled-channel calculations and continuum-discretized coupled-channel calculations extended to include target excitation. In general, both theoretical models give a reasonable description of the data. For the elastic and inelastic angular distributions taken at Elab=24 and 27 MeV, the continuum-discretized coupled-channel results are slightly better in comparison to the coupled-channel predictions. For the elastic and inelastic angular distributions measured at Elab=19 MeV, the effect of the break-up channel seems to be quite important. At this energy, the elastic scattering data can be well explained by coupled channel calculations in which a strong absorptive optical imaginary potential is considered. In particular, the continuum-discretized coupled-channel theoretical results provided the best description of the 3− excitation data at 19 MeV.

Ab Initio Prediction of the He 4 ( d , γ ) Li 6 Big Bang Radiative Capture

Article

Jul 2022

The rate at which helium (^{4}He) and deuterium (d) fuse together to produce lithium-6 (^{6}Li) and a γ ray, ^{4}He(d,γ)^{6}Li, is a critical puzzle piece in resolving the discrepancy between big bang predictions and astronomical observations for the primordial abundance of ^{6}Li. The accurate determination of this radiative capture rate requires the quantitative and predictive description of the fusion probability across the big bang energy window (30 keV≲E≲400 keV), where measurements are hindered by low counting rates. We present first-principle (or, ab initio) predictions of the ^{4}He(d,γ)^{6}Li astrophysical S factor using validated nucleon-nucleon and three-nucleon interactions derived within the framework of chiral effective field theory. By employing the ab initio no-core shell model with continuum to describe ^{4}He-d scattering dynamics and bound ^{6}Li product on an equal footing, we accurately and consistently determine the contributions of the main electromagnetic transitions driving the radiative capture process. Our results reveal an enhancement of the capture probability below 100 keV owing to previously neglected magnetic dipole (M1) transitions and reduce by an average factor of 7 the uncertainty of the thermonuclear capture rate between 0.002 and 2 GK.

Microscopic description of the H ( α , γ ) 2 Li 6 radiative capture reaction

Article

Jul 2022

A. S. Solovyev

The H(α,γ)2Li6 radiative capture responsible for the Li6 production during the big-bang nucleosynthesis is comprehensively studied within a microscopic approach. The approach implements microscopically clustering aspects of nuclear structure and dynamics in an oscillator-basis representation. The total astrophysical S factor of the reaction is calculated. All allowed partial electric quadrupole and magnetic dipole transitions between the He4+H2 continuum and the Li6 ground state are considered in the standard long-wavelength limit. Isospin-forbidden electric dipole transitions are taken into account in two ways. The first method is based on the expression for the electric dipole operator at the leading order of the long-wavelength approximation with the usage of the exact-mass prescription. In the second method, this operator is written at the first order beyond the leading-order approximation. Contributions of the transitions are compared to each other. The He4+H2 nuclear phase shifts for the initial channels of the considered reaction are computed. Important properties of the Li6 nucleus, such as the breakup threshold, the asymptotic normalization constants, and the electric quadrupole moment are also described. Deformation effects and their manifestations in Li6 are discussed. The obtained results are shown to be in good agreement with a large set of experimental data.

Exploring Stars in Underground Laboratories: Challenges and Solutions

Article

Jul 2022

For millennia, mankind has been fascinated by the marvel of the starry night sky. Yet, a proper scientific understanding of how stars form, shine, and die is a relatively recent achievement, made possible by the interplay of different disciplines as well as by significant technological, theoretical, and observational progress. We now know that stars are sustained by nuclear fusion reactions and are the furnaces where all chemical elements continue to be forged out of primordial hydrogen and helium. Studying these reactions in terrestrial laboratories presents serious challenges and often requires developing ingenious instrumentation and detection techniques. Here, we reveal how some of the major breakthroughs in our quest to unveil the inner workings of stars have come from the most unexpected of places: deep underground. As we celebrate 30 years of activity at the first underground laboratory for nuclear astrophysics, LUNA, we review some of the key milestones and anticipate future opportunities for further advances both at LUNA and at other underground laboratories worldwide. Expected final online publication date for the Annual Review of Nuclear and Particle Science, Volume 72 is September 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Charge Form Factor and radii of Li-6

Article

Feb 2021

In the present work, aimed to investigate the nuclear structure of 6Li, the charge form factor and the charge radius of 6Li have been calculated. Within the framework of Effective Field Theory (EFT) at low energy, the charge form factor and the root-mean-square charge radius of 6Li calculated in the zero-momentum-transfer limit based on cluster structure of 6Li. The results of this model for the rootmean- square charge radius of 6Li at low energies are comparable with the available experimental data and those of other theoretical models.

Low-energy studies for Nuclear Astrophysics (both above- and underground)

Article

Full-text available

Dec 2020

C. G. Bruno

Experimental investigation of nuclear properties of interest in low-energy pose astrophysical scenarios such as quiescent burning stars and classical novae face interesting challenges. Cross-sections are often too low for measurement on the surface of the Earth, and short-lived radioactive elements play a key role in a number stellar scenarios. In this short review, I will mention two experimental approaches to this challenge, namely the possibility to carry out measurements underground at the LUNA accelerator (LNGS, Italy) and a novel approach that employs storage rings pioneered at GSI Laboratory (Germany).

Underground experimental study finds no evidence of low-energy resonance in the 6Li(p,γ)7Be reaction

Article

Nov 2020

The astrophysical Li6(p,γ)Be7 reaction occurs during Big Bang nucleosynthesis and the pre-main sequence and main sequence phases of stellar evolution. The low-energy trend of its cross section remains uncertain, since different measurements have provided conflicting results. A recent experiment reported a resonancelike structure at center-of-mass energy 195 keV, associated to a positive-parity state of Be7. The existence of such resonance is still a matter of debate. We report a new measurement of the Li6(p,γ)Be7 cross section performed at the Laboratory for Underground Nuclear Astrophysics, covering the center-of-mass energy range E=60–350 keV. Our results rule out the existence of low-energy resonances. The astrophysical S-factor varies smoothly with energy, in agreement with theoretical models.

Reaction Rate calculation of d(α, γ)6Li process at low energy in framework of Effective Field Theory

Article

Jan 2021
NEW ASTRON

Comparative study of the direct α + d → 6Li + γ astrophysical capture reaction in few-body models

Article

Apr 2020
NUCL PHYS A

Underground Nuclear Astrophysics: pushing direct measurements toward the Gamow window

Article

Full-text available

Jan 2020

Paolo Prati

The aim of experimental nuclear astrophysics is to provide information on the nuclear processes involved in astrophysical scenarios at the relevant energy range. However, the measurement of the cross section of nuclear reactions at low energies present formidable difficulties due to the very low reaction rates often overwhelmed by the background. Several approaches have been proposed and exploited to overcome such severe obstacles: in such frame, the idea to install a low energy - high intensity ion accelerator deep underground, to gain high luminosity while reducing the cosmic ray background, brought more than 25 years ago, to the pilot LUNA experiment. LUNA stands for Laboratory for Underground Nuclear Astrophysics: in the cave under the Gran Sasso mountain (in Italy) first a 50 kV and then a 400 kV single-ended accelerator for protons and alphas were deployed and produced plenty of data mainly on reactions of the H-burning phase in stars. Recently, similar facilities have been installed and/or proposed in other underground laboratories in US and China. LUNA as well is going to make a big step forward, with a new machine in the MV range which will be able to provide intense beams of protons, alphas and carbon ions. The rationale of underground nuclear astrophysics will be presented together with the last updates on the ongoing research programs.

Few-Nucleon Reactions of Astrophysical Interest: A Review

Chapter

Aug 2019

We review the theoretical studies of the proton-deuteron and -deuteron radiative captures. The two theoretical frameworks used, the ab-initio and the cluster approach, respectively, are also briefly discussed.

Influence of orthogonalization procedure on astrophysical S-factor for the direct α + d →6Li + γ capture process in a three-body model

Article

Full-text available

Jan 2019

The astrophysical S-factor for the direct [Formula: see text] capture reaction is calculated in a three-body model based on the hyperspherical Lagrange-mesh method. A sensitivity of the E1 and E2 astrophysical S-factors to the orthogonalization method of Pauli forbidden states in the three-body system is studied. It is found that the method of orthogonalising pseudopotentials (OPP) yields larger isotriplet ([Formula: see text]) components than the supersymmetric transformation (SUSY) procedure. The E1 astrophysical S-factor shows the same energy dependence in both cases, but strongly different absolute values. At the same time, the E2 S-factor does not depend on the orthogonalization procedure. As a result, the OPP method yields a very good description of the direct data of the LUNA collaboration at low energies, while the SUSY transformation strongly underestimates the LUNA data.

Underground Nuclear Astrophysics: Present and future of the LUNA experiment

Article

Full-text available

May 2019

Carlo Gustavino

The evolution of celestial bodies is regulated by gravitation and thermonuclear reaction rates, while the Big Bang nucleosynthesis is the result of nuclear processes in a rapidly expanding Universe. The LUNA Collaboration has shown that, by exploiting the ultra low background achievable deep underground, it is possible to study the relevant nuclear processes down to the nucleosynthesis energy inside stars and during the first minutes of Universe. In this paper the main results of LUNA are overviewed, as well as the scientific program the forthcoming 3.5 MV underground accelerator.

The muon intensity in the Felsenkeller shallow underground laboratory

Article

Apr 2019
ASTROPART PHYS

The muon intensity and angular distribution in the shallow-underground laboratory Felsenkeller in Dresden, Germany have been studied using a portable muon detector based on the close cathode chamber design. Data has been taken at four positions in Felsenkeller tunnels VIII and IX, where a new 5 MV underground ion accelerator is being installed, and in addition at four positions in Felsenkeller tunnel IV, which hosts a low-radioactivity counting facility. At each of the eight positions studied, seven different orientations of the detector were used to compile a map of the upper hemisphere with 0.85 ∘ angular resolution. The muon intensity is found to be suppressed by a factor of 40 due to the 45 m thick rock overburden, corresponding to 140 m water equivalent. The angular data are matched by two different simulations taking into account the known geodetic features of the terrain: First, simply by determining the cutoff energy using the projected slant depth in rock and the known muon energy spectrum, and second, in a Geant4 simulation propagating the muons through a column of rock equal to the known slant depth. The present data are instrumental for studying muon-induced effects at these depths and also in the planning of an active veto for accelerator-based underground nuclear astrophysics experiments.

Radiative 3He(2H,γ)5Li capture at astrophysical energy and its role in accumulation of 6Li at the BBN

Article

Apr 2019
NUCL PHYS A

Big Bang Nucleosynthesis (BBN) relevance reactions ³ He( ² H, γ) ⁵ Li, ³ H( ³ He, γ) ⁶ Li, and ⁵ Li(n, γ) ⁶ Li as a key to approach for scenario of ⁶ Li formation are treated. The rates of reaction for these processes are analyzed. Comparison of the reactions rates and the prevalence of light elements leads to the assumption that the two-step process ² H + ³ He → ⁵ Li + γ and n + ⁵ Li → ⁶ Li + γ can make a significant contribution to the formation of ⁶ Li at the BBN at least at temperatures T 9 of the order of unity. Calculations of the total cross sections, astrophysical S-factor, and reaction rates have been performed for ³ He( ² H, γ) ⁵ Li radiative capture within the modified potential cluster model with forbidden states, which follow from the classification of the orbital cluster states according to Young diagrams. Numerical data and corresponding parametrizations cover the energy range up to 5 MeV and temperature range T 9 < 10. An updated compilation of detailed data for the reaction ³ He( ² H, γ) ⁵ Li are presented.

New Theoretical Results for Radiative 3 H(p, γ) 4 He, γ 3 He( 2 H, γ) 5 Li, 4 He( 2 H, γ) 6 Li, γ 4 He( 3 H, γ) 7 Li, and 4 He( 3 He, γ) 7 Be Captures at Astrophysical Energies

Article

Full-text available

Apr 2019
INT J MOD PHYS E

We have studied the proton capture reaction ³ H(p,γ) ⁴ He. It plays a role in the nucleosynthesis of primordial elements in the early Universe leading to the prestellar formation of ⁴ He nuclei. All results of our researches and more new data from works show that the contribution of the ³ H(p,γ) ⁴ He capture reaction into the processes of primordial nucleosynthesis is relatively small. However, it makes sense to consider this process for making the picture complete for the formation of prestellar ⁴ He and clearing of mechanisms of this reaction. Furthermore, we have considered the ³ He( ² H,γ) ⁵ Li reaction in the low energy. This reaction also forms part of the nucleosynthesis chain of the processes occurring in the early stages of formation of stable stars. They are possible candidates for overcoming the well-known problem of the A = 5 gap in the synthesis of light elements in the primordial Universe. Continuing the study, we have considered the radiative capture ⁴ He( ³ He,γ) ⁷ Be at superlow energies, which has a undeniable interest for nuclear astrophysics, since it takes part in the proton-proton fusion chain, and new experimental data on the astrophysical S-factors of this process at energies down to 90 and 23keV and data on the radiative capture reaction ⁴ He( ³ H,γ)7Li down to 50keV appeared recently. Moreover, radiative capture reactions ⁴ He( ³ He,γ) ⁷ Be and ⁴ He( ² H,γ) ⁶ Li may have played a certain role in prestellar nucleosynthesis after the Big Bang, when the temperature of the Universe decreased to the value of 0.3T9.

The

\alpha + d \to {}^{6}{\rm{Li}} + \gamma

reaction and the second Lithium puzzle

Article

Full-text available

Jan 2019

A brief review on the second Lithium problem is presented. In particular the focus is on the α+d→L6i+γ

\alpha + d \to {}^{6}{\rm{Li}} + \gamma

reaction and on the details of the different α−d

\alpha - d

potential models and the theoretical approximations done during the evaluation of the astrophysical S-factor.

Theoretical study of the α + d → Li 6 + γ astrophysical capture process in a three-body model. II. Reaction rates and primordial abundance

Article

Nov 2018

The astrophysical S factor and reaction rate of the direct capture process α+d→Li6+γ, as well as the abundance of the Li6 element, are estimated in a three-body model. The initial state is factorized into the deuteron bound state and the α+d scattering state. The final nucleus Li6(1+) is described as a three-body bound state α+n+p in the hyperspherical Lagrange-mesh method. Corrections to the asymptotics of the overlap integral in the S and D waves have been done for the E2 S factor. The isospin forbidden E1 S factor is calculated from the initial isosinglet states to the small isotriplet components of the final Li6(1+) bound state. It is shown that the three-body model is able to reproduce the newest experimental data of the LUNA Collaboration for the astrophysical S factor and the reaction rates within the experimental error bars. The estimated Li6/H abundance ratio of (0.67±0.01)×10−14 is in a very good agreement with the recent measurement (0.80±0.18)×10−14 of the LUNA Collaboration.

Potential cluster calculations for the astrophysical S-factor and reaction rate of the radiative 3He(4He,γ)7Be capture

Article

Sep 2018
INDIAN J PHYS

In the frame of a modified potential cluster model based on the classification of orbital states according to Young diagrams and revised interaction potential parameters for the bound states of ⁷Be in the ³He⁴He cluster model with forbidden states, the astrophysical S-factor for the radiative capture reaction ³He(⁴He,γ)⁷Be has been calculated from 10 keV. The result obtained, S(23 keV) = 0.561 keV·b, reproduces the latest experimental data at 23 keV. The calculated and parametrized reaction rate is compared with some known results in the range of temperatures from 0.05 to 5 T9.

Nuclear astrophysics at Gran Sasso Laboratory: the LUNA experiment

Article

Full-text available

Jan 2018

Francesca Cavanna

LUNA is an experimental approach for the study of nuclear fusion reactions based on an underground accelerator laboratory. Aim of the experiment is the direct measurement of the cross section of nuclear reactions relevant for stellar and primordial nucleosynthesis. In the following the latest results and the future goals will be presented.

New Results for Astrophysical S-Factors of Radiative 3Не4Не, 3Н4Не, and 2Н4Не Capture

Article

Full-text available

Nov 2017

Sergey B. Dubovichenko

Within the framework of the modified potential cluster model with classification of orbital states according to the Young tableaux and revised potential parameters for the ³He⁴He, ³H⁴He, and ²H⁴He cluster channels of the nuclei ⁷Be, ⁷Li, and ⁶Li, astrophysical S-factors of processes of radiative ³He⁴He capture from 20 keV, ³H⁴Hе capture from 10 keV, and ²Н⁴Не capture from 5 keV are considered. On the basis of the obtained results, the rates of all of the considered reactions are calculated in the temperature range from 0.05 to 5 T9 and a comparison with the results of other authors is carried out. © 2017 Springer Science+Business Media, LLC, part of Springer Nature

α + d → Li 6 + γ astrophysical S factor and its implications for Big Bang nucleosynthesis

Article

Oct 2017

The α+d→6Li+γ radiative capture is studied in order to predict the Li6 primordial abundance. Within a two-body framework, the α particle and the deuteron are considered the structureless constituents of Li6. Five α+d potentials are used to solve the two-body problem: four of them are taken from the literature, only one having also a tensor component. A fifth model is here constructed in order to reproduce, besides the Li6 static properties as binding energy, magnetic dipole, and electric quadrupole moments, also the S-state asymptotic normalization coefficient (ANC). The two-body bound and scattering problem is solved with different techniques, in order to minimize the numerical uncertainty of the present results. The long-wavelength approximation is used, and therefore only the electric dipole and quadrupole operators are retained. The astrophysical S factor is found to be significantly sensitive to the ANC, but in all the cases in good agreement with the available experimental data. The theoretical uncertainty has been estimated of the order of few percent when the potentials which reproduce the ANC are considered, but increases up to ≃20% when all five potential models are retained. The effect of this S-factor prediction on the Li6 primordial abundance is studied, using the public code PArthENoPE. For the five models considered here we find Li6/H=(0.9–1.8)×10−14, with the baryon density parameter in the 3-σ range of Planck 2015 analysis, Ωbh2=0.02226±0.00023.

Monte Carlo uncertainty of the He 3 ( α , γ ) Be 7 reaction rate

Article

Full-text available

Sep 2014

Background: The He3(α,γ)Be7 reaction is of critical importance in determining the flux of solar neutrinos through the pp-II and pp-III chains. For this reason and others, the description of the cross section and its extrapolation towards low-energy has always been a matter of intense debate. While large systematic differences have been present in the past, several recent measurements are all in excellent statistical agreement. Purpose: The convergence of the recent individual experimental measurements of the He3(α,γ)Be7 reaction prompts a global analysis of the reaction data. From the combined data, a more precise estimate of the low-energy cross section can be determined. Results: A global R-matrix fit is used to describe the He3(α,γ)Be7 data as well as scattering data over a similar energy range. The R-matrix fit is then subjected to a Monte Carlo analysis to extract the uncertainties on the cross section and corresponding reaction rate. Conclusion: By combining several recent measurements of the He3(α,γ)Be7 reaction, the combined data yield a zero energy S factor of S(0)=0.542±0.011(MCfit)±0.006(model)-0.011+0.019(phaseshifts) keV b. This gives a total uncertainty in S(0) of +0.023/-0.017 keV b.

First Direct Measurement of the 2H(α;γ)6Li Cross Section at Big Bang Energies and the Primordial Lithium Problem

Article

Full-text available

Jul 2014
PHYS REV LETT

Recent observations of 6Li in metal poor stars suggest a large production of this isotope during big bang nucleosynthesis (BBN). In standard BBN calculations, the 2H(α;γ)6Li reaction dominates 6Li production. This reaction has never been measured inside the BBN energy region because its cross section drops exponentially at low energy and because the electric dipole transition is strongly suppressed for the isoscalar particles 2H and α at energies below the Coulomb barrier. Indirect measurements using the Coulomb dissociation of 6Li only give upper limits owing to the dominance of nuclear breakup processes. Here, we report on the results of the first measurement of the 2H(α;γ)6Li cross section at big bang energies. The experiment was performed deep underground at the LUNA 400 kV accelerator in Gran Sasso, Italy. The primordial 6Li/7Li isotopic abundance ratio has been determined to be (1.5 +/- 0.3) × 10−5, from our experimental data and standard BBN theory. The much higher 6Li/7Li values reported for halo stars will likely require a nonstandard physics explanation, as discussed in the literature.

S-factor measurement of the 2H(alpha,gamma)6Li reaction at energies relevant for Big-Bang ucleosynthesis

Thesis

Full-text available

Jun 2013

Michael Anders

For about 20 years now, observations of 6Li in several old metal-poor stars inside the halo of our galaxy have been reported, which are largely independent of the star’s metallicity, and which point to a possible primordial origin. The observations exceed the predictions of the Standard Big-Bang Nucleosynthesis model by a factor of 500. In the relevant energy range, no directly measured S-factors were available yet for the main production reaction 2H(α,γ)6Li, while different theoretical estimations have an uncertainty of up to two orders of magnitude. The very small cross section in the picobarn range has been measured with a deuterium gas target at the LUNA acceler- ator (Laboratory for Underground Nuclear Astrophysics), located deep underground inside Laboratori Nazionali del Gran Sasso in Italy. A beam-induced, neutron-caused background in the γ-detector occurred which had to be analyzed carefully and subtracted in an appropriate way, to finally infer the weak signal of the reaction. For this purpose, a method to parameterize the Compton background has been developed. The results are a contribution to the discussion about the accuracy of the recent 6Li observations, and to the question if it is necessary to include new physics into the Standard Big-Bang Nucleosynthesis model.

Standard big bang nucleosynthesis and primordial CNO Abundances after Planck

Article

Full-text available

Oct 2014
J COSMOL ASTROPART P

Primordial or big bang nucleosynthesis (BBN) is one of the three historical strong evidences for the big bang model. The recent results by the Planck satellite mission have slightly changed the estimate of the baryonic density compared to the previous WMAP analysis. This article updates the BBN predictions for the light elements using the cosmological parameters determined by Planck, as well as an improvement of the nuclear network and new spectroscopic observations. The error bars of the primordial D/H abundance are narrower than previously and there is a slight lowering of the primordial Li/H abundance. However, this lithium value still remains typically 3 times larger than its observed spectroscopic abundance in halo stars of the Galaxy. In addition, for the first time, we provide confidence limits for the production of 6Li, 9Be, 11B and CNO, resulting from our extensive Monte Carlo calculation with our extended network. A specific focus is cast on CNO primordial production. Considering uncertainties on the nuclear rates around the CNO formation, we obtain CNO/H ~ (5-30)x10^{-15}. We further improve this estimate by analysing correlations between yields and reaction rates and identifyed new infuential reaction rates. These uncertain rates, if simultaneously varied could lead to a significant increase of CNO production: CNO/H~10^{-13}. This result is important for the study of population III star formation during the dark ages.

Simultaneous solution to the Li6 and Li7 big bang nucleosynthesis problems from a long-lived negatively charged leptonic particle

Article

Full-text available

Dec 2007

The Li6 abundance observed in metal-poor halo stars exhibits a plateau similar to that for Li7 suggesting a primordial origin. However, the observed abundance of Li6 is a factor of 103 larger and that of Li7 is a factor of 3 lower than the abundances predicted in the standard big bang when the baryon-to-photon ratio is fixed by Wilkinson microwave anisotropy probe. Here we show that both of these abundance anomalies can be explained by the existence of a long-lived massive, negatively charged leptonic particle during nucleosynthesis. Such particles would capture onto the synthesized nuclei thereby reducing the reaction Coulomb barriers and opening new transfer reaction possibilities, and catalyzing a second round of big bang nucleosynthesis. This novel solution to both of the Li problems can be achieved with or without the additional effects of stellar destruction.

NACRE II: An update of the NACRE compilation of charged-particle-induced thermonuclear reaction rates for nuclei with mass number A > 16

Article

Full-text available

Oct 2013
NUCL PHYS A

An update of the NACRE compilation [Angulo et al., Nucl. Phys. A 656 (1999) 3] is presented. This new compilation, referred to as NACRE II, reports thermonuclear reaction rates for 34 charged-particle induced, two-body exoergic reactions on nuclides with mass number

A<16

, of which fifteen are particle-transfer reactions and the rest radiative capture reactions. When compared with NACRE, NACRE II features in particular (1) the addition to the experimental data collected in NACRE of those reported later, preferentially in the major journals of the field by early 2013, and (2) the adoption of potential models as the primary tool for extrapolation to very low energies of astrophysical S-factors, with a systematic evaluation of uncertainties. As in NACRE, the rates are presented in tabular form for temperatures in the

10^{6}

\simeq\leq

\leq

10^{10}

K range. Along with the 'adopted' rates, their low and high limits are provided. The new rates are available in electronic form as part of the Brussels Library (BRUSLIB) of nuclear data. The NACRE II rates also supersede the previous NACRE rates in the Nuclear Network Generator (NETGEN) for astrophysics. [http://www.astro.ulb.ac.be/databases.html.]

A compilation of charged-particle induced thermonuclear reaction rates

Article

Full-text available

Aug 1999
NUCL PHYS A

Low-energy cross section data for 86 charged-particle induced reactions involving light (1 ⩽ Z ⩽ 14), mostly stable, nuclei are compiled. The corresponding Maxwellian-averaged thermonuclear reaction rates of relevance in astrophysical plasmas at temperatures in the range from 106 K to 1010 K are calculated. These evaluations assume either that the target nuclei are in their ground state, or that the target states are thermally populated following a Maxwell-Boltzmann distribution, except in some cases involving isomeric states.Adopted values complemented with lower and upper limits of the rates are presented in tabular form. Analytical approximations to the adopted rates, as well as to the inverse/direct rate ratios, are provided.

The LUNA II accelerator

Article

Full-text available

Jul 2003
NUCL INSTRUM METH A

A second high current accelerator of 400 kV has been installed at the underground laboratory of Gran Sasso, called LUNA II. We describe this new facility as well as measurements of the proton beam characteristics: absolute energy, energy spread, and long-term energy stability. The absolute energy was determined to a precision of ±300 eV at Ep=130- 400 keV using the energy of the capture γ-ray transition of 12C( p, γ) 13N as well as resonance energies at Ep=309- 389 keV of 23Na( p, γ) 24Mg, 26Mg( p, γ) 27Al, and 25Mg( p, γ) 26Al. The resonance studies led to a proton energy spread of better than 100 eV and a long-term energy stability of 5 eV per hour.

New high S/N observations of the (6Li) /(7) Li blend in HD 84937 and two other metal-poor stars

Article

Full-text available

Jan 1999

High S/N ratio spectra have been obtained at CFHT at a spectral resolution of 100 000 for HD 84397 and two other metal poor stars. For HD 84 937, the S/N of 650 per pixel was obtained, yielding Li-6/Li-7 = 0.052 with a sigma of 0.019. The Li-6 abundance is compared with recent models of formation of light elements LiBeB. This comparison shows that Li-6 is either undepleted or only moderatly depleted in the star of interest. The depletion of Li-7 in this star is estimated to be less than 0.1 dex. The abundance of lithium on the Spite plateau accordingly can be takien as representative of the cosmological primordial lithium. See the joint paper astro-ph/9811327. Comment: 11 pages 10 figures to be published in Astronomy and Astrophysics

Reexamination of the astrophysical S factor for the α+ d→^{6} Li+ γ reaction

Article

Full-text available

May 2011

Recently, a new measurement of the 6Li (150 A MeV)dissociation in the field of 208Pb has been reported [ Hammache and et al. Phys. Rev. C 82 065803 (2010)] to study the radiative capture α+d→6Li+γ process. However, the dominance of the nuclear breakup over the Coulomb one prevented the information about the α+d→6Li+γ process from being obtained from the breakup data. The astrophysical S24(E) factor has been calculated within the α-d two-body potential model with potentials determined from the fits to the α-d elastic scattering phase shifts. However, the scattering phase shift, according to the theorem of the inverse scattering problem, does not provide a unique α-d bound-state potential, which is the most crucial input when calculating the S24(E) astrophysical factor at astrophysical energies. In this work, we emphasize the important role of the asymptotic normalization coefficient (ANC) for 6Li→α+d, which controls the overall normalization of the peripheral α+d→6Li+γ process and is determined by the adopted α-d bound-state potential. Since the potential determined from the elastic scattering data fit is not unique, the same is true for the ANC generated by the adopted potential. However, a unique ANC can be found directly from the elastic scattering phase shift, without invoking intermediate potential, by extrapolation the scattering phase shift to the bound-state pole [ Blokhintsev and et al. Phys. Rev. C 48 2390 (1993)]. We demonstrate that the ANC previously determined from the α-d elastic scattering s-wave phase shift [ Blokhintsev and et al. Phys. Rev. C 48 2390 (1993)], confirmed by ab initio calculations, gives S24(E), which at low energies is about 38% less than the other one reported [ Hammache et al. Phys. Rev. C 82 065803 (2010)]. We recalculate also the reaction rates, which are lower than those obtained in that same study [ Hammache et al. Phys. Rev. C 82 065803 (2010)].

Neutron-induced background by an α-beam incident on a deuterium gas target and its implications for the study of the 2H(α, γ)6Li reaction at LUNA

Article

Full-text available

Jan 2013

The production of the stable isotope Li-6 in standard Big Bang nucleosynthesis has recently attracted much interest. Recent observations in metal-poor stars suggest that a cosmological Li-6 plateau may exist. If true, this plateau would come in addition to the well-known Spite plateau of Li-7 abundances and would point to a predominantly primordial origin of Li-6, contrary to the results of standard Big Bang nucleosynthesis calculations. Therefore, the nuclear physics underlying Big Bang Li-6 production must be revisited. The main production channel for Li-6 in the Big Bang is the 2H(alpha,gamma)6Li reaction. The present work reports on neutron-induced effects in a high-purity germanium detector that were encountered in a new study of this reaction. In the experiment, an {\alpha}-beam from the underground accelerator LUNA in Gran Sasso, Italy, and a windowless deuterium gas target are used. A low neutron flux is induced by energetic deuterons from elastic scattering and, subsequently, the 2H(d,n)3He reaction. Due to the ultra-low laboratory neutron background at LUNA, the effect of this weak flux of 2-3 MeV neutrons on well-shielded high-purity germanium detectors has been studied in detail. Data have been taken at 280 and 400 keV alpha-beam energy and for comparison also using an americium-beryllium neutron source.

Lithium Isotopic Abundances in Metal-poor Halo Stars

Article

Full-text available

Dec 2008

Very high quality spectra of 24 metal-poor halo dwarfs and subgiants have been acquired with ESO's VLT/UVES for the purpose of determining Li isotopic abundances. The derived one-dimensional, non-LTE 7Li abundances from the Li I 670.8 nm line reveal a pronounced dependence on metallicity but with negligible scatter around this trend. Very good agreement is found between the abundances from the Li I 670.8 nm line and the Li I 610.4 nm line. The estimated primordial 7Li abundance is 7Li/H = (1.1-1.5) × 10-10, which is a factor of 3-4 lower than predicted from standard big bang nucleosynthesis with the baryon density inferred from the cosmic microwave background. Interestingly, 6Li is detected in 9 of our 24 stars at the ≥2 σ significance level. Our observations suggest the existence of a 6Li plateau at the level of log ≈ 0.8; however, taking into account predictions for 6Li destruction during the pre-main-sequence evolution tilts the plateau such that the 6Li abundances apparently increase with metallicity. Our most noteworthy result is the detection of 6Li in the very metal-poor star LP 815-43. Such a high 6Li abundance during these early Galactic epochs is very difficult to achieve by Galactic cosmic-ray spallation and α-fusion reactions. It is concluded that both Li isotopes have a pre-Galactic origin. Possible 6Li production channels include protogalactic shocks and late-decaying or annihilating supersymmetric particles during the era of big bang nucleosynthesis. The presence of 6Li limits the possible degree of stellar 7Li depletion and thus sharpens the discrepancy with standard big bang nucleosynthesis.

Observation of interstellar lithium in the low-metallicity Small Magellanic Cloud

Article

Full-text available

Sep 2012
NATURE

The primordial abundances of light elements produced in the standard theory of Big Bang nucleosynthesis (BBN) depend only on the cosmic ratio of baryons to photons, a quantity inferred from observations of the microwave background. The predicted primordial (7)Li abundance is four times that measured in the atmospheres of Galactic halo stars. This discrepancy could be caused by modification of surface lithium abundances during the stars' lifetimes or by physics beyond the Standard Model that affects early nucleosynthesis. The lithium abundance of low-metallicity gas provides an alternative constraint on the primordial abundance and cosmic evolution of lithium that is not susceptible to the in situ modifications that may affect stellar atmospheres. Here we report observations of interstellar (7)Li in the low-metallicity gas of the Small Magellanic Cloud, a nearby galaxy with a quarter the Sun's metallicity. The present-day (7)Li abundance of the Small Magellanic Cloud is nearly equal to the BBN predictions, severely constraining the amount of possible subsequent enrichment of the gas by stellar and cosmic-ray nucleosynthesis. Our measurements can be reconciled with standard BBN with an extremely fine-tuned depletion of stellar Li with metallicity. They are also consistent with non-standard BBN.

Astrophysical S factor of the^{3} He (α, γ)^{7} Be reaction measured at low energy via detection of prompt and delayed γ rays

Article

Full-text available

Jun 2007

Solar neutrino fluxes depend both on astrophysical and on nuclear physics inputs, namely on the cross sections of the reactions responsible for neutrino production inside the Solar core. While the flux of solar 8 B neutrinos has been recently measured at Superkamiokande with a 3.5% uncertainty and a precise measurement of 7 Be neutrino flux is foreseen in the next future, the predicted fluxes are still affected by larger errors. The largest nuclear physics uncertainty to determine the fluxes of 8 B and 7 Be neutrinos comes from the 3 He(α,γ) 7 Be reaction. The uncertainty on its S-factor is due to an average discrepancy in results obtained using two different experimental approaches: the detection of the delayed γ rays from 7 Be decay and the measurement of the prompt γ emission. Here we report on a new high precision experiment performed with both techniques at the same time. Thanks to the low background conditions of the Gran Sasso LUNA accelerator facility, the cross section has been measured at E c.m. = 170, 106, and 93 keV, the latter being the lowest interaction energy ever reached. The S-factors from the two methods do not show any discrepancy within the experimental errors. An extrapolated S(0) = 0.560 ± 0.017 keV barn is obtained. Moreover, branching ratios between the two prompt γ -transitions have been measured with 5–8% accuracy.

Standard Big-Bang Nucleosynthesis up to CNO with an improved extended nuclear network

Article

Full-text available

Jul 2011

Primordial or Big Bang nucleosynthesis (BBN) is one of the three strong evidences for the Big- Bang model together with the expansion of the Universe and the Cosmic Microwave Background radiation. In this study, we improve the standard BBN calculations taking into account new nuclear physics analyses and we enlarge the nuclear network until Sodium. This is, in particular, important to evaluate the primitive value of CNO mass fraction that could affect Population III stellar evolution. For the first time we list the complete network of more than 400 reactions with references to the origin of the rates, including \approx 270 reaction rates calculated using the TALYS code. Together with the cosmological light elements, we calculate the primordial Beryllium, Boron, Carbon, Nitrogen and Oxygen nuclei. We performed a sensitivity study to identify the important reactions for CNO, 9Be and Boron nucleosynthesis. We reevaluated those important reaction rates using experimental data and/or theoretical evaluations. The results are compared with precedent calculations: a primordial Beryllium abundance increase by a factor of 4 compared to its previous evaluation, but we note a stability for B/H and for the CNO/H abundance ratio that remains close to its previous value of 0.7 \times 10-15. On the other hand, the extension of the nuclear network has not changed the 7Li value, so its abundance is still 3-4 times greater than its observed spectroscopic value.

High-energy breakup of 6Li as a tool to study the Big Bang nucleosynthesis reaction 2H(α,γ)6Li

Article

Full-text available

Nov 2010

The recently claimed observations of non-negligible amounts of 6Li in old halo stars have renewed interest in the Big Bang nucleosynthesis (BBN) of 6Li. One important ingredient in the predicted BBN abundance of 6Li is the low-energy 2H(α,γ)6Li cross section. Up to now, the only available experimental result for this cross section showed an almost constant astrophysical S factor below 400 keV, contrary to theoretical expectations. We report on a new measurement of the 2H(α,γ)6Li reaction using the breakup of 6Li at 150 A MeV. Even though we cannot separate experimentally the Coulomb contribution from the nuclear one, we find clear evidence for Coulomb-nuclear interference by analyzing the scattering angular distributions. This is in line with our theoretical description, which indicates a drop of the S24 factor at low energies as predicted also by most other models. Consequently, we find even lower upper limits for the calculated primordial 6Li abundance than before.

Big Bang Nucleosynthesis as a Probe of New Physics

Article

Full-text available

Nov 2010

Big bang nucleosynthesis (BBN), an epoch of primordial nuclear transformations in the expanding Universe, has left an observable imprint in the abundances of light elements. Precision observations of such abundances, combined with high-accuracy predictions, provide a nontrivial test of the hot big bang and probe non-standard cosmological and particle physics scenarios. We give an overview of BBN sensitivity to different classes of new physics: new particle or field degrees of freedom, time-varying couplings, decaying or annihilating massive particles leading to non-thermal processes, and catalysis of BBN by charged relics.

Big Bang Nucleosynthesis and Particle Dark Matter

Article

Full-text available

Oct 2009
NEW J PHYS

We review how our current understanding of the light element synthesis during the Big Bang Nucleosynthesis era may help shed light on the identity of particle dark matter.

Particle Data Group : The Review of Particle Physics

Article

Full-text available

Jul 2002

The PDG is an international collaboration that reviews particle physics and related areas of astrophysics, and compiles/analyzes data on particle properties. The Review of Particle Physics is the most cited publication in particle physics during the last decade. It summarizes most of particle physics: New measurements plus data from previous editions are compiled and evaluated in Particle Listings and Summary Tables. Included are properties of gauge bosons, leptons, quarks, mesons, and baryons, plus searches for hypothetical particles such as Higgs bosons, heavy neutrinos, monopoles, and supersymmetric particles. There are many reviews, tables, and plots on topics such as Standard Model, particle detectors, probability, and statistics.

Activation Measurement of the He3(α,γ)Be7 Cross Section at Low Energy

Article

Full-text available

Oct 2006

The nuclear physics input from the 3He(alpha,gamma)7Be cross section is a major uncertainty in the fluxes of 7Be and 8B neutrinos from the Sun predicted by solar models and in the 7Li abundance obtained in big-bang nucleosynthesis calculations. The present work reports on a new precision experiment using the activation technique at energies directly relevant to big-bang nucleosynthesis. Previously such low energies had been reached experimentally only by the prompt-gamma technique and with inferior precision. Using a windowless gas target, high beam intensity, and low background gamma-counting facilities, the 3He(alpha,gamma)7Be cross section has been determined at 127, 148, and 169 keV center-of-mass energy with a total uncertainty of 4%. The sources of systematic uncertainty are discussed in detail. The present data can be used in big-bang nucleosynthesis calculations and to constrain the extrapolation of the 3He(alpha,gamma)7Be astrophysical S factor to solar energies.

Nuclear Reaction Network for Primordial Nucleosynthesis: a detailed analysis of rates, uncertainties and light nuclei yields

Article

Full-text available

Sep 2004
J COSMOL ASTROPART P

We analyze in details the standard Primordial Nucleosynthesis scenario. In particular we discuss the key theoretical issues which are involved in a detailed prediction of light nuclide abundances, as the weak reaction rates, neutrino decoupling and nuclear rate modeling. We also perform a new analysis of available data on the main nuclear processes entering the nucleosynthesis reaction network, with particular stress on their uncertainties as well as on their role in determining the corresponding uncertainties on light nuclide theoretical estimates. The current status of theoretical versus experimental results for 2H, 3He, 4He and 7Li is then discussed using the determination of the baryon density as obtained from Cosmic Microwave Background anisotropies.

Thermonuclear Reaction Rates, III

Article

Jan 1983
ANNU REV ASTRON ASTR

LUNA data on the 2H(α,γ)6Li reaction and the Big Bang Nucleosynthesis

Article

Jan 2012

Carlo Gustavino

The 2H(α,γ)6Li reaction is the main process responsible for the production of the lithium isotope 6Li in standard Big Bang Nucleosynthesis. Recent observations of lithium isotopic abundances in metal-poor halo stars suggest that there might be a 6Li plateau, similar to the well known Spite plateau of 7Li. This calls for a reinvestigation of the standard production channel for 6Li. The 2H(α,γ)6Li cross section drops steeply at low energy and has never before been studied directly at Big Bang energies. Previous studies using the Coulomb dissociation of 6Li gave only upper limits due to the dominance of nuclear breakup. Exploiting the ultra-low background at the 400 keV LUNA accelerator, located deep underground in Italy's Gran Sasso laboratory, for the first time the reaction has been studied directly at Big Bang energies. The new data and their implications for Big Bang nucleosynthesis will be shown. © Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence.

Constraining Big Bang lithium production with recent solar neutrino data

Article

Jun 2015

The 3He({\alpha},{\gamma})7Be reaction affects not only the production of 7Li in Big Bang nucleosynthesis, but also the fluxes of 7Be and 8B neutrinos from the Sun. This double role is exploited here to constrain the former by the latter. A number of recent experiments on 3He({\alpha},{\gamma})7Be provide precise cross section data at E = 0.5-1.0 MeV center-of-mass energy. However, there is a scarcity of precise data at Big Bang energies, 0.1-0.5 MeV, and below. This problem can be alleviated, based on precisely calibrated 7Be and 8B neutrino fluxes from the Sun that are now available, assuming the neutrino flavour oscillation framework to be correct. These fluxes and the standard solar model are used here to determine the 3He(alpha,gamma)7Be astrophysical S-factor at the solar Gamow peak, S(23+6-5 keV) = 0.548+/-0.054 keVb. This new data point is then included in a re-evaluation of the 3He({\alpha},{\gamma})7Be S-factor at Big Bang energies, following an approach recently developed for this reaction in the context of solar fusion studies. The re-evaluated S-factor curve is then used to re-determine the 3He({\alpha},{\gamma})7Be thermonuclear reaction rate at Big Bang energies. The predicted primordial lithium abundance is 7Li/H = 5.0e-10, far higher than the Spite plateau.

Isotope Spectroscopy

Article

Jan 2014

The measurement of isotopic ratios provides a privileged insight both into nucleosynthesis and into the mechanisms operating in stellar envelopes, such as gravitational settling. In this article, we give a few examples of how isotopic ratios can be determined from high-resolution, high-quality stellar spectra. We consider examples of the lightest elements, H and He, for which the isotopic shifts are very large and easily measurable, and examples of heavier elements for which the determination of isotopic ratios is more difficult. The presence of 6Li in the stellar atmospheres causes a subtle extra depression in the red wing of the 7Li 670.7 nm doublet which can only be detected in spectra of the highest quality. But even with the best spectra, the derived

^6

Li abundance can only be as good as the synthetic spectra used for their interpretation. It is now known that 3D non-LTE modelling of the lithium spectral line profiles is necessary to account properly for the intrinsic line asymmetry, which is produced by convective flows in the atmospheres of cool stars, and can mimic the presence of 6Li. We also discuss briefly the case of the carbon isotopic ratio in metal-poor stars, and provide a new determination of the nickel isotopic ratios in the solar atmosphere.

Astrophysical S factor of 3He(α,γ)7Be

Article

Jun 2013

Background: The 3He(α,γ)7Be reaction is important for the neutrino production in the sun's core and the production of 7Li during big bang nucleosynthesis. The reaction mechanism is characterized by a strong direct capture component and nearby broad unbound resonance levels.Purpose: Recent experiments have opened up a new energy window into the reaction mechanism and it becomes more and more evident that, in order to understand the shape of the S factor, theoretical calculations need to take into account possible resonance contributions from higher energies as well.Method: In the present work, a relatively wide energy window was investigated, Ec.m.=300–1460 keV, by detecting the prompt γ rays from the reaction. An extensive R-matrix analysis was performed, utilizing all modern literature capture data, as well as elastic scattering data, which are important in constraining some R-matrix parameters.Results: The new experimental data agree very well with the modern literature data. The final result from the R-matrix fit gives a zero-energy S factor of S(0)=0.554(20) keV b. A table with the newly calculated reaction rate is given.Conclusions: The simultaneous R-matrix analysis of the 3He(α,γ)7Be and 3He(α,α)3He channels yielded a reliable fit, consistent with all the included experimental data sets. In order to further constrain the reaction rate within the R-matrix framework, additional high-energy capture data, γ-ray angular distributions, and the inclusion of other relevant reaction channels are necessary.

Primordial and Pre-Galactic Origins of the Lithium Isotopes

Article

Mar 2008

There are currently two cosmological lithium problems: compared with predictions from Big Bang Nucleosynthesis and models for Galactic cosmic ray production, the observed 7Li abundance in Galactic halo stars is too low while the 6Li content is too high. Here we report on new Keck/HIRES observations of the two extremely metal-poor stars G064-012 and G064-37, which both show distortions of the Li I 670.8 nm line consistent with a significant (~3sigma) presence of 6Li. If confirmed, these are the lowest metallicity 6Li detections and would suggest a cosmological or pre-Galactic origin for the isotope. Invoking stellar Li depletion to solve the above-mentioned 7Li discrepancy would further increase the inferred initial 6Li abundance by a factor of ~10. Possible 6Li production scenarios are decaying/annihilating supersymmetric particles within the first few minutes of the Big Bang and cosmological cosmic rays from the first stars, although stellar flare production can not be ruled out either. Work still remains, however, before one can unequivocally say that 6Li really has been detected in these and other halo stars, in particular whether convective atmospheric motions and non-LTE line formation can mimic the presence of 6Li in the observed line profiles.

Radiative Î±-capture cross sections from realistic nucleon-nucleon interactions and variational Monte Carlo wave functions

Article

Apr 2001

We report the first calculations of cross sections for the radiative capture reactions Â³H(Î±,Î³)â·Li and Â³He(Î±,Î³)â·Be below 2 MeV that use wave functions derived from realistic nucleon-nucleon interactions by the variational Monte Carlo technique. After examining several small corrections to the dominant E1 operator, we find energy dependences for the low-energy S factors that agree reasonably with experimental measurements. There is no contradiction with the previous theoretical understanding of these processes, but the zero-energy derivative of the Â³H(Î±,Î³)â·Li S factor is smaller than that in most models. While this method can, in principle, predict cross section normalizations, the normalizations of our results are mostly too low.

Observation of the capture reaction Â²H(. cap alpha. ,. gamma. )â¶Li and its role in production of â¶Li in the big bang

Article

Dec 1981

The capture of ..cap alpha.. particles by deuterium has been observed by using a magnetic analysis technique to detect the recoiling â¶Li ions. Measurements of the cross section down to 1 MeV in the center-of-mass system can be interpreted accurately in terms of a direct-capture model, and it is found that production of â¶Li in the big bang is 5 times smaller than has been assumed.

The lithium isotopic ratio in very metal-poor stars

Article

May 2013

Un-evolved, very metal-poor stars are the most important tracers of the cosmic abundance of lithium in the early universe. Combining the standard Big Bang nucleosynthesis model with Galactic production through cosmic ray spallation, these stars at [Fe/H]<-2 are expected to show an undetectably small 6Li/7Li isotopic signature. Evidence to the contrary may necessitate an additional pre-galactic production source or a revision of the standard model of Big Bang nucleosynthesis. We revisit the isotopic analysis of four halo stars, two with claimed 6Li-detections in the literature, to investigate the influence of improved model atmospheres and line formation treatment. For the first time, a combined 3D, NLTE (non-local thermodynamic equilibrium) modelling technique for Li, Na, and Ca lines is utilised to constrain the intrinsic line-broadening and to determine the Li isotopic ratio. We discuss the influence of 3D NLTE effects on line profile shapes and assess the realism of our modelling using the Ca excitation and ionisation balance. By accounting for NLTE line formation in realistic 3D hydrodynamical model atmospheres, we can model the Li resonance line and other neutral lines with a consistency that is superior to LTE, with no need for additional line asymmetry caused by the presence of 6Li. Contrary to the results from 1D and 3D LTE modelling, no star in our sample has a significant 2-sigma detection of the lighter isotope in NLTE. Over a large parameter space, NLTE modelling systematically reduces the best-fit Li isotopic ratios by up to five percentage points. As a bi-product, we also present the first ever 3D NLTE Ca and Na abundances of halo stars, which reveal significant departures from LTE. The observational support for a significant and non-standard 6Li production source in the early universe is substantially weakened by our findings.

Direct capture in the 3^{+} resonance of^{2} H (α, γ)^{6} Li

Article

Sep 1994

The cross section for the capture reaction2H(α,γ)6Li was measured in the energy range of about Eα,lab≊2 MeV corresponding to the 3+ resonance in 6Li at Ex=2186 keV. Calculations in a direct-capture model using double-folded α-d potentials reproduce strength and width of this resonance as well as the nonresonant capture cross section at lower and higher energies.

Influence of long-range effects on low-energy cross sections of He and HeX: The lithium problem

Article

Apr 2012

In this paper, we study the connection between the interaction and the low energy observables, in particular the cross section for He and HeX, the helium nucleus with a heavier particle attached, to explain problems with the observed lithium abundance in the big-bang nucleosynthesis. We treat the processes 4He+2H→6Li+γ and 4HEX−+2H→6Li+X− and primarily focus on the effects of the long-range part of the total potential on the cross section. Our results indicate that relatively small changes in the long-range part of the potential can have a profound affect. Additionally, we compare the relative impacts on the low energy cross section of the Coulomb barrier peak and the long-range part of the interaction. Our results confirm that the long-range potential dominantly influences the low energy observables.

Experimental, computational, and observational analysis of primordial nucleosynthesis

Article

Mar 1993

We present a comprehensive evaluation of the current status of the standard theory of primordial nucleosynthesis, determining the 12 nuclear reactions most important for the production of the light elements and conducting a detailed study of their rates and uncertainties; these are incorporated into a Monte Carlo analysis to evaluate uncertainties in the computed elemental abundances. These predicted abundances are compared with primordial abundances deduced from astronomical observations of the light elements D, He-3, He-4, and Li-7; consistent agreement exists over a narrow range of the baryon-to-photon ratio n, thereby supporting the standard theory of big bang nucleosynthesis. This n range corresponds to a constraint on the baryon density parameter of 0.01-0.09, where the primordial D + He-3 abundance sets the lower bound and the He-4 abundance sets the upper bound. The new reaction rates cause an increase in the upper bound from Li-7 by 40 percent over that determined in previous studies.

The 6Li/7Li ratio in the metal-poor halo dwarfs HD 19445 and HD 84937

Article

Apr 1993

High-resolution high SNR spectra of the Li I 6707 A line in the subdwarfs HD 19445 and HD 84937 have been analyzed for the presence of Li-6. By measurement of the Li I line's wavelength and analysis of its profile, the atmosphere of HD 84937 is shown to have a small amount of Li-6: R = Li-6/Li = 0.05 +/- 0.02. For HD 19445, an upper limit is set of R less than 0.02. The presence of Li-6 in HD 84937 is consistent with the mild depletion of Li-6 predicted by standard (nonrotating) models and the initial presence of Li-6 in the halo produced by (principally) alpha-on-alpha fusion reactions involving the cosmic rays that are required to account for the Be and B observed in subdwarfs. Depletion of Li-6 in the lower mass star HD 19445 is expected to remove the initial Li-6 content and, hence, the absence of Li-6 is expected. If Yale models of rotating subdwarfs are adopted, the predicted severe depletion of Li-6 and the observed survival of Li-6 in HD 84937 have to be reconciled. Four suggestions are made: the rotating models are inapplicable to halo dwarfs, production of Li-6 by cosmic rays has been underestimated, the required high initial Li-6 abundance of the halo was produced prior to the formation of the Galaxy, or the Li-6 was produced in stellar flares.

6Li detection in metal-poor stars: Can 3D model atmospheres solve the second lithium problem?

Article

Jun 2012

The presence of 6Li in the atmospheres of metal-poor halo stars is usually inferred from the detection of a subtle extra depression in the red wing of the 7Li doublet line at 670.8 nm. However, the intrinsic line asymmetry caused by convective flows in the photospheres of cool stars is almost indistinguishable from the asymmetry produced by a weak 6Li blend on a (presumed) symmetric 7Li profile. Previous determinations of the 6Li/ 7Li isotopic ratio based on 1D model atmospheres, ignoring the convection-induced line asymmetry, must therefore be considered as upper limits. By comparing synthetic 1D LTE and 3D non-LTE line profiles of the Li 670.8 nm feature, we quantify the differential effect of the convective line asymmetry on the derived 6Li abundance as a function of effective temperature, gravity, and metallicity. As expected, we find that the asymmetry effect systematically reduces the resulting 6Li/7Li ratios. Depending on the stellar parameters, the 3D-1D offset in 6Li/7Li ranges between -0.005 and -0.020. When this purely theoretical correction is taken into account for the Asplund 2006 sample of stars, the number of significant 6Li detections decreases from 9 to 5 (2 sigma criterion), or from 5 to 2 (3 sigma criterion). We also present preliminary results of a re-analysis of high-resolution, high S/N spectra of individual metal-poor turn-off stars, to see whether the "second Lithium problem" actually disappears when accounting properly for convection and non-LTE line formation in 3D stellar atmospheres. Out of 8 stars, HD84937 seems to be the only significant (2 sigma) detection of 6Li. In view of our results, the existence of a 6Li plateau appears questionable.

PArthENoPE: Public Algorithm Evaluating the Nucleosynthesis of Primordial Elements

Article

Jun 2008
COMPUT PHYS COMMUN

We describe a program for computing the abundances of light elements produced during Big Bang Nucleosynthesis which is publicly available at http://parthenope.na.infn.it/. Starting from nuclear statistical equilibrium conditions the program solves the set of coupled ordinary differential equations, follows the departure from chemical equilibrium of nuclear species, and determines their asymptotic abundances as function of several input cosmological parameters as the baryon density, the number of effective neutrino, the value of cosmological constant and the neutrino chemical potential. The program requires commercial NAG library routines.Program summaryProgram title: PArthENoPECatalogue identifier: AEAV_v1_0Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEAV_v1_0.htmlProgram obtainable from: CPC Program Library, Queen's University, Belfast, N. IrelandLicensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.htmlNo. of lines in distributed program, including test data, etc.: 10 033No. of bytes in distributed program, including test data, etc.: 46 002Distribution format: tar.gzProgramming language: Fortran 77Computer: PC-compatible running Fortran on Unix, MS Windows or LinuxOperating system: Windows 2000, Windows XP, LinuxClassification: 1.2, 1.9, 17.8External routines: NAG LibrariesNature of problem: Computation of yields of light elements synthesized in the primordial universe.Solution method: BDF method for the integration of the ODEs, implemented in a NAG routine.Running time: 90 sec with default parameters on a Dual Xeon Processor 2.4 GHz with 2 GB RAM.

Production and evolution of Li, Be and B isotopes in the Galaxy

Article

Mar 2012

N. Prantzos

We reassess the problem of the production and evolution of the light elements Li, Be and B and of their isotopes in the Milky Way, in the light of new observational and theoretical developments. The main novelty is the introduction of a new scheme for the origin of Galactic cosmic rays (GCR), which for the first time enables a self-consistent calculation of their composition during galactic evolution. The scheme accounts for key features of the present-day GCR source composition, it is based on the wind yields of the Geneva models of rotating, mass losing stars and it is fully coupled to a detailed galactic chemical evolution code. We find that the adopted GCR source composition accounts naturally for the observations of primary Be and helps understanding why Be follows closer Fe than O. We find that GCR produce ~70% of the solar B11/B10 isotopic ratio; the remaining 30% of B11 presumably result from neutrino-nucleosynthesis in massive star explosions. We find that GCR and primordial nucleosynthesis can make at most 30% of solar Li. At least half of solar Li has to originate in low-mass stellar sources (red giants, asymptotic giant branch stars or novae), but the required average yields of those sources are found to be much larger than obtained in current models of stellar nucleosynthesis. We also present radial profiles of LiBeB elemental and isotopic abundances in the Milky Way disc. We argue that the shape of those profiles - and the late evolution of LiBeB in general - reveals important features of the production of those light elements through primary and secondary processes.

The Primordial Lithium Problem

Article

Mar 2012

Brian D. Fields

Big-bang nucleosynthesis (BBN) theory, together with the precise WMAP cosmic baryon density, makes tight predictions for the abundances of the lightest elements. Deuterium and 4He measurements agree well with expectations, but 7Li observations lie a factor 3-4 below the BBN+WMAP prediction. This 4-5\sigma\ mismatch constitutes the cosmic "lithium problem," with disparate solutions possible. (1) Astrophysical systematics in the observations could exist but are increasingly constrained. (2) Nuclear physics experiments provide a wealth of well-measured cross-section data, but 7Be destruction could be enhanced by unknown or poorly-measured resonances, such as 7Be + 3He -> 10C^* -> p + 9B. (3) Physics beyond the Standard Model can alter the 7Li abundance, though D and 4He must remain unperturbed; we discuss such scenarios, highlighting decaying Supersymmetric particles and time-varying fundamental constants. Present and planned experiments could reveal which (if any) of these is the solution to the problem.

Measurements of the Coulomb dissociation cross section of 156 MeV Li 6 projectiles at extremely low relative fragment energies of astrophysical interest

Article

Dec 1991

Coulomb dissociation of light nuclear projectiles in the electric field of heavy target nuclei has been experimentally investigated as an alternative access to radiative capture cross sections at low relative energies of the fragments, which are of astrophysical interest. As a pilot experiment the breakup of 156 MeV â¶Li projectiles at Â²Â°â¸Pb with small emission angles of the Î± particle and deuteron fragments has been studied. Both fragments were coincidentally detected in the focal plane of a magnetic spectrograph at several reaction angles well below the grazing angle and with relative angles between the fragments of 0Â°--2Â°. The experimental cross sections have been analyzed on the basis of the Coulomb breakup theory. The results for the resonant breakup give evidence for the strong dominance of the Coulomb dissociation mechanism and the absence of nuclear distortions, while the cross section for the nonresonant breakup follows theoretical predictions of the astrophysical {ital S} factor and extrapolations of corresponding radiative capture reaction cross section to very low c.m. energies of the Î± particle and deuteron. Various implications of the approach are discussed.

The reaction d (α,γ ) 6 Li at low energies and the primordial nucleosynthesis of Li 6

Article

May 1996

We have searched for the reaction d(alpha,gamma)Li-6 at an alpha-d center-of-mass energy of 53 keV. An upper limit on the reaction S factor is 2.0 x 10(-7) MeV b at the 90% confidence level, corresponding to a limit on the synthesis of Li-6 from a Standard big bang of 0.9% of the present abundance for a total baryon-to-photon ratio 2.86<eta(10)<3.77. Equivalently, the Li-6-to-Li-7 isotopic abundance ratio immediately after a standard big bang is constrained to be less than 0.85%, considerably less than a recent measurement of this ratio in a metal-poor, Population II halo star.

Galactic Cosmic Ray Origin of Li, Be and B in Stars

Article

Jun 1970

A study of the implications of the hypothesis that high energy processes involving cosmic rays acting on the interstellar medium are the sources of the elements Li, Be and B present in stellar atmospheres and in the solar system.

Jan 1967
PHYS REV C

P Mohr
V Kölle
S Wilmes
U Atzrott
G Staudt
J W Hammer
H Krauss
H Oberhummer

Li at low energies and the primordial nucleosynthesis of 6 Li, Phys. Rev. C 53 (1996) 1967-1970, doi: 10. 1103/PhysRevC.53.1967. [18] P. Mohr, V. Kölle, S. Wilmes, U. Atzrott, G. Staudt, J.W. Hammer, H. Krauss, H. Oberhummer, Direct capture in the 3 + resonance of 2 H( α, γ ) 6

Cauldrons in the Cosmos

Jan 1988

C Rolfs
W Rodney

C. Rolfs, W. Rodney, Cauldrons in the Cosmos, University of Chicago Press, Chicago, 1988.

Li and its role in production of 6 Li in the big bang

Jan 1981
PHYS REV LETT
1867-1870

Li and its role in production of 6 Li in the big bang, Phys. Rev. Lett. 47 (1981) 1867-1870.

Jan 2006
ASTROPHYS J
229-259

M Asplund
D L Lambert
P E Nissen
F Primas
V V Smith

M. Asplund, D.L. Lambert, P.E. Nissen, F. Primas, V.V. Smith, Lithium isotopic abundances in metal-poor halo stars, Astrophys. J. 644 (2006) 229-259, doi: 10. 1086/503538.

Photoaktivierung des p-Kerns Mo-92 am Bremsstrahlungsmessplatz von ELBE

Jan 2010

M A Erhard

M.A. Erhard, Photoaktivierung des p-Kerns Mo-92 am Bremsstrahlungsmessplatz von ELBE, Technical University of Dresden, 2010 PhD Thesis.

The photoactivation setup at ELBE

Jan 2005
22

M Erhard
E Grosse
A Hartmann
A R Junghans
C Nair
K D Schilling
W Schulze
R Schwengner

M. Erhard, E. Grosse, A. Hartmann, A.R. Junghans, C. Nair, K.D. Schilling, W. Schulze, R. Schwengner, The photoactivation setup at ELBE, in: W. Enghardt, K. Fahmy, E. Grosse, B. Kämpfer, C. Schneidereit, A. Wagner (Eds.), Annual Report 2004, Institute of Nuclear and Hadron Physics, FZR-423, Forschungszentrum Rossendorf, 2005, p. 22.

Influence of long-range effects on low-energy cross sections of He and He x : the lithium problem Simultaneous solution to the 6 Li and 7 Li big bang nucleosynthesis problems from a longlived negatively charged leptonic particle

Jan 2007
121302

H Djapo
I Boztosun
G Kocak
A B Balantekin
M Kusakabe
T Kajino
R N Boyd
T Yoshida
G J Mathews

H. Djapo, I. Boztosun, G. Kocak, A.B. Balantekin, Influence of long-range effects on low-energy cross sections of He and He x : the lithium problem, Phys. Rev. C 85 (2012) 044602, doi: 10.1103/PhysRevC.85.044602. [45] M. Kusakabe, T. Kajino, R.N. Boyd, T. Yoshida, G.J. Mathews, Simultaneous solution to the 6 Li and 7 Li big bang nucleosynthesis problems from a longlived negatively charged leptonic particle, Phys. Rev. D 76 (2007) 121302, doi: 10.1103/PhysRevD.76.121302.

Erratum: Astrophysical S factor of the He3(α,γ)Be7 reaction measured at low energy via detection of prompt and delayed γ rays (Physical Review C (2007) 75 (065803))

Confortola F.
Bemmerer D.
Costantini H.
Formicola A.
Gyurky Gy
Bezzon P.
Bonetti R.
Trautvetter H.P.

Big Bang 6Li nucleosynthesis studied deep underground (LUNA collaboration)

Abstract

No full-text available

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