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C. Smorra,
T. R. Rodriguez,
T. Beyer,
K. Blaum,
M. Block,
Ch. E. Düllmann,
K. Eberhardt,
M. Eibach,
S. Eliseev,
K. Langanke, G. Martinez-Pinedo,
Sz. Nagy,
W. Nörtershäuser,
D. Renisch,
V. M. Shabaev,
I. I. Tupitsyn,
N. A. Zubova
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ABSTRACT: Os-184 has been excluded as a promising candidate for the search of
neutrinoless double-electron capture. High-precision mass measurements with the
Penning-trap mass spectrometer TRIGA-TRAP resulted in a marginal resonant
enhancement with = -8.89(58) keV excess energy to the 1322.152(22) keV 0+
excited state in W-184. State-of-the-art energy density functional calculations
are applied for the evaluation of the nuclear matrix elements to the excited
states predicting a strong suppression due to the large deformation of mother
and daughter states. The half-life of the transition in Os-184 exceeds T_{1/2}
> 1.3 10^{29} years for an effective neutrino mass of 1 eV.
09/2012;
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J Benlliure,
H Alvarez-Pol,
T Kurtukian-Nieto,
A I Morales,
L Audouin,
F Becker,
B Blank,
I Borzov,
E Casarejos,
D Cortina-Gil, [......],
J Giovinazzo,
D Henzlova,
B Jurado,
L Langanke, G Martinez-Pinedo,
P Napolitani,
J Pereira,
F Rejmund,
K -H Schmidt,
O Yordanov
[show abstract]
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ABSTRACT: The production of heavy neutron-rich nuclei approaching the r-process waiting point at N≈126 has been investigated in fragmentation reactions of relativistic 238U and 208Pb projectiles. Using this technique we were able to identify 73 new heavy neutron-rich nuclei expanding considerably the north-west frontier of the chart of nuclide. Moreover, we were able to determine the half lives of 13 of those nuclides. The measured values are significantly shorter than the predictions used for r-process model calculations. These shorter half lives are understood as due to the role of first-forbidden transitions in the decays of these nuclei. The confirmation of these results for r-process nuclei at N≈126 would indicate that the r-process at this point is faster than expected, leading to a larger production of the heaviest nuclei.
Journal of Physics Conference Series 02/2012; 337(1):012070.
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ABSTRACT: We present nucleosynthesis studies based on hydrodynamical simulations of core-collapse supernovae and their subsequent neutrino-driven winds. Although the conditions found in these simulations are not suitable for the rapid neutron capture (r-process) to produce elements heavier than A$\sim$130, this can be solved by artificially increasing the wind entropy. In this way one can mimic the general behavior of an ejecta where the r-process occurs. We study the impact of the long-time dynamical evolution and of the nuclear physics input on the final abundances and show that different nuclear mass models lead to significant variations in the abundances. These differences can be linked to the behavior of nuclear masses far from stability. In addition, we have analyzed in detail the effect of neutron capture and beta-delayed neutron emission when matter decays back to stability. In all our studied cases, freeze out effects are larger than previously estimated and produce substantial changes in the post freeze out abundances. Comment: 10 pages, 3 figures. Talk at Nuclei in the Cosmos XI (Heidelberg, 2010), to appear in Proceedings of Science
12/2010;
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[show abstract]
[hide abstract]
ABSTRACT: We use results from long-time core-collapse supernovae simulations to
investigate the impact of the late time evolution of the ejecta and of the
nuclear physics input on the calculated r-process abundances. Based on the
latest hydrodynamical simulations, heavy r-process elements cannot be
synthesized in the neutrino-driven winds that follow the supernova explosion.
However, by artificially increasing the wind entropy, elements up to A=195 can
be made. In this way one can reproduce the typical behavior of high-entropy
ejecta where the r-process is expected to occur. We identify which nuclear
physics input is more important depending on the dynamical evolution of the
ejecta. When the evolution proceeds at high temperatures (hot r-process), an
(n,g)-(g,n) equilibrium is reached. While at low temperature (cold r-process)
there is a competition between neutron captures and beta decays. In the first
phase of the r-process, while enough neutrons are available, the most relevant
nuclear physics input are the nuclear masses for the hot r-process and the
neutron capture and beta-decay rates for the cold r-process. At the end of this
phase, the abundances follow a steady beta flow for the hot r-process and a
steady flow of neutron captures and beta decays for the cold r-process. After
neutrons are almost exhausted, matter decays to stability and our results show
that in both cases neutron captures are key for determining the final
abundances, the position of the r-process peaks, and the formation of the
rare-earth peak. In all the cases studied, we find that the freeze out occurs
in a timescale of several seconds.
08/2010;
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ABSTRACT: The electron-to-nucleon ratio or electron fraction is a key parameter in many astrophysical studies. Its value is determined by weak-interaction rates that are based on theoretical calculations subject to unknown uncertainties. Consequently, it is important to have a model independent way of constraining the electron fraction value in different astrophysical environments. Here we show that nuclear statistical equilibrium combined with beta equilibrium can provide such a constraint. We test the validity of this approximation in presupernova models and give lower limits for the electron fraction that is expected in type Ia supernova and accretion-induced collapse. Comment: 10 pages, 9 figures, submitted to Astronomy and Astrophysics
02/2010;
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F-K Thielemann,
I Dillmann,
K Farouqi,
T Fischer,
C Fröhlich,
A Kelic-Heil,
I Korneev,
K-L Kratz,
K Langanke,
M Liebendörfer,
I V Panov, G Martinez-Pinedo,
T Rauscher
[show abstract]
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ABSTRACT: The processes discussed in this review are three of the four nucleosynthesis processes involved in producing heavy nuclei beyond Fe (not counting the rp-process in X-ray bursts). Opposite to the fourth process (the s-process), which operates in stellar evolution during He- and C-burning, they are all related to explosive burning phases, (presumably) linked to core collapse supernova events of massive stars. The (classical) p-process is identified with explosive Ne/O-burning in outer zones of the progenitor star. It is intitiated by the passage of the supernova shock wave and acts via photodisintegration reactions like a spallation process which produces neighboring (proton-rich) isotopes from pre-existing heavy nuclei. The reproduction of some of the so-called lighter p-isotopes with A < 100 faces problems in this environment. The only recently discovered νp-process is related to the innermost ejecta, the neutrino wind expelled from the hot proto-neutron star after core collapse in the supernova explosion. This neutrino wind is proton-rich in its early phase and reactions with neutrinos permit to overcome decay/reaction bottlenecks for the flow beyond the Fe-group, thus permitting the production of those p-isotopes, which face problems in the classical p-process scenario. The understanding of the r-process, being identified for a long time with rapid neutron captures – and passing through nuclei far from stability – is still experiencing major problems. These are on the one hand related to nuclear uncertainties far from stability (masses and half-lives), affecting the process speed and abundance peaks, on the other hand the site is still not definitely located, yet. Later neutron-rich, high entropy phases of the neutrino wind could permit its operation, other options include the ejection of very neutron-rich neutron star matter. Two different environments are required for a weak and a main/strong r-process, witnessed by observations of low metallicity stars.
Journal of Physics Conference Series 02/2010; 202(1):012006.
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ABSTRACT: The most promising astrophysical sources of kHz gravitational waves (GWs) are the inspiral and merger of binary neutron star(NS)/black hole systems. Maximizing the scientific return of a GW detection will require identifying a coincident electro-magnetic (EM) counterpart. One of the most likely sources of isotropic EM emission from compact object mergers is a supernova-like transient powered by the radioactive decay of heavy elements synthesized in ejecta from the merger. We present the first calculations of the optical transients from compact object mergers that self-consistently determine the radioactive heating by means of a nuclear reaction network; using this heating rate, we model the light curve with a one dimensional Monte Carlo radiation transfer calculation. For an ejecta mass ~1e-2 M_sun[1e-3 M_sun] the resulting light curve peaks on a timescale ~ 1 day at a V-band luminosity nu L_nu ~ 3e41[1e41] ergs/s (M_V = -15[-14]); this corresponds to an effective "f" parameter ~3e-6 in the Li-Paczynski toy model. We argue that these results are relatively insensitive to uncertainties in the relevant nuclear physics and to the precise early-time dynamics and ejecta composition. Due to the rapid evolution and low luminosity of NS merger transients, EM counterpart searches triggered by GW detections will require close collaboration between the GW and astronomical communities. NS merger transients may also be detectable following a short-duration Gamma-Ray Burst or "blindly" with present or upcoming optical transient surveys. Because the emission produced by NS merger ejecta is powered by the formation of rare r-process elements, current optical transient surveys can directly constrain the unknown origin of the heaviest elements in the Universe. Comment: 14 pages, 7 figures; accepted to MNRAS; title changed to highlight r-process connection and new figure added.
01/2010;
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Nuclear Physics A 01/2010; · 1.54 Impact Factor
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ABSTRACT: We explore the effects of r-process nucleosynthesis on fall-back accretion in neutron star(NS)-NS and black hole-NS mergers, and the resulting implications for short-duration gamma-ray bursts (GRBs). Though dynamically important, the energy released during the r-process is not yet taken into account in merger simulations. We use a nuclear reaction network to calculate the heating (due to beta-decays and nuclear fission) experienced by material on the marginally-bound orbits nominally responsible for late-time fall-back. Since matter with longer orbital periods t_orb experiences lower densities, for longer periods of time, the total r-process heating rises rapidly with t_orb, such that material with t_orb > 1 seconds can become completely unbound. Thus, r-process heating fundamentally changes the canonical prediction of an uninterrupted power-law decline in the fall-back rate dM/dt at late times. When the timescale for r-process to complete is > 1 second, the heating produces a complete cut-off in fall-back accretion after ~ 1 second; if robust, this would imply that fall-back accretion cannot explain the late-time X-ray flaring observed following some short GRBs. However, for a narrow, but physically plausible, range of parameters, fall-back accretion can resume after ~ 10 s, despite having been strongly suppressed for ~ 1-10 s after the merger. This suggests the intriguing possibility that the gap observed between the prompt and extended emission in short GRBs is a manifestation of r-process heating. Comment: 7 pages; 4 figures; submitted to MNRAS
08/2009;
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M. Madurga,
M. J. G. Borge,
M. Alcorta,
L. M. Fraile,
H. O. U. Fynbo,
B. Jonsond,
O. Kirsebom, G. Martinez-Pinedo,
T Nilsson,
G. Nyman,
A. Perea,
A. Poves,
K. Riisager,
O Tengblad,
E. Tengborn,
J. Van der Walle
[show abstract]
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ABSTRACT: Coincidences between charged particles emitted in the $\beta$-decay of $^{11}$Li were observed using highly segmented detectors. The breakup channels involving three particles were studied in full kinematics allowing for the reconstruction of the excitation energy of the $^{11}$Be states participating in the decay. In particular, the contribution of a previously unobserved state at 16.3 MeV in $^{11}$Be has been identified selecting the $\alpha$ + $^7$He$\to\alpha$ + $^6$He+n channel. The angular correlations between the $\alpha$ particle and the center of mass of the $^6$He+n system favors spin and parity assignment of 3/2$^-$ for this state as well as for the previously known state at 18 MeV. Comment: 13 pages, 6 figures
04/2009;
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E.-W. Grewe,
C. Baumer,
H. Dohmann,
D Frekers,
M. N. Harakeh,
S. Hollstein,
H Johansson,
K. Langanke, G. Martinez-Pinedo,
F. Nowacki,
I. Petermann,
Lucia-Ana Popescu,
S. Rakers,
D. Savran,
K. Sieja,
H. Simon,
J. H. Thies,
A. M. van den Berg,
H.J. Wortche,
A. Zilgers
[show abstract]
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ABSTRACT: The (d,2He) charge-exchange reaction on the double-beta decay (ββ) nucleus 64Zn has been studied at an incident energy of 183 MeV. The two protons in the 1S0 state (indicated as 2He) were both momentum analyzed and detected simultaneously by the BBS magnetic spectrometer and its position-sensitive detector. 2He spectra with a resolution of about 115 keV (FWHM) have been obtained allowing identification of many levels in the residual nucleus 64Cu with high precision. 64Zn is one of the rare cases undergoing a ββ decay in β+ direction. In the experiment presented here, Gamow-Teller (GT+ ) transition strengths have been extracted. Together with the GT− transition strengths from 64 Ni(3 He,t) data to the same intermediate nucleus 64Cu, the nuclear matrix elements of the ββ decay of 64Zn have been evaluated. Finally, the GT± distributions are compared with shell-model calculations and a critical assessment is given of the various residual interactions presently employed for the pf shell.
Physical Review C 06/2008; 77(6):064303. · 3.31 Impact Factor
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T. Kurtukian-Nieto,
J. Benlliure,
L. Audouin,
F. Becker,
B. Blank,
I. N. Borzov,
E. Casarejos,
M. Fernandez-Ordonez,
J. Giovinazzo,
D. Henzlova,
B. Jurado,
K. Langanke, G. Martinez-Pinedo,
J. Pereira,
F. Rejmund,
K. -H. Schmidt,
O. Yordanov
[show abstract]
[hide abstract]
ABSTRACT: Heavy neutron-rich nuclei close to N=126 were produced by fragmentation of a 1 A GeV 208Pb beam at the FRS at GSI. The beta-decay half-lives of 8 nuclides have been determined. The comparison of the data with model calculations including an approach based on the self-consistent ground-state description and continuum QRPA considering the Gamow-Teller and first-forbidden decays provide a first indication on the importance of first-forbidden transitions around A=195. The measured data indicate that the matter flow in the r-process to heavier fissioning nuclei is faster than previously expected.
12/2007;
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A. Jungclaus,
L. Caceres,
M Gorska,
M. Pfutzner,
S. Pietri,
E. Werner-Malento,
H. Grawe,
K. Langanke, G. Martinez-Pinedo,
F. Nowacki, [......],
M. Kmiecik,
R Kumar,
A. Maj,
S. Mandal,
F. Montes,
S. Myalski,
G.S. Simpson,
S.J. Steer,
S. Tashenov,
O. Wieland
[show abstract]
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ABSTRACT: The gamma decay of excited states in the waiting-point nucleus Cd-130(82) has been observed for the first time. An 8(+) two-quasiparticle isomer has been populated both in the fragmentation of a Xe-136 beam as well as in projectile fission of U-238, making Cd-130 the most neutron-rich N=82 isotone for which information about excited states is available. The results, interpreted using state-of-the-art nuclear shell-model calculations, show no evidence of an N=82 shell quenching at Z=48. They allow us to follow nuclear isomerism throughout a full major neutron shell from Cd-98(50) to Cd-130(82) and reveal, in comparison with Ni-76(48) one major proton shell below, an apparently abnormal scaling of nuclear two-body interactions.
Physical Review Letters 05/2007; 99:132501. · 7.37 Impact Factor
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ABSTRACT: We calculate parity-dependent level densities for the even-even isotopes 58,62,66 Fe and 58 Ni and the odd-A nuclei 59 Ni and 65 Fe using the Shell Model Monte Carlo method. We perform these calculations in the complete fp-gds shell-model space using a pairing+quadrupole residual interaction. We find that, due to pairing of identical nucleons, the low-energy spectrum is dominated by positive parity states. Although these pairs break at around the same excitation energy in all nuclei, the energy dependence of the ratio of negative-to-positive parity level densities depends strongly on the particular nucleus of interest. We find equilibration of both parities at noticeably lower excitation energies for the odd-A nuclei 59 Ni and 65 Fe than for the neighboring even-even nuclei 58 Ni and 66 Fe.
04/2007;
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ABSTRACT: A generalized method to calculate the excitation-energy dependent parity ratio in the nuclear level density is presented, using the assumption of Poisson distributed independent quasi particles combined with BCS occupation numbers. It is found that it is crucial to employ a sufficiently large model space to allow excitations both from low-lying shells and to higher shells beyond a single major shell. Parity ratios are only found to equilibrate above at least 5-10 MeV of excitation energy. Furthermore, an overshooting effect close to major shells is found where the parity opposite to the ground state parity may dominate across a range of several MeV before the parity ratio finally equilibrates. The method is suited for large-scale calculations as needed, for example, in astrophysical applications. Parity distributions were computed for all nuclei from the proton dripline to the neutron dripline and from Ne up to Bi. These results were then used to recalculate astrophysical reaction rates in a Hauser-Feshbach statistical model. Although certain transitions can be considerably enhanced or suppressed, the impact on astrophysically relevant reactions remains limited, mainly due to the thermal population of target states in stellar reaction rates.
04/2007;
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ABSTRACT: Advances in our understanding and the modeling of stellar core-collapse and supernova explosions over the past 15 years are reviewed, concentrating on the evolution of hydrodynamical simulations, the description of weak interactions and nuclear equation of state effects, and new insights into the nucleosynthesis occurring in the early phases of the explosion, in particular the neutrino-p process. The latter is enabled by the proton-richness of the early ejecta, which was discovered because of significant progress has been made in the treatment of neutrino transport and weak interactions. This progress has led to a new generation of sophisticated Newtonian and relativistic hydrodynamics simulations in spherical symmetry. Based on these, it is now clear that the prompt bounce-shock mechanism is not the driver of supernova explosions, and that the delayed neutrino-heating mechanism can produce explosions without the aid of multi-dimensional processes only if the progenitor star has an ONeMg core inside a very dilute He-core, i.e., has a mass in the 8--10 solar mass range. Hydrodynamic instabilities of various kinds have indeed been recognized to occur in the supernova core and to be of potential importance for the explosion. Neutrino-driven explosions, however, have been seen in two-dimensional simulations with sophisticated neutrino transport so far only when the star has a small iron core and low density in the surrounding shells as being found in stars near 10--11 solar masses. The explosion mechanism of more massive progenitors is still a puzzle. It might involve effects of three-dimensional hydrodynamics or might point to the relevance of rapid rotation and magnetohydrodynamics, or to still incompletely explored properties of neutrinos and the high-density equation of state.
01/2007;
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ABSTRACT: We have calculated the M1 strength distributions in the A=36,38 argon isotopes within large-scale shell model studies which consider valence nucleons in the sd and pf shells. While the M1 strength in 36Ar is well reproduced within the sd shell, the experimentally observed strong fragmentation of the M1 strength in 38Ar requires configuration mixing between the sd and the pf shells adding to our understanding of correlations across the N=20 shell gap.
09/2006;
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Int.Conf Nuclei in the Cosmos-IX, June 25,2006 CERN, Geneva, Switzerland, http://pos.sissa.it/archive/conferences; 09/2006
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ABSTRACT: The understanding of the abundance evolution in the interstellar medium, and especially the enrichment of heavy elements,
as a function of space and time reflects the history of star formation and the lifetimes of the diverse contributing stellar
objects. Therefore, the understanding of the endpoints of stellar evolution is essential. These are mainly planetary nebulae
and type II/Ib/Ic supernovae as evolutionary endpoints of single stars, but also events in binary systems can contribute,
like e.g. supernovae of type Ia, novae and possibly X-ray bursts and neutron star or neutron star - black hole mergers. Despite
many efforts, a full and self-consistent understanding of supernovae (the main contributors to nucleosynthesis in galaxies)
is not existing, yet. However, observed spectra, light curves, radioactivities/decay gamma-rays and galactic evolution witness
the composition of their ejecta and constrain model uncertainties. We focus on (i) neutrino-induced explosions for type II
supernovae and the innermost ejected layers, (ii) electron captures in type Ia supernovae and neutron-rich Fe-group nuclei
and finally (iii) galactic chemical evolution and possible r-process sites.
02/2006: pages 331-343;
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ABSTRACT: Core collapse supernovae are the leading actor in the story of the cosmic origin of the chemical elements. Existing models, which generally assume spherical symmetry and parameterize the explosion, have been able to broadly replicate the observed elemental pattern. However, inclusion of neutrino interactions produces noticeable improvement in the composition of the ejecta when compared to observations. Neutrino interactions may also provide a supernova source for light p-process nuclei. Comment: 7 pages, 2 figures, in proceedings of Astronomy with Radioactivities V, Clemson University, September 5-9, 2005, to appear in New Astronomy Reviews
11/2005;
