[show abstract][hide abstract] ABSTRACT: An analysis of six different sets of experimental data indicates that infinite, neutron-proton symmetric, neutral nuclear matter has a critical temperature of T c = 17.9 ± 0.4 MeV, a critical density of ρ c = 0.06 ± 0.01 nucleons/fm 3 , and a critical pressure of p c = 0.31 ± 0.07 MeV/fm 3 . These values have been obtained by analyzing data from six different reactions studied in three experiments: two "compound nuclear" reactions, 58 Ni + 12 C → 70 Se and 64 Ni + 12 C → 76 Se (both performed at the LBNL 88-in. cyclotron); and four "multifragmentation" reactions, 1 GeV/c π + 197 Au (performed by the Indiana Silicon Sphere Collaboration), 1 GeV/nucleon 197 Au+ 12 C, 1 GeV/nucleon 139 La+ 12 C, and 1 GeV/nucleon 84 Kr+ 12 C (all performed by the Equation of State Collaboration). The charge yields of all reactions as a function of the excitation energy were fit with a version of Fisher's droplet model modified to account for the dual components of the fluid (i.e., protons and neutrons), Coulomb effects, finite-size effects, and angular momentum arising from the nuclear collisions.
Physical Review C 05/2013; 87:054622. · 3.72 Impact Factor
[show abstract][hide abstract] ABSTRACT: The relationship between the volume and the surface energy coefficients
in the liquid drop A-1/3 expansion of nuclear masses is
discussed. The volume and surface coefficients share the same physical
origin and their physical connection is used to extend the expansion
with a curvature term. This connection between coefficients is used to
fit the experimental nuclear masses. The excellent fit obtained with a
smaller number of parameters validates the assumed physical connections
and the usefulness of the curvature term.
[show abstract][hide abstract] ABSTRACT: The relationship between the volume and the surface energy coefficients in the liquid drop A−1/3 expansion of nuclear masses is discussed. The volume and surface coefficients share the same physical origin and their physical connection is used to extend the expansion with a curvature term. A possible generalization of the Wigner term is also suggested. This connection between coefficients is used to fit the experimental nuclear masses. The excellent fit obtained with a smaller number of parameters validates the assumed physical connections and the usefulness of the curvature term.
Physical Review C 08/2012; 86:021303. · 3.72 Impact Factor
[show abstract][hide abstract] ABSTRACT: Infinite, neutron-proton symmetric, neutral nuclear matter has a critical
temperature of 17.9+-0.4 MeV, a critical density of 0.06+-0.01 nucleons per
cubic fermi and a critical pressure of 0.31+-0.07 MeV per cubic fermi. These
values have been obtained from our analysis of data from six different
reactions studied in three different experiments: two "compound nuclear"
reactions: 58Ni+12C-->70Se and 64Ni+12C-->76Se (both performed at the LBNL 88"
Cyclotron) and four "multifragmentation" reactions: 1 GeV/c pi+197Au (performed
by the ISiS collaboration), 1 AGeV 197Au+C, 1 AGeV 139La+12C and 1 AGeV
84Kr+12C (all performed by the EOS collaboration). The charge yields of all
reactions as a function of excitation energy were fit with a version of
Fisher's droplet model modified to account for the dual components of the fluid
(i.e. protons and neutrons), Coulomb effects, finite size effects and angular
momentum arising from the nuclear collisions.
[show abstract][hide abstract] ABSTRACT: The finite size of nuclei and the Coulomb interaction make it difficult
to describe systems interacting through the strong force into
thermodynamic terms. Our task is to extract the phase diagram of the
theoretical infinite symmetrical uncharged nuclear matter from
experiments of nuclear collisions where the systems are neither
infinite, symmetrical, nor uncharged. Decay yields from such experiments
are translated into coexistence densities and pressures by use of
Fisher's droplet model. This method is tested on model systems such as
the Ising model and a system of particles interacting via the
Lennard-Jones potential. The specific problems inherent to nuclear
reactions are considered. These include finite size effects, Coulomb
repulsion, and the lack of a physical vapor in contact with a decaying
system. Experimental data of compound nucleus experiments are studied
within this framework, which is also shown to extend to higher energy
reactions. Finally, the phase diagram of nuclear matter is extracted.
[show abstract][hide abstract] ABSTRACT: The modern investigation of clusters, for which 1 N ∞, requires a generalization of the thermodynamics developed for infinite systems. For instance, in finite systems, phase transitions and phase coexistence become ill-defined with ambiguous signals. The existence of phase transitions in nuclear systems, in particular of the liquid–vapor kind, has been widely discussed and even experimentally claimed. A consistent and unambiguous approach to this problem requires a connection between finite systems and the corresponding infinite systems. Historically, this has been achieved at temperature T = 0 by the introduction of the liquid drop model and the extraction of the volume term, which is a fundamental quantity of nuclear matter. This work extends this approach to T > 0, by determining the liquid–vapor coexistence line and its termination at the critical point. Since there is no known experimental situation where a nuclear liquid and vapor are in coexistence, we establish a relationship between evaporation rates and saturated vapor concentration and characterize the saturated vapor with Fisher's droplet model. We validate this approach by analyzing cluster concentrations in the Ising and Lennard-Jones models and extracting the corresponding first-order coexistence line and critical temperature. Since the vapor of clusters coexists with a finite liquid drop, we devise a finite size correction leading to a modified Fisher equation. The application of the above techniques to nuclear systems requires dealing also with the Coulomb force. Nuclear cluster evaporation rates can be corrected for Coulomb effects and can be used to evaluate the cluster concentrations in the 'virtual' equilibrium vapor. These cluster concentrations, determined over a wide temperature range, can be analyzed by means of a modified Fisher formula. This leads to the extraction of the entire liquid–vapor coexistence line terminating at the critical point. A large body of experimental data has been analyzed in this manner and the liquid–vapor phase diagram of nuclear matter has been extracted.
Journal of Physics G Nuclear and Particle Physics 09/2011; 38(11):113101. · 5.33 Impact Factor
[show abstract][hide abstract] ABSTRACT: a b s t r a c t Experimental results for the minor decay channels of fusion-evaporation in light projectile plus light target systems are presented. These new data were obtained during test campaigns to measure the opening of different decay channels. Experiments were designed to provide relative cross-section information on weakly populated channels for gamma-ray spectroscopy experiments in coincidence with charged-particles. The results are compared to publicly available fusion-evaporation codes. The data follow a simple estimate which is useful in predicting experimental conditions to make the fusion-evaporation reaction a viable nuclear structure tool to study weakly populated light neutron-rich nuclei. & 2011 Elsevier B.V. All rights reserved.
Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 07/2011; 648:109. · 1.14 Impact Factor
[show abstract][hide abstract] ABSTRACT: The cluster description of near coexistence phases (e.g. Fisher theory) requires an evaluation of cluster surface entropy. This surface degeneracy can be estimated with lattice models where clusters appear. The maximum probability lies near the maximum cluster surface. At low temperatures, clusters are forced to be nearly spherical by the surface energy and the associated Boltzmann factor. At higher temperatures and near criticality, the fractal dimension of clusters changes so that clusters become fractal. In the MIT bag model, where there is no surface energy, bags are always fractal.
Journal of Physics Conference Series 02/2011; 267(1):012060.
[show abstract][hide abstract] ABSTRACT: A gas of MIT bags has peculiar properties, one of which is that of not existing. We shall discuss its instability against coalescence. The absence of surface energy makes the bags already critical at their unique temperature TH. The addition of a surface energy does not seem to cure the problem.
Journal of Physics Conference Series 07/2010; 230(1):012024.
[show abstract][hide abstract] ABSTRACT: Both nuclear matter and hadronic matter at high excitations can be described by a liquid-vapor phase transition. For the hadronic systems, a system with an exponential mass spectrum (Hagedorn-like or bag-like) leads to a thermodynamics which is identical to that of a two phase coexistence at a fixed temperature.
Progress in Particle and Nuclear Physics 01/2009; 62:529-534. · 2.26 Impact Factor
[show abstract][hide abstract] ABSTRACT: The lifetime of the 2_+(1) state in 16C has been measured with the recoil distance method using the 9Be(9Be,2p) fusion-evaporation reaction at a beam energy of 40 MeV. The mean lifetime was measured to be 11.7(20) ps corresponding to a B(E2;2_+(1)-->0+) value of 4.15(73)e_2 fm_4 [1.73(30) W.u.], consistent with other even-even closed shell nuclei. Our result does not support an interpretation for "decoupled" valence neutrons.
[show abstract][hide abstract] ABSTRACT: Over the past three years we have studied various surrogate reactions (d,p), (3He,t), (α,α′) on several uranium isotopes 234U, 235U, 236U, and 238U. An overview of the STARS∕LIBERACE surrogate research program as it pertains to the actinides is discussed. A summary of results to date will be presented along with a discussion of experimental difficulties encountered in surrogate experiments and future research directions.
[show abstract][hide abstract] ABSTRACT: We have extracted the critical parameters of infinite uncharged nuclear matter from experimental nuclear fragmentation data. To do this, three obstacles had to be overcome: finite size effects, the Coulomb interaction, and an appropriate physical picture (not particles contained in a box) that reflects particle emission into a vacuum.
[show abstract][hide abstract] ABSTRACT: Fission excitation functions have been measured for a chain of neighboring compound nuclei from 207Po to 212Po. We present a new analysis which provides a determination of the fission barriers and ground state shell effects with nearly spectroscopic accuracy. The accuracy achieved in this analysis may lead to a future detailed exploration of the saddle mass surface and its spectroscopy.
[show abstract][hide abstract] ABSTRACT: We suggest, on general principles, that the isotopic distributions and
thus isoscaling are affected by an entropic symmetry term, which is
present even when the symmetry energy term is absent.
Physical Review C 02/2008; 77(3):37603. · 3.72 Impact Factor
[show abstract][hide abstract] ABSTRACT: The fusion-evaporation reaction 9Be(11B,2p) was used to populate excited states in 18N. New gamma-ray transitions were added to the 18N level scheme. The mean lifetime of the first excited state was measured to be 582(165) ps and its transition rate to the ground state was determined to be B(M1)=0.036(10) W.u. Shell model calculations in the full p-sd model space were used to investigate the low-lying configurations in 18N and in the N=11 isotones 17C and 19O. It was found that the role of the proton-neutron interaction is important in determining the ground state and low-lying excited state properties. The ground state spin inversion in these isotones is attributed to the increased importance of the quadrupole relative to the pairing interaction and is discussed within the framework of a schematic pairing + quadrupole model.
Physical Review C 01/2008; 77(5). · 3.72 Impact Factor
[show abstract][hide abstract] ABSTRACT: Previous information on excited states of ^18N has been obtained from selective reaction mechanisms such as beta-decay and charge exchange reactions only. This work is the first to successfully utilize the non-selective ^9Be(^11B,2p)^18N fusion-evaporation reaction to extract structure information. The LIBERACE-STARS detector array -- an array of large-area segmented silicon detectors (E-deltaE) and Compton suppressed HPGe Clover detectors -- was used to detect the charged particles and gamma radiation, respectively. New gamma transitions were added to the ^18N level scheme and the B(M1) from the first excited state to the ground state was determined to be 0.01 W.u. < B(M1) < 3.6 W.u. Shell model calculations were used to study the low-lying configurations of ^18N and its odd-A neighbors ^17C and ^19O (N=11 isotones). The role of proton holes in determining the evolution of ground state and low-lying excited state properties of these N=11 isotones will be discussed.
[show abstract][hide abstract] ABSTRACT: This document gives a historical review of the scaling of particles yields emitted from excited nuclei. The focus will be on what scaling is, what can be learned from scaling, the underlying theory of why one might expect particle yields to scale, how experimental particle yields have been observed to scale, model systems where particle (cluster) yields do scale and finally scaling observed in the particle yields of various low and medium energy nuclear reaction experiments. The document begins with a basic introduction to scaling in the study of critical phenomena and then reviews Fisher's theory which has all the aspects of scaling and can be directly applied to the counting of clusters, the most reliable measurement accessible to the experimental study of nuclear reactions. Also this document gives a history of the various scalings observed in nuclear reaction experiments and culminates with an estimate of the nuclear liquid-vapor phase boundary based upon measured particle yields.
[show abstract][hide abstract] ABSTRACT: We have deduced the cross section for 237U(n,f) over an equivalent neutron energy range from 0 to 20 MeV using the surrogate ratio method. A 55 MeV 4He beam from the 88 inch cyclotron at Lawrence Berkeley National Laboratory was used to induce fission in the following reactions: 238U(α,α′f) and 236U(α,α′f). The 238U reaction was a surrogate for 237U(n,f), and the 236U reaction was used as a surrogate for 235U(n,f). Scattered α particles were detected in a fully depleted segmented silicon telescope array over an angle range of 35° to 60° with respect to the beam axis. The fission fragments were detected in a third independent silicon detector located at backward angles between 106° and 131°.
Physical Review C 05/2006; 73(5). · 3.72 Impact Factor