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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. · 3.31 Impact Factor
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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.
03/2012;
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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. · 4.18 Impact Factor
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J Gibelin,
M Wiedeking,
L Phair,
P Fallon,
S Basunia,
L A Bernstein,
J T Burke,
D L Bleuel,
R M Clark,
M Cromaz, [......],
H B Jeppesen,
P T Lake,
I.-Y Lee,
S R Lesher,
A O Macchiavelli,
M A Mcmahan,
J Pavan,
E Rodriguez-Vieitez,
N D Scielzo, L G Moretto
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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.
Nucl. Instrum. Methods Phys. Res. A. 07/2011; 648:109.
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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.
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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.
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M Wiedeking,
P Fallon,
A O Macchiavelli,
J Gibelin,
M S Basunia,
R M Clark,
M Cromaz,
M-A Deleplanque,
S Gros,
H B Jeppesen, [......], L G Moretto,
J Pavan,
L Phair,
E Rodriguez-Vietiez,
L A Bernstein,
D L Bleuel,
J T Burke,
S R Lesher,
B F Lyles,
N D Scielzo
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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.
Physical Review Letters 04/2008; 100(15):152501. · 7.37 Impact Factor
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J. T. Burke,
L. A. Bernstein,
N. D. Scielzo,
D. L. Bleuel,
S. R. Lesher,
J. Escher,
L. Ahle,
F. S. Dietrich,
R. D. Hoffman,
E. B. Norman, [......],
E. Rodriguez‐Vieitez,
M. Wiedeking,
B. F. Lyles,
C. W. Beausang,
J. M. Allmond,
H. Ai,
J. A. Cizewski,
R. Hatarik,
P. D. O'Malley,
T. Swan
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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.
AIP Conference Proceedings. 04/2008; 1005(1):96-100.
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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. · 3.31 Impact Factor
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ABSTRACT: This is a note intended to complement our paper (nucl-th/0504010) and addressed to the attention of QGP workers interested in bag models, Hagedorn spectra, and the like. It tries to show that with a Hagedorn-like experimental spectrum the partition function can not be calculated and that a canonical description derived for the microcanonical ensemble exists only for a single, fixed temperature.
02/2006;
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ABSTRACT: The most prominent collective modes excited in deep-inelastic reactions are reviewed, and the natural hierarchy provided by their characteristic relaxation times is described. A model is presented which treats the relaxation of the mass asymmetry mode in terms of a diffusion process. Charge distributions and angular distributions as a function of Z calculated with this model are in good agreement with experimental data. An extension of this diffusion model which treats the transfer of energy and angular momentum in terms of particle transfer is described, and is successfully compared with experimental -ray multiplicities as a function of both Q-value and mass asymmetry. The problem of angular momentum transfer is again considered in connection with the sequential fission of heavy, deep-inelastic fragments and the excitation of collective modes in the exit channel is suggested. Lastly, the role of the giant El mode in the equilibration of the neutron-to-proton ratio is discussed.
01/2006: pages 150-165;
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ABSTRACT: A system H with a Hagedorn-like mass spectrum imparts its unique temperature T_H to any other system coupled to it. An H system radiates particles in preexisting physical and chemical equilibrium. These particles form a saturated vapor at temperature T_H. This coexistence describes a first order phase transition. An H system is nearly indifferent to fragmentation into smaller H systems. A lower mass cut-off in the spectrum does not significantly alter the general picture. These properties of the Hagedorn thermostats naturally explain a single value of hadronization temperature observed in elementary particle collisions at high energies and lead to some experimental predictions.
12/2005;
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R. M. Clark,
L. W. Phair,
M. Descovich,
M. Cromaz,
M. A. Deleplanque,
P. Fallon,
I. Y. Lee,
A. O. Macchiavelli,
M. A. McMahan, L. G. Moretto,
E. Rodriguez-Vieitez,
S. Sinha,
F. S. Stephens,
D. Ward,
M. Wiedeking,
L. A. Bernstein,
J. T. Burke,
J. A. Church
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ABSTRACT: We have investigated the population of nuclei formed in binary reactions involving 7Li beams on targets of 160Gd and 184W. The 7Li+184W data were taken in the first experiment to use the LIBERACE Ge array in combination with the STARS Si ΔE-E telescope system at the 88-Inch Cyclotron of the Lawrence Berkeley National Laboratory. By using the Wilczyński binary transfer model, in combination with a standard evaporation model, we are able to reproduce the experimental results. This is a useful method for predicting the population of neutron-rich heavy nuclei formed in binary reactions involving beams of weakly bound nuclei and will be of use in future spectroscopic studies.
Phys. Rev. C. 11/2005; 72(5).
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ABSTRACT: Analyses of multifragmentation in terms of the Fisher droplet model (FDM) and the associated construction of a nuclear phase diagram bring forth the problem of the actual existence of the nuclear vapor phase and the meaning of its associated pressure. We present here a physical picture of fragment production from excited nuclei that solves this problem and establishes the relationship between the FDM and the standard compound nucleus decay rate for rare particles emitted in first-chance decay. The compound thermal emission picture is formally equivalent to a FDM-like equilibrium description and avoids the problem of the vapor while also explaining the observation of Boltzmann-like distribution of emission times. In this picture a simple Fermi gas thermometric relation is naturally justified and verified in the fragment yields and time scales. Low energy compound nucleus fragment yields scale according to the FDM and lead to an estimate of the infinite symmetric nuclear matter critical temperature between 18 and 27 MeV depending on the choice of the surface energy coefficient of nuclear matter. Comment: Five page two column pages, four figures, submitted to Phys. Rev. C
07/2005;
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ABSTRACT: The effects of the finite size of a liquid drop undergoing a phase transition are described in terms of the complement, the largest (but mesoscopic) drop representing the liquid in equilibrium with the vapor. Vapor cluster concentrations, pressure, and density from fixed mean density lattice gas (Ising) calculations are explained in terms of the complement generalization of Fisher's model. Accounting for this finite size effect is important for extracting the infinite nuclear matter phase diagram from experimental data.
Physical Review Letters 06/2005; 94(20):202701. · 7.37 Impact Factor
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ABSTRACT: A microcanonical treatment of Hagedorn systems, i.e. finite mass hadronic resonances with an exponential mass spectrum controlled by the Hagedorn temperature $T_H$, is performed. We show that, in the absence of any restrictions, a Hagedorn system is a perfect thermostat, i.e. it imparts its temperature $T_H$ to any other system in thermal contact with it. We study the thermodynamic effects of the lower mass cut-off in the Hagedorn mass spectrum. We show that in the presence of a single Hagedorn resonance the temperature of any number of $N_B$ Boltzmann particles differs only slightly from $T_H$ up to the kinematically allowed limit $N_B^{kin}$. For $N_B > N_B^{kin}$ however, the low mass cut-off leads to a decrease of the temperature as $N_B$ grows. The properties of Hagedorn thermostats naturally explain a single value of hadronization temperature observed in elementary particle collisions at high energies and lead to some experimental predictions.
05/2005;
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ABSTRACT: A system H with a Hagedorn-like mass spectrum imparts its unique temperature TH to any other system coupled to it. An H system radiates particles in preexisting physical and chemical equilibrium. These particles form a saturated vapor at temperature TH. This coexistence describes a first order phase transition. An H system is nearly indifferent to fragmentation into smaller H systems. A lower mass cut-off in the spectrum does not significantly alter the general picture Comment: Four pages, one figure
04/2005;
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ABSTRACT: A study of the lattice gas (Ising) model shows the properties of saturated vapor in coexistence with a liquid to be independent of the system's fixed mean density ρfixed, in keeping with standard thermodynamics. This behavior ensures that Fisher scaling plots are unique, independent of ρfixed, and yield a unique characterization of the liquid–vapor phase diagram. The resulting phase diagram and critical parameters for the square lattice gas model are shown to agree with accepted values to within a few percent throughout the coexistence region.
Phys. Rev. C. 02/2005; 71(2).
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ABSTRACT: A detailed study of the lattice gas (Ising) model shows that the correct definition of cluster concentration in the vapor at coexistence with the liquid leads to Fisher plots that are unique, independent of fixed particle number density $\rho_{\text{fixed}}$, and completely reliable for the characterization of the liquid-vapor phase diagram of any van der Waals systems including nuclear matter.
06/2004;
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ABSTRACT: The surface partition of large fragments is derived analytically within a simple statistical model by the Laplace-Fourier transformation method. In the limit of small amplitude deformations, a suggested Hills and Dales Model reproduces the leading term of the famous Fisher result for the surface entropy with an accuracy of a few percent. The surface partition of finite fragments is discussed as well. Comment: 4 pages, 1 figure
06/2004;
