The cumulant ratios up to fourth order of the $Z$ distributions of the largest fragment in spectator fragmentation following $^{107,124}$Sn+Sn and $^{124}$La+Sn collisions at 600 MeV/nucleon have been investigated. They are found to exhibit the signatures of a second-order phase transition established with cubic bond percolation and previously observed in the ALADIN experimental data for fragmentation of $^{197}$Au projectiles at similar energies. The deduced pseudocritical points are found to be only weakly dependent on the $A/Z$ ratio of the fragmenting spectator source. The same holds for the corresponding chemical freeze-out temperatures of close to 6 MeV. The experimental cumulant distributions are quantitatively reproduced with the Statistical Multifragmentation Model and parameters used to describe the experimental fragment multiplicities, isotope distributions and their correlations with impact-parameter related observables in these reactions. The characteristic coincidence of the zero transition of the skewness with the minimum of the kurtosis excess appears to be a generic property of statistical models and is found to coincide with the maximum of the heat capacity in the canonical thermodynamic fragmentation model.
A statistical multifragmentation model (SMM) is applied to the experimentally observed multifragmentation events in an intermediate heavy ion reaction.Using the temperature and symmetry energy extracted from the isobaric yield ratio (IYR) method based on the Modified Fisher Model (MFM), SMM is applied to the reaction $^{64}$Zn + $^{112}$Sn at 40 MeV/nucleon. The experimental isotope distribution and mass distribution of the primary reconstructed fragments are compared without afterburner and they are well reproduced. The extracted temperature $T$ and symmetry energy coefficient $a_{sym}$ from …
Multifragment disintegrations, measured for central Au + Au collisions at E/A = 35 MeV, are analyzed with the Statistical Multifragmentation Model. Charge distributions, mean fragment energies, and two-fragment correlation functions are well reproduced by the statistical breakup of a large, diluted and thermalized system slightly above the multifragmentation threshold.
Distributions of the largest fragment charge are studied using the ALADIN data on fragmentation of $^{197}$Au projectiles at relativistic energies. The statistical measures skewness and kurtosis of higher-order fluctuations provide a robust indication of the transition point, linked to a phase transition in the thermodynamic limit. Extensive comparisons with predictions of a bond percolation model corroborate the high accuracy of this model in reproducing the distributions as well as the whole fragmentation pattern as represented by the measured charge correlations. In analogy to percolation, …
Study of Isoscaling with Statistical Multifragmentation Models
不同的统计多重碎裂模型已被用来研究等标度，即从两个反应的同位素比因子分解成质子和中子数的逸度项，R 21（N，Z）= Y 2（N，Z）/Y 1（N，Z）=C*exp（a*N+b*Z）。尽管由于激发碎片的蒸发，初级同位素分布与最终分布有很大不同，但a和b的值不会受到连续衰变的影响。A被示出主要对发射源的质子和中子组成敏感，并且可以用于研究核碰撞中的同位旋依赖性质，例如非对称核物质的状态方程中的对称能。
Nuclear multifragmentation is an important phenomenon, the study of which can throw light on reaction mechanism in heavy ion collisions at intermediate and high energies. Based on statistical and dynamical model studies, this thesis is concentrated mainly on, the following three aspects of nuclear multifragmentation reactions namely (i) production of exotic nuclei which are normally not available in the laboratory (ii) nuclear symmetry energy from heavy ion collisions at intermediate energies and (iii) Nuclear liquid-gas phase transition. In addition to these equivalence of statistical ensembl…
The bimodal behavior of the order parameter is studied in the framework of Boltzmann-Uehling-Uhlenbeck (BUU) transport model. In order to do that, simplified yet accurate method of BUU model is used which allow calculation of fluctuations in systems much larger than what was considered feasible in a well-known and already existing model. It is observed that depending on the projectile energy and centrality of the reaction, both entrance channel and exit channel effects can be at the origin of the experimentally observed bimodal behavior. Both dynamical and statistical bimodality mechanisms are…
Effect of neutron composition and excitation energy on the primary fragment yield distribution in multifragmentation reaction
本文研究了30、40和47 MeV/核子下$^{58}$ Fe + $^{58}$ Ni和$^{58}$ Fe + $^{58}$ Fe反应多重碎裂中初级和次级碎片产额分布的同位素性质。从所观察到的碎片产额分布的减少的中子和质子密度显示初级碎片产额分布经历强烈的次级去激发。在最低的激发能和最小的中子-质子比下，该效应较小，而在较高的激发能和较高的中子-质子比下，该效应变大。从约化中子密度推导出的初级碎片的对称能明显低于饱和密度下正常核的对称能，表明碎片是高度激发的，并在约化密度下形成。此外，还观察到对称能随着激发能的增加而缓慢减小。观察到的效果解释使用统计多重碎裂模型。
Theoretical calculations are performed to investigate the angular momentum and Coulomb effects on fragmentation and multifragmentation in peripheral heavy-ion collisions at Fermi energies. Inhomogeneous distributions of hot fragments in the freeze-out volume are taken into account by microcanonical Markov chain calculations within the Statistical Multifragmentation Model (SMM). Including an angular momentum and a long-range Coulomb interaction between projectile and target residues leads to new features in the statistical fragmentation picture. In this case, one can obtain specific correlation…
We present a brief overview of nuclear multifragmentation reaction. Basic formalism of canonical thermodynamical model based on equilibrium statistical mechanics is described. This model is used to calculate basic observables of nuclear multifragmentation like mass distribution, fragment multiplicity, isotopic distribution and isoscaling. Extension of canonical thermodynamical model to a projectile fragmentation model is outlined. Application of the projectile fragmentation model for calculating average number of intermediate mass fragments and the average size of largest cluster at different …
The study of liquid-gas phase transition in heavy ion collisions has generated a lot of interest amongst the nuclear physicists in the recent years. In heavy ion collisions, there is no direct way of measuring the state variables like entropy, pressure, energy and hence unambiguous characterization of phase transition becomes difficult. This work proposes new signatures of phase transition that can be extracted from the observables which are easily accessible in experiments. It is observed that the temperature dependence of the first order derivative of the order parameters in nuclear liquid g…
The properties of the kinetic energy spectra of light isotopes produced in the breakup of a nuclear source and during the deexcitation of its products are examined. The initial stage, at which the hot fragments are created, is modeled by the Statistical Multifragmentation Model, whereas the Weisskopf-Ewing evaporation treatment is adopted to describe the subsequent fragment deexcita- tion, as they follow their classical trajectories dictated by the Coulomb repulsion among them. The energy spectra obtained are compared to available experimental data. The influence of the fusion cross-section en…
The deexcitation of the primary hot fragments, produced in the breakup of an excited nuclear source, during their propagation under the influence of their mutual Coulomb repulsion is studied in the framework of a recently developed hybrid model. The latter is based on the Statistical Mul- tifragmentation Model (SMM), describing the prompt breakup of the source, whereas the particle emission from the hot fragments, that decay while traveling away from each other, is treated by the Weisskopf-Ewing evaporation model. Since this treatment provides an event by event descrip- tion of the process, in…
Multifragmentation vs. Evaporation vs. Binary-Decay in Fragment Production
本文介绍了LANL完成改进的级联激子模型（CEM03.01）和洛斯阿拉莫斯夸克胶子弦模型（LAQGSM.03.01）的“S”和“G”版本的部分进展报告。“S”版本使用Botvina等人的统计多重碎裂模型（SMM）考虑了在2A MeV以上的激发能的反应预平衡阶段后产生的复合核的碎裂。（“S”代表SMM），而“G”版本使用Charity等人的裂变类二元衰变模型GEMINI描述反应的蒸发/裂变阶段。（“G”代表GEMINI），而不是使用Furihata的广义蒸发模型GEM 2，该模型已纳入这些规范的标准版本中。本文分析了最近的660 MeV p +129 I和3.65 GeV p +112 Sn JINR测量结果，COSY新的1.2 GeV p +（从Al到Th的13个核）数据，GSI 300 MeV和1 GeV p +56 Fe逆运动学测量数据，以及GSI新的1 GeV/核子124 He和136 He + Pb数据。为了更好地了解碎片生产的机制，我们讨论了几个计算，但尚未测量的这些反应，这是预测SMM，GEMINI，和GEM 2是完全不同的产品的运动学特征。我们发现这些运动学量是潜在的有用的区分这些反应机制，如果它们可以在未来的实验中测量。
