Statistical Abrasion Research Articles

Determination of the neutron skin thickness from interaction cross section and charge-changing cross section for B, C, N, O, F isotopes

The effective neutron and proton root-mean-square radius of stable and unstable nuclei (12–15,17B, 12–20C, 14–21N, 16–24O and 18–21,23–26F) were deduced from the charge-changing cross section, \(\sigma _{\text{cc}}\), and the interaction cross sections, \(\sigma _{\text{I}}\), by using a statistical abrasion–ablation model calculation. The extracted proton radii are in good agreement with the data from the Atomic Data and Nuclear Data Tables within the errors. Furthermore, we can observe that the neutron skin thickness increases monotonously with the increasing neutron number in these isotopes, which is consistent with the systematical trend of theoretical calculations.

Effects of Neutron Skin Thickness in Peripheral Nuclear Reactions

Effects of neutron skin thickness in peripheral nuclear collisions are investigated using the statistical abrasion ablation (SAA) model. The reaction cross section, neutron (proton) removal cross section, one-neutron (proton) removal cross section as well as their ratios for nuclei with different neutron skin thickness are studied. It is demonstrated that there are good linear correlations between these observables and the neutron skin thickness for neutron-rich nuclei. The ratio between the (one-)neutron and proton removal cross section is found to be the most sensitive observable of neutron skin thickness. Analysis shows that the relative increase of this ratio could be used to determine the neutron skin size in neutron-rich nuclei.

A revisit to the neutron skin thickness of neutron-rich nuclei in the statistical abrasion ablation model

The cross sections of the fragments produced in the projectile fragmentation reactions of the even calcium isotopes from A = 36 to A = 52 are calculated using the statistical abrasion ablation model. The neutron skin thickness are studied by investigating the fragments isotopic cross section distributions. The neutron-skin thicknesses of the calcium isotopes have a good linear correlation to the peak positions of their fragment isotopic cross section distributions. The correlation between the neutron skin thickness and the neutron density distributions of 48Ca is investigated by introducing a parameter to adjust the diffuseness parameter in the fermi-type density distribution.

Neutron removal cross section as a measure of neutron skin

We study the relation between neutron removal cross section ($\sigma_{-N}$) and neutron skin thickness for finite neutron rich nuclei using the statistical abrasion ablation (SAA) model. Different sizes of neutron skin are obtained by adjusting the diffuseness parameter of neutrons in the Fermi distribution. It is demonstrated that there is a good linear correlation between $\sigma_{-N}$ and the neutron skin thickness for neutron rich nuclei. Further analysis suggests that the relative increase of neutron removal cross section could be used as a quantitative measure for the neutron skin thickness in neutron rich nuclei.

Systematic behavior in the isospin dependence of projectile fragmentation of mirror nuclei with A = 20–60

The cross sections of the fragments that are produced by the 80 A MeV |Tz| = 2 mirror nuclei 20Mg/20O, 24Si/24Ni, 36Ca/36S, 40Ti/40Ar, 44Ca/44Cr and 60Ni/60Ge colliding on the 12C target are calculated using the statistical abrasion–ablation model. The isospin dependence of the projectile fragmentation (or the isospin effect) in the fragment cross section distributions of the A = 20–60 mirror projectile nuclei is studied systematically. The isospin effect in the fragment cross section distributions is found to decrease and even disappear with increasing violence of the collisions. The isospin effect is found strongly related to the different proton and neutron density distributions. It is suggested that the isospin effect in the fragment cross section distributions may serve as an observation to extract the density distributions of asymmetric nucleus.

Disappearance of isospin effect in projectile fragmentation at intermediate energy

The 140 MeV/u 40,48Ca+9Be and 58,64Ni+9Be reactions are simulated by the statistical abrasion ablation model, and the simulation results are compared to the National Superconducting Cyclotron Laboratory (NSCL) experimental data. By comparing the fragment isotopic distributions of 40,48Ca and 58,64Ni, we study the isospin effect in the projectile fragmentation induced by the neutron-rich nuclei at intermediate energy experimentally and theoretically. It is found that the isospin effect in projectile fragmentation decreases and even disappears as the violence of the collision increases.

A possible experimental observable for the determination of neutron skin thickness

The dependence between neutron skin thickness and neutron abrasion cross section (σnabr) for neutron-rich nuclei is investigated within the framework of the statistical abrasion ablation model. Assuming that the density distributions for proton and neutron are of Fermi-type, and adjusting the diffuseness parameter of neutron density distribution in the droplet model, we find out the good linear correlation between the neutron skin thickness and the abrasion cross section σnabr for neutron-rich nuclei. The uncertainty of neutron skin thickness determined from σnabr is very small. It is suggested that σnabr can be used as a new experimental observable to extract the neutron skin thickness for neutron-rich nucleus. The scaling behaviours between neutron skin thickness and σnabr, separately, for isotopes of 26–35Na, 44–56Ar, 48–60Ca, 67–78Ni are also investigated.

Systematic study of isoscaling behavior in projectile fragmentation by the statistical abrasion–ablation model

The isospin effect and isoscaling behavior in projectile fragmentation have been systematically investigated by a modified statistical abrasion–ablation (SAA) model. The normalized peak differences and reduced isoscaling parameters are found to decrease with (Zproj − Z)/Zproj or the excitation energy per nucleon and have no significant dependence on the size of reaction systems. Assuming a Fermi-gas behavior, the excitation energy dependence of the symmetry energy coefficients is tentatively extracted from α and β which looks consistent with the experimental data. It is pointed out that the reduced isoscaling parameters can be used as an observable to study excitation extent of system and asymmetric nuclear equation of state in heavy ion collisions.

Total charge-changing cross sections of stable and neutron-deficient secondary projectiles around A = 60

Abstract Total nuclear charge-changing cross sections σΔz in a CH2 target were measured for 54 isotopically identified secondary beams around A = 60 produced from a 1A·GeV86Kr beam via projectile fragmentation. With secondary beams between T z = 1 2 and −3, the isospin dependence of σΔz was investigated systematically. Contrary to the predictions of so-called overlap formulae, the σΔz values are not a function of the projectile mass alone, but are found to depend on the projectile isospin. A comparison of the data with the predictions of the statistical abrasion model reveals that this behaviour can be understood by the combined influence of the abrasion and the ablation phase in relativistic heavy-ion collisions. On the basis of this improved understanding, previous findings of anomalously large cross sections of secondary-reaction products are discussed.

Production cross sections and the particle stability of proton-rich nuclei from 58Ni fragmentation.

Using a primary beam of $^{58}\mathrm{Ni}$ at 650 MeV/nucleon impinging on a beryllium target, production cross sections of proton-rich fragments from projectile fragmentation have been measured at the projectile-fragment separator FRS at Gesellschaft f\ur Schwerionenforschung Darmstadt m.b.H. The experimental data ranging from nickel to scandium for isotopes close to stability as well as for fragments at the proton drip line are compared to predictions of the microscopic ISApace code, to calculations with a revised abrasion-ablation model and with the statistical abrasion model, and to the results of the empirical parametrization EPAX. Besides these systematic measurements, evidence for the particle stability of $^{50}\mathrm{Ni}$ has been found for the first time, whereas the nuclei $^{49}\mathrm{Co}$ and $^{54}\mathrm{Cu}$ are shown to be unbound. These observations are compared to mass predictions.

Statistical abrasion of nucleons from realistic nuclear-matter distributions

A description of peripheral nuclear collisions at high energies in terms of quasi-free nucleon-nucleon collisions is proposed. The statistical removal of nucleons from diffuse nuclear-density distributions is formulated in the framework of the abrasion model. Based on the nucleon-nucleon cross sections, energy-dependent partial and total abrasion cross sections are obtained. The total abrasion cross section is found to be equivalent to the total interaction cross section resulting from a microscopic Glauber-type calculation. In contrast to geometrical and optical abrasion models, the statistical abrasion formalism describes the fluctuations of the prefragment neutron-to-proton ratio without need for further assumptions. The predictions of the statistical abrasion model are compared to experimental data.

Nuclear charge-changing reactions of secondary beams in the mass range 50 ⩽ A ⩽ 62

At the fragment separator FRS at GSI, relativistic secondary beams with nuclear mass numbers 50 ⩽ A ⩽ 62 were produced by the fragmentation of a 1 A ⊙ ot GeV 86Kr beam in a 9Be production target. The nuclear charge and mass numbers of the secondary-beam particles were determined by a Δ−t.o.f− Bϱ measurement. The fragmentation of stable and neutron-deficient manganese, iron, cobalt and nickel isotopes in a composite carbon-hydrogen target, placed behind the separator, was investigated. The element distributions of the secondary-fragmentation products were found to depend strongly on the neutron-to-proton ratio of the projectile. Calculations with a statistical abrasion model allow an explanation of the observed features by means of the different influences of the neutron-to-proton ratio of the projectile on the abrasion and ablation steps of the fragmentation r reaction.

Proton removal in peripheral nuclear collisions at relativistic energies

The projectile-fragment separator FRS, recently installed at the heavy-ion synchrotron SIS18 at GSI, was used to measure the formation cross sections and longitudinal-momentum distributions of fragments produced by removing one, two or three protons from 0.8 GeV· A 136 Xe and 1 GeV · A 197 Au projectiles impinging on targets of beryllium and aluminum, respectively. These data gave direct information on the high-energy nuclear collision with only little contribution from evaporation processes. The measured cross sections decrease by more than one order of magnitude per proton removed. They are well reproduced by the predictions of a statistical abrasion model and an intranuclear-cascade calculation. The momentum distributions are found to be much broader than predicted by empirical systematics. They are, however, in agreement with the momentum distribution of the abraded protons as calculated with the uniform-Fermi-gas model, if Fermi momenta as measured by quasi-elastic electron scattering are used.