Investigation of features of isotope effect

Isotope effect is investigated for the products formed in various channels of nuclear reactions. The separate consideration of neutron-poor and neutron-rich products shows difference in values of isoscaling parameters. The largest difference is observed for spallation products. This difference decreases with reduction of the mass number of products.     

Symmetry energy and the isoscaling in reactions on enriched tin isotopes

The coefficients of symmetry energy term for fragments with Z = 4, 11, 12 measured in multifragmentation reactions initiated by proton and deuteron with energy of 3.65 A GeV on enriched tin isotopes ^{112,118,120,124}Sn are determined. The dependence of isoscaling parameter on the excitation energy, the temperature of fragmenting systems and the density ratio for heavy mass products are analyzed.     

核子-核子碰撞截面对同位素标度参数α的介质效应

核子能量在40—60MeV能区范围,对在两对重离子中心碰撞系统⁴⁰Ca+⁴⁸Ca和⁶⁰Ca+⁴⁸Ca以及¹¹²Sn+¹¹²Sn和¹²⁴Sn+¹²⁴Sn 的反应中就同位素标度参数α对于核子-核子碰撞截面σ^med_NN(α_m)的介质 关键词： 同位素标度行为 介质效应 核子-核子碰撞截面 重离子碰撞     

Isospin and symmetry energy study in nuclear EOS

This paper summarizes the isoscaling and isospin related studies in asymmetry nuclear reactions by different dynamic and statistical models. Isospin dependent quantum molecular dynamics model (IQMD) and lattice gas model (LGM) are used to study the isoscaling properties and isoscaling parameters dependence on incident energies, impact parameters, temperature and other parameters. In the LGM model, the signal of phase transition has been found in free neutron (proton) chemical potential difference Δµ_n or Δµ_p as a function of temperature, or in free neutron and proton chemical potential difference Δµ_n−Δµ_p. Density dependence of symmetry energy coefficient C _sym(ρ/ρ ₀) is also studied in the frame of LGM, with the potential parameters which can reproduce the nuclear ground state property, soft density dependence of symmetry energy is deduced from the simulation results. Giant dipole resonance (GDR) induced by isospin asymmetry in entrance channel is also studied via IQMD model, and the dynamic dipole resonance shows isospin sensitivity on the isospin asymmetry of entrance channel and symmetry energy of the nuclear equation of state (EOS). GDR can also be regarded as a possible isospin sensitive signature.

     

Effect of secondary decay on isoscaling: Results from the canonical thermodynamical model

The projectile fragmentation reactions using ⁵⁸Ni and ⁶⁴Ni beams at 140 MeV/n on targets ⁹Be and ¹⁸¹Ta are studied using the canonical thermodynamical model coupled with an evaporation code. The isoscaling property of the fragments produced is studied using both the primary and the secondary fragments and it is observed that the secondary fragments also respect isoscaling though the isoscaling parameters α and β changes. The temperature needed to reproduce experimental data with the secondary fragments is less than that needed with the primary ones. The canonical model coupled with the evaporation code successfully explains the experimental data for isoscaling for the projectile fragmentation reactions.     

Formation of light isotopes by protons and deuterons of 3.65 GeV/nucleon on separated tin isotopes

We measure cross sections for residual nuclide formation in the mass range 7 ≤ A ≤ 96 caused by bombardment with protons and deuterons of 3.65-GeV/nucleon energy of enriched tin isotopes (^{112,118,120,124}Sn). The experimental data are compared with calculations by the codes FLUKA, LAHET, CEM03, and LAQGSM03. Scaling behavior is observed for the whole mass region of residual nuclei, showing a possible multifragmentation mechanism for the formation of light products (7 ≤ A ≤ 30). Our analysis of the isoscaling dependence also shows a possible contribution of multifragmentation to the production of heavier nuclides, in the mass region 40 ≤ A ≤ 80. The text was submitted by the authors in English.     

核子-核子碰撞截面对同位素标度参数α的同位旋效应

对两对重离子中心碰撞系统⁴⁰C+⁴⁰Ca 和⁶⁰Ca+⁴⁰Ca以及¹¹²Sn+¹¹²Sn和¹²⁴Sn+¹²⁴Sn反应中就同位素标度参数α对于核子-核子碰撞截面的同位旋效应进行了研究.计算结果表明α对同位旋相关核子-核子碰撞截面σ^med_{NN关键词： 同位旋效应 核子-核子截面 机理 同位素标度}     

Projectile fragmentation of <Superscript>40,48</Superscript>Ca and isotopic scaling in a transport approach

We investigate theoretically projectile fragmentation in reactions of ^40,48Ca on ⁹Be and ¹⁸¹Ta targets using a Boltzmann-type transport approach, which is supplemented by a statistical decay code to describe the de-excitation of the hot primary fragments. We determine the thermodynamical properties of the primary fragments and calculate the isotope distributions of the cold final fragments. These describe the data reasonably well. For the pairs of projectiles with different isotopic content we analyze the isotopic scaling (or isoscaling) of the final fragment distributions, which has been used to extract the symmetry energy of the primary source. The calculation exhibits isoscaling behavior for the total yields as do the experiments. We also perform an impact-parameter-dependent isoscaling analysis in view of the fact that the primary systems at different impact parameters have very different properties. Then the isoscaling behavior is less stringent, which we can attribute to specific structure effects of the ^40,48Ca pair. The symmetry energy determined in this way depends on these structure effects.     

Geometrical aspects of isoscaling

The property of isoscaling in nuclear fragmentation is studied using a simple bond percolation model with “isospin” added as an extra degree of freedom. It is shown, first, that with the assumption of fair sampling and with homogeneous probabilities it is possible to solve the problem analytically. Second, numerical percolations of hundreds of thousands of grids of different sizes and with different N to Z ratios confirm this prediction with remarkable agreement. It is thus concluded that isoscaling emerges even in the simple case of a classical non-interacting system such as two-species percolation under the assumption of fair sampling; if put in the nomenclature of the minimum information theory, isoscaling in percolation appears to require nothing more than the existence of equiprobable configurations in maximum entropy states.     

Isoscaling and fission modes in the yields of the Kr and Xe isotopes from photofission of actinides

Yields of Kr and Xe isotopes in photofission of ²³²Th, ²³⁸U, ²³⁷Np, ²⁴⁴Pu, ²⁴³Am, and ²⁴⁸Cm were tested for isoscaling dependence. Isoscaling for Kr is revealed. For Xe, isoscaling is found to be affected by the STI and STII fission modes governed by the N = 82 and N = 88 neutron shells. The work was performed at the Flerov Laboratory of Nuclear Reactions, Joint Institute for Nuclear Research (JINR).     

Isotopic temperature in spallation reactions

The possibility of applying the double-isotope-ratio method for calculating temperature to spallation products formed by high-energy protons is discussed. It is concluded that, at a specific incident-particle energy, spallation is characterized by a single temperature of the formation of products for targets in the mass range 56 ≤ A ≤ 208. No energy dependence of the temperature that was calculated by the double-isotope-ratio method was observed in the energy range 0.3 ≤ E ≤ 300 GeV.     

Isotopic Ratio,Isotonic Ratio,Isobaric Ratio and Shannon Information Uncertainty

The isoscaling and the isobaric yield ratio difference (IBD) probes, both of which are constructed by yield ratio of fragment, provide cancelation of parameters. The information entropy theory is introduced to explain the physical meaning of the isoscaling and IBD probes. The similarity between the isoscaling and IBD results is found, i.e., the information uncertainty determined by the IBD method equals to β-α determined by the isoscaling (α (β) is the parameter fitted from the isotopic (isotonic) yield ratio).     

Isoscaling of projectile-like fragments

In this paper, the isotopic and isotonic distributions of projectile fragmentation products have been simulated by a modified statistical abrasion--ablation model and the isoscaling behaviour of projectile-like fragments has been discussed. The isoscaling parameters α and β have been extracted respectively, for hot fragments before evaporation and cold fragments after evaporation. It looks that the evaporation has stronger effect on α than β. For cold fragments, a monotonic increase of α and β with the increase of Z and N is observed. The relation between isoscaling parameter and the change of isospin content is discussed.     

Isoscaling behavior studied by HIPSE model

The isoscaling behavior in the reaction system of 58,64Ni + 9Be has been studied by using the heavy-ion phase-space exploration(HIPSE) model. The extracted isoscaling parameters α and β for both heavy and light fragments for HIPSE model calculations are in good agreement with recent experimental data. The investigation shows that the parameters in the HIPSE model have some effect on the isoscaling parameter. The isoscaling parameters for hot and cold fragments have been extracted.     

Thresholds for front-side ablation and rear-side spallation of metal foil irradiated by femtosecond laser pulse

The mechanical action of laser exposure on a foil may result in the ablation of irradiated front layer and the rear-side spallation. The dynamics of an Al foil is studied by means of two-temperature (2T) hydrodynamics and molecular dynamics (MD). It is found that the rear-side spallation threshold F _s exceeds the front-side ablation threshold F _a. We propose to extend the common approach in laser-matter experiments by pump–probe measuring of the rear-side displacement.     

Deep spallation cross sections in high energy protons — Uranium interactions

Cross sections of deep spallation products — from phosphorus to hafnium — formed in uranium by high energy protons (E _p ? 10 GeV) have been calculated with a simple semi-empirical formula. The results are in excellent agreement with experimental data.     

Systematization of the yields of products of photonuclear reactions on enriched-tin targets at the bremsstrahlung-photon endpoint energy of 4.5 GeV

Yields of photonuclear-reaction products formed in targets from separated tin isotopes under the effect of beams of bremsstrahlung photons whose endpoint energy is 4.5 GeV were investigated. The systematization performed on this basis revealed an isoscaling character of the behavior of the production yields for various regions of reaction-product masses.     

Quantum molecular dynamics approach to estimate spallation yield from<Emphasis Type="Italic">p</Emphasis> +<Superscript>208</Superscript>Pb reaction at 800 MeV

The spallation yield of neutrons and other mass fragments produced in 800 MeV proton induced reaction on²⁰⁸Pb have been calculated in the framework of quantum molecular dynamics (QMD) model. The energy spectra and angular distribution have been calculated. Also, multiplicity distributions of the emitted neutrons and kinetic energy carried away by them have been estimated and compared with the available experimental data. The agreement is satisfactory. A major contribution to the neutron emission comes from statistical decay of the fragments. For mass and charge distributions of spallation products the QMD process gives rise to target-like and projectile-like fragments only.     

Spallation neutron spectrum on a massive lead/paraffin target irradiated with 1 GeV protons

The gamma-ray spectra emitted by decaying of residual nuclei produced by spallation neutrons in (n, xn), (n, xnyp), (n, p), (n, ) reactions with activation threshold detectors, i.e. ²⁰⁹Bi, ¹⁹⁷Au, ⁵⁹Co, ¹¹⁵In, ²³²Th, were measured in the Laboratory of Nuclear Problems (LNP), JINR, Dubna, Russia. Spallation neutrons were generated by bombarding a 20 cm long cylindrical lead target with 8 cm diameter surrounded by a 6 cm thick layer of paraffin moderator with 1 GeV proton beam from the NUCLOTRON accelerator. Reaction rates and a spallation neutron spectrum were measured and compared with CASCADE code calculations.     

Momentum transfer and product kinetic energies in the interaction of silver with 86 MeVA12C

Mean kinetic properties of target fragments have been derived from thick target-thick catcher recoil data in a study of the interaction of silver with $\text{86}\text{MeV}\text{A}$¹²C ions. The $\text{F}\text{B}$-ratios reach maximum values of ≈ 200, showing that the angular distributions in the laboratory system are strongly forward peaked. Heay products (A?70) are found to be produced in a normal spallation reaction. However, it is suggested that products found in the mass region A≈60 are to a large fraction binary fission products.