Applicability of particle and heavy ion transport code PHITS to the shielding design of spacecrafts

Development of HZE particle transport codes is severely required for the shielding design of spacecrafts. One-dimensional deterministic codes are generally adopted in the shielding calculation because of their reasonable computational time, but three-dimensional Monte Carlo codes are also to be employed especially in the final step of the design with fully optimized geometries. We are therefore developing a general-purpose Monte Carlo code PHITS, which can deal with the transports of all kinds of hadrons and heavy ions with energies up to . For the purpose of examining the applicability of PHITS to the shielding design, neutron and charged particle spectra inside the Space Shuttle were calculated for an imaginary vessel whose shielding distribution is fitted to that of the real shuttle. Absorbed doses and dose equivalents were estimated from the spectra by applying fluence to dose conversion coefficients. The agreements between the calculated spectra or doses and the corresponding experimental data were generally satisfactory, especially for the neutron spectra, which have been barely reproduced by other studies. We therefore concluded that PHITS has a great possibility of playing an important role in the design study of spacecrafts.     

PHITS—a particle and heavy ion transport code system

The paper presents a summary of the recent development of the multi-purpose Monte Carlo Particle and Heavy Ion Transport code System, PHITS. In particular, we discuss in detail the development of two new models, JAM and JQMD, for high energy particle interactions, incorporated in PHITS, and show comparisons between model calculations and experiments for the validations of these models. The paper presents three applications of the code including spallation neutron source, heavy ion therapy and space radiation. The results and examples shown indicate PHITS has great ability of carrying out the radiation transport analysis of almost all particles including heavy ions within a wide energy range.     

High energy heavy ion interactions studied with SSNTDs

We have continued our studies of heavy ion projectile fragmentation using nuclear track detectors. Based on automatic track measurement it was possible to perform experiments with high statistical significance. Beams of different ions from the Berkeley BEVALAC, the Dubna Synchrophasotron, the Brookhaven AGS and the GSI Darmstadt SIS have been used. With CR-39 and BP-1 glass detectors we have studied the process of electromagnetic dissociation, we investigated multifragmentation and continued the search for quark nuclear complexes. This paper gives an overview of these experiments. Details of the experimental technique are discussed.     

蒙特卡罗粒子输运程序JMCT研制

介绍了具有自主知识产权的蒙特卡罗(MC)粒子输运程序JMCT的初步研制成果。JMCT基于三维组合几何支撑软件框架JCOGIN,采用模块化,分成多层管理结构,可处理多群碰撞和连续能量碰撞,可进行粒子并行和区域分解并行两种并行方法,并具有良好的可扩展性和高速通信技术,同时配有可视化建模前处理软件。介绍了JMCT采用的多群物质碰撞机制,展示了程序模拟计算测试模型的结果,与MCNP程序计算结果一致。JMCT串行计算速度相比MCNP提高了约3 倍;在20 480个处理器核上模拟2109样本,并行效率可达70%。     

蒙特卡罗粒子输运程序JMCT研制

介绍了具有自主知识产权的蒙特卡罗(MC)粒子输运程序JMCT的初步研制成果。JMCT基于三维组合几何支撑软件框架JCOGIN,采用模块化,分成多层管理结构,可处理多群碰撞和连续能量碰撞,可进行粒子并行和区域分解并行两种并行方法,并具有良好的可扩展性和高速通信技术,同时配有可视化建模前处理软件。介绍了JMCT采用的多群物质碰撞机制,展示了程序模拟计算测试模型的结果,与MCNP程序计算结果一致。JMCT串行计算速度相比MCNP提高了约3 倍;在20 480个处理器核上模拟2109样本,并行效率可达70%。     

Role of single particle transfer in heavy ion fusion

Fusion excitation functions in heavy ion collision have been calculated taking into account the effect of random transfer of single particles in a classical dynamical model. The model has been applied to fusion of ¹⁶O+²⁷Al and ⁴⁰Ar +¹⁰⁹Ag. The transfer does not affect the low energy fusion excitation function but the effect of transfer is appreciable for high energies.     

Inertia effects in the mass transport of heavy ion reactions

The general trend of the multi differential cross section plots for the products obtained from the dissipation collisions of the three systems, forming almost the same composite systems but with different degrees of mass asymmetry in the entrance channel,⁵²Cr (261 MeV)+⁵⁶Fe,⁴⁰Ca (182 MeV)+⁶⁴Ni and¹⁶O (187 MeV)+⁹²Mo, were analysed in the frame of the Diffusion Model, assuming that the intermediate system decays with a statistical life time. A fairly good agreement has been obtained between the calculated multi differential plots and the experimental ones. The half life time of the composite systems seem to depend on the mass asymmetry of the entrance channel.     

Mass transport and energy equilibration in heavy ion collisions

The lack of mass drift observed in Kr-induced collisions is explained assuming energy and particle transfer from the light to the heavy fragment during the equilibration stage in asymmetric heavy-ion reactions. Transferred energy and particle number can be estimated from the interfragment thermal equilibrium distribution provided the initial partition is known which we calculate within a semiclassical theory based on TDHF. The experimental findings are consistent with the theoretical predictions. In particular, the experimental mass drift as function of total kinetic energy loss is quantitatively described within a modified diffusion model which takes into account the mass exchange prior to the transport stage.     

Thermal gas models and particle production in heavy ion collisions

A systematic study of particle production in nuclear S–S and S–W collisions at 200 GeV/A is presented within the context of an equilibrium interacting hadron gas model. It is shown that the results for strange particle multiplicities and for non-strange baryons obtained in the NA35 and WA85 experiments can be well described in terms of the considered model.     

Nucleon transport processes in fission and heavy ion reactions

The nucleon exchange process between two nuclei in close proximity and its application to an explanation of fragment mass and charge distributions in fission and in heavy ion deep inelastic collisions are reviewed. An analysis of the measured correlations between the energy loss from relative motion and the fragment mass and charge variances in the heavy ion deep inelastic collisions is presented. The recent data on fragment mass and charge variances as a function of the fragment kinetic energy in thermal neutron induced fission of²³⁵U, lends added support to the hypothesis that the nucleon transport process plays a similar role both in fission and in heavy ion deep inelastic collisions.     

蒙特卡罗粒子输运软件JMCT抽样工具库设计

为通用型蒙特卡罗粒子输运程序JMCT设计了抽样工具库,通过两种技术途径提供各分布的抽样。一是针对各种常见分布提供特定抽样子程序;二是提供一个通用型的抽样子程序,可以实现任意离散分布和任意一维有限区间上连续分布的自动抽样。在设计任意一维有限区间上连续分布的自动抽样工具时利用了部分开源代码,利用其功能提供给用户最大的方便性。对抽样工具库的检验表明,其可以正确、方便地实现各种输运模拟中常见分布的抽样。     

Study of neutron generation from relativistic heavy ion interactions

Study has been carried out on neutron generation in the interactions of 44 and 18 GeV ¹²C with Cu-and Pb-targets. The properties studied include, (1) Relative yields of secondary neutrons generated in 44 GeV versus in 18 GeV ¹²C bombardment to Cu target and also to Pb target. The ratios of these are 2.12±0.19 and 2.04±0.15, respectively, which is nearly in consistence with but somewhat larger than the values of theoretical calculations for Cu target. (2) Relative yields of secondary neutrons produced in Pb target versus in Cu target. The ratios obtained are 2.54±0.20 and 2.56±0.20 for 44 GeV and 18 GeV, respectively. More neutrons are generated in Pb target than in Cu target.     

Charged particle fluctuation as signal of the dynamics in heavy ion processes

We compare the dispersion of the charges in a central rapidity box according to the dual parton model with the predictions of statistical models. Significant deviations are found in heavy ion collisions at RHIC and LHC energies. Hence the charged particle fluctuations should provide a clear signal of the dynamics of heavy ion processes. They should allow one to directly measure the degree of thermalization in a quantitative way. Received: 7 November 2000 / Revised version: 4 September 2001 / Published online: 5 October 2001     

Quantum-coherent transport of a heavy particle in a fermionic bath

In this review, a detailed discussion of the behaviour of a heavy particle interacting with a Fermi sea is given. Particular emphasis is put on the issue of how strong correlations influence coherence and transport of the particle. First, we investigate the question of whether the heavy particle is a well defined quasiparticle at low temperatures. While in one dimension ( D = 1) and at a van Hove singularity in D = 2 the coherence of the particle is destroyed, the quasiparticle weight is finite in higher dimensions. The most important transport quantity is the diffusion constant or mobility of the heavy particle. We are able to describe both the well known high-temperature properties and the cross-over to the lowest temperatures in a unified approximation scheme based on a self-consistent evaluation of an effective action. Two strong-correlation effects of independent origin are discussed. The first arises if the scattering of the fermions from the heavy particle is nearly resonant, that is, if one of the scattering phase shifts δ is close to π/2. In this regime an anomalous exponent is observed in the temperature dependence of the mobility μ(T). In D = 3, for instance, the mobility is proportional to T^-3/2 rather than to T^-2. The second effect is a giant mass renormalization in the case of a large particle. In this situation, the low-temperature effective mass M* increases up to an exponentially large value, M* exp[c(r/λF)³], where r is the effective radius of the particle, λF the Fermi wavelength and c a non-universal constant of order one.     

Classical driven transport in open systems with particle interactions and general couplings to reservoirs

We study nonequilibrium steady states of lattice gases with nearest-neighbor interactions that are driven between two reservoirs. Density profiles in these systems exhibit oscillations close to the reservoirs. We demonstrate that an approach based on time-dependent density functional theory copes with these oscillations and predicts phase diagrams of bulk densities to a good approximation under arbitrary boundary-reservoir couplings. The minimum or maximum current principles can be applied only for specific bulk-adapted couplings. We show that they generally fail to give the correct topology of phase diagrams but can still be useful for getting insight into the mutual arrangement of different phases.     

Direct mechanisms of fast light particle formation in heavy ion collisions

Two direct mechanisms are considered for the heavy ion collisions which lead to fast α-particle emission: α-particle knock on by the incident ion and heavy fragment stripping of this ion. It is demonstrated that stripping mechanism allows to reproduce all the experimental characteristic features of the process except the cross-section dependence on α-particle separation energy in the target. Knock on process reproduces this feature as well. It is pointed that the analysis of experimental data on the hard part of α-particle spectrum allows to gain a unique information on the properties of the strongly rotating nuclei produced in these reactions.