Sadko-2 system for support of group-method calculations of the transfer of high-energy radiation

A large number of codes and program packages, for example, [1--4], have been developed to solve many radiationphysics probIems on charged-particle accelerators involving calculation of the transfer of high-energy radiation. However, no code or program is universal --each program is restricted with respect to energy, type of particles, size and geometry of the region computed, and so on. Outside their region of applicability the programs often lead to incorrect results. The possibilities of computational methods and their restrictions are not always clear to the user. For this reason, we feel that all codes must be verified. However, the programs cannot always be verified on experimental results: special experiments are expensive and the experimental data obtained are, as a rule, insufficient for comprehensive verification of the programs. The way out of this situation is to test the programs on computational results obtained with so-called exact codes, i.e., codes which are designed for definite conditions with a known and quite low methodological error. An example of such a code in a wide range of particle (n, p, x, K, 3') energies is the program-constants system ROZ-6N + Sadko [5--7], which is based on solving a kinetic equation by the method of discrete ordinates.Our objective in the present work is to make a comparative analysis of the computational results for radiation transfer with some known codes and program packages and with the use of the ROZ-6N+Sadko program system for a diverse range of primary-particle energies.Methods for calculating the transport of particles generated by high-energy hadrons. Almost all programs developed for calculating the transport of high-energy particles employ analog modeling of the particle trajectories by the Monte Carlo method. This method is chosen because of its advantages, such as the mathematical simplicity of the modeling algorithm, the possibility and simplicity of taking into account within the scope of the method any physical process, and the possibility of calculating radiation transfer in a complicated geometry. At the same time, the Monte Carlo method has a limitation that determines its region of application --the deep-penetration problem.The limit of applicability of the Monte Carlo analog method can be easily estimated on the basis of the following obvious considerations. The error in estimating the mathematical expectation of a functional N (for example, N can be the number of particles) behind a shield of thickness t by the method of random tests is determined by the formula ~ = 1/x/N. The functional N can be approximated by the well-known function N -N o exp (-fiX), where N o is the number of histories and X is the attenuation length. The computation time is related linearly to No: T = T0N o, where T O is the average time for analyzing one history. Combining the three expressions into one, we obtain an approximate exponential dependence of the computation time on the thickness of the shield T -T O exp(t/X)/e 2, whence it follows, for example, that 10 h of...

Comparison of computational results obtained with different programs for radiation transfer

Gorbatkov¹,

Kryuchkov²

1995

Sadko-2 system for support of group-method calculations of the transfer of high-energy radiation

Gorbatkov¹,

Kryuchkov²

1995

Computational investigation of the formation of radiation fields behind the radiation shield of accelerators is an important problem. Interest in the development of standard methods employed in reactor physics for extending radiationtransfer calculations (the multigroup approach in the description of the energy dependence of the cross sections and the method of discrete ordinates for solving kinetic equation) to the high-energy range has increased substantially in connection with more stringent requirements for computational accuracy, especially in problems of deep penetration of particles, electronuclear power generation, transmutation of long-lived radionuclides, and minimization of background loads on detectors [1--3], This approach makes it possible to separate the mathematical and physical aspects of the calculation of particle transport in matter. The computational programs are universal with respect to the type of particles and their energy, and the main initial physical information --nuclear constants for different types of particles and energy --is contained in libraries, prepared beforehand, of group cross sections.Examples of libraries of group nuclear constants are the BND-400 [4], HILO [1], and Sadko-1 [5] libraries. However, the first two libraries contain data only for neutrons in the energy range below 400 MeV and the Sadko-1 system makes it possible to perform calculations for protons and neutrons with energies up to 600 MeV.The development of a new fast code [6] for calculating the yield of secondary hadrons in inelastic hA-interactions, which would make it possible to obtain much more accurate nuclear data, to expand the energy range, and to increase the number of particle types supported, was the basis for a new version of a library of group nuclear cross sections. The Sadko system (version 2), developed at the Institute of High-Energy Physics, of hadron constants provides the constants necessary for performing calculations by group methods for protons and r-mesons in the energy range from 20 MeV to 10 TeV, neutrons from thermal energy to 10 TeV, and photons from 0.01 to 15 MeV.In the present paper we describe the structure and basic parameters of the new version of the system of constants. Structure of Sadko-2 (Fig. 1). The constituent parts of the system consist of independent blocks of programs and algorithms which are unified by the problem of producing a file of group cross sections in a definite format. The structure of Sadko is determined by the steps required to solve this problem: calculation of the total and double-differential cross sections for the inelastic hA-interaction for a given isotope and energy range;choice of the optimal number of energy groups and a rational method for averaging the cross sections, calculation of group microsections and the scattering phase function for an isotope in the energy range of protons, neutrons, and pions > 20 MeV and probabilities of transitions in a group for neutron energy < 20 MeV; preparation of a low-energy file of group interaction cross...

Kerma factors for calculating the absorbed dose of 15–150 MeV neutrons

Gorbatkov¹,

Kryuchkov²,

Sumaneev³

1996

The absorbed dose is the principal characteristic of the radiative interaction of ionizing radiation with matter. It is of special importance to be able to predict accurately its distribution in the biological tissue of patients undergoing a course of radiation therapy and also to determine the operating lifetime of the particle detectors and electronic equipment operating under conditions of a high radiation level.The absorbed dose of neutrons with energies lower than t00-150 MeV (D, GR) is calculated with satisfactory accuracy in the kerma approximationwhere F(E) is the fluence energy distribution in units of 1 cm-2.MeV -t , and k(E) is the kerma factor in units of 1 GR.cm 2.A large number of experimental and calculated data on the neutron kerma factors are presently known for the principal elements of tissue (see for instance [1]). Although the minimum error of the estimated kerma factors for energies in the region of 50 MeV for tissue elements is -20%, based on analyzing data from more than 20 studies, the real errors are considerably greater. In addition the errors increase as the neutron energy increases. It is therefore very important to improve the accuracy of the kerma factors for carbon, oxygen, and nitrogen.Data on kerma factors for the elements from which the particle detectors and electronics are composed are extremely scarce and their reliability is poor. At the same time, one of the main factors limiting the possibilities of operating the existing and planned apparatus is the change in the physical and chemical properties of their materials under the action of radiation. It is therefore an urgent problem in radiation physics to obtain information to enable one to predict, while still in the planning stage, the radiation loadings and service lifetimes of the experimental equipment. METHOD OF CALCULATIONThe kerma factor is defined as the sum of the initial kinetic energy of the charged particles created in elastic and inelastic interactions of a neutron with a nucleus, normalized to unit mass of the substance and unit fluence.Elastic scattering introduces an important contribution to the kerma factor for light isotopes and for neutron energies below 70 MeV. For example, in the case of carbon and for E n = 20 MeV it constitutes about 25%. In the work now presented the elastic scattering component for the kerma factor was taken into account for neutron energies below 70 MeV. (In the case of hydrogen the kerma factor is completely determined by elastic scattering, independently of the neutron energy.) The recoil energy of the nuclei was calculated from the well-known kinematic relationships, taking account of their angular distributions defined in terms of the Glauber model. The cross sections for the elastic scattering of neutrons by different nuclei were taken from the Sadko-2 library of nuclear data [2]. However, in the investigated range of energies the kerma factors for all nuclei with the exception of hydrogen are determined by inelastic scattering.The kerma factors for neutrons of energy less tha...