A new treatment of radiation behaviour beyond one-body observables 05/2008; DOI: 10.1051/ndata:07398


We propose a new treatment of radiation behaviour in transport calculations by introducing an event generator model in which we combine the nuclear data and the reaction models so as to trace all correlations of ejectiles keeping the energy and momentum conservation in a collision. By this new model, we can estimate the fluctuations around the mean values of one-body observables, for example, the deposit energy distribution in a cell, which cannot be obtained by the transport calculations based on the Boltzmann equation with the nuclear data.

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    • "Therefore, some particle transport simulation codes employ supplementary algorithms to perform transport calculations based on the cross-section data with conservation of energy and momentum (referred to as the event generator mode, EGM here- after). A good example is the EGM of PHITS (Particle and Heavy Ion Transport code System) [6], which samples the secondary neutron emission angles and energies based on the cross-section data and accordingly balances the energy and momentum through the excitation and recoiling of the residue. However, for reactions emitting more than one secondary particle, the evaporation model was used to sample the second and the subsequent outgoing neutrons in EGM. "
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    ABSTRACT: A new phenomenological approach is developed to reproduce the stochastic distributions of secondary particle energy and angle with conservation of momentum and energy in reactions ejecting more than one ejectiles using inclusive cross-section data. The summation of energy and momentum in each reaction is generally not conserved in Monte-Carlo particle transport simulation based on the inclusive cross-sections because the particle correlations are lost in the inclusive cross-section data. However, the energy and angular distributions are successfully reproduced by randomly generating numerous sets of secondary particle configurations which are compliant with the conservation laws, and sampling one set considering their likelihood. This developed approach was applied to simulation of (n,xn) reactions (x Z 2) of various targets and to other reactions such as (n,np) and (n,2nα). The calculated secondary particle energy and angular distributions were compared with those of the original inclusive cross-section data to validate the algorithm. The calculated distributions reproduce the trend of original cross-section data considerably well especially in case of heavy targets. The developed algorithm is beneficial to improve the accuracy of event-by-event analysis in particle transport simulation. & 2014 Elsevier B.V. All rights reserved.
    Full-text · Article · Jul 2014 · Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment
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    • "However, owing to the approximate treatment of the level structure above the first excitation state, the metastable state is not considered. PHITS [10] adopted a combination of a very simple nuclear de-excitation model and an event generator model [11] prior to this study. An alternative method is to transport particles based on evaluated nuclear data instead of using event generators [12] [13]. "
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    ABSTRACT: A new theoretical model to simulate gamma de-excitation of excited nuclei, EBITEM (ENSDF-Based Isomeric Transition and isomEr production Model), is developed based on the Evaluated Nuclear Structure Data File (ENSDF), supplementary evaluated data tables, and theories. In the model, reaction products after nucleon evaporation were de-excited by using theoretical calculations if the excitation energy was higher than 3000 keV and the mass number was greater than 40 amu. Otherwise, the nuclei were de-excited based on the scheme provided in the ENSDF. Thus by tracking nuclear de-excitation, production of prompt gamma-rays and isomers was simulated. The model is applicable for neutron capture products and spallation products of 1071 nuclear species from Li to Bk. Except for some of the light nuclei with discrete level structure, simulated isomer production and prompt gamma-ray spectra agree generally within 40% and a factor of 3, respectively.
    Full-text · Article · Apr 2014 · Nuclear Instruments and Methods in Physics Research Section B Beam Interactions with Materials and Atoms
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    ABSTRACT: The fluence to organ-absorbed-dose and effective-dose conversion coefficients for heavy ions with atomic numbers up to 28 and energies from 1 MeV/nucleon to 100 GeV/nucleon were calculated using the PHITS code coupled to the ICRP/ICRU adult reference computational phantoms, following the instruction given in ICRP Publication 103 (2007 (Oxford: Pergamon)). The conversion coefficients for effective dose equivalents derived using the radiation quality factors of both Q(L) and Q(y) relationships were also estimated, utilizing the functions for calculating the probability densities of absorbed dose in terms of LET (L) and lineal energy (y), respectively, implemented in PHITS. The calculation results indicate that the effective dose can generally give a conservative estimation of the effective dose equivalent for heavy-ion exposure, although it is occasionally too conservative especially for high-energy lighter-ion irradiations. It is also found from the calculation that the conversion coefficients for the Q(y)-based effective dose equivalents are generally smaller than the corresponding Q(L)-based values because of the conceptual difference between LET and y as well as the numerical incompatibility between the Q(L) and Q(y) relationships. The calculated data of these dose conversion coefficients are very useful for the dose estimation of astronauts due to cosmic-ray exposure.
    No preview · Article · Mar 2010 · Physics in Medicine and Biology
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