Testing of a Code for the Calculation of Spectra of Neutrons Produced in a Target of a Neutron Generator
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MODELING IN NUCLEAR TECHNOLOGIES
Testing of a Code for the Calculation of Spectra of Neutrons Produced in a Target of a Neutron Generator V. V. Gaganov Russian Federal Nuclear Center—All-Russian Research Institute of Experimental Physics, pr. Mira 37, Sarov, Nizhny Novgorod oblast, 607188 Russia e-mail: [email protected] Received November 21, 2016
Abstract—The correctness of calculations performed with the SRIANG code for modeling the spectra of DT neutrons is estimated by comparing the obtained spectra to the results of calculations carried out with five different codes based on the Monte Carlo method. Keywords: neutron generator, spectrum calculation, DT neutrons, deuteron scattering DOI: 10.1134/S1063778817090058
1. INTRODUCTION Accurate data regarding the energy and angular distribution of neutrons are needed to perform precision experiments with a neutron generator. The FORTRAN-code SRIANG [1] was developed for this purpose by the author of the present study. This code allows one to calculate DT neutron spectra with the observation angle and multiple deuteron scattering (during the stopping in the generator target) taken into account. The calculated spectra provide a detailed description of the DT neutron source (generator target). This description is used as the input data for codes modeling the process of neutron transport based on the Monte Carlo method. 2. DESCRIPTION OF THE CALCULATION ALGORITHM The code under consideration implements a twostage calculation algorithm: a set of deuteron trajectories within the target is first modeled using the TRIM code [2] (from the SRIM package version 2013.00), and then the spectrum of emitted DT neutrons is calculated by SRIANG on the basis of these trajectories. Each node of a model trajectory is characterized by the energy of a deuteron and its coordinates x(i), y(i), z(i). The direction of motion of a deuteron at the currently selected trajectory segment is defined by directional cosines: (i ) (i −1) cos α x = x − x , l
cos α y =
y (i ) − y (i −1) , l
(1)
(i ) (i −1) cos α z = z − z , l
where l is the length of the trajectory segment between the currently selected node and the preceding one. The detector position is characterized by the angle between the initial direction of deuteron motion and the vector from the target center to the detector (observation angle θR). In the case of a point detector, emission angle θn of neutrons incident on it is given by
cos θ n = cos α x cos θ R + cos α y sin θ R + cos α z ⋅ 0.
(2)
Length l of the trajectory segment, average energy Td of a deuteron at this segment, and emission angle θn of the detected neutron define its energy Tn(i ) and production probability Pn(i ):
Pn = σ (Td ,θ n ) lX ,
(3)
where σ(Td, θn) is the differential cross-section of the DT reaction and X is the normalization factor. Relativistic relations [3] obtained by applying the laws of energy and momentum conservation to the problem of inelastic collision of two bodies were used to calculate the neutron energy. The DT reaction cross-section was cal
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