Abstract
Beams of free neutrons are an important probe to analyze the structure and dynamics of condensed matter and are produced at neutron research reactors, neutron spallation sources or compact accelerator-based neutron sources (CANS). An efficient construction of CANS with a maximized neutron yield and brilliance requires reliable knowledge of the consequences of radiation-induced material damage, the predominating bottleneck of a target’s lifetime. In the framework of the Jülich High-Brilliance neutron Source project, the impact of proton- and neutron-induced material damage of a tantalum target was investigated. The Monte Carlo codes FLUKA and SRIM were utilized to extract the number of displacements per atom resulting from atomic rearrangements. The simulations performed distinctly identify the rear of the neutron target as the most vulnerable area, with the protons as main damage contributors. The minor contribution of neutrons is a material-specific phenomenon due to their high mean free path length in tantalum. Numerical results of the simulations served to calculate average and peak damage rates {R}_{mathrm{d}} (dpa/s), both in turn scaled to annual displacement doses for continuous operation in a full power year (dpa/fpy). Supplemented by the literature, a minimum target lifetime tau _{min } of 2.6 years (33 Ah) is concluded.
Highlights
As neutron scattering and analytics have become highly valuable tools to study the structure and dynamics of condensed matter and to perform chemical analyses of bulk samples in many areas of research over the last decades with a high output of publications from all over the world [1], the demand for neutron beam time remains consistently at high levels
Displaced atoms are termed as primary-knock on atoms (PKAs) and can in turn further kick out atoms, resulting in a collision cascade with a huge diversity of particles
The proton and neutron radiation-induced material damage produced in a tantalum target as described within the High-Brilliance neutron Source (HBS) project was assessed by means of simulations
Summary
As neutron scattering and analytics have become highly valuable tools to study the structure and dynamics of condensed matter and to perform chemical analyses of bulk samples in many areas of research over the last decades with a high output of publications from all over the world [1], the demand for neutron beam time remains consistently at high levels. The findings and conclusions obtained in this work contribute to the specific design and operation of the proposed HBS facility [6,7,8,9]. Independent of this, they are expected to be of benefit to the nuclear physics and engineering community as there yet exist many uncertainties and various routes to obtain dpa values. The simulation of the damage production and the discussion of its evolution over time are restricted to a primary proton beam energy of 70 MeV. A proton energy of 70 MeV results in a competitive neutron yield of 9.1 ⋅ 1014 s −1 mA−1 for the 181 Ta(p,xn)W reaction (∼ 0.10 n/p, estimated with MCNP and cross-sections for proton reactions taken from the TENDL 2017 database) [9] and keeps essential risks concerning the target integrity, such as hydrogen embrittlement and mechanical stress due to temperature gradients, in a moderate frame that can be handled and counteracted well
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