Author(s)

Habib Mohammadi^1*, Mohammad Mehdi Firoozabadi¹, Rouhollah Gheisari²

¹Department of Physics, University of Birjand, Birjand, Iran.
²Physics Department, Persian Gulf University, Bushehr, Iran.

At thermal ultra-cold neutron (UCN) sources (neutrons in thermal equilibrium with the moderator) only a very small fraction of neutrons have velocities ~6 m/s. Therefore, the UCN production rate cannot be substantially increased by simply lowering the temperature of the moderator. The new approach is to use the super-thermal principle, i.e., neutrons not in thermal equilibrium with the converter. We want to investigate scattering kernels for a super-thermal UCN source based on a two-layer arrangement of D₂O and solid D₂. The solid D₂ (sD₂) at temperature 8 K is kept in close contact with D₂O moderator at room temperature. Using the MCNP code, the fast neutron flux on the spallation target, the thermal flux in the D₂O near the sD₂, and the cold flux in the sD₂ are simulated. For a given cold flux, neutron transport equations are calculated. In order to obtain precise neutron scattering kernels, and consequently UCN flux and density, 330 neutron energy groups have been taken. The coupled energy dependent transport equations have been solved by combining MCNPX code with an analytical approach and using implicit method in MATLAB. We have obtained an optimal dimension for the UCN source. A suitable space step has been taken for the numerical stability.

Two-Layer UCN Source Based on D2O/sD2, Scattering Kernel, Monte Carlo Method, Implicit Method, Super-Thermal Principle

Mohammadi, H. , Firoozabadi, M. and Gheisari, R. (2014) Numerical Investigation of a UCN Source Based on Solid Deuterium by Combining a Simulation Code with an Analytical Approach. Journal of Modern Physics, 5, 1831-1838. doi: 10.4236/jmp.2014.517179.