Multiphysics Simulation of a Superconducting Neutron Detector

The detection of neutrons is crucial for both the operation of nuclear devices and the development of advanced imaging techniques. Recently, a hybrid superconducting niobium-boron sensor on a Si/SiO<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$_{\mathbf{2}}$</tex-math></inline-formula> substrate has been developed, aiming for high pulse shape discrimination and controllability of the relaxation time. This device detects thermal neutrons by leveraging the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^\mathrm{10}$</tex-math></inline-formula>B(n,<bold xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><inline-formula><tex-math notation="LaTeX">$\alpha$</tex-math></inline-formula></b>)<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^\mathrm{7}$</tex-math></inline-formula>Li reaction in the B layer and the interaction of the charged products with the Nb strip. To critically assess the operation of the Nb-B thermal neutron detector, a multiphysics modeling approach is presented here. The software COMSOL Multiphysics is used to provide thermal and electrical responses of this device during the transition-to-normal state and its recovery phase. The study takes into account the impact of the thermal irradiation of the cryostat lid and the joule heating on the operating conditions of the Nb strip. Moreover, a pulsed heat load is introduced in the model to simulate the energy released by either the <bold xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><inline-formula><tex-math notation="LaTeX">$\alpha$</tex-math></inline-formula></b> or the Li reaction products in the current-biased Nb strip. The SRIM software is used to obtain the deposited power density profiles and their mean volume of interaction within the sample. For simplicity, the reaction is assumed to take place at the half-thickness of the B layer and the particles propagate perpendicularly to the sample surface. Finally, an iterative procedure was applied to find the most favorable conditions to employ the device in a self-recovering mode by varying both the bias current and the cold finger temperature. This study presents a comprehensive understanding of the working mechanism of the Nb-B thermal neutron detector and proposes a computational approach to find the optimal working point of superconducting neutron detectors.