On the use of cosmic muons to assess the local attenuation of terrestrial cosmic neutrons in real-time SEB testing of power devices

Abstract

Real-time lifetime tests to define the survivability to terrestrial cosmic rays of power devices require characterizing the local flux of cosmic neutrons, which depends among others on the absorption by the local building and structural materials of the laboratory. Traditional neutron spectrometers are voluminous and prone to mechanical shocks. Therefore, they are not well-suited for this scope, especially for mobile applications. The proposed solution exploits the fact that the detection probability of cosmic muons in the energy range of interest is four orders of magnitude higher than for neutrons. For this scope, an original spectrometer for cosmic muons has been designed and implemented, which uses a solid-state semiconductor detector. Thanks to its ruggedness, the reduced size and the fact that it can be battery-powered, the spectrometer can be employed both in stationary, as well as in mobile tests (e.g. electric vehicles). According to the proposed procedure, the muon flux measured outdoors is compared with the flux measured indoors to extract the thickness of the shielding material. Finally, the local flux of cosmic neutrons is inferred from the thickness of the shielding material based either on tabulated correlation functions, or on Monte Carlo simulations. The paper presents an application of the proposed technique as well, as a detailed description of the dedicated semiconductor spectrometer.