A new pulse shape description for $α$ particle pulses in a highly-sensitive sub-Kelvin bolometer

Abstract

The next generation of cosmology space missions will be sensitive to parasitic signals arising from cosmic rays. Using a composite bolometer, we have investigated pulses produced by $α$ particles in order to understand the movement of energy produced by ionising radiation. Using a series of measurements at 100 mK, we have compared the typical fitting algorithm (a mathematical model) with a second method of pulse interpretation by convolving the detector's thermal response function with a starting profile of thermalised athermal phonons, taking into account the effects of heat propagation. Using this new fitting method, we have eliminated the need for a non-physical quadratic nonlinearity factor produced using more common methods, and we find a pulse form in good agreement with known aspects of thermal physics. This work is carried forward in the effort to produce a physical model for energy deposition in this detector. The modelling is motivated by the reproduction of statistical features in the experimental dataset, and the new interpretation of $α$ pulse shapes represents an improvement in the current understanding of the energy propagation mechanisms in this detector.

Presented at SPIE Astronomical Telescopes and Instrumentation 2018 (Austin, TX), published in Proc. SPIE 10698, Optical Infrared and Millimetre Wave, 1069863 on 12 July 2018