Design and optimization of 90Sr–Si betavoltaic nuclear battery and its comparison with a direct charge nuclear battery based on 90Sr radioactive source

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In present work, the 90Sr radioisotope with half-life of 28.8 years and activity of 16.328 mCi was considered as a source. The purpose of this paper is to compare a direct charge nuclear battery (DCNB) with a betavoltaic nuclear battery in constant volume. In this comparison the volume of the batteries, the dimensions of the source and the activity of the source are constant. First, the beta spectrum of 90Sr + 90Y was calculated. Then, the type of collector (materials), the distance between the source and the collector, and collector thickness were investigated and optimized for the case of a DCNB by Monte Carlo N–Particle (MCNPX) code. It was found that the best parameters for this DCNB are the use of the Be as a collector, the distance between the source and the collector 25 μm and collector thickness 1400 μm. Under these parameters, the short circuit current and open circuit voltage are 0.08997 nA and 549 kV, respectively. If there is a semiconductor material instead of a vacuum in the DCNB, it will be converted into a betavoltaic nuclear battery. Therefore, the semiconductor material (Si) was considered in the distance between the source and the collector instead of the vacuum. Then the best thickness for silicon was determined.By discussing the effect of doping concentration and minority carrier diffusion length on the optimization of betavoltaic battery utilizing a90Sr radioisotope source and Si as the converter material, it was found that junction depth of 0.9 μm, semiconductor thickness 728 μm, Na (doping concentration in P-type semiconductor) = 1.5 × 1015 cm−3 and Nd (doping concentration in N-type semiconductor) = 3.0 × 1015 cm−3. Therefore, the short circuit current and open circuit voltage are 3920 nA and 0.309 V, respectively. In other words, at constant volume, constant source dimensions and constant activity, the use of the semiconductor instead of the vacuum increases the short circuit current of the nuclear battery by about 44,000 times.