Theoretical Maximum Efficiency for a Linearly Graded Alphavoltaic Nuclear Battery

This paper presents a study on the optimization of the amount of energy deposited by alpha particles in the depletion region of a silicon carbide (SiC) alphavoltaic cell using Monte Carlo models. Three Monte Carlo codes were used in this study: SRIM/TRIM, GEANT4, and MCNPX. The models examined the transport of 5.307-MeV alpha particles emitted by ²¹⁰Po. Energy deposition in a 1-m depletion region of SiC was calculated using an isotropic alpha source for a spherical geometry using GEANT4, and a monodirectional alpha source for a slab geometry using both SRIM/TRIM and GEANT4. In addition, an isotropic point source was modeled using GEANT4 and MCNPX for a slab geometry. These geometries were optimized for the maximum possible alphavoltaic energy efficiency. The models, which match very well, indicate that the maximum theoretical energy conversion efficiency, which was optimized for a SiC alphavoltaic cell, is [approximately]3.6% for the isotropic alpha source on a slab geometry and 2.1% for both the monodirectional alpha source on a slab geometry and the isotropic alpha source at the center of a sphere. This study provides a useful guide governing the upper limit of expected efficiency for an alphavoltaic cell using a linearly graded single junction SiC transducer.