Understanding efficiency differences of betavoltaic batteries measured by electron gun mimicked source and radioactive β source

Abstract

Electron guns have been widely used to mimic the radiation of radioactive β sources in many fields, including radiation effects and material modification, due to their unique advantages such as steerable irradiation area, adjustable electron energy, and flux. However, it is still unclear whether the results and conclusions drawn from the mimicking experiments can provide effective guidance and reference for real radiation. In this work, we systematically investigated the difference of electron guns and radioactive β sources on the efficiency measurement of betavoltaic batteries and gave a quantitative analysis on the causes. Geant 4 simulations of the energy deposition of electrons emitted from electron guns and 63Ni sources demonstrate that the energy dispersion and the incident direction distribution of electrons are the major causes of the difference of the energy deposition ratio and profile in energy conversion units. The single emission direction of electrons leads to an overestimation around 30% in the conversion efficiency measured using an electron gun. The device structure also contributes to the efficiency difference. The efficiency difference of three SiC samples with different structures measured under electron guns and 63Ni sources varies from 20.6% to 32.0% in three samples, which agrees very well with the simulation results. This work provides a valuable guidance to evaluate the results generated from electron-gun mimicked β sources. The physics discussed here would provide good references for other applications using mimicked β sources.