Resistive all boron carbide neutron detectors

Semiconducting boron carbide is a promising material for true solid-state neutron detection [1]. An all boron carbide (BC) layer was deposited on sapphire (Al$_{2}$O$_{3})$ with sputtered Chrome/Gold electrical contacts. Resistance vs. temperature measurements indicate a T$^{-3/2}$ dependence and a band gap of $\sim $ 0.17eV. X-ray diffraction measurements confirm the similarities in crystal structure of the films grown on Al$_{2}$O$_{3}$ and Si. Detection area ranged from 0.25mm$^{2}$ to 1mm$^{2}$ and the thickness of the films ranged from 280nm to 600nm. Neutron detection measurements show no sharp spectral peaks but a long high energy tail which increased in counts as the reactor power was increased, in agreement with both monte carlo simulations and simple model calculations [2]. The low thermal neutron capture cross section of Al and O ensures that the entire neutron signal observed is from the resistive boron carbide layer, thus demonstrating the fabrication of an all boron carbide neutron detector. We show plots as a function of reactor power and thickness. [1] B.W. Robertson, S. Adenwalla, A. Harken, et al., \textit{Appl. Phys. Lett.} \textbf{80}, 3644 (2002). [2] C. Lundstedt, A. Harken, E. Day, B. W. Robertson, S. Adenwalla, submitted to NIM.