We report further studies on the neutron detection capabilities of boron carbide/Si heterjunction diodes. In particular, we investigate the behavior of these diodes in the presence of low neutron flux. The spectrum is compared with previous data obtained in the high neutron flux environment in the irradiation sample well of a TRIGA reactor.
Semiconducting boron-rich boron-carbon alloys have been deposited by plasma-enhanced chemical vapor deposition. Heterojunction diodes made with 276nm thick nanocrystalline layers of these alloys have been used as real-time solid-state neutron detectors. Individual neutrons were detected and signals induced by gamma rays were determined to be insignificant. Linearity of detection was demonstrated over more than two orders of magnitude in flux. The neutron detection performance was unaffected by > 1 x 10<sup>15</sup> neutrons / cm<sup>2</sup>. The source gas closo-1,2-dicarbadodecaborane (ortho-carborane) was used to fabricate the boron carbon alloys with only the natural isotopic abundance of <sup>10</sup>B. Devices made of thicker boron carbon alloy layers enriched in <sup>10</sup>B could lead to increased detection efficiency.