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Previous work [1] described the semiconductor properties of high-purity, crystalline, beta-rhombohedral boron. It was shown that the temperature coefficient of the resistivity is high and that ohmic contacts can reliably be attached to the material. This led to the development of boron thermistors, devices which sense changes in temperature as changes in resistance. The present work uses pairs of thermistors, where the two members of a pair are matched with respect to their semiconductor properties, but differ in their nuclear properties. One thermistor is made of B11, the other of B10. Born isotopes are stable, but, when exposed to neutrons with thermal energies, only B10 atoms undergo nuclear reactions according to Open image in new window The energy released causes the B10 thermistor to become warmer than the B11 thermistor. This temperature difference is converted into an electrical signal as usual. Experiments in a water-moderated research reactor showed that a neutron flux of 1011n/cm2-sec or more gives a reproducible electrical signal in this fashion. Signals caused by other nuclear effects, such as transmutations, nuclear damage, and gamma-radiation heating, were either negligible or could be eliminated by comparing the results from a B10 thermistor, a B11 thermistor, and a blank. These results were obtained with simple prototypes [2] carrying crystalline boron layers with platinum and silver contacts on alumina plates. Preliminary experiments with B10/B11 thermistor pairs made of very high-purity boron rods and the detection of the thermal neutron part of a nuclear radiation pulse are also discussed. |
