B10 Diffused Junctions in N-Type Silicon

Abstract

Silicon diffused junction detectors were prepared by diffusion of boron-10 into n-type silicon of resistivity 1000-3800 ohm-cm at a temperature of 1000°C. Detector diameters ranged from 3 mm to 2 cm. With the junction edge exposed in air or in vacuum, these detectors were extremely unstable. The use of organic silanes and ordinary waxes as a coating on the exposed junction edge provided stability. For some detectors the treatment with silanes was followed by a decrease in leakage current during subsequent storage. For alpha particles a resolution width (FWHM) of 40-45 kev was obtained for 6 Mev alpha particles in a detector of diameter 3-4 mm. For 2-cm-diameter detectors the resolution width at this energy was 80-100 kev, but reduced to 40 kev for alpha particles at a higher energy of 9 Mev. The peak-to-valley ratio for fission fragments from Cf252 was constant and equal to 1.40 at a detector reverse voltage of 15 volts or higher. The use of boron-10 allows identification of the energies of the products of fission reactions that occur within the detector, although similar detectors may be prepared using ordinary boron. For the present detectors the energies of the reaction products from the reaction n(B10, Li7) ? (and their sum were resolved with a resolution width of approximately 250 kev, and with energy corresponding to the known energies to within 5%.