High Precision Irradiation Techniques for NTD Silicon at the University of Missouri Research Reactor

Abstract

The design factors which governed the construction of present NTD irradiation facilities at MURR were efficient utilization of reflector space, good doping accuracy, good doping uniformity, and potential for growth. The present MURR flux integration system will be described. This system consists of 1.5 mm diameter, self- powered neutron detectors and high precision analogue current integrators. These are utilized at each sample position to achieve an overall fluence accuracy of better than ± 1%. The integration system is used to determine the 50% of total fluence point at which samples are flipped end-for-end. This technique, as opposed to flux flattening or sample spiraling, provides a very efficient utilization of reflector space without compromising axial uniformity. Axial uniformity obtainable in any position is better than ± 4% of target over sample lengths of 250 mm. Sample rotators are used to obtain radial uniformity of better than ± \% up to 86 mm diameter. Present irradiation positions consist of two 750 mm long x 85 mm diameter, two 750 mm long x 60 mm diameter, seven 750 mm long x 80 mm diameter, and a high precision variable flux facility. The present MURR capacity is of the order of 15–20 ppb-tonnes per year.