Neutron Doping of Silicon in the Harwell Research Reactors
The irradiation of silicon, for the purpose of transmutation doping with phosphorus, has been carried out in the research reactors, DIDO and PLUTO since 1975. Ton quantities of material have been irradiated for various customers and the high utilization of the two reactors, with their offset operating cycles, guarantees production throughout the entire year.
The present facilities offer a capacity of some 15 tons of medium resistivity material per year under conditions of good thermal to fast neutron ratios. Flux profile modifications have been made to provide uniformity of dopant along crystal length; the methods adopted and the results are illustrated and discussed.
The irradiations are carried out on a commercial contract basis and the specification of target resistivity, distribution, variations and guarantee of accuracy with an indicative pricing structure are discussed. The methods applied for Quality Assurance and Control are described.
Measurements of decay rates of induced radioactivity and the system of clearance and certification such as to allow the silicon to be internationally transported as “Exempt Material,” as defined in IAEA Regulations, are dealt with.
Plans are at an advanced stage for the provision of additional facilities, specifically designed to produce material in the 5–10 ohm-cm range, each capable of producing about 20 tons of doped silicon per year.
KeywordsResearch Reactor Radioactive Contamination Irradiation Position Flux Profile Dope Silicon
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