AN IRRADIATION RIG FOR NEUTRON TRANSMUTATION DOPING OF SILICON IN THEIEA-R1 RESEARCH REACTOR

An irradiation rig with simple design has been constructed and install ed in the IEA-R1 research reactor for neutron transmutation doping (NT D) of silicon with phosphorus. Crystal ingots with 3 and 4 in. diamete r can be irradiated in this device. By adopting a procedure in which t wo ingots of 20 cm long each are irradiated simultaneously and their p ositions interchanged at a point when precisely half the total necessa ry neutron dose has been received, it has been possible to achieve the desired axial uniformity of the neutron dose. This method avoids the use of neutron absorbing shields around the crystals which necessarily compromise the overall irradiation capacity of the reactor. Test irra diations were performed with 50 float zone silicon crystals, and the r esults of radial and axial uniformities in the final resistivity value s as well as the doping accuracy obtained in the test irradiations sho w an excellent doping quality achieved.