Pile oscillator measurements of highly irradiated plutonium

Samples of plutonium alloyed with aluminium have been irradiated up to a maximum neutron dosage of 1·7 n/kb in the NRX reactor at Chalk River. At this irradiation over 80 per cent of the original ²³⁹Pu is destroyed. The resultant changes in cross-section have been measured with the pile oscillator in Gleep. The results are in agreement with theoretical predictions based upon present world nuclear data for plutonium isotopes as compiled by Westcott (1958). This agreement gives added confidence in the ability to predict reactivity changes due to plutonium formation or destruction in power reactors.