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Effects from Clare-in Fallaut itlllUWIER I DISCLAIMER This report was prepared as an account of work sponsored by an agency of the United States Government.

The average energy of the neutron spectrum for reactor sources may be evaluated to good approximation by a threshold-reaction technique using the activation of only two threshold-reaction foils. For plutonium (effective threshold 0.001 MeV) and sulfur (effective threshold 3.0 MeV) foils the average energy of a reactor spectrum is found to be Ē=7.42R+0.30 MeV, where R is the ratio of the number flux measured above the sulfur threshold to the number flux measured above the plutonium threshold. The carrier removal rate per unit flux has been measured for vacuum floating zone n-type silicon (phosphorus-doped) as a function of the average energy of the reactor spectrum as measured by the two-foil method. Resistivities of 1-, 10-, and 100-Ω-cm samples were used in these irradiations at seven different reactor spectra. The carrier removal rate is found to be proportional to the average energy of the neutron spectrum. The highest average energy realized in the experimental work was 2.3 MeV.