Direct determination of the ratio of 232Th(n, 2n) and (n, γ) reactions in a fast reactor

Integral measurement of the 232 Th(n, 2n) reaction has been carried out relative to 232 Th(n, γ) in a pin-geometry GCFR lattice. A single thorium foil was used for the irradiation, and a HPGe detector system employed for simultaneous γ-counting of the induced 231 Th and 233 Pa activities. Standardization of detector efficiency was carried out using α-calibrated 235 U and 237 Np deposits containing equilibrium amounts of their daughters ( 231 Th and 233 Pa, respectively). An accuracy of ±2.5% was thereby achieved for the lattice measurement of the 232 Th (n, 2n) to (n, γ) ratio.