Measurement of pair production cross sections κ n in the 1.21–11.775 MeV energy range and systematics of κ n up to 100 MeV in Ge

Abstract

Pair production cross-sections κ n at 54 values of the photon energy have been determined for the 1.21–11.775 MeV energy range in germanium ( Z = 32) using a 37.0 mm deep Ge(Li) γ-ray detector. Pair production cross sections for higher energy γ-rays ( E γ ≳ 4 MeV) have been measured with an accuracy of 4%. Experimental cross sections have been compared with the theoretical cross sections of Bethe and Heitler (BH), Tseng and Pratt (TP) and Øverbø (OV). For low energy region (1.12 ⩽ E γ ⩽ 2.5 MeV) BH predictions fail while TP and OV reproduce experimental pair production cross sections with a varying degree of success. Above that 2.5 MeV all three predictions, viz. BH, TP and OV, reproduce the experimental pair production cross sections nicely. Finally two simple empirical relations have been derived—one for the energy range 1.08–1.70 MeV and the other for the energy range 1.50–100.0 MeV. These expressions reproduce the measured cross sections in the energy range 1.08–1.70 MeV with an accuracy of 2–3% and values given by Hubbell et al. in the energy range 1.5–100.0 MeV with an accuracy of 1% or better.