Assessment of Photon Contributions in Gadolinium Neutron Capture Reactions-A Preliminary Study

Abstract

Gadolinium neutron capture reactions (GNCR) result in emission of gamma rays with the maximal energy of 7.9 MeV followed by a series of secondary gamma rays and 29 to 180 KeV internal conversion electrons (Greenwood 1978). Approximately 65% of the dose comes from 70 KeV electrons having a range of 75 µm in tissue, and 29 KeV electrons having a range of 16.tm in tissue. These gamma rays and electrons, however, have not been fully evaluated experimentally in terms of dose. Our previous cell survival study suggests that the electron dose was considerably greater than the gamma dose (Akine et al 1992). This study was attempted to evaluate the contribution of gamma rays by cell survival assays. Cell suspensions were contained in a very small vessel placed in a cuvette which was filled with culture medium. Gd-157 was present either in the cell suspensions or the medium in the cuvette. In cases where Gd-157 was present only in the medium in the cuvette, the gamma rays from the cuvette medium would reach the cells but not electrons because of the thickness of the vessel wall. Preliminary results suggest that the gamma rays effectively inactivate the cells inside the vessel, in the absence of any contribution from electrons.