In vivo analysis with 14 MeV neutrons

In the letter from Horowitz, Dubi and Mordechai (1976, Phys. Med. Biol., Vol. 21, 306) the authors commented on the disparity of the results of two descriptions of fast neutron flux uniformity in a body irradiated with 14 MeV neutrons (Battye, C.K., Tomlinson, R.W.S., Anderson, J., and Osborn, S.B., 1967, in Nuclear Activation Techniques in the Life Sciences, STI/PUB/155, Vienna: IAEA; Palmer, H.E., Nelp, W.B., Murano, R., and Rich, C., 1968, Phys. Med. Biol., Vol. 13, 269). It is pointed out that much of the disparity in the quoted non-uniformities of +- 10% and +- 40% respectively is due to two experimental factors. The first factor is the different target-to-skin distances (TSD) used in the two experiments (150 and 100 cm) and the second factor is that the result of +- 10% (Palmer et al) refers to a phantom of thickness 23 cm while the larger non-uniformity quoted by Battye et al is for a 32 cm thick phantom. When the results of Battye et al are normalized to the same TSD and phantom thickness as those used by Palmer et al, the magnitude of the non-uniformity is reduced to +- 19%, which greatly reduces the disparity. However, the remaining discrepancy still requires an explanation. Measurements have been made of the activity of 13N produced in samples of nitrogen (in the form of melamine) by the reaction 14N(n,2n)13N, giving the fast flux distribution in a phantom irradiated with 14 MeV neutrons. These results agreed with those of Battye et al. (author)