Characterization of neutron fields around high energy X-ray radiotherapy machines

The photoneutron spectra around a SATURNE 43 linear accelerator were characterized using a Bonner sphere spectrometer with a small 3He proportional counter. The summary neutron ambient dose equivalent values range roughly from 100 to 150 μSv/Gy; the percentages for the groups of 10-9 to 10-3 MeV, 10-3 to 1 MeV, and 1-20 MeV at 50 cm, 100 cm, 150 cm, and maze entry are tabulated. It is concluded that the neutron ambient dose equivalent to the whole body as derived from the observed neutron spectral fluence amounts approximately to 10-4 of the X-ray dose. (P.A.)