Spectral energy measurements in a fast neutron therapy field

Abstract

Various basic physical parameters are needed to convert a specific dosimeter reading in air to tissue kerma or to absorbed dose in a phantom. In a neutron radiation field, spectral information is required for the evaluation of these parameters. Using NE213 liquid scintiillator as a proton recoil spectrometer, neutron spectra were measured in the collimated d(16)+ Be beam of the Pretoria fast neutron therapy facility. The neutron events wer eidentified by means of pulse shape discrimination and a well established computer code employed to unfold the acquired pulse height data. The analysed neutron spectrum was used to compute the neutron kerma ratio ( K t/ K m) N and the ratio of the average energies W N/ W c required to create an ion pair in an A-150/TE gas ionization chamber. The determined values concur with published data from other centres with similar neutron beams. The mean neutron energy E n of the therapy beam was also calculated from the spectral distribution.