Calculation of the neutron W value for neutron dosimetry below the MeV energy region

The effective neutron W value for tissue-equivalent gas in the energy regio n from 5 keV to 5.7 MeV has been calculated using W values for recoil parti cles (protons, alpha particles, oxygen, carbon and nitrogen ions), which ar e produced by incident neutrons. The W value is assumed to be an energy-flu ence-average over the W values of the recoil particles. The energy fluence spectra for the recoil particles are calculated by using a continuous slowi ng-down approximation (CSDA). For the W values of recoil particles in the l ow-energy region, the recently evaluated data by Siebert et al and Taylor e t al were used. Results are presented which show that the effective neutron W value depends strongly on energy in the low-energy region. This result i ndicates that neutron dose measurements using ionization chambers need a co nsiderable correction of the W value in the low-energy region.