Fluence to Dose Equivalent Conversion Data and Radiation Weighting Factors for High Energy Radiation

Abstract

Calculations of conversion coefficients from fluence to ambient dose equivalent and from fluence to maximum dose equivalent, along the principal axis of the ICRU sphere, have been performed for protons, muons and pions of energies up to 10 TeV. All of the results were obtained using the Monte Carlo transport code FLUKA. The values of the effective quality factors at 10 mm depth and at the depth at which the maximum occurs have been derived. The calculated results have been compared with the data sets of ICRP Publication 51. The application of the ICRP's recommended approximation to radiation weighting factors when they are not explicitly given (ICRP Publication 60, Section A.8., Paragraph (A14)), and of the recommended depth for measuring the ambient dose equivalent (ICRU Report 51, Paragraph I.4.3.1.1), have been analysed in the high energy region. The values of the radiation weighting factors for positive and negative pions have been determined as a function of incident pion energy. Three main conclusions can be achieved: (1) compared with the value of effective quality factor at 10 mm depth in the ICRU sphere, the value of 5, recommended for the radiation weighting factor of protons, appears overestimated by a factor of between 2.5 and 4.5 depending on proton energy; (2) for all kinds of radiation investigated, the ambient dose equivalent, H*(10), gives a conservative estimate of the effective dose only in a limited low energy range; (3) as far as ambient dose equivalent is concerned, there is no depth d of the ICRU sphere that is appropriate for area monitoring at very high energies.