Neutron Dose Equivalent Conversion Coefficients Have Changed in the Last Forty Years...Haven't They?

Abstract

Conversion coefficients relating neutron fluence to dose equivalent were first made available forty years ago, and subsequently many versions of the coefficients have been published in the scientific literature. These conversion coefficients have been tabulated in a number of formats that related, for example, the fluence rate to maximum dose equivalent rate; the fluence rate, in a period of 40 h, producing a maximum dose equivalent of 1 mSv; and the fluence to ambient dose equivalent. The dose equivalent quantities have been specified in a number of phantoms, including: semi-infinite slabs of tissue-equivalent materials, right-circular and elliptical cylinders, and the ICRU sphere. Significant changes in the definitions of the radiation protection quantities have taken place. Interestingly, the neutron conversion coefficients have remained nearly invariant. It appears that the current set of conversion coefficients are adequate for radiation protection dosimetry and that, barring any unexpectedly large changes in neutron cross section or risk data, further changes are neither necessary nor desirable in the foreseeable future.