New operational quantities (RBE × D _{p lens}/Φ) for eye lens neutron dosimetry as a function of energy and angle of incidence in the ICRU 95 formalism

Abstract

This paper presents and discusses computed personal absorbed dose (Dp lens/Φ), and a Relative Biological Effectiveness (RBE)-weighted absorbed dose (in terms of an newly proposed operational quantity RBE × Dp lens/Φ), conversion coefficients for the lens of the eye for neutron exposure at incident energies from thermal to ~ 20 MeV and at angles of incidence from 0° to 90° in 15o increments, at 180o and for rotational (ROT) irradiation geometry (from 0° to 360° in 5° increments). These conversion coefficients were obtained from a simulation model developed for this study that contains the stylised eye model, embedded in the adult UF-ORNL mathematical phantom, whereby the previously stated RBE-weighted absorbed dose was obtained using the proposed RBE versus neutron energy distribution compiled in a previous paper by the authors. The simulations carried out for this study using the Monte Carlo N-Particle transport code MCNP version 6.2, were conducted in a realistic human eye model, for the left and right sensitive and whole volume of the lens of the eye, considering the recent proposed redefinition of the operational quantities for external radiation exposure in ICRU report 95.