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This paper is a continuation of a study published recently by the authors. It presents and discusses computed personal absorbed dose in the lens of the eye ( D p lens / Φ ), and a relative biological effectiveness (RBE)-weighted absorbed dose (in terms of an newly proposed operational quantity RBE × D p 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 15° increments, at 180° and for rotational incidence 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 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 International Commission on Radiation Units and Measurements (ICRU) report 95. A comprehensive set of tabulated data for neutron fluence-to-dose conversion coefficients ( D p lens / Φ in pGy cm 2 ) and RBE-weighted absorbed dose (RBE × D p lens / Φ in pGy cm 2 ) conversion coefficients is included in this paper as a function of incident neutron energy and angle of incidence. Data for D p lens / Φ (pGy cm 2 ) are compared to similar data from the literature for validation of our model. Data for RBE × D p lens / Φ (in pGy cm 2 ), were also compared to the equivalent operational quantity H p (3,α)/ Φ (in pSv cm 2 ) conversion coefficients calculated at 3 mm depth in a cylindrical phantom for different incident neutron energies and angles of incidence from 0 ° to 75 ° in 15 ° increments to demonstrate the relevance of this newly proposed operational quantity for doses resulting in tissue reactions (deterministic effects) which should be quoted in Gray (RBE-weighted absorbed dose, RBE × D (Gy)), rather than Sievert (Sv) which is reserved for stochastic effects. The current neutron weighted absorbed dose (RBE × D p lens ) is proposed for the tissue reactions in the eye-lens for neutron radiation as per National Council on Radiation Protection and Measurements report 180 and in line with the recent proposal for the review and revision of the System of Radiological Protection to Keeping the International Commission on Radiological Protection (ICRP) recommendations fit for purpose. This method would bring better alignment between the dose limits in ICRP 118 and the new operational quantity consistent with the units of the new eye-lens dose limits without being overly conservative. The utilization of the proposed new operational quantities, as outlined in ICRU 95, has the potential to address the ongoing challenge in enforcing regulatory limits for neutron eye dose, specifically the use of Gy instead of Sv. It should be noted that the applicability of this will vary from country to country as in many countries the legislation is likely to mandate the use of H p (3) until the regulation is amended. This approach can serve as an interim solution while awaiting the issuance of the new ICRP general recommendations, which is expected to take several years. Implementing the new operational quantities can contribute to enhancing the accuracy and effectiveness of neutron eye dose limit enforcement., (© 2023 Society for Radiological Protection. Published on behalf of SRP by IOP Publishing Limited. All rights reserved.)

In 2012, the International Commission on Radiological Protection issued new recommendations, in publication 118, regarding the dose limits to the eye-lens. New analyses of historical exposure data had indicated that radiation-induced cataracts may appear at lower doses than previously assumed. This spurred largescale efforts in a variety of fields including dosimetry, radiation effects simulations, and the review of national regulatory limits. On the simulation side, much work led to the publication of dose rate conversion factors (DRCFs), to calculate the dose to the radiosensitive part of the eye-lens, and to the whole eye-lens as functions of the incident fluence of electron, photon, positron, and neutron radiation. The standard, ISO-15382 (2015 Radiological Protection-Procedures for Monitoring the Dose to the Lens of the Eye, the Skin and the Extremities ), from the International Organization for Standardization (ISO), stated that the direct contact of a hot radioactive particle on the eye-lens represents a special contamination condition that must be considered. The aim of this work was to produce tabulated data of eye-lens dose rates, per activity (MBq), for a variety of radionuclides. In this work, the dose to the eye-lens from contamination directly in contact with the cornea, expressed in terms of DRCFs for eye-lens, in units of Gy h -1 MBq -1 , are presented for 102 radionuclides of interest. These radionuclides were selected as they had been considered by the International Atomic Energy Agency of importance for skin dose. The method consisted of two steps. The first was the determination of the DRCFs for mono-energetic electrons and photons for a hot particle in contact with the eye-lens, followed by the folding of these quantities with the emissions of the radionuclides of interest. Contributions from spontaneous fission neutrons were considered separately. Exposure geometries for spherical hot particles of different dimensions, materials and locations on the cornea were considered. In addition, partial surface coverage of the cornea, consistent with an accidental exposure to a contaminated liquid, was also modelled. Resulting radionuclide DRCFs were verified, for a few specific geometries and radionuclides with dedicated Monte Carlo simulations. The final data are presented in several tables included in this paper., (© 2023 Society for Radiological Protection. Published on behalf of SRP by IOP Publishing Limited. All rights reserved.)