Neutron dose coefficients for the lens of the eye.

The International Commission on Radiation Units and Measurements (ICRU) Report Number 95 (2020 Operational quantities for external radiation exposureICRU Rep. 95 J. ICRU20) recommends new definitions ffor operational quantities as estimators of the International Commission on Radiological Protection radiation protection quantities. As part of this report, dose coefficients for neutron fluences are included for energies from 10-9-50 MeV. For lens of the eye dosimetry, several changes in the ICRU recommended quantities are of particular interest. First, an updated eye model is used that includes segmentation of the sensitive lens region. In addition, the use of absorbed dose instead of dose equivalent has been selected as the appropriate operational quantity since deterministic (i.e. non-stochastic) effects are of primary importance for the lens of the eye. The ICRU report also addresses computational parameters, such as absorbed dose tally volumes, depths, source areas and source rotational angles. In this work, neutron dose coefficients calculated for the lens of the eye in support of the ICRU report are presented. Dose coefficients for mono-energetic neutrons and reference neutron spectra are presented. The source is a parallel beam, and the mono-energetic dose coefficients are provided for rotational angles with respect to the front face of the head ranging from 0°-90°. In addition, monoenergetic dose coefficients for the parallel beam incident on the back of the head (180°) and for a rotational source geometry where the head is irradiated from all angles are reported. For all scenarios, absorbed doses to the complete lens and the sensitive volume of each eye were calculated. Eye lens absorbed dose coefficients,Dp,slab(3,0)/Φ, were also calculated in an ICRU tissue slab phantom at a depth of 3 mm for a parallel beam irradiating the slab perpendicular to the front face, and these results are compared to the values determined using the eye phantom.

Neutron dose coefficients for local skin.

A draft report by the International Commission on Radiation Units and Measurements (ICRU) Report Committee 26 (RC26) will recommend alternative definitions of the operational quantities that are better estimators of radiation protection quantities. Dose coefficients for use with physical field quantities-fluence and, for photons, air kerma-are given for various particle types over a broad energy range. For the skin dosimetry, several changes are of particular interest. Specifically, the use of absorbed dose instead of dose equivalent has been selected as the operational quantity since deterministic effects are of primary interest in the skin. In addition, newly recommended phantoms are specified for computing the operational dose coefficients. The report also addresses computational approaches such as tally volumes, depths, source areas, and rotational angles. In this work, dose coefficients calculated for local skin in support of the ICRU report are presented. Energy-dependent dose coefficients were calculated in phantoms specified for the trunk (slab), the ankle or wrist (pillar), and the finger (rod). The phantom specifications in this work were taken directly from the draft report. Full transport of secondary charged particles from neutron interactions was performed and an analysis of the depth-dose profiles in the slab phantom is presented, The last complete set of neutron dose coefficients for the extremities was published more than 25 years ago. Given the limited data available, it is difficult for many facilities to obtain clear guidance on how monitoring should be performed and how dosimeters should be calibrated so spectra from commonly encountered neutron sources were used to generate source-specific dose coefficients in each of the phantoms. Both energy-dependent and source-specific dose coefficients are provided for rotational angles up to 180 degrees for the rod and pillar phantoms and up to 75 degrees for the slab phantom.

A biokinetic model for trivalent or hexavalent chromium in adult humans.

Chromium exists in several oxidation states, with the trivalent state (Cr(III)) being the dominant naturally occurring form. Chromium in other oxidation states tends to be converted to the trivalent oxide in the natural environment and in biological systems. Chromium(III) has been shown to be an essential nutrient for humans and several non-human species. Chromium(VI), the second most stable form of chromium, is an important environmental contaminant that is mostly of industrial origin and is associated with lung cancer and nose tumours in chromium workers. This paper proposes a biokinetic model for chromium that addresses the distinctive behaviours of Cr(III) and Cr(VI) following uptake to blood of an adult human. The model is based on biokinetic data derived from relatively short-term studies involving administration of chromium tracers to adult human subjects or laboratory animals, supplemented with data on the long-term distribution of chromium in adult humans as estimated from autopsy measurements. The model is part of a comprehensive update of biokinetic models of the International Commission on Radiological Protection, used to project or evaluate radiation doses from occupational intake of radionuclides.

Organ and effective dose rate coefficients for submersion exposure in occupational settings.

External dose coefficients for environmental exposure scenarios are often computed using assumption on infinite or semi-infinite radiation sources. For example, in the case of a person standing on contaminated ground, the source is assumed to be distributed at a given depth (or between various depths) and extending outwards to an essentially infinite distance. In the case of exposure to contaminated air, the person is modeled as standing within a cloud of infinite, or semi-infinite, source distribution. However, these scenarios do not mimic common workplace environments where scatter off walls and ceilings may significantly alter the energy spectrum and dose coefficients. In this paper, dose rate coefficients were calculated using the International Commission on Radiological Protection (ICRP) reference voxel phantoms positioned in rooms of three sizes representing an office, laboratory, and warehouse. For each room size calculations using the reference phantoms were performed for photons, electrons, and positrons as the source particles to derive mono-energetic dose rate coefficients. Since the voxel phantoms lack the resolution to perform dose calculations at the sensitive depth for the skin, a mathematical phantom was developed and calculations were performed in each room size with the three source particle types. Coefficients for the noble gas radionuclides of ICRP Publication 107 (e.g., Ne, Ar, Kr, Xe, and Rn) were generated by folding the corresponding photon, electron, and positron emissions over the mono-energetic dose rate coefficients. Results indicate that the smaller room sizes have a significant impact on the dose rate per unit air concentration compared to the semi-infinite cloud case. For example, for Kr-85 the warehouse dose rate coefficient is 7% higher than the office dose rate coefficient while it is 71% higher for Xe-133.

Effective dose rate coefficients for exposure to contaminated soil.

The Oak Ridge National Laboratory Center for Radiation Protection Knowledge has undertaken calculations related to various environmental exposure scenarios. A previous paper reported the results for submersion in radioactive air and immersion in water using age-specific mathematical phantoms. This paper presents age-specific effective dose rate coefficients derived using stylized mathematical phantoms for exposure to contaminated soils. Dose rate coefficients for photon, electron, and positrons of discrete energies were calculated and folded with emissions of 1252 radionuclides addressed in ICRP Publication 107 to determine equivalent and effective dose rate coefficients. The MCNP6 radiation transport code was used for organ dose rate calculations for photons and the contribution of electrons to skin dose rate was derived using point-kernels. Bremsstrahlung and annihilation photons of positron emission were evaluated as discrete photons. The coefficients calculated in this work compare favorably to those reported in the US Federal Guidance Report 12 as well as by other authors who employed voxel phantoms for similar exposure scenarios.

External dose reconstruction for the former village of Metlino (Techa River, Russia) based on environmental surveys, luminescence measurements, and radiation transport modelling.

In the first years of its operation, the Mayak Production Association, a facility part of the Soviet nuclear weapons program in the Southern Urals, Russia, discharged large amounts of radioactively contaminated effluent into the nearby Techa River, thus exposing the people living at this river to external and internal radiations. The Techa River Cohort is a cohort intensely studied in epidemiology to investigate the correlation between low-dose radiation and health effects on humans. For the individuals in the cohort, the Techa River Dosimetry System describes the accumulated dose in human organs and tissues. In particular, organ doses from external exposure are derived from estimates of dose rate in air on the Techa River banks which were estimated from measurements and Monte Carlo modelling. Individual doses are calculated in accordance with historical records of individuals' residence histories, observational data of typical lifestyles for different age groups, and age-dependent conversion factors from air kerma to organ dose. The work here describes an experimentally independent assessment of the key input parameter of the dosimetry system, the integral air kerma, for the former village of Metlino, upper Techa River region. The aim of this work was thus to validate the Techa River Dosimetry System for the location of Metlino in an independent approach. Dose reconstruction based on dose measurements in bricks from a church tower and Monte Carlo calculations was used to model the historic air kerma accumulated in the time from 1949 to 1956 at the shoreline of the Techa River in Metlino. Main issues are caused by a change in the landscape after the evacuation of the village in 1956. Based on measurements and published information and data, two separate models for the historic pre-evacuation geometry and for the current geometry of Metlino were created. Using both models, a value for the air kerma was reconstructed, which agrees with that obtained in the Techa River Dosimetry System within a factor of two.

ORGAN AND EFFECTIVE DOSE COEFFICIENTS FOR CRANIAL AND CAUDAL IRRADIATION GEOMETRIES: NEUTRONS.

Dose coefficients based on the recommendations of International Commission on Radiological Protection (ICRP) Publication 103 were reported in ICRP Publication 116, the revision of ICRP Publication 74 and ICRU Publication 57 for the six reference irradiation geometries: anterior-posterior, posterior-anterior, right and left lateral, rotational and isotropic. In this work, dose coefficients for neutron irradiation of the body with parallel beams directed upward from below the feet (caudal) and downward from above the head (cranial) using the ICRP 103 methodology were computed using the MCNP 6.1 radiation transport code. The dose coefficients were determined for neutrons ranging in energy from 10-9 MeV to 10 GeV. At energies below about 500 MeV, the cranial and caudal dose coefficients are less than those for the six reference geometries reported in ICRP Publication 116.

Reducing Statistical Uncertainties in Simulated Organ Doses of Phantoms Immersed in Water.

In this article, methods are addressed to reduce the computational time to compute organ-dose rate coefficients using Monte Carlo techniques. Several variance reduction techniques are compared including the reciprocity method, importance sampling, weight windows and the use of the ADVANTG software package. For low-energy photons, the runtime was reduced by a factor of 105 when using the reciprocity method for kerma computation for immersion of a phantom in contaminated water. This is particularly significant since impractically long simulation times are required to achieve reasonable statistical uncertainties in organ dose for low-energy photons in this source medium and geometry. Although the MCNP Monte Carlo code is used in this paper, the reciprocity technique can be used equally well with other Monte Carlo codes.

Effective Dose Rate Coefficients for Immersions in Radioactive Air and Water.

The Oak Ridge National Laboratory Center for Radiation Protection Knowledge (CRPK) has undertaken a number of calculations in support of a revision to the United States Environmental Protection Agency (US EPA) Federal Guidance Report on external exposure to radionuclides in air, water and soil (FGR 12). Age-specific mathematical phantom calculations were performed for the conditions of submersion in radioactive air and immersion in water. Dose rate coefficients were calculated for discrete photon and electron energies and folded with emissions from 1252 radionuclides using ICRP Publication 107 decay data to determine equivalent and effective dose rate coefficients. The coefficients calculated in this work compare favorably to those reported in FGR12 as well as by other authors that employed voxel phantoms for similar exposure scenarios.

COMPARISON OF MONOENERGETIC PHOTON ORGAN DOSE RATE COEFFICIENTS FOR STYLIZED AND VOXEL PHANTOMS SUBMERGED IN AIR.

As part of a broader effort to calculate effective dose rate coefficients for external exposure to photons and electrons emitted by radionuclides distributed in air, soil or water, age-specific stylized phantoms have been employed to determine dose coefficients relating dose rate to organs and tissues in the body. In this article, dose rate coefficients computed using the International Commission on Radiological Protection reference adult male voxel phantom are compared with values computed using the Oak Ridge National Laboratory adult male stylized phantom in an air submersion exposure geometry. Monte Carlo calculations for both phantoms were performed for monoenergetic source photons in the range of 30 keV to 5 MeV. These calculations largely result in differences under 10 % for photon energies above 50 keV, and it can be expected that both models show comparable results for the environmental sources of radionuclides.

ER degradation of a misfolded luminal protein by the cytosolic ubiquitin-proteasome pathway.

Secretion of proteins is initiated by their uptake into the endoplasmic reticulum (ER), which possesses a proteolytic system able to degrade misfolded and nonassembled proteins. The ER degradation system was studied with yeast mutants defective in the breakdown of a mutated soluble vacuolar protein, carboxypeptidase yscY (CPY*). The ubiquitin-conjugating enzyme Ubc7p participated in the degradation process, which was mediated by the cytosolic 26S proteasome. It is likely that CPY* entered the ER, was glycosylated, and was then transported back out of the ER lumen to the cytoplasmic side of the organelle, where it was conjugated with ubiquitin and degraded.