ESTIMATES OF RADIATION DOSES TO THE SKIN FOR PEOPLE CAMPED AT WALLATINNA DURING THE UK TOTEM 1 ATOMIC WEAPONS TEST.

A group of Aboriginal people was camped at Wallatinna in South Australia, ~170 km downwind from Emu Field, where an atomic test (the Totem 1 test) was carried out at 07.00 on 15 October 1953 local time (21.30 on 14 October 1953 GMT (Greenwich Mean Time)). They left the camp ~24 hours later. These people stated that a phenomenon that has become known as a 'black mist' rolled through their camp site ~5 hours after detonation and that some of them subsequently became sick, displaying skin reddening and nausea. They feared that the sickness was a result of exposure to high levels of radiation. The purpose of this paper is to determine if these people could have received ionising radiation doses high enough to cause the symptoms displayed. The methodology used for the dose estimates is described in the paper. The exposure modes considered were external exposure due to the passage of a contaminated plume over the camp site, inhalation of material from this plume, external exposure from material deposited on the ground as the plume passed, and consumption of contaminated food and water. The contaminants considered in the airborne cloud and the ground plume were fission products and unburnt plutonium from the nuclear detonation, and neutron activation products caused by vaporisation of the tower used to position the weapon. The source was approximated by a line source. An upper estimate of the effective doses received is ~4 mSv, which is well below the level at which acute radiation effects are observed. This estimate is consistent with earlier assessments, which did not consider inhalation of the contribution from neutron activation products.

Solid cancer risks from radiation exposure for the Australian population.

Estimates are made of the risks to the Australian population as a function of age and gender for mortality or morbidity for all solid cancers after exposure to radiation. Excess relative risk (ERR) and excess absolute risk (EAR) models are used. The model coefficients are re-evaluated for radiation doses expressed as effective dose using data from the Japanese Life Span Study. Life-table methods are used throughout and the risk measures studied are: the risk of exposure related death, RERD and the risk of exposure related cancer, RERC. Australian life-table data and the age-specific cancer incidence and mortality rates of Australian males and females are taken from recent published tables. No dose and dose-rate effectiveness factor is applied. Sources of uncertainty used to calculate the confidence regions for the estimated risks include the statistical uncertainties of the model parameters and of the extrapolation of the risks beyond the period supported by the epidemiological data. Summary values of the risks are reported as averages of those calculated from the ERR and the EAR models. For males, the mortality risks per sievert range from 14% for 0-9 year age group, 7% at 30-39 years and 4% at 50-59 years. Corresponding values for females are 20%, 10% and 6%. Incidence risks are higher: for males the estimates are 32% for the 0-9 year group, 12% at 30-39 and 5% at 50-59. Corresponding values for females are 56%, 20% and 8%. The 90% confidence regions are about +/- 50% of these values. Estimates are given for the risks from CT whole-body scanning or virtual colonoscopy which could be used for cancer screening. If used at 3 year intervals and the effective dose per procedure is 10 mSv, then the RERD for males beginning screening at 40, 50 and 60 years is 0.4%, 0.3% and 0.1%, respectively and for females, 0.6%, 0.4% and 0.2%, respectively. RERD estimates for a 5 year interval between screens are about one-third smaller.

Sensitivity of coefficients for converting entrance surface dose and kerma-area product to effective dose and energy imparted to the patient.

We investigate the sensitivity of the conversions from entrance surface dose (ESD) or kerma-area product (KAP) to effective dose (E) or to energy imparted to the patient (epsilon) to the likely variations in tube potential, field size, patient size and sex which occur in clinical work. As part of a factorial design study for chest and lumbar spine examinations, the tube potentials were varied to be +/-10% of the typical values for the examinations while field sizes and the positions of the field centres were varied to be representative of values drawn from measurements on patient images. Variation over sex and patient size was based on anthropomorphic phantoms representing males and females of ages 15 years (small adult) and 21 years (reference adult). All the conversion coefficients were estimated using a mathematical phantom programmed with the Monte Carlo code EGS4 for all factor combinations and analysed statistically to derive factor effects. In general, the factors studied behaved independently in the sense that interaction of the physical factors generally gave no more than a 5% variation in a conversion coefficient. Taken together, variation of patient size, sex, field size and field position can lead to significant variation of E/KAP by up to a factor of 2, of E/ESD by up to a factor of 3, of epsilon/KAP by a factor of 1.3 and of epsilon/ESD by up to a factor of 2. While KAP is preferred to determine epsilon, the results show no strong preference of KAP over ESD in determining E. The mean absorbed dose D in the patient obtained by dividing epsilon (determined using KAP) by the patient's mass was found to be the most robust measure of E.

An EGS4 based mathematical phantom for radiation protection calculations using standard man.

This note describes an Electron Gamma Shower code (EGS4) Monte Carlo program for calculating radiation transport in adult males and females from internal or external electron and gamma sources which requires minimal knowledge of organ geometry. Calculations of the dose from planar gamma fields and from computerized tomography illustrate two applications of the package.

A nationwide survey of 222Rn and gamma radiation levels in Australian homes.

A nationwide survey of Australian homes was conducted to determine the average annual dose equivalents to the Australian population from exposure to Rn and gamma radiation. The exposure to Rn was measured using solid-state track detectors (SSTD), while the gamma radiation dose was concurrently determined using thermoluminescent dosimetry. Dosimeters were placed in approximately 3,400 randomly distributed homes (representing about 1 in 1,400 occupied dwellings) for 12 mo. The average Rn concentration in Australian homes measured over a year is 11 Bq m-3. Using appropriate conversion factors, the annual average effective dose equivalents to the Australian population were determined to be 0.5 mSv and 0.9 mSv for Rn and gamma radiation exposure, respectively.

Performance of a diffusion barrier charcoal adsorption 222Rn monitor under conditions of varying humidity and temperature.

An investigation of the performance of a diffusion barrier, charcoal-based 222Rn monitor under several artificial environmental conditions showed that both temperature and relative humidity levels affect 222Rn uptake. A physical model was developed adequately describing the temperature effects, while an empirical model was used to summarize the combined effects of temperature and atmospheric water concentration.

Dose conversion factors for radon daughters in underground and open-cut mine atmospheres.

As uranium will be mined in Australia by open-cut methods, previous work on calculating dose conversion factors for radon daughters has been re-examined. The fractions of radon daughters deposited on lung airways and the factors for converting from equilibrium activity of radon daughters on airways to dose to basal cells are re-calculated. The variation around these estimates through variability of lung morphology and the depth of the basal cells is discussed. Average dose conversion factors calculated for atmospheres which may be typical of underground mines range from 12 mGy/WLM to 33 mGy/WLM. Use has been made of measurement results on unattached fraction at an open-cut mine in the Northern Territory, Australia, to derive dose conversion factors, ranging from 50 mGy/WLM to 135 mGy/WLM which are applicable to this environment.