Parameter Values for Estimation of Internal Doses from Ingestion of Radioactive Fallout from Nuclear Detonations

Modeling Fallout from Nuclear Weapon Detonations: Efficient Activity and Dose Calculation of Radionuclides and Their Progeny

ABSTRACT

The purpose of this paper is to present a practical method for quick determination of potential radiological doses and contaminations by fallout from nuclear detonations, or other releases, that includes the contributions from all nuclides. We precalculate individual (total) activities of all radionuclides from any initial cocktail and all their ingrowing progeny at a set of pinpoints in time with a logarithmic time-spacing. This is combined with the set of dose conversion factors (DCC) for any exposure pathway to obtain a time-dependent cocktail for the whole release as if it is one substance. An atmospheric dispersion model then provides the thinning coefficient of the released material to give local concentrations and dose rates. Progeny ingrowth is illustrated for pure 238 U and for a nuclear reactor that has been shut down. Efficient dose assessment is demonstrated for fallout from nuclear detonations and compared with the traditional approach of preselecting nuclides for specific endpoints and periods-of-interest. The compound cocktail DCC reduces the assessment of contaminations and potential dose-effects from fallout after a nuclear detonation to (the atmospheric dispersion of) only one tracer substance, representing any cocktail of nuclides and their progeny. This removes the need to follow all separate nuclides or an endpoint-specific preselection of "most important nuclides." As the cocktail DCCs can be precalculated and the atmospheric dispersion of only one tracer substance has to be modelled, our method is fast. The model for calculating cocktail DCCs is freely available, easily coupled to any regular atmospheric dispersion model, and therefore ready for operational use by others.

A Historical Survey of Key Epidemiological Studies of Ionizing Radiation Exposure

In this article we review the history of key epidemiological studies of populations exposed to ionizing radiation. We highlight historical and recent findings regarding radiation-associated risks for incidence and mortality of cancer and non-cancer outcomes with emphasis on study design and methods of exposure assessment and dose estimation along with brief consideration of sources of bias for a few of the more important studies. We examine the findings from the epidemiological studies of the Japanese atomic bomb survivors, persons exposed to radiation for diagnostic or therapeutic purposes, those exposed to environmental sources including Chornobyl and other reactor accidents, and occupationally exposed cohorts. We also summarize results of pooled studies. These summaries are necessarily brief, but we provide references to more detailed information. We discuss possible future directions of study, to include assessment of susceptible populations, and possible new populations, data sources, study designs and methods of analysis.

The overview of neutron-induced 56Mn radioactive microparticle effects in experimental animals and related studies

Investigation into the risks associated with radiation exposure has been carried out on those exposed to radiation in Hiroshima and Nagasaki, Semipalatinsk and other parts of the world. These risks are used as a guidance standard for the protection for radiation workers and the general public when exposed to radiation, and it sets upper regulatory limits for the amount of radiation exposure. However, the effects of internal exposure to radioactive microparticles have not been considered in these studies. These effects cannot be ignored since the exposure dose increases are inversely proportional to the square of the distance to the vicinity of the particles and can exceed tens of thousands of mGy. So far, only retrospective studies of people who have been exposed to radiation have been conducted, therefore we hypothesized that animal experiments would be necessary to investigate these effects. As a result, we found specific effects of radioactive microparticles. One particularly noteworthy finding was that internal exposure to radioactive microparticles resulted in pathological changes that were more than 20 times greater than those caused by the same level of external exposure. In contrast, there were other results that showed no such effects, and the reasons for this discrepancy need to be clarified. We also conducted RNA expression experiments and found that there was a difference between external exposure to 60Co gamma rays and internal exposure to 56Mn microparticles. In the future, we will need to study the mechanisms behind these findings. If the mechanism can be confirmed, it is expected to lead to the development of protective and therapeutic methods.

A Methodology for Calculation of Internal Dose Following Exposure to Radioactive Fallout from the Detonation of a Nuclear Fission Device

ABSTRACT

The purpose of this paper is to provide a methodology for the calculation of internal doses of radiation following exposure to radioactive fallout from the detonation of a nuclear fission device. Reliance is on methodology previously published in the open literature or in reports not readily available, though some new analysis is also included. Herein, we present two methodologic variations: one simpler to implement, the other more difficult but more flexible. The intention is to provide in one place a comprehensive methodology. Pathways considered are (1) the ingestion of vegetables and fruits contaminated by fallout directly, (2) the ingestion of vegetables and fruits contaminated by continuing deposition by rain- or irrigation-splash and resuspension, (3) the ingestion of vegetables and fruits contaminated by absorption of radionuclides by roots after tillage of soil, (4) the non-equilibrium transfer of short-lived radionuclides through the cow-milk and goat-milk food chains, (5) the equilibrium transfer of long lived radionuclides through milk and meat food chains, and (6) inhalation of descending fallout. Uncertainty in calculated results is considered. This is one of six companion papers that describe a comprehensive methodology for assessing both external and internal dose following exposures to fallout from a nuclear detonation. Input required to implement the dose-estimation model for any particular location consists of an estimate of the post-detonation external gamma-exposure rate and an estimate of the time of arrival of the fallout cloud. The additional data required to make such calculations are included in the six companion papers.

Dose Estimation for Exposure to Radioactive Fallout from Nuclear Detonations

ABSTRACT

In recent years, the prospects that a nuclear device might be detonated due to a regional or global political conflict, by violation of present nuclear weapons test ban agreements, or due to an act of terrorism, has increased. Thus, the need exists for a well conceptualized, well described, and internally consistent methodology for dose estimation that takes full advantage of the experience gained over the last 70 y in both measurement technology and dose assessment methodology. Here, the models, rationale, and data needed for a detailed state-of-the-art dose assessment for exposure to radioactive fallout from nuclear detonations discussed in five companion papers are summarized. These five papers present methods and data for estimating radionuclide deposition of fallout radionuclides, internal and external dose from the deposited fallout, and discussion of the uncertainties in the assessed doses. In addition, this paper includes a brief discussion of secondary issues related to assessments of radiation dose from fallout. The intention of this work is to provide a usable and consistent methodology for both prospective and retrospective assessments of exposure from radioactive fallout from a nuclear detonation.

A Method for Estimating the Deposition Density of Fallout on the Ground and on Vegetation from a Low-yield, Low-altitude Nuclear Detonation

ABSTRACT

This paper describes a relatively simple model developed from observations of local fallout from US and USSR nuclear tests that allows reasonable estimates to be made of the deposition density (activity per unit area) on both the ground and on vegetation for each radionuclide of interest produced in a nuclear fission detonation as a function of location and time after the explosion. In addition to accounting for decay rate and in-growth of radionuclides, the model accounts for the fractionation (modification of the relative activity of various fission and activation products in fallout relative to that produced in the explosion) that results from differences in the condensation temperatures of the various fission and activation products produced in the explosion. The proposed methodology can be used to estimate the deposition density of all fallout radionuclides produced in a low yield, low altitude fission detonation that contribute significantly to dose. The method requires only data from post-detonation measurements of exposure rate (or beta or a specific nuclide activity) and fallout time-of-arrival. These deposition-density estimates allow retrospective as well as rapid prospective estimates to be made of both external and internal radiation exposure to downwind populations living within a few hundred kilometers of ground zero, as described in the companion papers in this volume.