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.

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

“…Initial retention is higher on wet surfaces (at the time of deposition) than on dry surfaces, and cations are retained better than anions. The primary concern is particles less than about 50 μm in size, which are most readily retained by vegetation ( Gordeev et al 2006 ; Anspaugh et al 2022 ; Beck et al 2022 ). In the deposition model described by Beck et al (2022) , it is assumed that, for the most part, only particles < 50 μm in size will be intercepted and retained on vegetation.…”

“…The primary concern is particles less than about 50 μm in size, which are most readily retained by vegetation ( Gordeev et al 2006 ; Anspaugh et al 2022 ; Beck et al 2022 ). In the deposition model described by Beck et al (2022) , it is assumed that, for the most part, only particles < 50 μm in size will be intercepted and retained on vegetation. Thus, the activity of a given radionuclide i intercepted and initially retained by vegetation of a particular type is defined as the deposition density of radionuclide i on particles < 50 μm in size, DD i,veg (Bq m −2 ).…”

“…The present paper provides parameter values and distributions for use in estimating radionuclide activity concentrations in foodstuffs and drinking water following deposition of radioactive fallout. The activity concentrations in foodstuffs and drinking water are based on estimated deposition densities ( Beck et al 2022 ) and are used to estimate internal doses due to ingestion of the foodstuffs ( Anspaugh et al 2022 ) as part of an overall dose assessment for a given nuclear fallout event ( Simon et al 2022 ). Anspaugh et al (2022) describe two methods for estimation of the internal dose from ingestion of contaminated foods: an aggregated approach based on a time-integrated intake of radionuclides per unit deposition and the traditional method based on examination of individual processes.…”

Dose Estimation for Exposure to Radioactive Fallout from Nuclear Detonations

“…While the term fallout , referring to the radioactive debris particles, and the process of their movement from the atmosphere to the ground is more or less universally understood, other concepts are briefly discussed here so as to ensure a consistent understanding: (1) temporal definitions, (2) empirical and theoretical assessment models, (3) time-dependent (dynamic) and time-integrated assessment models, and (4) dose units. The subject of dosimetric uncertainty, an important over-arching component to fallout dose assessments, is discussed throughout the five companion publications ( Beck et al 2022 ; Bouville et al 2022 ; Anspaugh et al 2022 ; Thiessen et al 2022 ; Melo et al 2022 ) and summarized here.…”

“…Given the recognition of the potential scale of nuclear-related terrorism as well as the goals of the NIAID program on Radiation and Nuclear Countermeasures ( https://www.niaid.nih.gov/research/radiation-nuclear-countermeasures-program ), this paper and five others ( Beck et al 2022 ; Bouville et al 2022 ; Anspaugh et al 2022 ; Melo et al 2022 ; Thiessen et al 2022 ) present a well described method that remedies the absence of clear documentation of a dose-assessment method suitable for estimating doses from exposure to radioactive fallout at locations where exposure is entirely from fallout. The models presented can apply to both rural and urban locations, though some values of parameters would be strikingly different for the two environments.…”