A Methodology for Estimating External Doses to Individuals and Populations Exposed to Radioactive Fallout from Nuclear Detonations

Abstract

A methodology of assessment of the doses from external irradiation resulting from the ground deposition of radioactive debris (fallout) from a nuclear detonation is proposed in this paper. The input data used to apply this methodology for a particular location are the outdoor exposure rate at any time after deposition of fallout and the time-of-arrival of fallout, as indicated and discussed in a companion paper titled "A Method for Estimating the Deposition Density of Fallout on the Ground and on Vegetation from a Low-yield Low-altitude Nuclear Detonation." Example doses are estimated for several age categories and for all radiosensitive organs and tissues identified in the most recent ICRP publications. Doses are calculated for the first year after the detonation, when more than 90% of the external dose is delivered for populations close to the detonation site over a time period of 70 y, which is intended to represent the lifetime dose. Modeled doses in their simplest form assume no environmental remediation, though modifications can be introduced. Two types of dose assessment are considered: (1) initial, for a rapid but only approximate dose estimation soon after the nuclear detonation; and (2) improved, for a later, more accurate, dose assessment following the analysis of post-detonation measurements of radiation exposure and fallout deposition and the access of information on the lifestyle of the exposed population.

Fig. 1

Conceptual drawing showing variation of the exposure-rate data vs. time as a means to define TOA at any location following a nuclear weapons detonation (based on Thompson et al. 1994).

Fig. C1

Variation of the normalized exposure rates with time after detonation for seven nuclear weapons tests for a fractionation level, R/V, of 0.5 (Henderson 1991; Hicks 1981, 1984; Bouville et al. 2010).

Fig. B1

Estimated corrections on the exposure rate for weathering effects at times after deposition (Gibson et al. 1969).

Fig. C2

Ratio of the exposure rates calculated by means of a power function ${\stackrel{·}{X}}_p\left(t\right)$, denoted as “t^−1.2”, and of a multi-exponential function ${\stackrel{·}{X}}_e\left(t\right)$, denoted as “actual”. Both functions were normalized to an exposure rate of 1 mR h⁻¹ at H + 12 h. It is assumed in the calculations that no weathering took place.

Fig. C3

Variation of the exposure with time, calculated with the power function, ${\stackrel{·}{X}}_p\left(t\right)$, and with the multi-exponential function, ${\stackrel{·}{X}}_e\left(t\right)$. The ground deposition is assumed to have occurred 1 hour after detonation. The data labelled X_p and X_e refer to the exposures calculated with the power and multi-exponential functions, respectively.

Fig. C4

Variation of the exposure with time, calculated with the power function, ${\stackrel{·}{X}}_p\left(t\right)$and with the multi-exponential function, ${\stackrel{·}{X}}_e\left(t\right)$. The ground deposition is assumed to have occurred 48 hours after detonation. The data labelled X_p and X_e refer to the exposures calculated with the power and multi-exponential functions, respectively.

Fig. C6

Estimated variation with time of the exposure rate (mR h⁻¹) for the three climate types and for a situation when no weathering is assumed to occur. The time-of-arrival of fallout is assumed to be 1 h after the detonation. The exposure rates are normalized to 1 mR h⁻¹ at H + 12 h.

Fig. C7

Estimated variation with time of the exposure (mR) for the three climate types and for a situation when no weathering is assumed to occur. The time-of-arrival of fallout is assumed to be 1 h after the detonation. The exposure rates are normalized to 1 mR h⁻¹ at H + 12 h.

Fig. C5

Estimated reductions in the exposure rate, relative to the exposure rate obtained in the absence of weathering, as a function of time after ground deposition, for the three climate types.