The Methodology Used to Assess Doses from the First Nuclear Weapons Test (Trinity) to the Populations of New Mexico

Abstract

Trinity was the first test of a nuclear fission device. The test took place in south-central New Mexico at the Alamogordo Bombing and Gunnery Range at 05:29 AM on 16 July 1945. This article provides detailed information on the methods that were used in this work to estimate the radiation doses that were received by the population that resided in New Mexico in 1945. The 721 voting precincts of New Mexico were classified according to ecozone (plains, mountains, or mixture of plains and mountains), and size of resident population (urban or rural). Methods were developed to prepare estimates of absorbed doses from a range of 63 radionuclides to five organs or tissues (thyroid, active marrow, stomach, colon, and lung) for representative individuals of each voting precinct selected according to ethnicity (Hispanic, White, Native American, and African American) and age group in 1945 (in utero, newborn, 1-2 y, 3-7 y, 8-12 y, 13-17 y, and adult). Three pathways of human exposure were included: (1) external irradiation from the radionuclides deposited on the ground; (2) inhalation of radionuclide-contaminated air during the passage of the radioactive cloud and, thereafter, of radionuclides transferred (resuspended) from soil to air; and (3) ingestion of contaminated water and foodstuffs. Within the ingestion pathway, 13 types of foods and sources of water were considered. Well established models were used for estimation of doses resulting from the three pathways using parameter values developed from extensive literature review. Because previous experience and calculations have shown that the annual dose delivered during the year following a nuclear test is much greater than the doses received in the years after that first year, the time period that was considered is limited to the first year following the day of the test (16 July 1945). Numerical estimates of absorbed doses, based on the methods described in this article, are presented in a separate article in this issue.

Fig. 1

Map of New Mexico with isopleths of exposure rates (mR h⁻¹) at H+12 h after the test (Quinn 1987; Cederwall and Peterson 1990). These isopleths are derived from measurements of exposure rate conducted during the first few days following the test. Fuzzy spots show the locations of the 8 cities with 1945 populations greater than 10,000. The approximate centerline of the fallout trace is represented by two segments.

Fig. 2

Map of recorded precipitation, expressed in tenths of millimeters per day, on 16 July 1945 in all measuring stations of New Mexico (derived from the Global Historical Climatology Network–Daily Database; Menne et al. 2012).

Fig. 3

Map of rivers in New Mexico (derived from US Census).

Fig. 4

Map of milk regions (derived from NCI 1997).