Assessment of Internal Radiation Dose from the Fallout of Nuclear Explosions

Abstract

A general view of internal radiation dose caused by local fallout from nuclear explosions is provided. Four aspects involved in the estimation of this dose are discussed including physical and chemical properties of local fallout, metabolic parameters of fission products in the human body, anatomical and physiological parameters for reference Chinese adults, and the methods of rapid estimation of intake of early fallout and internal radiation dose caused by it. Following the nuclear explosions, people located in downwind areas of resultant radioactive fallout can be exposed to both external and internal doses from the radiation primarily generated by the fission part of the weapon. During the occurrence of fallout, the external dose is caused by radioactive particles passing overhead and deposited on the ground surface, while internal dose is caused by inhalation and ingestion of radioactivity (Glasstone and Dolan, 1977; SIPRI, 1981; Harwell et aI., 1984; Conlin and Walker, 1987). Since the 1950s, extensive studies have been made on the magnitude of external dose to humans from fallout following nuclear explosions, but the literature on internal dose estimation from local fallout in a nuclear war situation is far less abundant than that for external dose. Whicher and Kircher (1987) referred to studies indicating that "".doses to most organs from external radiation from fallout on the ground tend to be of the same order to roughly ten fold higher than internal dose via ingestion". Rotblat's estimation was that internal dose is roughly 20% of the external dose from local fallout (peterson and Shapiro, 1992) with confirmation provided by the result from other studies (Levanon and Pernick, 1988; Ng et al., 1990). The internal dose from fallout following nuclear explosions are also relevant to Chinese health physicists. This paper is intended as a preliminary discussion in this field based upon Chinese data. 1. Physical and Chemical Properties of Local Fallout Fallout particles created in the nuclear explosions incorporate the fission products, the radioactive weapon residues and the induced active materials. On the view of internal dosimetry in respiratory systems and the gastrointestinal tract, the decay index, the b particle energy, the size and solubility offallout etc., are the important physico-chemical properties. It was reported that a programme of serial atmospheric nuclear tests was performed in the Semipalatinsk Nuclear Test Site during 1961-1962. The fallout was sampled on the northern part of Xingjing, a province of the northwest region in China, at China-FSU border, and the results showed that the decay indexes were not constant values depending on the time after explosion, and the average b energy was in the range of 0.3 - 0.5 MeV. The solubility offallout collected before the date of explosion announced was higher than that of the fallout sampled after that date. Higher values were found when the solution of pH=4 was used than with the pH= 1 0 solution. The rare-earth radioisotopes, barium, strontium, iodine, were the major constituents (Hou, 1963). Similar studies were made for local fallout (downwind less than 100