groups such as children and fetuses may have special sensitivity. These facts render it very difficult to accumulate reliable information about the correlation between small doses and their effects either in individuals or in large populations. (UNSCEAR, 1958, p. 42)

With respect to radiation-induced leukemia identified in the Japanese populations exposed to atomic radiation well above the low-dose limit, UNSCEAR concluded that the threshold and no-threshold models of radiation injury had equal validity. This conclusion was contested by the Committee on Pathologic Effects of Atomic Radiation of the National Academy of Sciences/National Research Council (NAS/NRC), which stated unequivocally that "a considerable body of experimental evidence" favored nonlinearity and hence presumably a threshold, and urged that nonlinear relationships between dose and effect should be given greater attention (NAS/NRC, 1959). The following year, the short-lived U.S. Federal Radiation Council (FRC, see Appendix G) observed that the linear, no-threshold model merely presented an extrapolated upper limit of radiation risk for low exposure levels (FRC, 1960). In UNSCEAR reports in the 1960s, the committee emphasized that extrapolation of the linear, no-threshold curve provided an upper limit to the risk of low-level exposures (UNSCEAR, 1962, 1964). This position was endorsed by the International Commission on Radiological Protection (ICRP, 1966).

Joint Committee on Atomic Energy Hearings, 1957–1960s

Meanwhile, in the late 1950s, the congressional Joint Committee on Atomic Energy (JCAE) conducted hearings that had a major influence on the thinking of both the scientific community and the public with regard to radiation hazards. The hearings began in 1957 with an inquiry into the nature of radioactive fallout from weapons testing and its possible effects on humans (JCAE, 1957). Testimony from scientific experts addressed but left unresolved the issue of the most appropriate model for estimating the degree of hazard at low exposure levels. The JCAE addressed this issue again in its 1959 hearings (JCAE, 1959) and again left it unresolved. However, the hearing report (p. 59) included testimony by K.Z. Morgan, Director of Health and Human Physics at the Oak Ridge National Laboratory, claiming that certain bioeffects, including genetic mutations, leukemia induction, and life shortening, occur without a threshold dose. Also influential was the testimony of E.B. Lewis, professor of biology at the University of California, San Francisco, who strongly supported the linear, no-threshold hypothesis as a model for radiation protection standards. Lewis proposed the concept of protection called "as low as reasonably achievable" (ALARA) (JCAE, 1960). In subsequent hearings over the course of the 1960s, the JCAE moved slowly to the endorsement of the linear, no-threshold model of radiation risk.



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