SLIDE 31 Absorbed dose estimates. External thyroid absorbed dose estimates were based on integrated photon exposure and based on an adjustment for living pattern in a variable exposure rate environment. External beta radiation penetrating to the depth of the thyroid was not thought by us to be important. The thickness of tissue overlying the thyroid ranges from 0.4 to 2.0 cm (0.2 to 0.8 in), average 0.82cm (0.3 in), and does not correlate with age or body weight very well (ICRP74). The minimum beta energy for penetration of 0.82 cm (0.3 in) of tissue was estimated to be 1.8 MeV. At Rongelap Island about 70% of the population had skin lesions on some part of the neck appearing about 21 days post exposure (Cr56). This would imply a skin surface dose of tens of gray (several thousand rad). Only a small per cent of the beta flux was above 1.8 MeV in kinetic energy. Of this higher energy flux, only a small fraction would penetrate 0.82 cm (0.3 in) of tissue and deposit energy in the thyroid. Thus thyroid dose from this pathway was considered insignificant. For internal emitters, thyroid absorbed dose per unit intake was compiled from values generated by Johnson (Jo82). An exponential interpolation of nonadult values was performed. Thyroid absorbed dose commitment was calculated because the nuclides of interest had half-lives much shorter than 50 years. Absorbed dose was generated based on the assumption of a quality factor of one. The absorbed dose per unit activity intake values for adults were those given by Johnson directly (Jo82). The values for the tellurium isotopes were generated from reference man data contained in Limits for Intakes of Radionuclides by Workers (ICRP79). Tellurium isotope values for the ages less than adult were generated by ratio of the Johnson values for the appropriate iodine daughters. The thyroid absorbed dose for any age per unit intake of any tellurium isotope was assumed directly proportional to the product of the adult value and the ratio of the itodine value. ABSORBED DOSE ESTIMATES 33