Oe pe er aa LO ne Meade ee Discussion of the Piolesicel Facinr, As longer periods of time are i involved in the delivery of a given radiation dose, lesser biological effects may be expected. Frau the tine of fallout until the time of evacuation prokebly wili be a matter of hours, which has teen dose factor is 1/1. From tne time evacuation could be accomplished to time of return probably would be a matter of several days, so the biological factor has been estimated at 3/4. From 15 days after : ~ fallout until one year Jeter is essentially ae duration of one year, so the biological factor kes been estinated ct 2/3, eit > considered essentially an izstanieneovs dose, i.e., the blologica: BO It will be noted there is no calculation after one rear, because it is expected under actual conditicns of radiological cecsay and weathering that protabiy no significant dose will be delivered after a year's time in populated areas around the Mevada Test Site. rs It is recognizcd thet the precise cuantities sugsested for the biological factor cannot ts supported by conclusive evidence. Itis reasonable to expect that ine delivery cf » given radiaticn dese over & period of many days will heve less biologicel effectiveness than an instantaneous one (neglecting genetic effects) and thet the extension of the period to essentially one yeer should yield a still lower tiolesical factor. One piece of supportive evidence is the work of Strandgvist* where X-ray doses to the skin were fractionated into daily amounts, end © the biological effects compared to a one-treatment dose. A log-log plot of total doses versus days after initial treatment yielded straight lines. For example, the curve for skin necrosis indicated a ratio of 3000/6700 roentgens for a one-treatment versu i ally frec- *Sievert, Rolf M. "The Tolerance Dose and the Prevention of Injuries Caused by Ionizing Radiations". Eritish Journal of Radiology, Vol. M, No, 236, Aug. 1947. er a ee > '