— Another report* indicates a beta to gamma ratio of 150 to 1 based on theoretical computations. A third report** suggests a radically lower ratio: however, there may be some doubt as to its conclusions since the ionization chamber used to measure gammas only, had a wall thickness 2£ 1 mm cf bakelite which "...excluded a small part of the total gamma dose present, as well as a lerge, but unknown, fraction of the beta." (The range of 0.35 Mev betas is about 100 mp/em” or approx- imately 1 mm of bakelite.) For our discussion here, we will assume a Surface beta to gamma ratio of 150 to 1. In estimating the beta dose to the basal layer of the epidermis, one may refer to the work of Henriques***, He exposed the skin of Chester White pigs to plaques containing different radioisotopes. Pertinent dats are abstracted as follows: Asoione Yttrium?+ Strontium’20 Yttrium? Energy - Surface Dose Required To Produce Recognizable Transepidermal Injury (Roentgen-equivalent= eta) 1.53 0.61 2.20) Estimated Amount of Radiation That Pens— trated Skin To A Depth . of 0,09 mm, (red) 2,500 1,200 1,500 1,400 The average maximum energy of the beta particles from fallout mater- jal varies with time but will be assumed to be roughly comparable, in 5 respect to depth dose, to Yttrium’ or Sr?0-y%, Since the gamma dose at a depth of 7 me/om” would not be significantly different from the surface gamma dose, the ratio of 130 to 1 for beta-gamma will be assumed at the basel layer of the epidermis, *"An Estimste of the Relative Eazard of Beta and Gamma Radiation from Fission Products". Sullivan, Williem H., NRDL. April 1949. CONFIDENTIAL. **UKP=37. Project 4.7. "Gamma-beta Ratio in the Post-shot Contaminated Area". June 1953. CONFIDENTIAL-RESTRICTED DATA. ee¥UEffect of Beta Rays on the Skin As A Function of the Energy, Intensity, and Durationof Radiation". war A Henriques, F.W. Laboratory Investigation. |