RETO to parts of the gastrointestinal tract as a function of time.) Therefore, Graph Two is based on the activity at time of ingestion to produce one rad of dose to the lower intestine. For example, Graph Two shows that if about 1\8 microcuries are ingested on the 2)th hour after detonation, the lower large intestine may receive one rad of radiation dose. Step 1. This was calculated in the following manner. Determine the total number of disintegrations in the lower large intestine necessary to produce 1.0 rad. Fram equation (1) (Number of disintegrations) (0.)) 8.0 x 1077) 150 Number of disintegrations = Step 2. =1 ].7 x 1010 Determine the activity at time of intake to produce 4.7 x 1019 disintegrations within the large intestine. 4.7 x 1010 wig 0 x 101° 9 we From equation (2) disintegrations intake required (assuming 10% solubility). 5.2 x 10 = (5) (Az7) (372-2) /97-O+2 ~ 55-027 * Ag © 3.7 x 109 d/nr. Ap}, * 6.2 x 107 d/nr. Ao), = 47 pe #% If the time of intake is the 2th hour, then the start of irradiation of the lower large intestine is 2) + 13 = 37th hour, according to reference one. Graph Two has been used in estimating radiation doses to the lower large intestine for prolonged periods of ingestion (Table Two). The fol- lowing calculations are illustrative for the period of 2th to the 120th DOE ARCHIVES