Hi This is the question.... The population of the Marshall Islands were exposed to fallout from atomic bomb tests in the middle of the last century. A significant quantity of the fallout was in the form of 131Iodine, a gamma emitter which is avidly absorbed by the human thyroid. The average thyroid dose received by an islander was 1.5 Gy. The population of the islands was approximately 11000. How many islanders might be expected to die following this exposure to their thyroids? [Useful Data : the radiation weighting factor for gamma rays is 1 and the tissue weighting factor for the thyroid is 0.04] and I have been given an answer to it: Thyroid dose 1500 mGy, gamma emitter thus equivalent dose 1500 mSv Effective dose is 1500 x 0.04 = 60 mSv Risk is 5 in 100,000 per mSv i.e. 300 in 100,000 (or 3 in 1000) for 60 mSv In population of 11,000, 33 at risk I understand everything up to where he says the risk is 5/100,000. Where has he got that from? If you know any better ways of answering the question, feel free to comment. Thanks in advance!