Found this reference:
An excellent reference for all manner of questions regarding the A-bomb survivors is the book by William J Schull, Effects of Atomic Radiation: A Half-Century of Studies from Hiroshima and Nagasaki, Wiley-Liss, Inc., 605 Third Avenue, New York, NY 10158-0012 (1995) ; ISBN # 0-471-12524-5. This is a scholarly book and yet is written at a level that the intelligent layperson can understand. It has a wealth of historical as well as scientific information about the studies, spanning the entire time period since the bombs were dropped. Following are answers to the specific questions asked:
Much information is available; for example, in the book cited above.
In 1995, 50 years after the atomic bombings, approximately 50 percent of the survivors were still alive. The exact number is difficult to state, but it could exceed 100,000. (For example, 284,000 survivors were identified in the 1950 census; this would indicate that there were about 142,000 remaining survivors in 1995.)
No genetic effects have been detected in a large sample (nearly 80,000) of offspring. By this, we mean that there is no detectable radiation-related increase in congenital abnormalities, mortality (including childhood cancers), chromosome aberrations, or mutations in biochemically identifiable genes.
Unfortunately, the epidemiologic studies on the survivors who received low doses of radiation (in the range of 0.01 Sv to 0.2 Sv) are equivocal regarding good measures of the risk of long-term health effects. This is because, even though the statistical sample available in the survivor studies is very large (nearly 100,000 subjects in the Life Span Study), it can be shown that many, many more subjects would be needed to draw reasonable statistically valid inferences from the data. Thus the data at low doses have large error bars and can be fit to mathematical models that show a threshold, no threshold, reduced effect, and in some cases even a beneficial (protective) effect, depending on the model one picks. There is no model that seems to be more valid than the others. Therefore, the consensus of the community of scientists interested in the A-bomb, as well as other, radiation studies seems to be that epidemiologic studies do not have the statistical power to give us answers to the low-dose questions. This issue is thoroughly discussed in the book by William J. Schull.
John D. Zimbrick, Ph.D. School of Health Sciences Purdue Univerity
Also this: http://content.nejm.org/cgi/content/extract/334/8/545