Is this a fiction or nonfiction movie?
"Little Boy" on Hiroshima killed 140,000 people within one year. "Fat Man" on Nagasaki, though more powerful, caused less deaths due to geographics and population - 70,000 people died by the end of the year. Temperature rose to 7,000 degree F so this was a major factor. However a single rapid dose of radiation can kill anyone instantly.
"Radiation dose is measured in several different units, but all relate to the amount of energy deposited. The units include the roentgen (R), the gray (Gy), and the sievert (Sv). The sievert and gray are similar, except the sievert takes into account the biologic effects of different types of radiation....The average person receives a total of about 3 to 4 mSv (1 mSv = 1/1000 Sv) per year from natural radiation and man-made sources....Three Mile Island and the Chernobyl...received only about 0.08 mSv additional radiation. However, people living near the Chernobyl plant were exposed to about 430 mSv of radiation." 30 people died near the same day but there are hundreds, if not thousands, of cancer related deaths just coming to surface today from both these events, especially Chernobyl. Therefore we still don't know the exact fatal amount over a long period of time, nor the affects.
"350 rads will cause a 50% fatality rate within two months"
http://www.artsci.wustl.edu/~copeland/atomicbomb.html
Radon levels measured in picocuries per liter (pCi/L): "The lifetime risk of developing lung cancer from household water that contains 1,000 pCi/L of radon is roughly 3 to 13 in 10,000; from water with 10,000 pCi/L of radon, the risk is approximately 3 to 13 in 1,000; for water containing 100,000 pCi/L is about 3 to 12 in 100."
http://www.wellowner.org/awaterquality/radon.shtml
"Continuous or frequent annual external radiation exposure to a population should not exceed 100 millirem per year. A limit of 500 millirem per year for an individual should be applied for an infrequent annual exposure."
http://www.roger-russell.com/jeffers/radiumdials.htm