Note: For most purposes of radiation protection in humans, Roentgen (R), radiation absorbed dose (rad) and radiation equivalent man (rem) are considered roughly equivalent. The SI unit of radiation is the sievert. One sievert equals 100 rem. Radiation dose rate at the Fukushima reactor briefly reached a high of 1557 microseiverts/hour, then dropped. This would correspond to a total dose of about one rad if you were exposed for 10 hours. Not a big deal.
Here is a table showing radiation effects on humans for various acute doses:
0 to 25 rads:
- No easily detectable clinical effect in humans
- However, at about 15 rads there could be temporary sterility in males
- Some epidemiological studies suggest an increased risk of cancer in this dose range, but the data suggest that risks in the 15‐20 rad dose range are very small and difficult to measure
- Above 10 rad there appears to be a significant risk of thyroid cancer due to radioactive iodine exposure in children 15 years of age and younger
- Some studies have shown a link between low dose radiation exposure and childhood leukemia and non-Hodgkins lymphoma, but other studies of children exposed to radiation at Chernobyl and Hiroshima, show no link.
- Slight short‐term reduction in blood cells
- Disabling sickness not common
- Nausea and fatigue
- Vomiting if dose is greater than 125 rads
- Longer‐term reduction in number of some types of blood cells
- Nausea and vomiting on the first day of exposure
- Up to a two‐week latent period followed by appetite loss, general malaise, sore throat, pallor, diarrhea, and moderate emaciation
- Recovery in about three months unless complicated by infection or injury
- Nausea, vomiting, and diarrhea in first few hours
- Up to a one‐week latent period followed by loss of appetite, fever, and general malaise in the second week, followed by bleeding, inflammation of mouth and throat, diarrhea, and emaciation
- Some deaths in two to six weeks
- Eventual death for 50% if exposure is above 450 rads
- Others recover in about six months
- Nausea, vomiting, and diarrhea in the first few hours, followed by rapid emaciation and death in 2nd week
- Eventual death of nearly 100%
Information from JP Laboratories, Inc., KI4U.com, and Steve Quayle's Radiation Measurement Conversion Tables.