Page 4: General Overview
Measuring radiation doses and biological risks
Scientists use different terms when measuring radiation. The terms can either refer to radiation from a radioactive source, the radiation dose absorbed by a person, or the risk that a person will suffer health effects from exposure to radiation. When a person is exposed to radiation, energy is deposited in the body’s tissues. The amount of energy deposited per unit of weight of human tissue is called the absorbed dose. This is measured using the rad or the SI Gy. The rad, which stands for radiation absorbed dose, has largely been replaced by the Gy. One Gy is equal to 100 rad.
The curie (symbol Ci) is a unit of radioactivity. It has largely been replaced by the Becquerel, which is the unit of radioactivity. One Becquerel is defined as the number of atoms which decay per second in a sample. The curie unit is named after Marie and Pierre Curie, who conducted pioneering research on radiation.
A person's biological risk (i.e. the risk that a person will suffer health effects from an exposure to radiation) is measured using the conventional unit rem or the SI unit Sv.
CHART 2. EFFECTS OF DIFFERENT LEVELS OF RADIATION
|Radiation dose in rems||Health impact
||Possible chromosomal damage.|
|20-100||Temporary reduction in number of white blood cells. Mild nausea and vomiting. Loss of appetite. Fatigue, which may last up to four weeks. Greater susceptibility to infection. Greater long-term risk of leukaemia and lymphoma is possible.|
|100-200||Mild radiation sickness within a few hours: vomiting, diarrhea, fatigue; reduced resistance to infection. Hair loss. In sufficient amounts, I-131 can destroy all or part of the thyroid gland, leading to thyroid abnormalities or cancer. Temporary male sterility.|
|200-300||Serious radiation sickness effects as in 100-200 rem. Body cells that divide rapidly can also be destroyed. These include blood cells, gastrointestinal tract cells, reproductive cells, and hair cells. DNA of surviving cells is also damaged.|
|300-400||Serious radiation sickness. Bone marrow and intestine destruction. Haemorraging of the mouth.|
|400-1000||Acute illness, possible heart failure. Bone marrow almost completely destroyed. Permanent female sterility probable.|
|1000-5000||Acute illness, nerve cells and small blood vessels are destroyed. Death can occur in days.|
The United States' Nuclear Testing Programme