Radiation causes ionizations in the molecules of living cells. These ionizations result in the removal of electrons from the atoms, forming ions or charged atoms. The ions formed then can go on to react with other atoms in the cell, causing damage. An example of this would be if a gamma ray passes through a cell, the water molecules near the DNA might be ionized and the ions might react with the DNA causing it to break.
At low doses, such as what we receive every day from background radiation, the cells repair the damage rapidly. At higher doses (up to 1 Sv), the cells might not be able to repair the damage, and the cells may either be changed permanently or die. Most cells that die are of little consequence, the body can just replace them. Cells changed permanently may go on to produce abnormal cells when they divide. In the right circumstance, these cells may become cancerous. This is the origin of our increased risk in cancer, as a result of radiation exposure.
At even higher doses, the cells cannot be replaced fast enough and tissues fail to function. An example of this would be "radiation sickness." This is a condition that results after high acute doses to the whole body (>2 Gy), the body's immune system is damaged and cannot fight off infection and disease. Several hours after exposure nausea and vomiting occur. This leads to nausea, diarrhea and general weakness. With higher whole body doses (>10 Gy), the intestinal lining is damaged to the point that it cannot perform its functions of intake of water and nutrients, and protecting the body against infection. At whole body doses near 7 Gy, if no medical attention is given, about 50% of the people are expected to die within 60 days of the exposure, due mostly from infections.
If someone receives a whole body dose more than 20 Gy, they will suffer vascular damage of vital blood providing systems for nervous tissue, such as the brain. It is likely at doses this high, 100% of the people will die, from a combination of all the reasons associated with lower doses and the vascular damage.
There a large difference between whole body dose, and doses to only part of the body. Most cases we will consider will be for doses to the whole body.
For more information on Acute radiation doses and its effects, check here
What needs to be remembered is that very few people have ever received doses more than 2 Gy. With the current safety measures in place, it is not expected that anyone will receive greater than 0.05 Gy in one year where these sicknesses are for sudden doses delivered all at once. Radiation risk estimates, therefore, are based on the increased rates of cancer, not on death directly from the radiation.
Non-Ionizing radiation does not cause damage the same way that ionizing radiation does. It tends to cause chemical changes (UV) or heating (Visible light, Microwaves) and other molecular changes (EMF). Further information on EMF that may be of interest.
Roentgen (R) The Roentgen is a unit used to measure a quantity called exposure. This can only be used to describe an amount of gamma and X-rays, and only in air. One Roentgen is equal depositing to 2.58 x 10-4 coulombs per kg of dry air. It is a measure of the ionizations of the molecules in a mass of air. The main advantage of this unit is that it is easy to measure directly, but it is limited because it is only for deposition in air, and only for gamma and x rays. RAD (Radiation Absorbed Dose) The RAD is a unit used to measure a quantity called absorbed dose. This relates to the amount of energy actually absorbed in some material, and is used for any of radiation and any material. One RAD is defined as the absorption of 100 ergs per gram of material. The unit RAD can be used for any of radiation, but it does not describe the biological effects of the different radiations. Radiation Radiation is energy in transit in the form of high speed particles and electromagnetic waves. We encounter electromagnetic waves every day. They make up our visible light, radio and television waves, ultra violet (UV), and microwaves with a spectrum of energies. These examples of electromagnetic waves do not cause ionizations of atoms because they do not carry enough energy to separate molecules or remove electrons from atoms. Ionizing radiation Ionizing radiation is radiation with enough energy so that during an interaction with an atom, it can remove tightly bound electrons from their orbits, causing the atom to become charged or ionized. Examples are gamma rays and neutrons. Radiation is measured in many ways, and commonly expressed in units of RAD. Non-ionizing radiation Non-ionizing radiation is radiation without enough energy to remove tightly bound electrons from their orbits around atoms. Examples are microwaves and visible light. Radioactive Fallout - General Information A number of factors, such as weather conditions and the strength of the weapon, affected the distribution of radioactive fallout from nuclear weapons tests. "The earlier, low-yield fission weapons deposited much of their debris in the general area around the test sites, whereas the high-yield thermonuclear weapons tested later produced radioactive fallout on a global scale," according to Appendix B of the National Council on Radiation Protection and Measurements Report 94. "For the tests in Nevada, the yield was only about 0.5 percent of the global total. However, while much of the exposure has been quite uniformly distributed on a hemispheric basis, there is still some interest in the doses delivered locally from testing in Nevada." Radioactive Fallout - Global and National Effects The United Nation Scientific Committee on the Effects of Atomic Radiation periodically publishes a report to the General Assembly on the sources, effects, and risks of ionizing radiation. The 1988 report (UNSCEAR 88) summarized conclusions reached in previous UNSCEAR reports regarding radiation doses received from nuclear explosions. "In the first four UNSCEAR Reports (1958-1966), the Committee described in detail the meteorological processes that deplete the stratospheric inventory of radioactive debris. For man, the highest exposure was found to be due to long-lived radioactive material that causes radiation exposures over many years. The dominant radionuclides were strontium-90 (half-life:28 years), cesium-137 (30 years) and carbon-14 (5700 years). Some gamma-emitting radionuclides from tropospheric fallout, e.g., zirconium-95 and ruthenium-106, could also contribute significantly through exposure from the ground deposition." People in some areas of the United States received external and internal radiation exposure from short-lived radioactive materials for a few days or weeks following the weapons tests until the radioactive materials had decayed to levels indistinguishable from normal background radiation. One short-lived radioactive material of interest for internal exposure was iodine-131. A recently published National Institute of Health (NIH) document described the deposition of radioactive iodine across the United States from nuclear weapons testing. David V. Becker, M.D.| Limits for Exposures | Exposure | Range | |
| Occupational Dose limit (US - NRC) | 50 mSv/year | ||
| Occupational Exposure Limits for Minors | 5 mSv/year | ||
| Occupational Exposure Limits for Fetus | 5 mSv | ||
| Public dose limits due to licensed activities (NRC) | 1 mSv/year | ||
| Occupational Limits (eye) | 150 mSv/year | ||
| Occupational Limits (skin) | 500 mSv/year | ||
| Occupational Limits (extremities) | 500 mSv/year | ||
| Source of Exposure | |||
| Average Dose to US public from All sources | 3.6 mSv/year | ||
| Average Dose to US Public From Natural Sources | 3.0 mSv/year | ||
| Average Dose to US Public From Medical Sources | 530 microSv/year | ||
| Average dose to US Public from Weapons Fallout | < 10 microSv/year | ||
| Average Dose to US Public From Nuclear Power | < 1 microSv/year | ||
| Coal Burning Power Plant | 1.65 microSv/year | ||
| X-rays from old TV set (1 inch) | 5 microSv/hour | ||
| Airplane ride (39,000 ft.) | 5 microSv/hour | ||
| Nuclear Power Plant (normal operation at plant boundary) | 6 microSv/year | ||
| Natural gas in home | 90 microSv/year | ||
| Average Natural Background | 0.008 mR/hour | 0.006-0.015 mR/hour | |
| Average US Cosmic Radiation | 270 microSv/year | ||
| Average US Terrestrial Radiation | 280 microSv/year | ||
| Terrestrial background (Atlantic coast) | 160 microSv/year | ||
| Terrestrial background (Rocky Mountains) | 400 microSv/year | ||
| Cosmic Radiation (Sea level) | 260 microSv/year | ||
| Cosmic Radiation (Denver) | 500 microSv/year | ||
| Background Radiation Total (East, West, Central US) | 460 microSv/year | 350-750 microSv/year | |
| Background Radiation Total (Colorado Plateau) | 900 microSv/year | 750-1400 microSv/year | |
| Background Radiation Total (Atlantic and Gulf in US) | 230 microSv/year | 150-350 microSv/year | |
| Radionuclides in the body (i.e., potassium) | 390 microSv/year | ||
| Building materials (concrete) | 30 microSv/year | ||
| Drinking Water | 50 microSv/year | ||
| Pocket watch (radium dial) | 60 microSv/year | ||
| Eyeglasses (containing thorium) | 60 - 110 microSv/year | ||
| Coast to coast Airplane roundtrip | 50 microSv | ||
| Chest x-ray | 80 microSv | 50 - 200 microSv | |
| Extemities x-ray | 10 microSv | ||
| Dental x-ray | 100 microSv | ||
| Head/neck x-ray | 200 microSv | ||
| Cervical Spine x-ray | 220 microSv | ||
| Lumbar spinal x-rays | 1.30 mSv | ||
| Pelvis x-ray | 440 microSv | ||
| Hip x-ray | 830 microSv | ||
| Shoe Fitting Fluroscope (not in use now) | 1.70 mSv | ||
| Upper GI series | 2.45 mSv | ||
| Lower GI series | 4.05 mSv | ||
| Diagnostic thyroid exam (to the thyroid) | 0.5 Gy | ||
| Diagnostic thyroid exam (to the Whole Body) | 0.35 mGy | ||
| CT (head and body) | 11 mSv | ||
| Therapeutic thyroid treatment (dose to the thyroid) | 50-100 Gy | ||
| Therapeutic thyroid treatment (dose to the whole body) | 7 cSv | 5-15 cGy | |
| Earliest Onset of Radiation Sickness | 0.75 Gy | ||
| Onset of hematopoietic syndrome | 3 Gy | 1 to 8 Gy | |
| Onset of gastrointestinal syndrome | 10 Gy | 5 - 12 Gy | |
| Onset of cerebrovacular syndrome | 100 Gy | >500 Gy | |
| Thershold for cataracts (dose to the eye) | 2 Gy | ||
| Expected 50% death without medical attention | 4 Gy | 3 to 5 Gy | |
| Doubling dose for genetic effects | 1 Gy | ||
| Doubling dose for cancer | 5 Gy | (8% per Sv, natural level at 20%) | |
| Dose for increase cancer risk of 1 in a 1,000 | 1.250 cSv | (8% per Sv) | |
| Consideration of theraputic abortion threshold (dose in utero) | 10 cSv | ||
| SL1 Reactor Accident highest dose to survivor | 27 cSv | ||
| Three Mile Island (dose at plant duration of the accident) | 0.80 mSv |