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Radiation Safety Training Module
Radiation Safety Training
Study Guide
ISU Technical Safety Office, Campus Box 8106
Pocatello, ID 83209
(208) 282-2311/2310

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sources of exposure to radiation

Natural exposure

The average annual radiation dose to a member of the general U. S. population from natural radiation sources is about 360 millirem (mrem).
 
The four major sources of natural radiation exposures are:
  • Cosmic radiation
  • Terrestrial radiation (sources in the earth's crust)
  • Sources in the human body (internal sources)
  • Radon

Medical exposure

X-ray Procedure                                                                        Average Dose*
Normal chest examination                                                              10 millirem
Normal dental examination                                                             10 millirem
Rib cage examination                                                                     140 millirem
Gall bladder examination                                                                170 millirem
Barium enema examination                                                           500 millirem
Pelvic examination                                                                           600 millirem
 

*Variations by a factor of 2 (above and below) are not unusual.

Nuclear medicine procedures tend to deliver even higher doses.

Occupational exposure

Any individual whose official duties or authorized activities include handling, operating or working in the presence of any type of radiation source or radiation producing device is a subject to occupational exposure.



Types of radiation exposure

Chronic radiation exposure
involves low levels of ionizing radiation over a long period of time.  Among the possible effects of chronic exposure are the increased risk of developing delayed somatic effects such as cancer and cataracts.  Also, research indicates possible genetic effects in humans from radiation damage to sperm and egg cells.  Genetic damage may result in birth defects passed along to future generations.
  • Somatic effect is the biological effect that occurs on the exposed individual.
  • Genetic effect refers to biological changes on the descendants of the exposed individuals due to
          mutation of their genetic materials.
  • Hereditary effect is a genetic effect that is inherited or passed onto an offspring.
  • Teratogenic effects are birth defects, experienced when an embryo or fetus is exposed to large doses of radiation. Radiation induced genetic abnormalities have not been identified in human populations. However, they have been observed in less genetically complex species.  

Acute radiation exposure is delivered in a short period of time.  Larger acute exposures are often associated with deterministic effects. The following possible outcomes can be produced as a result of a large acute exposure:

25 - 100 rads

Minor blood changes, some illness anticipated

100 - 300 rads


Illness (lowering of the white blood cell count, nausea, bacterial infections, vomiting, loss of appetite, diarrhea, fatigue, hair loss, and possible sterility), at the end of this range death may occur  but this is infrequent and would be associated with those individuals undergoing simultaneous physiological stress. These are the classic signs and symptoms of the radiation sickness syndromes.

300 - 450 rads

Anticipated death of 50% of population within 30 days, if medical assistance is not provided. Death caused by complications associated with radiation sickness syndromes.

When severely exposed, the victim may suffer fever, abdominal pains, explosive diarrhea, internal bleeding, infection, shock, convulsions, coma, and ultimately death.  Acute exposure delivering 300 rads and above in a short period of time could possibly produce these outcomes.

 
Radiosensitivity is a term that describes how sensitive a given cell is to radiation damage.  Scientists have found that the rate of mitosis and the degree of cellular differentiation determine radiation sensitivity.

The possible effects that could occur due to radiation exposure to cells are:
  • There is no cell damage
  • Cells repair the damage and operate normally and/or cannot reproduce.
  • Cells are damaged and operate abnormally.
  • The cells die as a result of the damage.
The following cells are considered to be the most radiosensitive because of their reproductive rate:
  • Cells of the unborn child.     
  • Blood and blood producing organs.          
  • Reproductive cells (sperm/egg).
  • Digestive tract cells.
  • Immature white blood cells.
Those, which reproduce slowly and are considered the least radiosensitive are nerve, muscle and bone cells.  Of course, radiation affects each person differently depending on such factors as total dose, dose rate, type of radiation, the area of body exposed, cell sensitivity, individual sensitivity, age, medical history, and physiological condition.
 
 
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