NATURAL & TYPICAL RADIATION EXPOSURE LEVELS

Natural background radiation is the radiation exposure or dose that is received daily from normal sources. Natural background radiation comes from cosmic radiation, internally deposited radioactive materials in the body, and radiation such as radon from environmental sources such as soil. It also comes from food we eat, e.g., potassium-40 (0.01% of potassium is radioactive). The average natural background radiation in the United States is about 300 mrads or 3.0 mGy per year with the radon exposure being responsible for about half of the total. There is also man made background radiation from nuclear weapons, nuclear accidents, production of nuclear power and the use of radioactive materials in consumer products. The estimated average human exposure from man made background radiation is about 70 mrem/year.

We get exposed to ionizing radiation. Table 2 shows typical radiation exposures.

Table 2: Typical radiation exposures.

Event	Dose
Chest X-ray	0.03 rad
Natural background	0.3 rad/year
Gastric fluoroscopy	0.4 rad
Radiation Workers	5 rads/yr (Limit)
CT (head and body)	1.1 rad
Hiroshiima/Nagasaki	20 rads (Average)
Acute radiation sickness	~100 rads
50% chance of death	>450 rads

Federal regulations prohibit radiation workers from receiving more than five rems annually.