Jochen's High Voltage Page

Elementary radiation safety


When ionizing radiation passes through your body (or any material), it looses energy by ionizing atoms and molecules along its path. If some amount of material is irradiated, this energy loss per mass of the material is called dose and is measured in Gray (Gy) (old unit 1 rad = 0.01 Gy). Different kinds of radiation have different effects, so the energy loss for a particular kind is multiplied by a quality factor (RBE, relative biological effectiveness) characteristic to this kind, and the result is the so-called equivalent dose, measured in Sievert (Sv) (old unit 1 rem = 0.01 Sv).

Type of radiationRBE
Gamma, X-ray1

There is also a unit called Roentgen (R) which refers directly to the ionization produced by radiation. For practical purposes (in human tissue) 1 R = 1 rad = 0.01 Gy .

Biological effects of radiation

Two types of biological effects are usually distinguished:

0.8-2 Gy nausea etc., chronic damage
4 Gy LD50: 50% mortality after 4 weeks
6-8 Gy LD100: 100% mortality after about 3 weeks.
100 Gy more or less immediate death

Radiation protection

Again two cases have to be differentiated:

Irradiation is to be avoided by

Alphas are not a problem here, as the have a very limited range in air and are absorbed by the outer layers of the skin. Betas can be shielded relatively easily by 4mm aluminium or 1cm plexiglass. Lighter elements are preferred as absorbers, because in heavier elements betas produce more bremsstrahlung (gamma radiation), which then in turn has to be shielded. Gamma radiation is best absorbed by lead or avoided by distance. For small sources, the inverse-square-distance law holds:

Intensity decreases proportional to the inverse square of the distance.
Double distance -> quarter intensity

Incorporation is particularly dangerous, because the substances remain in you body for long times and there is no skin to protect sensitive organs. Alpha sources are particularly nasty because of their high RBE factor. Incorporation can be avoided by

Pratical hints

The sources mentioned on my page are of course not excessively dangerous (otherwise they wouldn't be available). However, the following rules are in any case good practice:

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