Elementary radiation safety
Dosimetry
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 radiation | RBE |
| Alpha | 10 |
| Beta | 1 |
| Gamma, X-ray | 1 |
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:
- Dose proportional or stochastic effects double when the dose is doubled. This means that there is no threshold below which radiation causes no damage. In principle, very single particle counts. This type includes genetic and carcinogenic effects.
- Threshold type effects cause so-called somatic damage when a certain threshold dose is passed. Note that the dose may be accumulated over a longer period of time. Below the threshold, repair mechanisms in our bodies prevent damage. This type includes (but is not limited to!) the radiation syndrom with symptoms such as nausea, fever etc.
| Dose | symptoms |
| 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 from external (not inside your body) sources,
- Incorporation of radioactive substances into your body.
Irradiation is to be avoided by
- shielding,
- distance,
- short duration.
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.
OR
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
- sealing the radioactive source
- protective clothing (including gloves, dust masks etc.)
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:
- Always keep radioactive sources as far away as possible, and keep handling time as short as possible. Do not carry sources in your pocket, unless they are shielded (lead container).
- Do not touch radioactive sources. When handling them, use gloves or tweezers etc.
- Do not inhale or swallow radioactive sources. When handling them do not eat, drink or smoke.
- Always wash your hands after handling radioactive sources.
- Label radioactive sources as such, and do not keep them near food etc.
- Keep radioactive sources out of reach of children.
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