How much radiation is safe per day


? Radiation effects and radiation protection?

questions and answers=> Radiation effect => question and answer
 
 Question:
Which radiation doses are dangerous and which can be neglected?


Short answer

Doses in the Sievert (Sv) range lead to acute damage (question 102) and are certainly dangerous. Doses in the µSv (millionth of Sievert) range are much smaller than the fluctuation range of naturally caused doses and can therefore be forgotten. The risk of long-term damage with effective doses between 1 mSv and 100 mSv can be assessed by comparison with the naturally caused radiation dose and purely mathematically. For occupationally exposed persons, a limit of 20 mSv per year (StSV) applies.

illustration

Some dose values ​​as an order of magnitude and their evaluation; the area of ​​the circles corresponds to the effective dose



Explanation

Radiation doses that lead to acute damage are dangerous and must be prevented. Such doses are greater than a threshold dose that is a few Sieverts for sensitive organs such as the bone marrow, intestines or lungs. Such doses occurred after the bombs in Hiroshima and Nagasaki, after Chernobyl and in other accidents.

The following can be used as a yardstick for assessing an additional radiation risk for doses in the order of magnitude of the limit value for occupationally exposed persons and smaller doses:
  1. A comparison with the naturally generated radiation dose and its range of variation.

  2. An additional radiation dose caused (e.g. by an X-ray or by remnants of radioactivity from Chernobyl) cannot be assessed in isolation, but is added to the dose as a result of natural radiation. This annual dose varies from around 1 mSv to around 10 mSv and averages around 3 mSv. It is important to know that our body has efficient mechanisms for repairing radiation damage. If an additional dose of artificial origin is much smaller than the range of variation of the dose of natural origin, its effect is negligible and can be neglected (order of magnitude µSv = thousandths of a mSv).

  3. Risk factors for cancer and hereditary defects.

  4. In the area of ​​the limit value for persons exposed to radiation and below, the additional risk of cancer and hereditary defects can be calculated with the help of the risk factors (see question 102). It should again be noted that this additional risk adds to an already existing spontaneous risk. In Europe, for example, the risk of cancer is around 25%, i.e. every fourth inhabitant dies on average from cancer. It can also be said that every resident has this probability of about 25% dying of cancer. This figure of 25% also has a range of variation. If the additional risk is within this range of variation, additional cancer cases cannot in principle be detected, even if they exist and can even be calculated. If, for example, someone ingests 1 mSv dose per year from artificial sources for 70 years, this figure increases from 25% to 25.35% in purely mathematical terms.
From the above it follows that it is not possible to give an exact separation between the negligible doses (µSv) and the dangerous doses (Sv). Unnecessary doses should be avoided if the effort is reasonable, and a cost-benefit optimization should be undertaken. At least it can be assumed that the limit required for the general public of no more than 1 mSv additional dose per year guarantees adequate protection and that the limit value also represents an acceptable occupational risk for people who are occupationally exposed to radiation.

Hugo Loosli August 04

Reference:
StSV: Radiation Protection Ordinance (in Switzerland), 1994,
or StrlSchV: Radiation Protection Ordinance (in Germany)