Harmful Effects :We have already mentioned that alpha, beta and gamma radiations emitted in the process of radioactive disintegration of unstable nuclei can damage the living tissues. Among these radiations, alpha has the lowest penetrating power, while gamma has the highest penetrating power, so gamma radiations are more harmful. When they fall on the human body, they kill the living tissues and cause radiation bums (or damage).
The biological effects of nuclear radiations are of three types: (i) short term recoverable effects (ii) long term recoverable effects and(iii) genetic effect. The first two effects are limited to the individuals who are actually exposed to the radiations, while the third effect appears in the later generations.
The exposure to radiations can be acute if there is an accidental burst of radiation from an unshielded source. Similarly, it is chronic in case of radiographers or persons working in atomic energy establishments when they get exposed to radiations. Therefore the people working with radioactive materials are required to follow strictly the safety rules which are given below.
- They should put on special lead lined aprons and lead gloves.
- They should handle the radioactive materials with long lead tongs
- The safety limit of each type of radiation is known and care is taken that no one is exposed beyond the safety limit in any case. For this, special film badges are used which are tested from time to time to know the amount of radiations to which a particular person has been exposed.
- The radioactive substances are kept ill thick lead containers with a very narrow opening so as to stop radiation, coming out from other directions. A container should be such that it absorbs the radiations which strike on its walls. Alpha particles can easily be stopped by a thin metal sheet, but for beta particles we need a thicker metal sheet, whereas gamma radiations need very thick lead sheets.
Radiation and living cells
When radiation collides with molecules in living cells it can damage them. If the DNA in the nucleus of a cell is damaged, the cell may become cancerous. The cell then goes out of control, divides rapidly and causes serious health problems.
Radiation warning symbol
The greater the dose of radiation a cell gets, the greater the chance that the cell will become cancerous. However, very high doses of radiation can kill the cell completely. We use this property of radiation to kill cancer cells, and also harmful bacteria and other micro-organisms.
The hazard symbol is shown on containers of radioactive substances to warn of the danger.
Alpha, beta and gamma radiation
The degree to which each different type of radiation is most dangerous to the body depends on whether the source is outside or inside the body.
If the radioactive source is inside the body, perhaps after being swallowed or breathed in:
- Alpha radiation is the most dangerous because it is easily absorbed by cells.
- Beta and gamma radiation are not as dangerous because they are less likely to be absorbed by a cell and will usually just pass right through it.
If the radioactive source is outside the body:
- Alpha radiation is not as dangerous because it is unlikely to reach living cells inside the body.
- Beta and gamma radiation are the most dangerous sources because they can penetrate the skin and damage the cells inside.
Notice that these effects are opposites and make sure you get them the right way around.