Radiation

Radiation is the process of emitting energy as waves or particles. There are two types: non-ionizing radiation and ionizing radiation. The last one is the radiation which has enough energy to produce ions. If this type of radiation passes trough the body, it can produce damage in DNA.

Measurement

Radiation is measured in dose. The amount of energy absorbed per unit weight of the organ or tissue is called Absorbed Dose. Its unit is Gray (Gy). One Gray is equivalent to one joule radiation energy absorbed per kilogram of organ or tissue weight.

Equal doses of all types of ionizing radiation are not equally harmful. For example, alpha particles produce greater harm than beta particles and gamma and X-rays for a given absorbed dose. That's why we express radiation dose as Equivalent Dose that is equal to "absorbed dose" multiplied by a "radiation weighting factor" (Wr). Its expressed in units of Silverts(Sv) or rem. 1 rem=10 mSv.

Some parts of the body are more sensitive than others. We define Effective Dose the sum of the product of the equivalent dose and the tissue weighting factor. The tissue weighting factor represents relative sensitivity of organs for developing cancer. Its units is also the Silverts or rem.

Effective dose=sum of [equivalent dose * tissue weighting factor]

The total effective dose allowed in a period of five years is 100 mSv, however, in a year the effective dose cannot be greater than 50 mSv.

The effects

The radiation effects on a cell are random. That is, the same Equivalent Dose could strike the cell many times and have different effects, including no effect, each time. However, the more radiation that strikes the same cell, the greater the chances of occurring a harmful effect.

There are four possible effects when some radiation is absorbed by the cell:

1. The cell may suffer enough damage to cause loss of proper function, and the cell will die.
2. The cell may lose its ability to reproduce.
3. The cell’s genetic code (DNA) may be damaged, and the future copies of the cell could be altered, and result in a cancerous growth.
4. No adverse effect.

Cells are made up of molecules. Cell damage may be caused by interaction of radiation with these molecules. Some cells are more likely to be affected by radiation than others, for example, cells that multiply rapidly are the most susceptible. That is why cells can often repair radiation damage, but if the cell multiplies before it has had time to repair the most recent radiation damage, the new cell might not be accurate copies of the old one.