An understanding of the biological effects of nuclear and X-ray radiation is important for evaluating many potential uses and dangers. This is pertinent in the present scenario of technology advances wherein the use of X-rays in the form of CT scans, PET-CT scans and radioisotopes in diagnosis and therapy are being used extensively. Some types of radiation are more damaging than others. Alpha radiation is the most damaging to human tissues because its particles are strongly ionizing. Neutrons are also damaging to cells, because they interact very easily with body tissue, which contains a lot of water. They are a highly penetrating form of radiation. Beta and gamma radiation are the least damaging forms of nuclear radiation but they are able to penetrate deeper into the body than alpha radiation. Gamma radiation and X-rays pass through the body easily. This chapter will not cover hazards due to ultraviolet , infrared and microwave radiations but relate to ionizing radiations
It is important to know that one is constantly being exposed to a variety of natural and man made background radiations. Gamma rays from space and from the earth as cosmic radiation which is equal to 1mSv/yr on earth and in space 27mSv/yr. Cacogenic radionuclide’s ( C14,Be7and He3 )account for 0.28mSv/yr and natural radon in the air exposures are 0.1mSv/yr. Radioactive potassium 40 atoms are naturally present in the body and undergo several thousand nuclear disintegrations every second. This accounts for 0.26mSv/yr. Medical exposures account for 20% , and natural background exposures for 80% of average exposures to world populations.
A wide variety of ionizing radiations can interact with biological systems, but there are only five types of radiation of importance, they are gamma, neutron, beta, alpha and X-rays.
Gamma radiation which emanates from the nucleus of an atom is highly energetic , penetrating so that a significant part will pass through the human body without interaction. This energy deposition may occur anywhere along a given photon's path. Because of its penetrating ability, the effects of gamma irradiation can be independent of the location of the source, (i.e., internal or external to the body).Gamma rays are commonly used for diagnostic and therapy purposes.
Since neutrons are uncharged particles and can react only with the nuclei of target atoms, the probability of interaction of neutrons in the energy range is roughly comparable to that of low-energy gamma photons. The energy deposition will not be uniform.Its present clinical application is in neutron beam therapy in some forms of cancer treatment.
High speed electrons in the form of beta radiation lose most of their energy after penetrating only a few millimeters of tissue. If the beta emitting material is on the surface of the skin, the resulting beta irradiation causes damage to the basal stratum of the skin. Damaged cells may be of greater significance to the total organism than killed cells, particularly if they go on to become malignant or otherwise malfunction. Killed cells are replaced quickly in most tissues with any degree of reserve capacity and do not cause significant overall clinical effects unless the cells involved are highly critical or the fraction of cells killed in a given organ is large.Beta rays are used in radioisotope therapies.
The energy of these relatively heavy, positively charged particles is fully absorbed within the first 20 micrometers of an exposed tissue mass. Because of this, alpha radiation is not an external hazard. If alpha emitting material is internally deposited, all the radiation energy will be absorbed in a very small volume of tissue immediately surrounding each particle . These rays are highly effective in targeted radioisotope therapies.There is now a significant progress in