Radiation

Radiations

History

Radiation was first detected by a French scientist Henry Becquerel, who was conducting an experiment with photographic plates. He found that elements like uranium, thorium and potassium emitted certain rays, which had an affect on the plates, making them foggy. However, the type of radiations and their effect on living beings, vary drastically. There are different sources of radiation. Some of it is inherent in the planet's atmosphere, and living beings have an in-built mechanism to deal with it. While other sources of radiation are activities like nuclear fission and fusion (Acharya, 1975).

Since its discovery by Henri Becquerel in 1896 much has been learned about radioactive elements and their properties. This knowledge has led to many beneficial applications of the numerous radioisotopes.

Radiation consists of three types of rays, each with a different capacity to penetrate bodies. These are alpha, beta and gamma rays. Radiation is not harmful in all cases. In fact, some types of radiations are unavoidable, like cosmic radiation which originates from stars. The Sun too, radiates cosmic energy produced by nuclear reactions on its surface, consisting of short wavelength emissions of electrons and neutrons. A lead object, one inch thick, can be easily penetrated by such radiations. Thus, you can have an idea about the effect; cosmic radiations can have on living beings. As you move upwards from the surface of the Earth, the effects of this radiation goes on increasing. Therefore, frequent fliers and astronauts are more exposed to cosmic radiation than others (Acharya, 1975).

Nuclear Radiations

Nuclear radiations are so energy-rich that they ionise the surrounding matter by ejecting electrons from the atoms of the matter exposed to them. This is why they are considered as ionising radiations. Thus, nuclear radiations can damage living tissues. This quality makes nuclear radiations (radioactivity) harmful and even dangerous, but it also preconditions them for medical applications (nuclear medicine).

Types of Radioactive Rays

There are three types of radiations corresponding to three types of radioactivity.

Alpha radioactivity corresponds to the emission of a helium nucleus, a particularly stable structure consisting of two protons and two neutrons, called an alpha particle.

Beta radioactivity corresponds to the transformation, in the nucleus:

Either of a neutron into a proton, beta- radioactivity, characterized by the emission of an electron e-

Or of a proton into a neutron, beta+ radioactivity, characterized by the emission of an anti-electron or positron e+. It only appears in artificial radioactive nuclei produced by nuclear reactions.

Gamma radioactivity, unlike the other two, is not related to a transmutation of the nucleus. It results in the emission, by the nucleus, of an electromagnetic radiation, like visible light or X-rays, but more energetic.

Gamma radioactivity can occur by itself or together with alpha or beta radioactivity (Lewis et al., 1950).

The three principal types of nuclear radiations, a, b and g rays, penetrate into matter at different levels. We have to protect ourselves against nuclear radiations by suitable shielding, the nature and thickness of which being a function of the penetration power of the different radiations.

Alpha Rays

Alpha rays are the least penetrating ones, ...