It is the process in which certain unstable atomic nuclei (plural of nucleus) emit radiations to become stable. The elements that emit radiations are called radioactive materials. The common examples of radioactive materials are uranium (U), radium (Ra), polonium (Po), thorium (Th), Radon (Rn) etc.
There are three types of radiations: They are alpha particles, beta particles and gamma Radiations. Radioactivity is a random process; it means that in a radioactive sample one cannot predict which atomic nucleus is going to emit radiation at any particular time, but the probability of emission is constant.
Radioactivity is spontaneous; it means that it does not depend on the environmental conditions. Radioactive emission is same at all temperature and pressure. Radioactivity cannot be speed up or slow down by any scientific method.
Background radiation is the low intensity radiation present in the earth’s atmosphere. These are low level radiations that our body can tolerate. The sources of these radiations are:
– radiation from earth’s crusts (rocks) which contain radioactive elements,
– radiation from outer space from stars and planets and
– emission from nuclear experiments and nuclear power stations.
When detecting and measuring the radiation from a radioactive source it is important to subtract the background radiations for the counter readings.
All ionising radiation is invisible to the naked eye, but it affects photographic plates. Individual particles of ionising radiation can be detected using a Geiger-Muller tube.
A Geiger–Müller tube consists of a tube filled with a low-pressure (~0.1 Atm) inert gas such as helium, neon or argon (usually neon. The tube contains electrodes, between which there is a potential difference of several hundred volts, but no current flowing. The walls of the tube are either entirely metal or have their inside surface coated with a conductor to form the cathode while the anode is a wire passing up the center of the tube.
When ionizing radiation passes through the tube, some of the gas molecules are ionized, creating positively charged ions, and electrons. The strong electric field created by the tube’s electrodes accelerates the ions towards the cathode and the electrons towards the anode. The ion pairs gain sufficient energy to ionize further gas molecules through collisions on the way, creating an avalanche of charged particles.
This results in a short, intense pulse of current which passes (or cascades) from the negative electrode to the positive electrode and is measured or counted. Most detectors include an audio amplifier that produce an audible click on discharge.