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Unit 5.2: Radioactivity
Detection of radioactivity
The radiation from the environment to which we are exposed all the time is
called background radiation.
Background radiation is caused mainly by (i) the gas radon, (ii) rocks and
buildings, (iii) food and drink and (iv) cosmic rays.
All background radiation is not caused by natural causes. There are also
artificial causes such as the nuclear industry and X-rays.
Background radiation is a type of ionizing nuclear radiation. All ionizing
nuclear radiations can be measured using a detector connected to a
counter.
Usually, we use a Geiger-Counter (Geiger-Muller tube connected to a
counter) to measure radiation in counts/min or counts/second.
We can use background radiation measures to find a corrected count rate.
So if a radioactive source is placed in front of a counter and the counter
measures a rate of 350 counts/min but the background radiation is 20
counts/min, the corrected count rate for the source is 350-20 = 330
counts/min.
Thus, Corrected count rate = Measured count rate - background radiation
3 Types of Nuclear emission
Radiation is emitted by the nucleus of an atom which is unstable. It might
have an isotope for which the nucleus is too heavy and thus decays or
because it contains too many neutrons.
Whatever the case, radiation tends to be spontaneous and completely
random, meaning we cannot predict which nucleus will decay next or when
it will happen, or which direction the radiation will go in.