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What is Half–Life?
The halflife of a radioactive element is the time taken for half its mass to decay. The halflife of an element is a constant value for the particular element, irrespective of the quantity of the element present.
Knowing the halflife of an element makes it possible to detect it and to calculate the quantity that had decayed, or the quantity left over a given time.
The rate at which radioactive disintegration occurs (i.e., halflife) vary from very slow to very rapid. For radium, the halflife is 1590 years.
This means that, on the average, half of the radium atoms contained in a particular sample
will disintegrate in 1590 years, etc. Halflife periods vary from fourteen billion years for one of the isotopes of thorium to less than one billionth of a second for one of the isotopes of polonium.
The longer the halflife of a substance, the weaker will be the intensity of its radiation.
Therefore, since in humans physiological effects result from exposures to radiations, such effects are milder from substances with longer halflife.
Example: A sample of radioactive element with halflife of 2 mins initially contains 8 x 10^{6} atoms, find the time at which the number of atoms of the original element of the sample is 2 x 10^{6} atoms.
Solution:
I.e., the substance went through two disintegrations, \ total time taken is
2+2 = 4 mins.
