Different forms
of an element,
45. Radioactive substances undergo a constant disintegration process. The
each having a
different atomic
entire mass of a sample of radioactive material does not disintegrate
mass.
simultaneously. Relatively few of the great number of nuclei present in an
ordinary sample will disintegrate in any small-time interval. The term 'half
life' is used to indicate the time required for half of the number of radioactive
atoms initially present to disintegrate. When the half life of uranium 234 is
said to be 269,000 years, this means that, on the average, half of the atoms
of uranium present in a given sample will disintegrate in 269,000 years and
half of the remaining atoms will disintegrate by half in the next 269,000
years. The half life of a radioactive element varies form element to element,
ranging from 14 billion years for thorium 232 to a fraction of a second for
polonium 212. Stating the half life is a way of indicating the rate at which the
nuclei of a radioactive element will disintegrate.
The half life of a radioactive element is the time required for
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IT0341
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