Nuclear Power Engineering
The atomic mass of an element is fractional, because

It may have isobars
Of uncertainty principle
It may have isotopes
It contains neutrons

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Nuclear Power Engineering
The half life period of a radioactive substance is best determined by counting the number of alpha particles emitted per second in a Geiger Muller counter from its known quantity. If the half life period of a radioactive substance is one month, then

It will completely disintegrate in two months
3/4th of it will disintegrate in two months
L/8th of it will remain intact at the end of four months
It will completely disintegrate in four months

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