Question #5eb9c

1 Answer
Mark C.
Nov 18, 2017

Some nuclides deviate sufficiently from the ‘line of stability’ that they emit ionising radiation.

Explanation:

Some nuclei are fissile (but only a few of the most massive), some are neutron-rich and tend to emit beta particles, some have an excess of protons (positron emitters.) Have a look a time the diagram below and you can see the pattern:

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Taken from: https://en.m.wikipedia.org/wiki/Stable_nuclide

A relatively large number emit alpha particles and this brings me to the point ... all nuclides are attempting to become stable through these transitions, because this means lowering their internal energy. Only the (relatively few) black dots are stable on this diagram!

Emitting alpha particles is harder to explain using this model, but an alternative way of looking at the nucleus may help explain it (the liquid drop model of the nucleus.) Because an alpha particle is so stable it is relatively likely to “pinch” off a nucleus.

The final point I’d like to make is that very often a nucleus, having emitted a decay product or undergone fission, is left in an excited state, it will then emit a gamma ray as a means of shedding the excess energy.

Sorry it’s been such a long answer!

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