When a nucleus undergoes radioactive decay, what is its new mass number?

1 Answer
David G.
Feb 22, 2016

In an #alpha# decay the mass number increases by 4, in a #beta# decay it is unchanged.

Explanation:

Whether or not the mass number changes depends on the type of decay.

An #alpha# decay means that the nucleus loses two protons and two neutrons so its mass number (also, and probably better, called the 'nucleon number') decreases by 4.

In a #beta# decay a neutron decays to give a proton and an electron, so the mass number is unchanged, but the atomic number increases by 1.

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