So A’ = 234 and Z’ = 90. Note that it was not necessary to know the chemical species of the isotopes
to do this problem. However, it would have been possible to look at the periodic table and see that Z
= 92 means X is uranium-238 and that Z = 90 means Y is thorium-234 .
Beta Decay. Beta decay is the emission of a β-particle, which is an electron given the symbol e– or β–.
Despite the equivalence between electrons and β– particles, it is important to realize that these
particles are not electrons that would normally be found around the nucleus in a neutral atom, but
are products of decay emitted by the nucleus: in particular, when a neutron in the nucleus decays
into a proton and an electron. Since an electron is singly charged, and about 1,836 times lighter
than a proton, the beta radiation from radioactive decay is more penetrating than alpha radiation.
β decay means that a neutron disappears and a proton takes its place, ejecting a newly formed
electron as a β-particle in the process. Hence, the parent’s mass number is unchanged and the
parent’s atomic number is increased by 1. In other words, the daughter’s A is the same as the
parent’s, and the daughter’s Z is one more than the parent’s.
The generic beta decay reaction is:
Example: Suppose a cobalt-60 nucleus beta-decays:
What is the element Y and what are A’ and Z’?
Solution: 60 = A ́ + 0