given the symbol e+ or β+. Positron emission is sometimes referred to as β+ decay, as distinguished
from the kind of beta decay (or β– decay) discussed on the previous page.
In positron decay, a proton splits into a positron and a neutron. Therefore, a β+ decay means that
the parent’s mass number is unchanged and the parent’s atomic number is decreased by 1. In other
words, the daughter’s A is the same as the parent’s, and the daughter’s Z is one less than the
parent’s. In equation form:
The generic positive beta decay or positron emission is:
Example: Suppose a parent isotope emits a β+ and turns into an excited state of the isotope
, which then γ-decays to , which in turn α-decays to . If W is ^60 Fe, what is
?
Solution: Since the final daughter in this chain of decay is given, it will be necessary to work
backward through the reactions. By looking at the periodic table one finds that W = Fe
means Z’’’ = 26; hence the last reaction is the following α decay:
By balancing the atomic and mass numbers you find:The second-to-last reaction is a γ decay that simply releases energy from the nucleus but does not
alter the atomic number or the mass number of the parent. That is: Z’ = Z” = 28 and A’ = A” = 64. So
the second reaction is: