Nucleus $X$ undergoes $\beta^+$ decay. The resulting products are nucleus $Y$ with proton number $Z$, a $\beta^+$ particle, and a further particle $P$. $X \rightarrow Y + \beta^+ + P$. Which particle is $P$, and what is the proton number of nucleus $X$?
Physics 9702 · AS & A Level · Atoms, nuclei and radiation