Linear character and p-rationality

Question

Let $G$ a group and $\chi$ a linear character, p$\ne$2 a prime number with $|G|$=$p^a$$m$ and $(p,m)=1$. Show that $\chi$ is p-rational if and only if p doesn't divide the order of $\chi$ (as element of the dual of $G$). Can everyone help me to demonstrate this sentence? Thank you to everyone!