Answer
$$9.0 \times 10^{2} \mathrm{\ fm} $$
Work Step by Step
We know that $$m c^{2}=0.511 \mathrm{MeV}$$ using Table $37-3,$ and $$h c=1240 \mathrm{MeV} \cdot \mathrm{fm} .$$ Using Eq. $37-54$ and $\mathrm{Eq.} 38-13,$ we obtain
$\begin{aligned} \lambda &=\frac{h}{p}=\frac{h c}{\sqrt{K^{2}+2 K m c^{2}}} \\ &=\frac{1240 \mathrm{MeV} \cdot \mathrm{fm}}{ \sqrt { |1.0 \mathrm{MeV}|^{2}+2 | 1.0 \mathrm{MeV} |\ \ |0.511 \mathrm{MeV} |} } =9.0 \times 10^{2} \mathrm{fm} \end{aligned}$
