Question 705073

Wavelength $\lambda = \frac{hc}{E} = \frac{1240 \text{ MeV fm}}{420 \text{ MeV}} \approx 2.95 \text{ fm}$. Condition for first minimum: $\sin \theta = \frac{1.22\lambda}{d}$. With $\theta = 45^\circ$, $d = \frac{1.22 \times 2.95}{\sin 45^\circ} \approx 5.09 \text{ fm}$. Radius $r = \frac{d}{2} \approx 2.54 \text{ fm}$.