a b c d

b

$ R = \frac{mv}{qB} = \frac{\sqrt {2mE}}{qB}$ $\frac{R_p}{R_d} = \sqrt {\frac{m_p}{m_d}} \sqrt {\frac{E_p}{E_d}} $ $ 1 = \sqrt{\frac{1}{2}} \sqrt{\frac{E_p}{50KeV}}$ $ E_p = 2\times 50KeV = 100KeV$