Gaokao Physics Practice Question

下列核反应方程中，属于 $\alpha$ 衰变的是

1. A.${ }_{7}^{14} \mathrm{~N}+\stackrel{4}{2} \mathrm{He} \rightarrow_{8}^{17} \mathrm{O}+_{1}^{1} \mathrm{H}$
2. B.${ }_{92}^{238} \mathrm{U} \rightarrow{ }_{90}^{234} \mathrm{Th}+_{2}^{4} \mathrm{He}$
3. C.$_{1}^{2} \mathrm_{1} \mathrm{H}+_{1}^{3} \mathrm{H} \rightarrow_{2}^{4} \mathrm{He}+_{0}^{1} \mathrm{n}$
4. D.${ }_{90}^{234} \mathrm{Th} \rightarrow ^{234}_{91} \mathrm{~Pa}+^{0}_{-1} \mathrm{e}$