A thorium nucleus $^{230}_{90}\text{Th}$, while moving, emits an $\alpha$-particle without any external cause. The product is a radium nucleus $^{226}_{88}\text{Ra}$, as illustrated. Which statement is correct?
- AThe kinetic energy of the $\alpha$-particle equals the kinetic energy of the radium nucleus.
- BThe momentum of the $\alpha$-particle equals the momentum of the radium nucleus.
- CThe total momentum before the emission equals the total momentum after the emission.
- DThe velocity of the $\alpha$-particle equals the velocity of the radium nucleus.