When a nucleus at rest emits a beta particle, it is found that the velocities of the recoiling nucleus and the beta particle are not along the same straight line. How can this be possible in view of the principle of conservation of momentum?

Question

Philoid · Accepted Answer

In view of the principle of conservation of momentum, an antineutrino is also emitted along with the beta particle. The momentum of the recoiling nucleus and beta particle along with the antineutrino particle vectorially adds up to make the total momentum zero as was before the decay. So, the momentum is conserved in this way.