Question

23. 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 ?​

Answer 1

Answer:

Since the nucleus is at rest, therefore the initial momentum of the nucleus is zero

When the nucleus emits a beta particle, and the velocity of it is v then the nucleus must itself go in the opposite direction with momentum equal to v times the mass of beta particle but this doesn't happen because alongwith beta particle, an antinutrino is also emitted from the nucleus.

The total momentum is still conserved but the direction of the recoiling nucleus depends upon the combined momentum of beta particle and antinutrino.

Hope this helps.