Quick question: Explain why momentum of an alpha particle is greater if the daughter nucleus cannot recoil?

Question

During Alpha decay, an alpha particle is emitted from a nucleus at v velocity. Explain why the velocity of the alpha particle is greater if the daughter nucleus is not free to move.

If conservation of momentum is applied, the initial momentum is 0 and the final must be zero, but because only the alpha particle has momentum, it has no other "momentum" to counter it to total zero. I can't get it to work out so the alpha particle moves faster if the daughter nucleus cannot move. Please help.

Answer 1

If the daughter does not recoil it must be embedded in a solid of large mass M then mv- MV=0 the larger M the greater v