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When it comes to conserving certain properties of subatomic particles before and after interactions, spin confuses me. Must the total spin of a system after an interaction be the same as it was before the interaction? Take neutron decay for example:Neutron → Proton + Electron + AntineutrinoThe spin of all of these particles is 1/2. However, I've also read that spin can be +1/2 or -1/2. In this case, one could imagine that the original neutron had a spin of +1/2, and that the spins of the proton and the electron are also +1/2, with the antineutrino having a spin of -1/2. This negative spin cancels out one of the positive spins and the net result is +1/2 spin of the products (equal to the original neutron).However, some things seem not to do this. Take the absorption of a photon by a hydrogen atom. The photon has a spin of 1, and the electron has a spin of 1/2. The electron absorbs the photon and is raised into a higher energy state. However, all electrons have a spin of 1/2 and this cannot change (as far as I know). So what happened to the photon's spin of 1 during the electron's excitement? Did it just disappear? Does the nuclear spin play a role here?Is there any way to predict the spin of the products of an interaction based on the spin of the particles entering the interaction?
Does quantum spin involve angular momentum?
Quote from: DoctorBeaver on 27/09/2008 08:19:46Does quantum spin involve angular momentum?Yes.