In reply to Bob Cook's message of Thu, 13 Feb 2014 18:59:06 -0800: Hi, [snip] >Axil I believe electrons have a spin of +1/2, not 1/2. The outgoing >neutrino would have to have a 1/2 spinmaybe an electron anti neutrino or >whatever its calleda positron neutrino. Bob
AFAIK The spin quantum number is just the absolute value of the allowed instantaneous values. I.e. a particle with spin=1/2 could have an actual instantaneous spin of either +1/2 or -1/2. This goes for all Fermions. The actual value being an indication of the direction of the angular momentum vector, which could be either up or down at any given instant. Obviously each combination of particles has a combination of spins that has a minimum energy. For D this means both the proton and the neutron have the same angular momentum vectors, and hence the deuteron has spin 1, when it's energy is minimal. When you are making a deuteron from its parts, you are free to choose what instantaneous spin values each of the constituents has, so you could choose e.g. P (- 1/2) + N (- 1/2) -> D (-1) (absolute value 1), or P (+1/2) + N (+ 1/2) -> D (+1) (absolute value 1). The only difference between the two D's is that one is "upside down" relative to the other. However given thermal and zero point motion, the relative orientation of the two nuclei would rapidly change (independently), so it doesn't usually make much sense to speak of signed spins. My point is that the individual building blocks (Fermions) can have either + or - spins at the time that they combine, so determining the final spin is not just a matter of adding 1/2's. However you need to be careful that if you start with an odd number of Fermions, then you also end up with an odd number of Fermions (ditto for even). Regards, Robin van Spaandonk http://rvanspaa.freehostia.com/project.html
