Hey, I am new to the forum, and would certainly appreciate help in understanding spin - although I realize that perhaps no one really understands spin. If a beam of spin polarized electrons are absorbed in a target, then the target will start to rotate. This kind of makes sense on a macroscopic scale, since the beam has a collective angular momentum that must be conserved, i.e., apparently some fraction of the absorbed electrons will change their spin direction and therefore the target should rotate in order to conserve angular momentum. What I find peculiar on the microscopic scale is the electron really does not impart it's angular momentum to the target when it is absorbed unless it changes it spin direction, i.e., apparently the target does not rotate upon absorbing the electron if the electron maintains the same spin direction after being captured (correct me if I am wrong about this). Maybe the simplest example is when a positron captures an electron and forms positronium for a brief period before annihilation. Is there any spin dependency in the life time of positronium? Maybe it is not appropriate to think of positronium as rotating, but if the spins of the electron and/or positron have changed direction, wouldn't a resulting rotation of the collective pair be logical?