A unit of angular momentum used in particle physics. The spin unit is equal to Planck's constant h divided by 2pi, or approximately 105.457 27 x 10-36 joule second (J·s). The spin of an elementary particle is always a simple multiple of this unit
Russ Rowlett (Director), How Many? A Dictionary of Units of Measurement, Center for Mathematics and Science Education University of North Carolina, USA 2005. http://www.unc.edu/~rowlett/units/dictA.html, (Unit of Meas and Covr Factors - Amer) {608}