  We propose a three-terminal spin-valve setup, to determine experimentally the
spin-dependent shot noise, which carries information on the spin-relaxation
processes. Based on a spin-dependent Boltzmann-Langevin approach, we show that
the spin Fano factor, defined as the spin shot noise to the mean charge
current, strongly depends on the spin-flip scattering rate in the normal wire.
While in the parallel configuration the spin Fano factor always decreases below
its unpolarized value with increasing spin injection, for the antiparallel case
it varies nonmonotonically. We also show that in contrast to the charge current
Fano factor, which varies appreciable only in the antiparallel case, the spin
Fano factor allows for a more sensitive determination of the spin-flip
scattering rate.
