  We determine a lower bound for the entanglement of pairs of electron spins
injected into a mesoscopic conductor. The bound can be expressed in terms of
experimentally accessible quantities, the zero-frequency current correlators
(shot noise power or cross-correlators) after transmission through an
electronic beam splitter. The effect of spin relaxation (T_1 processes) and
decoherence (T_2 processes) during the ballistic coherent transmission of the
carriers in the wires is taken into account within Bloch theory. The presence
of a variable inhomogeneous magnetic field allows the determination of a useful
lower bound for the entanglement of arbitrary entangled states. The decrease in
entanglement due to thermally mixed states is studied. Both the entanglement of
the output of a source (entangler) and the relaxation (T_1) and decoherence
(T_2) times can be determined.
