The HERMES internal polarized hydrogen and deuterium target

The HERMES experiment at the electron ring of HERA at DESY studies the spin structure of proton and neutron by deep inelastic scattering of polarized electrons off the nucleons of a highly polarized internal gas target. The t arget makes use of a storage cell to increase the target density. The polar isation of a sample of the atoms in the cell is measured with a Breit-Rabi polarimeter. A relaxation model based on the diffusion equation has been de veloped, which is used to calculate the corrections which are needed to det ermine the absolute target polarization using the measured values.