Radiolytic hydrogen formation in transition metal sulphate crystals containing water of crystallization

The G-values for H2 are measured for MnSO4 x 5H2O, FeSO4 x 7H2O, CoSO4 x 7H2O, NiSO4 x 7H2O, MgSO4 x 7H2O and 3 CdSO4 x 8H2O. Also the hydrogen yields are measured for FeNH4(SO4)2 x 12H2O and AlNH4(SO4)2 x 12H2O. The yield depends upon the dimensions of the crystals, except for FeSO4 x 7H2O, MnSO4 x 5H2O and 3CdSO4 x 8H2O. The G-values lie in the range between 0.56 and 0.002. Substitution of small amounts of Fe2+ for Ni2+ in NiSO4 x 7H2O and for Mg2+ in MgSO4 x 7H2O increases G(H2). Substitution of Cd2+ for Fe2+ in FeSO4 x 7H2O reduces G(H2) to about 35%. A reaction scheme is proposed for the observed phenomena in NiSO4 x 7H2O. It is concluded that the oxidizing species, which is created upon irradiation is more mobile in the crystal than the reducing species, and that inside the crystals a considerable fraction of the initially formed species recombines. Also there are indications that a fraction of the hydrogen formed inside the crystal is reoxidized before it can diffuse out of the crystal. (orig.)