The hydrogen atom yield in the pulse radiolysis of H₂ at high dose rates was measured by four independent calibration techniques, using reactions of H with O₂, ClNO, and HI. Spectrophotometrical detection of HO₂ in the reaction H + O₂ + H₂ → HO₂ + H₂ (1), of ClNO in H + ClNO → HCl + NO (2), of HI in H + HI → H₂ + I (3), and of I₂ in (3) followed by I + I + NO + H₂ → I₂ + NO + H₂ allowed determination of the hydrogen yield in 1 bar of H₂. The H atom yield was compared with the O₃ yields in pure O₂ and in O₂/SF₆ mixtures under identical irradiation conditions, which lead to relative G(H) values: G(H)_H2 = 1.38G(O₃)_o2 and G(h)_H2 = 2.07G(O₃)_O2/SF6. On the basis of G(O₃)_O2 = 12.8 a value G(H) = 17.6 is obtained. The rate constants of reactions 1, 2, and I + NO + H₂ → INO + H₂ (4) were measured as k₁ = 2.17 × 10¹⁶ cm⁶ mol^-2 s^-1, k₂ = 9.24 × 10¹² cm³ mol^-1 s^-1, and k₄ = 2.7 × 10¹⁵ cm⁶ mol^-2 s^-1.