Radiation-Induced Outgassing from Type 304 Stainless Steel

A Type 304 stainless-steel vacuum system has been designed and constructed to study radiation-induced outgassing when this material is exposed to ⁶⁰Co gamma radiation. An analytical model has been developed that predicts the outgassing from Type 304 stainless steel to be 5 X 10^-10 Paℓ/cm^{2 .} s per Mrad/h. Experiments determined the value for Type 304 stainless steel after bakeout at 300°C to be (1.03 ± 0.58) X 10^-9 Pa ℓ/cm² s per Mrad/h, in fair agreement with the analytical model predictions. Studies on thermally induced outgassing from Type 304 stainless steel showed that after bakeout at temperature T*, thermal outgassing ∆ obeys the relationship ∆ = ∆₀ exp(∼Q/RT), where both the constant ∆₀ and the average desorption energy Q are functions of T*. Water vapor and hydrogen were the principal residual gases in a Type 304 stainless-steel vacuum system, with hydrogen being dominant at low pressures after bakeout.