Pulse and continuous stimulated emission was obtained from a preionization CO2 laser operating in the active zone of a stationary nuclear reactor. A gas mixture of the CO2:N2:3He = 1:4:5 composition was ionized by the products of the 3He (n, p)T reaction. The parameters of a non-self-sustaining discharge excited in the active region were determined and the threshold characteristics were found of an atmospheric-pressure laser preionized by fluxes up to 1014 neutrons·cm–2·sec–1.