Gamma irradiation induced isotope exchange in nitrogen sensitized by helium, neon and argon

Abstract

Irradiated inert gases may transfer absorbed energy to nitrogen, resulting in the production of excited nitrogen molecules, ions and N atoms. These processes may promote nitriding of fast reactor components if the cover gas contains nitrogen impurity. This paper describes an investigation of energy transfer to nitrogen from helium, neon and argon. The efficiency of N atom formation was determined by 60Co gamma irradiation of rare gases containing 14N14N and 15N15N, with measurement of the product 14N15N by mass spectrometry. The results are correlated with the energy levels of the states produced on irradiation of the rare gases. Helium ions and metastable atoms are very efficient at producing N atoms by energy transfer to nitrogen. The helium ions have sufficient energy to produce N+, N+3 and excited N+2 ions, resulting in increased N atom formation. Neon ions and metastables give N+2 ions but not the higher ionic states. In the argon system, only Ar+ gives efficient production of N atoms. N atoms are not produced in low concentrations of nitrogen in argon. Sodium vapour caused no enhancement of N atom formation in argon, and it is concluded that N atoms would not be produced in a fast reactor cover gas if argon is used, but will be formed in a helium cover gas.