Scintillations and Energy Transfer in Argon—Nitrogen Mixtures

Abstract

Pulse-height measurements have been made on scintillations produced by the complete stopping of alpha particles in gaseous argon, nitrogen, and argon—nitrogen mixtures. The results are correlated with the published results of spectrographic studies to derive information about energy transfer in collisions among Ar and N2 molecules. The optical system responds to light within the spectral range 2200–6000 Å. Total pressures varied from 3.5 to 6 atm. It was observed that the pulse height is greatest for pure argon. As nitrogen is added, the pulse height decreases, then increases, and finally decreases again. From this behavior and the effect of total pressure, it is concluded that the detectable light consists of three components: (1) that emitted by argon excited directly; (2) that emitted by a nitrogen state, probably C 3Πu, excited by energy transfer from an argon state that does not emit in the detection range, apparently the lower metastable state, (3) that emitted by nitrogen excited directly. The states that emit Components (1) and (2) are quenched by nitrogen in the ground state. For three pairs of competing processes, one pair associated with (1) and two with (2), values of the product (lifetime)×(cross section)×(relative velocity) have been obtained by fitting kinetic equations to the pulse-height data. The breakdown of the products into individual factors is discussed.