Kinetic processes of the scintillation in helium excited by alpha particles

The time dependence of the scintillations in pure helium excited by alpha particles has been measured in the pressure range of 100 to 1200 Torr by using a single photon counting technique. The time dependence of helium scintillation in the vacuum-ultraviolet region consists of a slow component and a fast one. The slow component emission appears to arise from two-body Frank-Condon collisions involving a 21S atomic state and from the deexcitation of the A1Σsub(u)sup(+) molecular state created from three-body conversion of a 21S state. The fast component emission arises from the deexcitation of the D1Σsub(u)sup(+) molecular state formed by three-body collisions involving a 21P atomic state. Radiative decay constant for the D1Σsub(u)sup(+) molecules is (2.2 +- 0.2) x 108sec -1. (author)