ISSN:
1089-7690
Source:
AIP Digital Archive
Topics:
Physics
,
Chemistry and Pharmacology
Notes:
Emission spectra and their decay were measured along the path of 4 MeV/amu N ions impinged into dense helium gas near 5.2 K and 420 Torr. Specific scintillation, dL/dX, and scintillation efficiency, dL/dE, for each emission band were measured separately on total, fast initial-rise (〈2 ns), fast decay (〈100 ns), and stationary (afterglow) components in order to elucidate the detailed dependence of production and decay of excimers on the stopping power, dE/dX. The curves of dL/dX and dL/dE vs dE/dX are shown to have a bend at 6 MeV mg−1 cm2: Some of the emissions increased abruptly as the stopping power exceeded this value, while the other emissions decreased or their rates of increase were suppressed. This bend point corresponds to the starting point of a rapidly decreasing yield of δ rays. The result shows that helium has a good scintillation response to high-density excitation occurring at the termination of tracks of N ions, in contrast to usual scintillators, where scintillation decreases abruptly with decreasing δ-ray yield. The large yields of emissions at high-density excitation are explained by the direct excitation, induced emission, and cyclic regeneration of excimers by bimolecular reactions between the nonradiative metastable state, a3, in addition to a very low probability of quenching in helium. Furthermore, it is shown that the present results support the tentative assignment made in part I of this report that the new triplet bands centered at 4587 A(ring) result from an excimer–dimer. Also, it is proposed that an excimer–dimer is composed of the a3 and c3, b3, or d3.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.450409
