Scintillation Response of NaI(T1) and KI(T1) to Channeled Ions

The scintillation pulse-height response of NaI(T1) and KI(T1) to ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ and ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ ions in the 2-60-MeV range has been studied with the ion beam aligned along low-index planes and axes and also aligned along a random direction. The scintillation efficiency increases by as much as 50% when the ion beam is channeled along a major symmetry direction. The effect of channeling has been observed by recording the pulse-height spectra for monoenergetic ions oriented along {100}, {110}, and {111} planes, and along $〈100〉$, $〈110〉$, and $〈111〉$ axes. The increase in pulse-height response is in semiquantitative agreement with recent model calculations. Observation of this effect permits study of channeling phenomena in thick crystals that are scintillators. In particular, this paper reports a measurement of the critical angle for channeling of 15-MeV ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ along a {100} plane.