Previous experiments with aligned positive-ion beams on NaI(Tl) showed that the scintillation pulse-height spectrum exhibits two characteristic peaks: one due to those particles that are never channeled, and one at higher pulse height due to those particles that remain in a channeled trajectory throughout their range. This paper reports experiments with improved instrumental resolution. Pulse-height spectra for ${}_{}{}^4{}_{}{}^{}\mathrm{He}$, ${}_{}{}^7{}_{}{}^{}\mathrm{Li}$, ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$, ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$, and ${}_{}{}^{32}{}_{}{}^{}\mathrm{S}$ ions aligned along the $〈100〉$ axis of NaI(Tl) were recorded in the MeV range. In certain cases a clearly defined intermediate third peak was observed. The third peak is attributed to a maximum in the dechanneling probability per unit length as a function of penetration depth. Data are analyzed in terms of a parameter describing the stability of the channeling trajectory.

• Received 2 August 1976

DOI:https://doi.org/10.1103/PhysRevB.15.23