Channeling Effect and Improvement of the Efficiency of Charged Particle Registration with Crystal Scintillators

TL;DR

This work argues that channeling of keV-range recoil ions in NaI(Tl) crystal scintillators can substantially enhance scintillation efficiency, potentially driving the quenching factor toward $q\approx 1$ for iodine recoils. It surveys stopping-power theory for amorphous solids, details how crystalline channeling shifts energy loss into electronic processes, and discusses mechanisms—such as quasi-molecular bond formation and Tl$^{+}$-induced dechanneling—that can further modulate light yield. The author provides quantitative estimates of a ~20% channeling probability for 4 keV recoils and computes a near-Earth daemon flux $f_\oplus \sim 6\times10^{-7}\ \text{cm}^{-2}\ \text{s}^{-1}$ during June, arguing these results can account for DAMA/NaI signals within the daemon paradigm. The paper emphasizes the need for dedicated keV-ion-beam calibrations of crystal scintillators and suggests that channeling effects have significant implications for interpreting dark matter searches using crystal detectors.

Abstract

The importance is emphasized of taking into account the channeling along the low index crystallographic axes and planes of a part of low-energy (1-10 keV) recoil ions in measurements of their parameters with crystal scintillators of the type of NaI(Tl) etc. Because the nucleus stopping power in channels is low as compared with electronic stopping power, the light yield of the scintillator must be, accordingly, higher in the given case than that for ions having higher energy (tens keV and more), which lose most part of their energy via nuclear collisions outside channels. Hence, in particular, it follows that the DAMA/NaI observations in Gran Sasso of the annual modulation of the signal frequency in a narrow range of scintillations with an amplitude of 2-6 keV electron equivalent may be due to incidence onto the Earth of exceedingly massive particles (of the type of Planckian objects) from elongated Earth-crossing heliocentric orbits at a velocity of 30-50 km/s. In NaI(Tl), these particles create the iodine recoil ions with just the energy of 2-6 keV.