We measure and explain scintillator non-proportionality and gamma quenching of CaWO4 at low energies and low temperatures. Phonons that are created following an interaction in the scintillating crystal at temperatures of 15mK are used for a calorimetric measurement of the deposited energy, and the scintillation light is measured with a separate cryogenic light detector. Making use of radioactivity intrinsic to the scintillating crystal, the scintillator non-proportionality is mapped out to electron energies <5keV. The observed behavior is in agreement with a simple model based on Birks' law and the stopping power dE/dx for electrons. We find for Birks' constant kB=(18.5±0.7)nm/keV in CaWO4. Gamma lines allow a measurement of the reduced light yield of photons with respect to electrons, as expected in the presence of scintillator non-proportionality. In particular, we show that gamma-induced events in CaWO4 give only about 90 percent of the light yield of electrons, at energies between 40keV and 80keV.
@article{arxiv.0910.4414,
title = {Scintillator Non-Proportionality and Gamma Quenching in CaWO4},
author = {R. F. Lang and G. Angloher and M. Bauer and I. Bavykina and A. Bento and A. Brown and C. Bucci and C. Ciemniak and C. Coppi and G. Deuter and F. von Feilitzsch and D. Hauff and S. Henry and P. Huff and J. Imber and S. Ingleby and C. Isaila and J. Jochum and M. Kiefer and M. Kimmerle and H. Kraus and J. -C. Lanfranchi and M. Malek and R. McGowan and V. B. Mikhailik and E. Pantic and F. Petricca and S. Pfister and W. Potzel and F. Pröbst and S. Roth and K. Rottler and C. Sailer and K. Schäffner and J. Schmaler and S. Scholl and W. Seidel and L. Stodolsky and A. J. B. Tolhurst and I. Usherov and W. Westphal},
journal= {arXiv preprint arXiv:0910.4414},
year = {2009}
}