Retracted: “Measurements of Scintillation Light Yield Non-Proportionality in NaI(Tl) Detector” [ASME Journal of Nuclear Engineering and Radiation Science, 2021, 7(4), p. 042007; DOI: 10.1115/1.4050932

Abstract

Abstract The Sodium-iodide with Active Background REjection (SABER) experiment is planned to consist of 50 kg of ultrapure sodium iodide with thallium doped (NaI(Tl)) scintillator contained within approximately 10, 500 kg liquid scintillator (LS) veto detector, and will search for dark matter interactions in the inner NaI(Tl) detectors. The relative scintillation light yield in NaI(Tl) scintillator for different incident particle energies is not constant and is important for characterizing the detector response. The relative scintillation light yield in two different NaI(Tl) scintillators was measured with a 370,000 Bq (10 μCi) 137Cs radioactive source using the Compton coincidence technique (CCT) for scattering angles 30°–135°, corresponding to electron recoil energies ranging from 20 to 600 keVee, and these measurements were compared to the previously published results. The light yield was proportional within 3 ± 0.3% between 60 and 600 keVee, but nonproportionality increased drastically below 60 keVee. This may be due to the nonuniform ionization density of photons and multiple Compton scattering background events in the scintillator. An improved experimental setup using ultrapure NaI(Tl) scintillator and better coincidence timing of radioactive events could allow the scintillation light yield to be measured at a lower electron recoil energy (less than 20 keV). Such light yield nonproportionality results will be useful for the SABER dark matter detector experiment to characterize the NaI(Tl) detector response.