Characterization of a CsI(Tl) Scintillator Coupled to a SiPM at Cryogenic Temperatures
M. Mirzakhani, R. Mahapatra, M. Platt
TL;DR
This work addresses achieving sub-keV energy sensitivity in scintillation detectors by coupling a $1~\mathrm{cm^3}$ CsI(Tl) crystal to a cryogenic SiPM readout with a custom transimpedance amplifier, evaluated from $100~\mathrm{K}$ to room temperature. The authors implement a comprehensive readout, shielding, and data-analysis strategy, including PCA-based event selection and quadratic light-yield calibration with $^{241}\mathrm{Am}$ and $^{55}\mathrm{Fe}$ sources. They observe a peak in the figure of merit at $175~\mathrm{K}$, a baseline resolution of $\sigma \approx 1~\mathrm{keV}$, and an effective energy threshold of $3~\mathrm{keV}$, demonstrating sub-keV sensitivity suitable for low-background rare-event searches. The results support potential applications in dark matter and CEvNS experiments and outline future work to improve readout by fiber-coupling and phonon–photon readout schemes.
Abstract
We report on the scintillation characterization of a 1 cm^3 CsI(Tl) crystal coupled to a 6 x 6 mm^2 SiPM read out with a custom transimpedance amplifier at cryogenic temperatures. The crystal was prepared with optical-grade surfaces and enclosed in a multi layer shielding system to suppress ambient light and background radiation. The detector response was studied at temperatures ranging from 100 K to room temperature. A figure of merit, defined as the ratio of the 59.5 keV peak position to the baseline resolution, showed a maximum at 175 K, indicating optimal photon detection efficiency. Pulse shape analysis demonstrated temperature-dependent variations in scintillation decay. At 175 K, the baseline resolution was sigma ~ 1 keV, corresponding to an effective threshold of ~ 3 keV. These results confirm the capability of the CsI(Tl) SiPM system to operate at low thresholds for rare-event searches and low-energy particle detection.