TY - JOUR
T1 - A study of afterglow signatures in NaI and CsI scintillator modules for the background and transient observer instrument on COSI
AU - Gulick, Hannah
AU - Yoneda, Hiroki
AU - Takahashi, Tadayuki
AU - Chen, Claire
AU - Nakazawa, Kazuhiro
AU - Nagasawa, Shunsaku
AU - Ando, Mii
AU - Okuma, Keigo
AU - Joens, Alyson
AU - Al Nussirat, Samer
AU - Shimizu, Yasuyuki
AU - Fujisawa, Kaito
AU - Kohmura, Takayoshi
AU - Hagino, Kouichi
AU - Kitamura, Hisashi
AU - Zoglauer, Andreas
AU - Oliveros, Juan Carlos Martinez
AU - Tomsick, John A.
N1 - Publisher Copyright:
© 2025
PY - 2025/4
Y1 - 2025/4
N2 - We present measurements of the afterglow signatures in NaI(Tl) and CsI(Tl) detector modules as part of the Background and Transient Observer (BTO) mission detector trade-study. BTO is a NASA Student Collaboration Project flying on the Compton Spectrometer and Imager (COSI) Small Explorer mission in 2027. The detectors utilized in this study are cylindrical in shape with a height and diameter of 5.1 cm and were read out by silicon photomultipliers (SiPMs). We conducted a radiation campaign at the HIMAC accelerator in Japan where the scintillators were irradiated with a 230 MeV/u helium beam (He beam) and 350 MeV/u carbon beam (C beam). We find that both the CsI and NaI scintillators exhibit afterglow signatures when irradiated with the C and He beams. The CsI crystal exhibits a stronger afterglow intensity with afterglow pulses occurring for an average 2.40 ms for C and 0.9 ms for He after the initial particle pulse. The duration of afterglow pulses in CsI is 8.6× and 5.6× the afterglow signal duration in NaI for C and He (0.28 ms and 0.16 ms, respectively). Although CsI has advantages such as a higher light yield and radiation hardness, the stronger afterglows in the CsI detector increase the complexity of the electronics and lead to a ∼7× larger dead time per afterglow event or a ∼3× higher energy threshold value. We use the measured dead times to predict the amount of observing time lost to afterglow-inducing events for an instrument like BTO in low Earth orbit. We simulate the background rates in a BTO-like orbit and find a total value of 114 counts/s for the full two-detector system. Based on the particle energies in the HIMAC experiment, we then determine that an event with sufficient energy to produce an afterglow signal occurs once every ∼70 s and ∼1.4 s in NaI and CsI detectors, respectively. Thus, we conclude that NaI is the better choice for the BTO mission.
AB - We present measurements of the afterglow signatures in NaI(Tl) and CsI(Tl) detector modules as part of the Background and Transient Observer (BTO) mission detector trade-study. BTO is a NASA Student Collaboration Project flying on the Compton Spectrometer and Imager (COSI) Small Explorer mission in 2027. The detectors utilized in this study are cylindrical in shape with a height and diameter of 5.1 cm and were read out by silicon photomultipliers (SiPMs). We conducted a radiation campaign at the HIMAC accelerator in Japan where the scintillators were irradiated with a 230 MeV/u helium beam (He beam) and 350 MeV/u carbon beam (C beam). We find that both the CsI and NaI scintillators exhibit afterglow signatures when irradiated with the C and He beams. The CsI crystal exhibits a stronger afterglow intensity with afterglow pulses occurring for an average 2.40 ms for C and 0.9 ms for He after the initial particle pulse. The duration of afterglow pulses in CsI is 8.6× and 5.6× the afterglow signal duration in NaI for C and He (0.28 ms and 0.16 ms, respectively). Although CsI has advantages such as a higher light yield and radiation hardness, the stronger afterglows in the CsI detector increase the complexity of the electronics and lead to a ∼7× larger dead time per afterglow event or a ∼3× higher energy threshold value. We use the measured dead times to predict the amount of observing time lost to afterglow-inducing events for an instrument like BTO in low Earth orbit. We simulate the background rates in a BTO-like orbit and find a total value of 114 counts/s for the full two-detector system. Based on the particle energies in the HIMAC experiment, we then determine that an event with sufficient energy to produce an afterglow signal occurs once every ∼70 s and ∼1.4 s in NaI and CsI detectors, respectively. Thus, we conclude that NaI is the better choice for the BTO mission.
KW - All-sky gamma-ray survey
KW - Gamma-ray scintillators
KW - Scintillator afterglow
KW - Time-domain astrophysics
UR - http://www.scopus.com/inward/record.url?scp=85216718581&partnerID=8YFLogxK
U2 - 10.1016/j.nimb.2025.165631
DO - 10.1016/j.nimb.2025.165631
M3 - Article
AN - SCOPUS:85216718581
SN - 0168-583X
VL - 561
JO - Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms
JF - Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms
M1 - 165631
ER -