Response of wavelength-shifting and scintillating-wavelength-shifting fibers to ionizing radiation

TL;DR

The paper addresses how wavelength-shifting and scintillating-wavelength-shifting fibers respond to ionizing radiation and transport light, comparing BCF-91A with EJ-160I/II. Light yield and attenuation are characterized by irradiating ~1.4 m fibers with α, β, and γ sources and fitting the SiPM readout to a double-exponential form for attenuation, $I = I_{ ext{long}} e^{-x/ ext{λ}_{ ext{long}}} + I_{ ext{short}} e^{-x/ ext{λ}_{ ext{short}}}$. Key results show EJ-160I/II deliver ~5–7× higher light yields than BCF-91A for β and γ, and ~2.9–3.6× for α, with EJ-160I having longer attenuation length than EJ-160II. The work supports ongoing development of radiopure Sci-WLS fibers and provides a framework for simulating light yield and transport in such fibers for future experiments like LEGEND-1000.

Abstract

We report results of characterizing the response and light transport of wavelength-shifting (WLS) and scintillating-wavelength-shifting (Sci-WLS) fibers under irradiation by radioactive $α$, $β$, and $γ$ sources. Light yield and light transmission were measured for the WLS fiber BCF-91A from Saint-Gobain and for a new Sci-WLS fiber EJ-160 from Eljen Technology. The two variants with different fluor mixtures, EJ-160I and EJ-160II, exhibited approximately five and seven times higher light yield than BCF-91A, respectively, while their attenuation lengths were 3.80\,m for BCF-91A, 4.00\,m for EJ-160I, and 2.50\,m for EJ-160II.

Figures (13)

• Figure 1: Absorption (left) and emission (right) spectra of the WLS fibers (manufacturers' data). For reference, we include the emission spectra of tetraphenylbutadiene (TPB) from TPB-Leonhardt-JINST-2024, which is often used for shifting scintillation light of liquid argon or liquid xenon, and the quantum efficiency of Silicon Photomultiplier (SiPM) S13360 from Hamamatsu Photonics hamamatsu. All fibers and TPB spectra are normalized to their respective maxima.
• Figure 2: Pictures of diamond fly-cut cross sections of the three tested fibers. These images were captured under a microscope with external illumination to highlight the core/cladding boundaries.
• Figure 3: Left: SiPM readout board with the Hamamatsu Photonics SiPM S13360-3050CS coupled to a fiber. Fiber ends were polished using a diamond fly-cutter and coupled to the SiPM using optical grease. Right: Photon detection efficiency of the same SiPM hamamatsu.
• Figure 4: Left: Typical SiPM signal traces recorded on the oscilloscope with a 0.5 photoelectron (p.e.) trigger threshold. Right: Histogram of SiPM ADC amplitudes obtained under LED excitation, yielding higher p.e. count. The legend shows the frequency of pulse generator and pulse width applied to the LED.
• Figure 5: A schematic view of the setup for irradiation along a 138 cm-long fiber coupled to SiPM's at both ends for $\beta$ and $\gamma$ irradiation studies.