Development and characterization of BaF2 gamma detector for BaFFLD Array

Gamma-ray angular correlation measurements give critical nuclear structure information needed to interpret T-violation searches in resonance neutron reactions. Identifying individual cascade events in background radiation requires fast-timing scintillator detectors with sub-nanosecond time resolution. Barium fluoride scintillators are ideally suited for this application due to their fast-timing UV emission at 220 nm, enabling precise coincidence measurements. However, conventional photomultiplier tubes cannot detect this UV component directly—it must be wavelength-shifted to visible light using tetraphenyl butadiene (TPB) coatings. TPB coating quality and uniformity directly impact detector performance, making coating optimization critical for the BaFFLD array.

We present TPB coating optimization studies for BaF₂ detectors. Three techniques were evaluated on glass slides: spin coating, submersion, and pipette application. Coatings were characterized for density, uniformity, and thickness using SEM, with wavelength-shifting efficiency quantified via fluorescence spectroscopy under 220 nm excitation. Preliminary results show pipette application achieves sufficient thickness in single applications, while spin coating requires multiple applications but provides superior uniformity. The optimized coating protocol was applied to BaF₂ crystals coupled with photomultiplier tubes via optical fibers, enabling assembly of detector modules for the BaFFLD array