Study of wavelength-shifting chemicals for use in large-scale water Cherenkov detectors

TL;DR

This study investigates the effectiveness of water-soluble wavelength-shifting chemicals in enhancing light yield and neutron detection in large-scale water Cherenkov detectors, demonstrating significant improvements with specific compounds.

Contribution

It introduces and characterizes three wavelength-shifting chemicals, showing their impact on light yield and detector performance in large-scale Cherenkov detectors.

Findings

4-Methylumbelliferone increased PMT response by 1.88 times at 1 ppm

The response was stable over 50 days with minimal variation

Neutron detection efficiency improved with 4-Methylumbelliferone addition

Abstract

Cherenkov detectors employ various methods to maximize light collection at the photomultiplier tubes (PMTs). These generally involve the use of highly reflective materials lining the interior of the detector, reflective materials around the PMTs, or wavelength-shifting sheets around the PMTs. Recently, the use of water-soluble wavelength-shifters has been explored to increase the measurable light yield of Cherenkov radiation in water. These wave-shifting chemicals are capable of absorbing light in the ultravoilet and re-emitting the light in a range detectable by PMTs. Using a 250 L water Cherenkov detector, we have characterized the increase in light yield from three compounds in water: 4-Methylumbelliferone, Carbostyril-124, and Amino-G Salt. We report the gain in PMT response at a concentration of 1 ppm as: 1.88 $\pm$ 0.02 for 4-Methylumbelliferone, stable to within 0.5% over 50 days, 1.37 $\pm$ 0.03 for Carbostyril-124, and 1.20 $\pm$ 0.02 for Amino-G Salt. The response of 4-Methylumbelliferone was modeled, resulting in a simulated gain within 9% of the experimental gain at 1 ppm concentration. Finally, we report an increase in neutron detection performance of a large-scale (3.5 kL) gadolinium-doped water Cherenkov detector at a 4-Methylumbelliferone concentration of 1 ppm.