Speaker
Description
The Budker Institute of Nuclear Physics is developing a two-phase (gas and liquid) detector based on argon. Liquid argon detectors are widely used in experiments to search for dark matter, to study neutrino oscillations and coherent elastic scattering of neutrinos on nuclei, and as veto systems in double beta decay experiments.
Argon has a high light yield (20000 — 40000 photons/MeV), but the light emission occurs in the vacuum ultraviolet (VUV), where photodetectors have low quantum efficiency. For this reason, it is necessary to use a wavelength shifters, among which 1,1,4,4-tetraphenyl-1,3-butadiene (TPB) is the most suitable. Measuring the re-emission efficiency and studying the aging effects of TPB films are critical aspects for the operation of two-phase detectors and, therefore, for the ultimate sensitivity of low-energy physics experiments.
In this study, the re-emission efficiency of TPB films with thicknesses of 20, 100, and 200 µg/cm² obtained by vacuum deposition was measured. At the initial moment of time, the efficiency was the same, 1.16 re-emitted photons in the visible range per one absorbed VUV photon. For a film with a thickness of 100 µg/cm², the efficiency did not change over the year of observations, but for a film with a thickness of 20 µg/cm², the efficiency decreased to 0.75. Optical and electron microscope images were taken, and X-ray fluorescence analysis was conducted to find the reasons for the decrease in re-emission efficiency.
Fundings
This work is supported in the framework of the State project “Science” by the Ministry of Science and Higher Education of the Russian Federation under the contract 075-15-2024-541.