A lens-coupled scintillation counter in cryogenic environment

TL;DR

This paper introduces a cryogenic-compatible scintillation counter that uses a lens system to couple light from inside a cryostat to a photodetector outside, avoiding direct light guides and maintaining performance at 3K.

Contribution

It presents a novel lens-coupled scintillation detector design that operates effectively at cryogenic temperatures, with a high coupling efficiency and no continuous light guide.

Findings

Reliable operation down to 3K temperature

Coupling efficiency of about 50% with specified components

Effective light transmission through optical windows

Abstract

In this work we present an elegant solution for a scintillation counter to be integrated into a cryogenic system. Its distinguishing feature is the absence of a continuous light guide coupling the scintillation and the photodetector parts, operating at cryogenic and room temperatures respectively. The prototype detector consists of a plastic scintillator with glued-in wavelength-shifting fiber located inside a cryostat, a Geiger-mode Avalanche Photodiode (G-APD) outside the cryostat, and a lens system guiding the scintillation light re-emitted by the fiber to the G-APD through optical windows in the cryostat shields. With a 0.8mm diameter multiclad fiber and a 1mm active area G-APD the coupling efficiency of the "lens light guide" is about 50%. A reliable performance of the detector down to 3K is demonstrated.