Use Of Wavelength Shifters Research Articles

Measurement of the photon detection efficiency of Hamamatsu VUV4 SiPMS at cryogenic temperature

Liquid argon time projection chambers (TPC) are widely used in neutrino oscillation and dark matter experiments. Detection of scintillation light in liquid argon TPC’s is challenging because of its short wavelength, in the VUV range, and the cryogenic temperatures (∼86 K) at which the sensors must operate. Wavelength shifters (WLS) are typically needed to take advantage of the high Photon Detection Efficiency (PDE) in the visible range of most of photondetectors. The Hamamatsu VUV4 S13370–6075CN SiPMs can directly detect VUV light without the use of WLS, which main benefit is an improved PDE at these short wavelengths, but also the visible light from WLS. The manufacturer (Hamamatsu Photonics K.K.) provides a complete characterization of these devices at room temperature; however, previous studies have indicated a decrease of the PDE at cryogenic temperature for VUV light. In this work, we present the measurement of the PDE of VUV4 SiPMs at cryogenic temperature for different wavelengths in the range [270, 570] nm. A dedicated measurement at 127 nm is also shown.

Measurement of the photon detection efficiency of Hamamatsu VUV4 SiPMs at cryogenic temperature

Liquid argon time projection chambers play a crucial role in neutrino oscillation and dark matter experiments. Detecting scintillation light in these chambers is challenging due to the short wavelengths in the VUV range and the extremely low cryogenic temperatures (˜87 K) at which sensors operate. To take advantage of the higher photon detection efficiency (PDE) at the visible range, the use of wavelength shifters (WLS) is extended along the community. The Hamamatsu VUV4 S13370-6075CN Silicon PhotoMultiplier (SiPM) are VUV-sensitive sensors that can directly detect VUV light without the use of WLS, providing an improved PDE at these short wavelengths, and at the same time can detect the visible light from WLS if needed. The manufacturer provides a complete characterization of these sensors at room temperature. In this work we present the developed experimental setups used to measure the PDE of VUV4 SiPMs at cryogenic temperatures for different wavelengths in the range from 127 nm to 570 nm.

Aerogel Cherenkov counters with wavelength shifters and micro-channel plate photo-tubes

A system of aerogel Cherenkov counters with light collection on wavelength shifters is suggested for particle identification in the KEDR detector. This system will be able to work in 1.8 T magnetic field and will provide pion/kaon identification in the momentum region of 0.6 1.5 GeV/c (1.05 refractive index aerogel). A distinctive feature of these counters is the use of wavelength shifters of two types – `blue' and `green', and the use of micro-channel plate photo-tubes with multi-alcali photocathode. Owing to this, it is possible to reduce essentially the photocathode surface comparing with the direct light collection. Results of Monte Carlo calculations are presented.

Measurement and calculation of the spatial and spectral distribution of wavelength shifter radiation at BESSY

Calculable synchrotron radiation (SR) from BESSY dipole magnets has been used by PTB for radiometry from the visible to the soft x-ray region with very low uncertainties for many years. The use of wavelength shifter (WLS) radiation bears the potential of extending the usable spectral range for radiometry with calculable SR to higher photon energies. Initial investigations on the feasibility of this approach have been performed: an energy dispersive high-purity germanium detector (HPGe) was used to characterize the radiation of the new BESSY WLS with a magnetic field of B=3.2 T. The HPGe detector has previously been calibrated and so the absolute spectral photon flux could be determined. The measured spectral photon flux was then compared to calculations and good agreement was found in the order of ±5%. Although this is to our knowledge the best agreement demonstrated so far for an absolute comparison of measured WLS radiation to calculations, further improvements are needed for a future radiometric use of WLS radiation. This will be discussed.

On the increase of ultraviolet radiation detection efficiency in nuclear particle detectors with the help of transparent wavelength shifter films

The performance of transparent wavelength shifters (WLS) on the base of polymethylmethacrylate and organic luminophors has been studied. Measurements have been carried out in the near and far ultraviolet. Using multicomponent WLS covering the photomultiplier (PM) window, the maximum quantum efficiency of the PM photocathode was increased up to 30%. Due to the use of WLS in the gas Cherenkov counter (radiator Fr-12) a photoelectric efficiency 2.3 times higher than for FEU-110 has been obtained. Now the FEU-110 photoelectric efficiency equals to photoelectric efficiency of the 56DUVP PM.

The effect of sample composition and vial type on Ĉerenkov counting in a liquid scintillation counter

The effect of sample vial type and sample composition on the Ĉerenkov count rate detected from 32P and 36Cl was studied using a liquid scintillation counter. When counting was done in the noncoincident mode, glass vials allowed higher counting efficiency than plastic vials. In the coincident mode light scattering caused by polyethylene and polyproplyene vials allowed higher counting efficiency than glass vials. Highest coincident counting efficiency was from plastic minivials in a glass carrier vial. Increased solute concentration in samples caused increased counting efficiency due to changes in the refractive index of the solution. This can cause significant counting efficiency changes with no sample channel ratio change in density gradient fractions. The use of wavelength shifters is shown to be inappropriate when the sample pH varies, as this can change the fluorescent properties of the shifters and thereby the observed count rate.

Liquid Helium Scintillation Detection with Germanium Photodiodes

Special high-purity germanium photodiodes have been developed for the direct detection of vacuum ultraviolet scintillations in liquid helium. The photodiodes are immersed in the liquid helium, and scintillations are detected through one of the bare sides of the photodiodes. Test results with scintillation photons produced by 5.3MeV α particles are presented. The use of these photodiodes as liquid helium scintillation detectors may offer substantial improvements over the alternate detection method requiring the use of wavelength shifters and photomultiplier tubes.

Method for elimination of quartz-face phototubes in Cherenkov counters by use of wavelength-shifter

The feasibility of the use of organic wavelength-shifters in conjunction with normal glass phototubes and suitably transparent gases in Cherenkov counters is investigated. It is shown that such a combination gives performance at least the equal of that obtained from quartz-face phototubes.