Low Dark Rate Research Articles

Advances in the Large Area Picosecond Photo-Detector (LAPPDTM): 8" × 8" MCP-PMT with Capacitively Coupled Readout

We present advances made in the Large Area Picosecond Photodetector (LAPPD), an 8" × 8" microchannel plate photomultiplier tube (MCP-PMT), since pilot production was initiated at Incom, Inc. in 2018. The Gen-I LAPPD utilizes a stripline anode for direct charge readout. The novel Gen-II LAPPD employs an internal resistive thin-film which capacitively couples to a customizable external signal readout board, streamlining production and increasing customer flexibility. The Gen-II LAPPD, with an active area of 373 cm2, is capable of high single photoelectron (PE) gain of ∼107, low dark rates (∼1 kHz/cm2), single PE (SPE) timing resolution of ∼65 ps, and 𝒪(mm) position resolution. Coupled with a UV-grade fused silica window, the LAPPD features a high quantum efficiency (QE) bialkali photocathode of >30% at 365 nm with spectral response down to ∼165 nm. The LAPPD is an excellent candidate for electromagnetic calorimeter (ECAL) timing layers, photon-based neutrino detectors, high energy collider experiments, medical imaging systems, and nuclear non-proliferation applications.

UV/visible high-sensitivity MCP-PMT single-photon GHz counting detector for long-range lidar instrumentations

In this paper, the focus is on the implementation of Photonis MCP-PMT single-photon counting detector for long-range lidar applications. The properties of fast MCP-PMTs, based on UV–visible Hi-QE (sensitivity above 30%), low dark rate (< 100 Hz) photocathodes, and on Hi-CE MCPs with collection efficiency approaching 100%, are studied at low and high levels of illumination. GHz detection capability for burst photon fluxes is demonstrated, non-linearity effects for high average rate of illumination are studied, MCP-PMTs with extended linearity are presented, and the operational lifetime of the detector at nominal gain of 105 is proved to be about 10 C (4 C/cm2) of integrated anode charge. Along with these properties, the implementation of Photonis extended lifetime next technology and possibility of fast gating makes these devices unique for future atmospheric and altimetry lidar missions.

Reflectance of VUV-sensitive SiPM surfaces in liquid xenon

The nEXO experiment will operate an ultra-low background time projection chamber filled with 5 t of isotopically enriched liquid xenon (LXe) for the search for the neutrinoless double beta decay in Xe-136. The detector will use 4 m 2 of silicon photomultipliers (SiPMs) operated at about − 104 ∘ C to collect the scintillation light. There are strong requirements on the background levels, light collection efficiency and SiPM performance to set the most stringent limits on the half-life. Detecting the 0 ν β β -decay would have wide-spread implications for neutrino physics. The SiPMs need to be sensitive to the vacuum-ultraviolet scintillation light of LXe at 178 nm which is not given for off-the-shelf SiPMs. The SiPM performance requirements adopted by nEXO are (among others) a photon detection efficiency of at least 15% at 178 nm , a correlated avalanche probability of less than 20% and a low dark-rate. Additionally, the VUV-reflectance of the SiPM surface in LXe is an important parameter for optimal light collection and thus the energy resolution of nEXO. We present measurements with state-of-the-art VUV-sensitive SiPMs focusing on the surface VUV-reflectance in liquid xenon. • SiPM surfaces reflect up to 17% of incident VUV light when immersed in liquid xenon. • Due to the surface micro-structure, reflectance spectra reveal additional artefacts. • Knowing the surface reflectivity is vital for simulating large scale LXe detectors.

Development of a single ion detector for radiation track structure studies

The track structure of ionizing radiation predominantly determines the biological effects after irradiation. A new detector to register 3D track structure segments in low pressure gas was proposed in a previous work. The device combines the operational principle of thick gas electron multipliers (THGEM), working in reverse polarity, and resistive plate chambers. In this work, the detector was further developed. Optimization of THGEM thickness, hole pitch and cathode resistivity were studied. A new detector prototype was built and tested with a microbeam providing different radiation qualities. The detector rate capability and ion collection efficiency were also investigated. Results show that the detector efficiency increases with increasing THGEM thickness and decreasing cathode resistivity. Preliminary results show that the ion collection efficiency is low and that the detector performance is limited by a long dead time. The detector is able to register single ions with a low dark rate. However, further development is needed in order to obtain the efficiency necessary to reconstruct 3D track structure.

Diurnal variation in acetylene reduction by white clover

Abstract Mean daily rates of acetylene (C2H2) reduction were determined from regular assays conducted over periods of up to 72 h. Time of occurrence of the daily mean was determined by reference to the diurnal pattern. Simple diurnal patterns of high daylight and lower dark rates were often observed, but there was substantial day-to-day variation on some occasions. This lead to differences in the time of occurrence of the mean but a strong trend for the mean value to occur later in the day from spring to autumn was apparent. Where C2H2 reduction sampling is restricted to once in a day, the diurnal patterns need to be carefully established if errors in total daily rates are to be avoided.

Measurement of Rayleigh ratio for several pure liquids using a laser and monitored photon counting

The Rayleigh ratios of several liquids have been measured using a He–Ne laser and established techniques of high-speed, monitored photon counting with dead-time corrections and low dark rate. A simple well-defined geometry at 90° scattering angle was used and the following values of R90,u (× 106) at 633 nm and 22°C were obtained: carbon disulfide 42.64, benzene 8.51, toluene 10.38, methanol 1.422, carbon tetrachloride 2.954, and water 0.494. Errors are estimated to be less than 2%. These values are in generally good agreement with other recent measurements at narrow angle at the same wavelength, but after scaling by the accepted formula would seem to be somewhat smaller than quoted values at shorter wavelengths.