Gaseous Photomultiplier Research Articles

Photon Induced Scintillation Amplifier — The PISA concept

Photoelectron signal amplification in gas photomultipliers (GPMs) is achieved through charge avalanche development in the holes of a cascade of hole-type microperforated foils. When a voltage difference is applied between the metal film electrodes that are deposited on both surfaces of those foils, an electric field with a high intensity is established inside the holes. As a consequence, each electron entering those holes produces an electron avalanche that emerges from the other side of the holes. A cascade of few foils is necessary for a single primary electron to produce a final avalanche intense enough to be read out, in the anode electrode, above the electronic noise. We propose the Photon Induced Scintillation Amplifier (PISA), where the photoelectron signal amplification is obtained by reading out the photon scintillation produced in the charge avalanches of solely one Micro-Hole-and-Strip-Plate-type microstructure with SiPMs. The optical readout has the advantage of having the extra gain from the photosensor and is less sensitive to electronic noise. A large photosensor gain produces large output signals that can travel over long distances without significant degradation. This allows for the readout electronics to be placed away from the photosensor and, thus, from the detector sensitive volume. The scintillation readout plane can be made of a 2D-array of SiPMs, with size and pitch in accordance with the needed scintillation level and position resolution. A first basic prototype was assembled to present a proof-of-principle of the PISA concept.

Fast-neutron and gamma-ray imaging with a capillary liquid xenon converter coupled to a gaseous photomultiplier

Gamma-ray and fast-neutron imaging was performed with a novel liquid xenon (LXe) scintillation detector read out by a Gaseous Photomultiplier (GPM). The 100 mm diameter detector prototype comprised a capillary-filled LXe converter/scintillator, coupled to a triple-THGEM imaging-GPM, with its first electrode coated by a CsI UV-photocathode, operated in Ne/5%CH4 at cryogenic temperatures. Radiation localization in 2D was derived from scintillation-induced photoelectron avalanches, measured on the GPM's segmented anode. The localization properties of 60Co gamma-rays and a mixed fast-neutron/gamma-ray field from an AmBe neutron source were derived from irradiation of a Pb edge absorber. Spatial resolutions of 12± 2 mm and 10± 2 mm (FWHM) were reached with 60Co and AmBe sources, respectively. The experimental results are in good agreement with GEANT4 simulations. The calculated ultimate expected resolutions for our application-relevant 4.4 and 15.1 MeV gamma-rays and 1–15 MeV neutrons are 2–4 mm and ∼ 2 mm (FWHM), respectively. These results indicate the potential applicability of the new detector concept to Fast-Neutron Resonance Radiography (FNRR) and Dual-Discrete-Energy Gamma Radiography (DDEGR) of large objects.

Liquid-Xe detector for contraband detection

We describe progress made with a liquid-Xe (LXe) detector coupled to a gaseous photomultiplier (GPM), for combined imaging and spectroscopy of fast neutrons and gamma-rays in the MeV range. The purpose of this detector is to enable the detection of hidden explosives and fissile materials in cargo and containers. The expected position resolution is about 2m and 3.5mm for fast neutrons and gamma-rays, respectively. Experimental results obtained using an 241Am source yielded energy and time resolutions of 11% and 1.2ns RMS, respectively. Initial results obtained with the position-sensitive GPM are presented.

Study of new substrate THGEMs with low neutron scattering and low radioactivity

New types of Thick Gaseous Electron Multipliers (THGEMs) made of PCB-type substrates, including Ceramic, Kapton, PTFE, and in addition to FR-4, were developed for applications requiring low neutron absorption, scattering, and low natural radioactivity, such as the THGEM-based neutron detector, and the THGEM-based gaseous multiplier (GPM). Using Geant4 simulation, the result of the total neutron absorption and scattering ratio of bare substrate is Kapton(high) > FR-4 > Ceramic > PTFE (low). The Ceramic and PTFE substrates have lower ratios about 0.707% and 0.635% per layer(0.2 mm thick) respectively. The gamma-induced electron background is the reverse, Ceramic > PTFE > FR-4 > Kapton, from 1.5% to 0.7% at 1.0 MeV, which induces highest electron background in the range of 0∼7 MeV. The natural radioactivity background was measured for these types of substrate samples. The Ceramic substrate has lower radioactivity, 232Th = 8.8±0.9 Bq/kg, 238U = 6.3±0.9 Bq/kg, and 40K is too low to be detected. Some THGEM samples were produced by these four types of substrates in the same shape: 0.2-mm thickness, 0.2-mm hole diameter, 0.6-mm pitch, and 70-μm rim. The performances of these new substrate THGEMs are promising. The effective gain is at the 104 level and the gain was stable during more than 100 hours continuous test. The energy resolution @ Ar+IsoB = 97:3 is at the level of 20% to 27%. These new substrate THGEMs are available in 200×200 mm2 size and even larger, some of them are applied to neutron flux monitor detector and gaseous photomultipliers (GPM).

First results of a large-area cryogenic gaseous photomultiplier coupled to a dual-phase liquid xenon TPC

We discuss recent advances in the development of cryogenic gaseous photomultipliers (GPM), for possible use in dark matter and other rare-event searches using noble-liquid targets. We present results from a 10 cm diameter GPM coupled to a dual-phase liquid xenon (LXe) TPC, demonstrating—for the first time—the feasibility of recording both primary (``S1'') and secondary (``S2'') scintillation signals. The detector comprised a triple Thick Gas Electron Multiplier (THGEM) structure with cesium iodide photocathode on the first element; it was shown to operate stably at 180 K with gains above 105, providing high single-photon detection efficiency even in the presence of large α particle-induced S2 signals comprising thousands of photoelectrons. S1 scintillation signals were recorded with a time resolution of 1.2 ns (RMS). The energy resolution (σ/E) for S2 electroluminescence of 5.5 MeV α particles was ∼ 9%, which is comparable to that obtained in the XENON100 TPC with PMTs. The results are discussed within the context of potential GPM deployment in future multi-ton noble-liquid detectors.

Cryogenic gaseous photomultipliers and liquid hole- multipliers: advances in THGEM-based sensors for future noble-liquid TPCs

Dual-phase noble-liquid TPCs are presently the most sensitive instruments for direct dark matter detection. Scaling up existing ton-scale designs to the multi-ton regime may prove to be technologically challenging. This includes both large-area coverage with affordable high-QE UV-photon detectors, and maintaining high precision in measuring the charge and light signals of rare events with keV-scale energy depositions. We present our recent advances in two complementary approaches to these problems: large-area cryogenic gaseous photomultipliers (GPM) for UV-photon detection, and liquid-hole multipliers (LHM) that provide electroluminescence light in response to ionization electrons and primary scintillation photons, using perforated electrodes immersed within the noble liquid. Results from a 10 cm diameter GPM coupled to a dual-phase liquid- xenon TPC demonstrate the feasibility of recording - for the first time - both primary (“S1”) and secondary (“S2”) scintillation signals, over a very broad dynamic range. The detector, comprising a triple-THGEM structure with CsI on the first element, has been operating stably at 180 K with gains larger than 105; it provided high single-photon detection efficiency - in the presence of massive alpha-particle induced S2 signals; S1 scintillation signals were recorded with time resolutions of 1.2 ns (RMS). Results with the LHM operated in liquid xenon yielded large photon gains, with a pulse-height resolution of 11% (RMS) for alpha-particle induced S2 signals. The detector response was stable over several months. The response of the S2 signals to rapid changes in pressure lead to the conclusion that the underlying mechanism for S2 light is electroluminescence in xenon bubbles trapped below the immersed THGEM electrode. Both studies have the potential of paving the way towards new designs of dual- and single-phase noble-liquid TPCs that could simplify the conception of future multi-ton detectors of dark matter and other rare events.

Cryogenic Gaseous Photomultiplier for position reconstruction of liquid argon scintillation light

Presented here are first tests of a Gaseous Photomultiplier based on a cascade of Thick GEM structures intended for gamma-ray position reconstruction in liquid argon. The detector has a MgF2 window, transparent to VUV light, and a CsI photocathode deposited on the first THGEM . A gain of 8⋅ 105 per photoelectron and ∼ 100% photoelectron collection efficiency are measured at stable operation settings. The excellent position resolution capabilities of the detector (better than 100 μm) at 100 kHz readout rate, is demonstrated at room temperature. Structural integrity tests of the detector and seals are successfully performed at cryogenic temperatures by immersing the detector in liquid Nitrogen, laying a good foundation for future operation tests in noble liquids.

Cryogenic THGEM–GPM for the readout of scintillation light from liquid argon

A GPM (Gaseous Photo Multiplier) based on GEMs (Gas Electron Multipliers) and THGEMs (Thick Gas Electron Multipliers) is a promising detector for VUV (Vacuum Ultra Violet) photon readouts in rare event experiments which use cryogenic two-phase detectors with detection media of Ar and Xe. A GPM based on THGEM made of PTFE (herein named PTFE-THGEM) was developed inspired by the wide use of PTFE (polytetrafluoroethene) boards as low radioactive background PCB in rare event experiments. The efficiencies of the THGEM, a CsI photocathode, and finally a GPM are presented here. At low temperature (113K) and 1.1atm, the quantum efficiency of the GPM for VUV photons from liquid Ar in a two-phase detector is estimated to be 8.1% and the low threshold of the detector system for initial electrons prior to multiplication is 12 using 5N purity Ar (0.99999).

Performance study of a cesium iodide photocathode-based UV photon detector in Ar/CH_4 mixture

The detection efficiency of a gaseous photomultiplier depends on the photocathode quantum efficiency and the extraction efficiency of photoelectrons into the gas. In this paper we have studied the performance of an UV photon detector with P10 gas in which the extraction efficiency can reach values near to those in vacuum operated devices. Simulations have been done to compare the percentage of photoelectrons backscattered in P10 gas as well as in the widely used neon-based gas mixture. The performance study has been carried out using a single stage thick gas electron multiplier (THGEM). The electron pulses and electron spectrum are recorded under various operating conditions. Secondary effects prevailing in UV photon detectors like photon feedback are discussed and its effect on the electron spectrum under different operating conditions is analyzed.

Newly developed gaseous photomultiplier

A new micromesh gas (Micromegas) detector has been developed for a gaseous photomultiplier tube (PMT) with a bialkali photocathode. A basic performance test of the Micromegas detector was carried out for a Ne (90%) + CF4 (10%) gas mixture using an X-ray beam. We constructed gaseous PMTs with a bialkali photocathode and Micromegas detectors. The photoelectron collection efficiencies in several gases and the suppression of ion feedback were investigated.

On Dark Matter detector concepts with large-area cryogenic Gaseous Photo Multipliers

Large Liquid Xenon Time Projection Chambers already heavily contributed to the search of non-baryonic Dark Matter in the form of WIMPs. However, with a sensitivity goal in the 10−48 cm−2 cross section range even more sensitive detectors are required in the near future with lower radioactive background, lower detection threshold, and a much larger target while keeping the costs within reasonable limits. We propose therefore to develop large area cryogenic Gaseous Photo Multiplier to replace the presently used Photo Multiplier Tubes to detect the VUV scintillation light of xenon. Replacing not only the PMT arrays, but also the PTFE reflectors will favor a single phase detector scheme with proportional scintillation in the liquid. Thus, it is expected that besides many technical advantages the sensitivity can be enhanced without increasing the xenon mass.

Liquid Hole-Multipliers: A potential concept for large single-phase noble-liquid TPCs of rare events

A novel concept is proposed for large-volume single-phase noble-liquid TPC detectors for rare events. Both radiation-induced scintillation-light and ionization-charge are detected by Liquid Hole-Multipliers (LHM), immersed in the noble liquid. The latter may consist of cascaded Gas Electron Multipliers (GEM), Thick Gas Electron Multiplier (THGEM) electrodes or others, coated with CsI UV-photocathodes. Electrons, photo-induced on CsI by primary scintillation in the noble liquid, and event-correlated drifting ionization electrons are amplified in the cascaded elements primarily through electroluminescence, and possibly through additional moderate avalanche, occurring within the holes. The resulting charge-signals or light-pulses are recorded on anode pads or with photosensors – e.g. gaseous photomultipliers (GPM), respectively. Potential affordable solutions are proposed for multi-ton dark-matter detectors; open questions are formulated for validating this dream.

Position sensitive VUV gaseous photomultiplier based on Thick-multipliers with resistive line readout

In this work, a new position sensitive gas photomultiplier (GPM) based on a cascade configuration is proposed. The GPM is composed by two THGEMs, followed by a 2D-THCOBRA being operated in Ne/CH4(5%), at a pressure of 1 bar in VUV single photon mode. The 2D-THCOBRA is a hybrid microstructure which combines the benefits of a THGEM and a 2D-MHSP, presenting two independent charge multiplication stages. The position capability is performed by using two orthogonal resistive lines crossing each one the readout electrodes. The position is obtained by measuring the charge sharing in both ends of each resistive line, by using only 2 readout channels. This work focuses the study of the detector gain, Ion Back Flow (IBF) and spatial resolution. A charge gain of 106 and an Ion Back Flow (IBF) values of about 20% were measured. Position resolutions below 300 μm (FWHM) were obtained for single VUV photon counting mode operation.

A concise quantum efficiency measurement system for gaseous photomultipliers

We have been developing gaseous photomultiplier tubes (PMTs) with a bialkali photocathode combined with micropattern gas detectors (MPGDs). The sensitivity of a PMT is described in terms of its quantum efficiency (QE). The QE is very important in many experiments, particularly when dealing with low photon statistics. A concise QE measurement system has been developed to evaluate the characteristics of a sealed gaseous PMT with a bialkali photocathode. This QE measurement system consists of a Xe arc lamp source, reflective optics and filters, a monochromator, and a reference Si photodiode detector. Using the system, we evaluated the QE, gain, and long-term stability of the gaseous PMT. Here, we report the results of our evaluation.

Study of electron focusing in thick GEM based photon detectors using semitransparent photocathodes

The detection efficiency of a GEM based UV sensitive gaseous photomultiplier (GPM) depends on the focusing of electrons from the drift gap to the GEM aperture. We have studied the effect of drift parameters on the efficiency of electron focusing into Thick GEM (THGEM) holes in a GPM with semitransparent UV photoconverter. This study comprises simulation of electron focusing into THGEM holes using GARFIELD for different Ar and Ne based gas mixtures and experimental investigations of the same with P10 gas mixture.

A Gaseous Compton Camera using a 2D-sensitive gaseous photomultiplier for Nuclear Medical Imaging

A new Compton Camera (CC) concept based on a High Pressure Scintillation Chamber coupled to a position-sensitive Gaseous PhotoMultiplier for Nuclear Medical Imaging applications is proposed. The main goal of this work is to describe the development of a ϕ25×12cm3 cylindrical prototype, which will be suitable for scintimammography and for small-animal imaging applications. The possibility to scale it to an useful human size device is also in study. The idea is to develop a device capable to compete with the standard Anger Camera. Despite the large success of the Anger Camera, it still presents some limitations, such as: low position resolution and fair energy resolutions for 140keV. The CC arises a different solution as it provides information about the incoming photon direction, avoiding the use of a collimator, which is responsible for a huge reduction (10−4) of the sensitivity. The main problem of the CC's is related with the Doppler Broadening which is responsible for the loss of angular resolution. In this work, calculations for the Doppler Broadening in Xe, Ar, Ne and their mixtures are presented. Simulations of the detector performance together with discussion about the gas choice are also included .

Development of a new imaging device using a VUV scintillator and a gas photomultiplier with a μ-PIC and GEM

We have developed a new imaging device consisting of a VUV scintillator coupled to a gas photomultiplier (gas PMT) with a CsI photocathode, micro pixel chamber (μ-PIC) and gas electron multipliers (GEMs). Generally, the VUV scintillator has a short decay time of less than ∼ 10 nsec. Thus the new detector could be used under the high rate counting ( ∼ 10 MHz) in the hard X-ray to soft-gamma ray region. Our goal in this paper is to obtain a soft gamma-ray image at 0.1 MeV with our gas PMT combined with the VUV scintillator as a high rate counter, and we have optimized electric fields in the gas PMT and developed a new VUV scintillator with a higher light output. In order to obtain a higher collection efficiency of photoelectrons and suppress the ion feedback in the gas PMT, we first optimized the electric field. Then we decided the electric field in the drift, transfer, and induction region to be 0.25, 1.0 and 3.0 kV/cm, respectively. The total gas gain of the gas PMT was approximately 2 × 105, and the gas PMT was estimated to have a quantum efficiency (QE) of 0.7% at 178 nm. Additionally, as a consequence of new VUV scintillators search, Nd:LuLiF4 and Nd:LuF3 with a volume of 10 mm × 10 mm × 5 mm were found to have higher light outputs than Nd:LaF3, which is a conventional VUV scintillator, by a factor of 2.1, and 2.6, respectively, and the Nd:LuF3 irradiated with 5.5−MeV alpha−rays had a light output of approximately 400 photons. Finally, we succeeded in obtaining the crystal images upon 5.5 MeV alpha and 0.122 MeV gamma rays excitation from 241Am− and 57Co sources, respectively, using the gas PMT with the Nd:LuF3.

Hybrid multi micropattern gaseous photomultiplier for detection of liquid-xenon scintillation

Gaseous PhotoMultipliers (GPM) are a very promising alternative of vacuum PMTs especially for large-size noble-liquid detectors in the field of Functional Nuclear Medical Imaging and Direct Dark Matter Detection. We present recent characterization results of a Hybrid-GPM made of three Micropattern Gaseous Structures; a Thick Gaseous Electron Multiplier (THGEM), a Parallel Ionization Multiplier (PIM) and a MICROMesh GAseous Structure (MICROMEGAS), operating in Ne/CF4 (90:10). Gain values close to 107 were recorded in this mixture, with 5.9keV x-rays at 1100mbar, both at room temperature and at that of liquid xenon (T=171K). The results are discussed in term of scintillation detection. While the present multiplier was investigated without photocathode, complementary results of photoextraction from CsI UV-photocathodes are presented in Ne/CH4 (95:5) and CH4 in cryogenic conditions.

On the operation of a micropattern gaseous UV-photomultiplier in liquid-Xenon

Operation results are presented of a UV-sensitive gaseous photomultiplier (GPM) coupled through a MgF2 window to a liquid-xenon scintillator. It consisted of a reflective CsI photocathode deposited on top of a THick Gaseous Electron Multiplier (THGEM); further multiplication stages were either a second THGEM or a Parallel Ionization Multiplier (PIM) followed by a MICROMEsh GAseous Structure (MICROMEGAS). The GPM operated in gas-flow mode with non-condensable gas mixtures. Gains of 104 were measured with a CsI-coated double-THGEM detector in Ne/CH4(95:5), Ne/CF4(95:5) and Ne/CH4/CF4 (90:5:5), with soft X-rays at 173 K. Scintillation signals induced by alpha particles in liquid xenon were measured here for the first time with a double-THGEM GPM in He/CH4(92.5:7.5) and a triple-structure THGEM/PIM/MICROMEGAS GPM in Ne/CH4(90:10) with a fast-current preamplifier.

CsI-THGEM gaseous photomultipliers for RICH and noble-liquid detectors

The properties of UV-photon imaging detectors consisting of CsI-coated THGEM electron multipliers are summarized. New results related to detection of Cherenkov light (RICH) and scintillation photons in noble-liquid are presented.