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 10 5 , providing high single-photon detection efficiency even in the presence of large alpha 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 alpha 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.

A new detector concept is presented for combined imaging and spectroscopy of fastneutrons and gamma rays. It comprises a liquid-Xenon (LXe) converter and scintillator coupled to a UV-sensitive gaseous imaging photomultiplier (GPM). Radiation imaging is obtained by localization of the scintillation-light from LXe with the position-sensitive GPM. The latter comprises a cascade of Thick Gas Electron Multipliers (THGEM), where the first element is coated with a CsI UV-photocathode.We present the concept and provide first model-simulation results of the processes involved and the expected performances of a detector having a LXe-filled capillaries converter. The new detector concept has potential applications in combined fast-neutron and gamma-ray screening of hidden explosives and fissile materials with pulsed sources.

Recently, a new detector concept, for combined imaging and spectroscopy of fast-neutrons and gamma was presented. It encompasses a liquid-xenon (LXe) converter-scintillator coupled to a UV-sensitive gaseous Thick Gas Electron Multiplier (THGEM)-based imaging photomultiplier (GPM).In this work we present and discuss the results of a systematic computer-simulation study aiming at optimizing the type and performance of LXe converter. We have evaluated the detector spectral response, detection efficiency and spatial resolution for gamma-rays and neutrons in the energy range of 2-15 MeV for 50 mm thick converters consisting of plain LXe volume and LXe-filled capillaries, of Teflon, Polyethylene or hydrogen-containing Teflon (Tefzel). Neutron detection efficiencies for plain LXe, Teflon-capillaries and Tefzel-capillaries converters were about 20% over the entire energy range. In polyethylene capillaries converters the neutron detection efficiency was about 10% at 2 MeV and increased up to about 20% at 14 MeV. Detection efficiencies of gammas in Teflon, Tefzel and polyethylene converters were ~35%. The plain-LXe converter provided the highest gamma-ray detection efficiency, of ~40-50% for 2-15 MeV energy range. Optimization of LXe-filled Tefzel capillary dimensions resulted in spatial resolution of ~1.5mm (FWHM) for neutrons and up to 3.5 mm (FWHM) for gamma-rays.Simulations of radiographic images of various materials using two discrete energy gammarays (4.4 MeV and 15.1 MeV) and neutrons in broad energy range (2-10 MeV) were performed in order to evaluate the potential of elemental discrimination.

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 60 Co gamma-rays and a mixed fastneutron/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 60 Co 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. and simulations (interaction of radiation with matter, interaction of photons with matter, interaction of hadrons with matter, etc); Micropattern gaseous detectors (MSGC, GEM, THGEM, RETHGEM, MHSP, MICROPIC, MICROMEGAS, InGrid, etc); Photon detectors for UV, visible and IR photons (gas) (gas-photocathodes, solid-photocathodes); Neutron detectors (cold, thermal, fast neutrons); Gamma detectors (scintillators, CZT, HPG, HgI etc); Detection of contraband and drugs; Detection of explosives 2 1 IntroductionGamma-ray and fast-neutron imaging technologies are currently applied for investigating the content of aviation-and marine-cargo containers, trucks and nuclear waste containers (see for example [1, 2]). MeV-scale x-ray or gamma-ray radiographic inspection methods, such as Dual Energy Bremsstrahlung Radiography (DEBR) [3][4][5] or Dual-Discrete-Energy Gamma Radiography (DDEGR) [6], are used for the detection of concealed Special Nuclear Materials (SNM), providing high-resolution images of object shapes and densities and some selectivity between high-Z elements.DEBR makes use of continuous x-ray spectra, generated by accelerated electrons at two different bombarding energies. DDEGR relies on two discrete gamma-rays, of 4.4 MeV and 15.1 MeV, emitted by the 11 B(d,nγ) 12 C reaction. Fast-neutron imaging methods, such as Fast-Neutron Resonance Radiography (FNRR) [7], utilize a broad neutron spectrum of 2-10 MeV to provide a sensitive probe for identifying low-Z elements such as H, C, N and O; these are the main constituents of explosives and narcotics. In addition, FNRR provides a means for identifying the type of the explosive by determination of the density ratios of its main constituent elements [7]. FNRR has been also proposed recently for determining of oil and water content in drilled formation cores [8].The r...

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