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We propose an alternative approach for the detection of fast neutrons in the energy range from 10-4 to 5 MeV based on 10B-RPCs (hybrid double-gap Resistive Plate Chambers with 10B4C neutron converters) surrounded by a polyethylene moderator. The detection efficiency as a function of the neutron energy is obtained in Monte Carlo simulations performed with the Geant4 toolkit for several detector configurations. The thickness of the neutron converter is optimized for the maximum efficiency. The results show that for this type of detector it is possible to obtain an average detection efficiency larger than 50% with a weak dependence on the neutron energy. The dark count rate and gamma sensitivity are also discussed.

Resistive plate chambers (RPC) lined with $^{10}B_{4}$C neutron converters is a promising cost effective technology for position-sensitive thermal neutron detection capable to outperform $^{3}$He-based detectors in terms of spatial resolution and timing. However, as for the other types of gaseous detectors with a single layer of $^{10}B_{4}$C at normal beam incidence, the detection efficiency to thermal neutrons of a single-gap $^{10}B$-RPC is only about 6%. Aiming to overcome this limitation, we introduce a multi-layer $^{10}B$-RPCs detector with a stack of ten double-gap hybrid RPCs. A description of the detector design and the results of its characterization performed at the TREFF neutron beamline at the FRM II neutron facility are presented. The results demonstrate that the detection efficiency exceeds 60% for neutrons with a wavelength of 4.7 \r{A} and the spatial resolution (FWHM) is about 0.25 mm and 0.35 mm in the X and Y direction, respectively.

Multilayer position-sensitive 10B-RPC thermal neutron detectors offer an attractive combination of sub-millimeter spatial resolution and high (>50%) detection efficiency. Here we describe a new position reconstruction method based on a statistical approach. Using experimental data, we compare the performance of this method with that of the centroid reconstruction. Both methods result in a similar image linearity/uniformity and spatial resolution. However, the statistical method allows to improve the image quality at the detector periphery, offers more flexible event filtering and allows to develop automatic quality monitoring procedures for early detection of situations when a change in the detector operation conditions starts to affect reconstruction quality.

We present experimental results on the counting rate measurements for several single-gap $^{10}$B lined resistive plate chambers ($^{10}$B-RPCs) with anodes made from standard float glass, low resistivity glass and ceramic. The measurements were performed at the V17 monochromatic neutron beamline (3.35 \.A) at the Helmholtz-Zentrum Berlin. For the $^{10}$B-RPCs with 0.28 mm thick float glass a maximum counting rate density of about $8\times 10^{3}$ $Hz/cm^{2}$ was obtained. In the case of low resistivity glass and ceramic, the counting rate density did not deviate from linear dependence on the neutron flux up to the maximum flux available at this beamline and exceeded a value of $3\times 10^{4}$ $Hz/cm^{2}$.

International audience; We present characterization results of a neutron Anger camera based on a lithium-6 loaded cerium activated silicate glass scintillator (33.3 × 33.3 × 1 mm3) and an array of 64 silicon photomultipliers. Reconstruction of the scintillation events is performed with a statistical method, implemented on a graphics processing unit (GPU). We demonstrate that the light response model of the detector can be obtained from flood irradiation calibration data using an unsupervised iterative procedure. The useful field of view is 28 × 28 mm2. The spatial resolution measured at 2.5 Å neutron beam is better than 0.6 mm FWHM and the energy resolution at the neutron peak is 11%.

The results of an experimental feasibility study of a position sensitive thermal neutron detector based on a resistive plate chamber (RPC) are presented. The detector prototype features a thin-gap (0.35 mm) hybrid RPC with an aluminium cathode lined with a 2 ${\mu}$m thick $^{10}B{_4}C$ neutron converter layer enriched in $^{10}B$ and a float glass anode. A detection efficiency of ${\approx}$ 6.2 ${\%}$ was measured for the neutron beam (${\lambda}$ =2.5 ${\AA}$) at normal incidence. A spatial resolution better than 0.5 mm FWHM was demonstrated.

The effect of gas contamination on light emission properties of CF 4 is presented. The study was performed in the UV (220–450 nm) and visible (450–800 nm) wavelength ranges and the relative light emission intensity and effective decay times were measured. Gas contamination effects, as well as the effect of controllable addition of small quantities of gas admixtures were investigated for both the primary and secondary scintillation. The primary ionization was produced by alpha-particles from an Am-241 alpha source, and MSGC plates were used for electron multiplication and secondary light production. Two types of commercial gas purifiers were tested.

The effect of an electric field on the primary scintillation from CF4 in the ultraviolet and visible wavelength regions (200–800 nm) is reported. The study was performed in the pressure range from 1 to 5 bar and at electric fields of up to 2 kV/cm. Photon emission spectra, fully corrected for the detection response, and the absolute photon yields in the ultraviolet and visible regions are reported. The CF4 emission spectra and the photon fluxes show no variations with the field at low pressures ( ∼ 1 bar ) , while at higher pressures the effect of the field on the scintillation is strong: the ultraviolet emission intensity increases and the visible intensity decreases with the field strength. Time spectra of the primary scintillation for several applied electric field strengths are also reported for the two wavelength regions of light emission.

Carbon tetrafluoride (CF4) photon yield, defined as the number of photons emitted per 1 MeV of energy deposited in the gas is reported for the ultraviolet (220–500 nm) and visible (500–800 nm) emission in the pressure range from 0.5 to 5 bar. An Am-241 α-source was used for gas excitation. Emission spectra (corrected for the response of the detection system) are given in the range from 200 to 800 nm. The visible emission, which is weak at 0.5 bar, strongly increases with gas pressure and dominates the emission spectrum at 5 bar.

We report the first results on the operation of an optical double GEM TPC, read out by four photomultipliers in a square array. The detector, operated with Ar + 5 % CF 4 at atmospheric pressure, was tested with 241Am alpha particles emitted in various orientations. We obtained a typical track angle resolution of 2 ∘ ( σ ) at 45 ∘ and achieved a point position resolution of better than 1 mm (FWHM) for the X- and Y-directions in the GEM plane.

Position sensitive detectors based on gaseous scintillation proportional counters with Anger-type readout are being used in several research areas such as neutron detection, search for dark matter and neutrinoless double beta decay. Design and optimization of such detectors are complex and time consuming tasks. Simulations, while being a powerful tool, strongly depend on the light transport models and demand accurate knowledge of many parameters, which are often not available. Here we describe an alternative approach based on the experimental evaluation of a detector using an isotropic point-like light source with precisely controllable light emission properties, installed on a 3D positioning system. The results obtained with the developed setup at validation conditions, when the scattered light is strongly suppressed, show good agreement with simulations., Proceedings of IWORID2015 (Hamburg). Submitted to JINST. 7 pages, 6 figures

Light emitted during the development of electron avalanches in a gas electron multiplier (GEM) can be efficiently used for optical readout of the detector. We report on measurements of total light yields in Ar/CF 4 , He/CF 4 , Ar/TEA and Xe/TEA mixtures. Information on the energy resolution obtained with low-energy X-ray photons is also presented. The spectral distribution of the light produced in the GEM is analysed and the mechanisms associated with the process of light production are considered.

The software package ANTS (Anger-camera type Neutron detector: Toolkit for Simulations), developed for simulation of Anger-type gaseous detectors for thermal neutron imaging was extended to include a module for experimental data processing. Data recorded with a sensor array containing up to 100 photomultiplier tubes (PMT) or silicon photomultipliers (SiPM) in a custom configuration can be loaded and the positions and energies of the events can be reconstructed using the Center-of-Gravity, Maximum Likelihood or Least Squares algorithm. A particular strength of the new module is the ability to reconstruct the light response functions and relative gains of the photomultipliers from flood field illumination data using adaptive algorithms. The performance of the module is demonstrated with simulated data generated in ANTS and experimental data recorded with a 19 PMT neutron detector. The package executables are publicly available at http://coimbra.lip.pt/~andrei/

A 2D position sensitive gas scintillation detector for thermal neutrons is under development as part of the European FP7 NMI3 JRA program (Project 226507). The aim of the project is to have a detector with: sub-millimetre position resolution, high rate capability (>1 MHz), high efficiency (>50% for 1 Angstrom neutrons) and an active area of 200×200 mm2. A detector with these characteristics is of interest for retlectometry and micro-focusing SANS instruments at the neutron scattering facilities. The detector under development is a gas scintillation proportional counter (GSPC) that uses the light emitted in the gas avalanche to determine the position of neutrons absorbed inside the detector using the Anger camera principle. The device for the gas multiplication is an MSGC and the gas is a mixture of 3He and CF4, Despite the worldwide shortage of 3He, it still represents a valid option for small detectors that require high efficiency like the one under development in this project. The status of the project will be reported in the following sections.

A gas scintillation Anger camera for thermal neutron imaging is being developed in the frame of the NMI3 FP7 Project 226507 collaboration. The detection medium is a high pressure gas mixture of 3He and CF 4 . An array of photomultiplier tubes (PMTs) registers photons of the CF 4 the PMTs. Several secondary scintillation generated in the electron avalanches at the MSGC (MicroStrip Gas Chamber) plate. The detector is expected to have sub-millimeter spatial resolution, high counting rate (up to 1 MHz) and good (>50%) detection efficiency. A custom and fully interactive Monte Carlo simulation package (ANTS: Anger camera Neutron detector Toolkit for Simulations) was developed to optimize the design of the detector in order to reach the highest possible spatial resolution. The simulation code accounts for all relevant physical processes in the gas: neutron capture, energy deposition, electron drift, electron multiplication and secondary scintillation. Individual photons are tracked through the gas and the output window (wavelength-resolved refraction and transmission are implemented). Photo-detection accounts for the angular response, active area non-uniformity, gain and single-photon spectra of the PMTs. Several PMT read-out patterns and localization algorithms are implemented in the package. The results of simulations reproduce well the preliminary results obtained with small-scale detector prototypes.

Experiments at the anticipated intense spallation neutron sources require neutron detection with typically millimeter position resolution. We are investigating the possibility of applying the gas electron multiplier (GEM) for this purpose. For efficient detection, /sup 3/He gas at up to 10 bar is required with some stopping gas at a differential pressure of 3-5 bar, i.e., high enough to sufficiently reduce the range of the neutron capture reaction products to achieve the required resolution. Due to the large initial charge deposition in the gas, only a small gain (10-100) is necessary. However, at the high pressures involved, it is not clear if even this can be achieved. We present first results of experiments using a range of gases, pressures, and, in this case, GEM hole sizes of 60 and 80 /spl mu/m to investigate this question. We observed the highest gain in an Ar/DME mixture, but this mixture does not meet the resolution criterion. The use of Xe (an effective stopping gas) in a Xe/DME mixture is ruled out, as no signal can be detected at pressures above 2 bar.

The optical readout of GEMs, presented a few years ago, is currently being considered for several detector projects. Although using suitable gaseous mixtures the GEM avalanches emit a large number of photons in the visible and/or NIR regions, many gaseous mixtures of great interest for detectors scintillate mainly in the UV, and the readout of these detectors is usually inefficient or very expensive. In this work we report on the operation of GEMs coated with a wavelength converter. We show that using a GEM with an optimal geometry the wavelength conversion process can be quite efficient and does not degrade the intrinsic position resolution of the detector, an usual drawback of the utilisation of wavelength shifters. http://www.sciencedirect.com/science/article/B6TJM-4C7B66V-1/1/ea672f73675fd42cd4f864c479c5bfbe

We have developed a novel type of two-dimensional, large area, low granularity gaseous position sensitive detector using a gas electron multiplier foil (GEM) and a standard CCD camera with glass optics. First results obtained with a 10/spl times/10 cm/sup 2/ GEM foil demonstrate that the position resolution with 7 keV X-rays using a Xe-CO/sub 2/ mixture is better than 100 /spl mu/m (RMS). The complete system is described and experimental results on position resolution, efficiency and linearity are shown. Data on light efficiency for mixtures of interest for detection of other types of radiation, such as neutrons, are also presented. Possible applications of this type of detector are considered.

The time structure of light pulses from GEM detectors operated in scintillation mode with He/CF4 mixtures, previously used with integrating readout devices for neutron detection, has been investigated. A system using photomultipliers (PMs) and charge preamplifiers coupled to a fast digitizer has been used to measure simultaneously both the charge and light signals of the avalanches and the dependence of these signals on the operating conditions of the GEM, such as gain, transfer yield and collection field. The present results show that detectors relying on photon counting techniques, using of position sensitive PMs or arrays of avalanche photodiodes, are most promising as fast position sensitive neutron detectors. http://www.sciencedirect.com/science/article/B6TJM-48408MT-T/1/d28fe3c77462b34770621afe4d9da89d

Although the GEM has been mainly used as a gaseous preamplifier device, it has been shown that using suitable gaseous mixtures the avalanches emit a large number of photons, in the UV, visible and/or NIR bands. This scintillation, readout by CCDs, has been used recently for the development of imaging detectors to be used with X-rays, alpha particles and neutrons. The luminescence process in the GEM and a summary of its applications will be presented. The latest developments, including the operation of the GEMs in photon counting mode, will also be referred. http://www.sciencedirect.com/science/article/B6TJM-49FGX8X-B/1/95c4ce32cbe642552741e1461297c1de

We report on the optical readout of the gas electron multiplier (GEM) operated with a gaseous mixture suitable for the detection of thermal neutrons: 3He-CF4. A CCD system operating in the 400-1000 nm band was used to collect the light. Spectroscopic data on the visible and NIR scintillation of He-CF4 are presented. Images of the tracks of the proton and triton recorded with a triple GEM detector are also shown. http://www.sciencedirect.com/science/article/B6TJM-45HFC9M-2D/1/c77549a88a84ef08c2d169c0b4e97ed8

We present an overview of results from our recent studies on the use of the visible and NIR scintillation emitted by the gas electron multiplier (GEM) and on the possibility of using detectors operated with cascaded GEMs to build tracking chambers. http://www.sciencedirect.com/science/article/B6TJM-44DHYY7-10/1/0076b77e06804d2654d892c3d6126c90

A custom and fully interactive simulation package ANTS (Anger-camera type Neutron detector: Toolkit for Simulations) has been developed to optimize the design and operation conditions of secondary scintillation Anger-camera type gaseous detectors for thermal neutron imaging. The simulation code accounts for all physical processes related to the neutron capture, energy deposition pattern, drift of electrons of the primary ionization and secondary scintillation. The photons are traced considering the wavelength-resolved refraction and transmission of the output window. Photo-detection accounts for the wavelength-resolved quantum efficiency, angular response, area sensitivity, gain and single-photoelectron spectra of the photomultipliers (PMTs). The package allows for several geometrical shapes of the PMT photocathode (round, hexagonal and square) and offers a flexible PMT array configuration: up to 100 PMTs in a custom arrangement with the square or hexagonal packing. Several read-out patterns of the PMT array are implemented. Reconstruction of the neutron capture position (projection on the plane of the light emission) is performed using the center of gravity, maximum likelihood or weighted least squares algorithm. Simulation results reproduce well the preliminary results obtained with a small-scale detector prototype. ANTS executables can be downloaded from http://coimbra.lip.pt/~andrei/.

Secondary scintillation (defined here as photon emission originating from electron avalanches) was studied for two gaseous micropattern detectors: MSGC (MicroStrip Gas Chamber) and GEM (Gas Electron Multiplier) operated in pure CF4. For MSGC, the study was performed in the pressure range from 1 to 5 bar; for GEM all experiments were carried out at a fixed pressure of 1 bar. Charge gains from ~ 10 to ~ 150 were used in both cases. The primary ionization of the gas was produced by alpha particles from an Am-241 source. Emission spectra of the secondary scintillation were recorded in the wavelength range from 200 to 800 nm and corrected for the response of the detection system. Photon yields (number of photons generated per electron collected at MSGC or GEM) were measured for the integrated UV (200–500 nm) and visible (500–800 nm) emission bands. The obtained emission spectra and photon-per-electron ratios were compared to the corresponding data for the primary scintillation.

A tracking device based on gas electron multiplier scintillation using a high-resolution cooled charge-coupled device (CCD) camera was developed. The CCD is sensitive to the 400-1000 nm band, and standard glass photographic lenses are used. The active gas is an Ar-CF/sub 4/ mixture. The prototype detector is described and images of single alpha tracks are presented. The light yield and detector performance for several other gaseous mixtures, such as /sup 4/He-CF/sub 4/, are also investigated.

In the framework of development of a single-GEM detector for thermal neutron detection, with a position resolution of 1 mm, the charge multiplication in the GEM has been studied for different stopping gases at pressures up to 8 bar. The effect on the gain of addition of several bars of He to these gases has been determined. It has been found that a Penning mixture of Xe/TMA has the highest gain. At a pressure of 7 bar Xe+2.5% TMA a gain of 10 could still be obtained for a 50 /spl mu/m thick GEM with 80 /spl mu/m holes. A gain of 100 is possible in a mixture of 4 bar Xe, 2.5% TMA and 6 bar He, which makes the above mentioned position resolution possible. In addition it has been found that the Xe/TMA mixture scintillates around 300 nm in the multiplication process in the GEM. The light yield per secondary electron depends only slightly on the Xe pressure or the TMA concentration.

The possibility of using microgap structures in pressurized gaseous devices for high rate synchrotron radiation detectors has been presented before; one of their main drawbacks is the limited maximum safe gain at which they can be operated. In this study we present data on the performance of microgap plates with several widths of the anodes (4 to 12 micron) and of the insulating layer (6 to 30 micron). Krypton and xenon based gaseous mixtures were used at pressures of 1, 3 and 6 bar under irradiation by /sup 55/Fe and /sup 109/Cd X-ray sources and an X-ray tube. The dependence of gain on anode voltage is analyzed, as well as the effects of drift field on gain and charge collection. We also present data on the measured safe maximum gain before breakdown versus count rate.