Recent development of the Multi-Grid detector for large area neutron scattering instruments
- ILL-ESS-LiU collaboration, CRISP project, Institut Laue Langevin - ILL, Grenoble (France)
Most of the Neutron Scattering facilities are committed in a continuous program of modernization of their instruments, requiring large area and high performance thermal neutron detectors. Beside scintillators detectors, {sup 3}He detectors, like linear PSDs (Position Sensitive Detectors) and MWPCs (Multi-Wires Proportional Chambers), are the most current techniques nowadays. Time Of Flight instruments are using {sup 3}He PSDs mounted side by side to cover tens of m{sup 2}. As a result of the so-called '{sup 3}He shortage crisis{sup ,} the volume of 3He which is needed to build one of these instruments is not accessible anymore. The development of alternative techniques requiring no 3He, has been given high priority to secure the future of neutron scattering instrumentation. This is particularly important in the context where the future ESS (European Spallation Source) will start its operation in 2019-2020. Improved scintillators represent one of the alternative techniques. Another one is the Multi-Grid introduced at the ILL in 2009. A Multi-Grid detector is composed of several independent modules of typically 0.8 m x 3 m sensitive area, mounted side by side in air or in a vacuum TOF chamber. One module is composed of segmented boron-lined proportional counters mounted in a gas vessel; the counters, of square section, are assembled with Aluminium grids electrically insulated and stacked together. This design provides two advantages: First, magnetron sputtering techniques can be used to coat B{sub 4}C films on planar substrates, and second, the neutron position along the anode wires can be measured by reading out individually the grid signals with fast shaping amplifiers followed by comparators. Unlike charge division localisation in linear PSDs, the individual readout of the grids allows operating the Multi-Grid at a low amplification gain, hence this detector is tolerant to mechanical defects and its production accessible to laboratories equipped with standard equipment. Prototypes of different configurations and sizes have been developed and tested. A demonstrator, with a sensitive area of 0.8 m x 3 m, has been studied during the CRISP European project; it contains 1024 grids, and a surface of isotopically enriched B{sub 4}C film close to 80 m{sup 2}. Its size represented a challenge in terms of fabrication and mounting of the detection elements. Another challenge was to make the gas chamber mechanically compatible with operation in a vacuum TOF chamber. Optimal working condition of this detector was achieved by flushing Ar-CO{sub 2} at a pressure of 50 mbar, and by applying 400 Volts on the anodes. This unusual gas pressure allows to greatly simplifying the mechanics of the gas vessel in vacuum. The detection efficiency has been measured with high precision for different film thicknesses. 52% has been measured at 2.5 Angstrom, in good agreement with the MC simulation. A high position resolution has been achieved by centre of gravity measurement of the TOT (Time-Over-Threshold) signals between neighbouring grids. These results, as well as other detection parameters, including gamma sensitivity and spatial uniformity, will be presented. (author)
- Research Organization:
- Institute of Electrical and Electronics Engineers - IEEE, 3 Park Avenue, 17th Floor, New York, N.Y. 10016-5997 (United States)
- OSTI ID:
- 22531216
- Report Number(s):
- ANIMMA-2015-IO-159; TRN: US16V0473102157
- Resource Relation:
- Conference: ANIMMA 2015: 4. International Conference on Advancements in Nuclear Instrumentation Measurement Methods and their Applications, Lisboa (Portugal), 20-24 Apr 2015; Other Information: Country of input: France
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
AMPLIFIERS
BORON CARBIDES
CARBON DIOXIDE
EUROPEAN SPALLATION SOURCE
GAIN
HE-3 COUNTERS
MAGNETRONS
MULTIWIRE PROPORTIONAL CHAMBERS
NEUTRON DIFFRACTION
PHOSPHORS
POSITION SENSITIVE DETECTORS
READOUT SYSTEMS
SENSITIVITY
THERMAL NEUTRONS
TIME-OF-FLIGHT METHOD