Micromegas neutron beam monitor neutronics

Abstract

The Micromegas is a type of ionising radiation detector that consists of a gas chamber sandwiched between two parallel plate electrodes, with the gas chamber divided by a Frisch grid into drift and amplification gaps. Investigators have applied it to a number of different applications, such as charged particle, X-ray and neutron detection. A Micromegas device has been tested as a neutron beam monitor at CERN and is expected to be used for that purpose at the Spallation Neutron Source (SNS) under construction in Oak Ridge, TN. For the Micromegas to function effectively as neutron beam monitor, it should cause minimal disruption to the neutron beam in question. Specifically, it should scatter as few neutrons as possible and avoid neutron absorption when it does not contribute to generating useful information concerning the neutron beam. Here, we present the results of Monte Carlo calculations of the effect of different types of wall materials and detector gases on neutron beams and suggest methods for minimising disruption to the beam.

Neutron beam monitor based on a boron-coated GEM

“…The detector mainly consists of the neutron convertor, the double GEM, the special electronics for pad readout, the gas cycle system and shielding for neutron and electromagnetism. Compared with the highly reactive and expensive 6 Li, a solid 10 B layer seems to be much more favourable and suitable for use as a neutron converter. It can easily be produced in reasonable sizes using evaporation or sputtering techniques.…”

“…The currently employed neutron beam monitors do not fulfil all of the requirements in Table 1 very well. To overcome these limitations, intensive R&D efforts with micro-pattern gas detectors are recently being made by numerous groups such as the GEM-based monitor [4] with 10 B at J-PARC, the micromegas-based monitor with 10 B and 6 Li at CERN [5] and at the University of Tennessee [6] for SNS, the MSGD-based monitor filled with 3 He in ISIS [7]. Various types of slow-neutron detectors are under development.…”

Fabrication and Characterization of Pb(Zr,Ti)O3Microcantilever for Resonance Sensors

“…Compared with the highly reactive and expensive 6 Li, a solid 10 B layer seems to be much more favourable and suitable for use as a neutron converter. It can easily be produced in reasonable sizes using evaporation or sputtering techniques.…”

“…The currently employed neutron beam monitors do not fulfil all of the requirements in Table 1 very well. To overcome these limitations, intensive R&D efforts with micro-pattern gas detectors are recently being made by numerous groups such as the GEM-based monitor [4] with 10 B at J-PARC, the micromegas-based monitor with 10 B and 6 Li at CERN [5] and at the University of Tennessee [6] for SNS, the MSGD-based monitor filled with 3 He in ISIS [7]. Various types of slow-neutron detectors are under development.…”

“…A GEM can achieve enough gain and it can be operated in a harsh environment. With a neutron sensitive convertor such as 10 B, 6 Li and 155,157 Gd, it is convenient for a GEM to detect neutrons, especially with a low efficiency. To overcome the size limitation, a compact readout system for a GEM has been under design, which will be small, simple and cost-effective, and can be moved, constructed and easily used.…”