NeuLAND - FAIR

B. Neutron MRPC Results in Details
The final NeuLAND design is based on a fully active detector of organic scintillator
material. However, in the past also an alternative scheme using passive converters and
a multigap resistive plate chamber (MRPC) based detector had been investigated in
detail, including the construction and test of a fully operational 2 m long prototype.
The scintillator-based design shows significantly better performance than the MRPC option,
therefore it is adopted for the technical design of NeuLAND. The present appendix
summarizes the main results of the MRPC studies for reference.
B.1. Principle of Operation of an MRPC-Based Neutron
Detector with a Thick Iron Converter
The principle of operation for an MRPC-based neutron detector is derived from the
existing Large Area Neutron Detector (LAND) [Bla-92] at GSI, which has a face size of
2×2 m 2 . LAND converts neutrons into charged particles in 5 mm thick iron plates, and
subsequently detects the charged particles in plastic scintillators of the same thickness.
With LAND, typical detection efficiencies above 90% have been reached for 400 MeV
neutrons [Bor-03], see sections 4.2 and 4.1.2 for details.
Detectors that are similar to LAND have been used elsewhere, e.g. at Forschungszentrum
Jülich [Roz-05] and with the MONA detector at Michigan State University [Bau-05]. It
should be noted, however, that in the MONA case the converter is presently not used.
For the MRPC-based neutron-detector prototype, a setup similar to LAND is used,
but the scintillator is replaced with an MRPC. As converter material, stainless steel is
selected for practical reasons. In an MRPC, a charged particle passing through a gas
volume causes ionization. Owing to the electrical field strength of ≈100 mV/cm, an
avalanche is caused by this ionization. The mirror charge of the avalanche on a readout
electrode is used as signal.
MRPC’s are well-known for their excellent time resolution, as low as σt = 20 ps for special
configurations [An-08]. They are only weakly sensitive to γ-rays [Ali-07], eliminating
an important source of background. In the literature there are reports of successful
operation of large-scale MRPC structures on the scale of 1.5 m [Bla-02, Abb-09] for
minimum ionizing particles. However, besides the neutron MRPC option presented
here, to date no high-energy neutron detector involving MRPCs has been developed.
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