Detection efficiency, spatial and timing resolution of thermal and cold neutron counting MCP detectors
Introduction
Recently there has been a rapid progress in neutron sources and neutron instrumentation, enabling novel high resolution non-destructive testing techniques for material sciences, investigation of hydrogen content and storage, magnetic properties, imaging of archeological objects, to name the few. The increased brightness of modern neutron sources as well as pulsed nature of some of them, allows high resolution neutron tomography, energy resolved neutron radiography, as well as texture and residual strain analysis by measuring the shifts in Bragg diffraction edges. The performance of detection devices has to meet the challenges posed by those new techniques in order to achieve the desired resolution, reduce the data acquisition times and fully utilize the capabilities of modern neutron sources [1], [2]. Detection efficiency, spatial and timing resolutions are among the key detector parameters determining the accuracy of mentioned techniques.
Neutron counting detectors with microchannel plates suggested by Fraser [3] provide some unique capabilities for high resolution applications. Our detailed theoretical study of the detection process [4], [5] indicate that the MCP detectors can reach efficiencies as high as 50% for thermal neutrons. The preliminary experiments with out optimal microchannel plates [6] agree with the results of our predictions for the particular MCP geometry used in the measurements. In addition, detectors with neutron-sensitive MCPs can count thermal and cold neutrons with spatial resolution comparable to the pore dimensions of 10 μm [7].
Section snippets
Experimental results
In this paper we present the results of detailed experimental evaluation of MCP-based neutron counting detector, which consisted of one 10B-doped microchannel plate (8 μm pores on 11 μm centers, 100:1 L/D, 33 mm diameter) followed by a stack of two standard glass MCPs (10 μm pores on 12 μm centers, 40:1 L/D, 33 mm diameter) and a Medipix2 readout [8] positioned 0.7 mm behind the MCP stack. Muros2 [9] back-end electronics allowing externally triggered acquisition frames was used for signal processing.
Conclusion
The neutron counting MCP/Medipix2 detectors proved to have high detection efficiency—43% at the cold beam and 16% at thermal neutron beam; high spatial resolution—55 μm in high counting rate mode and <15 μm at slow counting rate with event centroiding and frame-based timing resolution of a few μs. Combination of these performance parameters makes the MCP detectors very attractive for high resolution neutron radiography, transmission Bragg edge spectroscopy and energy-resolved imaging.
Acknowledgements
The authors would like to thank their colleagues at the Czech Technical University for the Pixelman data acquisition software [15]. The work was partially funded by the DOE STTR Grants DE-FG02-07ER86322 and DE-FG02-08ER86353.
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