The theory of compact and efficient circular-pore MCP neutron collimators

Abstract

A novel type of thermal and cold neutron collimators based on microchannel plates (MCPs) doped with neutron absorbing atoms is discussed. Opposite to widely used Soller slit collimators, the microchannel plates collimate a beam of neutrons in 2 dimensions simultaneously and they are very compact. A detailed model of the circular-pore MCP collimator performance, described in this paper, can be used for optimization of MCP parameters in order to achieve the most efficient collimation for a given application.Among these parameters are the MCP geometrical dimensions, the type of absorbing atoms and their concentration in the MCP glass mixture, all constrained by the manufacturing limitations. The model predicts that the MCP collimators can be very efficient (rocking curve <0.1 o wide with high background suppression in the wings) and very compact (only few mm thick). In addition to collimation, the same microchannel plates can also be used for neutron imaging with a high spatial (~20 µm) and temporal * Corresponding author. E-mail address: ast@ssl.berkeley.edu (A.S. Tremsin) (~1 µs) resolution, opening up new possibilities for simultaneous beam collimation and monitoring.

High resolution neutron radiography with very compact and efficient neutron collimators

“…Obviously, at a short distance to the active area the beam divergence does not substantially blur the detected image and therefore we should not expect an improvement of the spatial resolution by a neutron collimator. However, it is important to show that the presence of our compact collimator does not introduce image distortions, as it was predicted by our modelling [9,10]. Figure 4 shows the transmission radiographies of the test mask obtained with the collimator in the beam and without it.…”

“…To fully utilize the recent progress in detection systems enabling spatial resolution on a sub-15 µm scale [6]- [8] both high collimation and high intensity beams are required if reasonable image acquisition times are to be realized. Very compact (few mm thick) and efficient (as narrow as ±0.05 degree) neutron polycapillary collimators [9,10] can be a very attractive alternative to the single input aperture or Soller type collimator approaches and in some cases can substantially increase the neutron flux for a given beam divergence. It is achieved by beam collimation by millions of highly parallel pores with diameters on the scale of <10 µm, which match the achievable detector spatial resolution, and thus do not introduce image distortions [9,10].…”

The physics of solid-state neutron detector materials and geometries

“…electron multiplication and detection) are beyond the scope of this review. However, here again, benefiting from the advances of the x-ray and charged particle detection communities, the MCP-based neutron detectors are poised to provide excellent two-dimensional spatial (<15 μm) and temporal (1 μs) [324,325] or one-dimensional temporal (50 ns) [326] resolution on a platform that can theoretically compete in total thermal neutron detection efficiency (from 2-12% [323] to 50% [326] calculated) with the planar and threedimensional detector classes described above. Unfortunately, the direct incident neutron energy information is made nearly undecipherable by the charge multiplication process, but with such excellent timing resolution, time-of-flight studies in the proper geometry (vide infra) could be possible [326].…”

Determination of the Spatial Resolution in the Case of Imaging Magnetic Fields by Polarized Neutrons

“…The spatial detector resolution approaches the 1 µm size, driven by different techniques such as micro-channel plate (MCP), microscope-like devices, gadolinium oxysulfide scintillators, absorbing grids, observing tracks from neutron capture events, hybrid pixel detector (Medipix [10]), coded source imaging (CSI) system [11], fiber optics taper (FOT), etc. [8,[12][13][14][15][16][17][18][19][20][21], and inaccuracies associated with use of precision test objects, such as a slit or an edge can be reduced [22,23] and misalignment of an edge with respect to detector pixel columns or rows can be taken into account [6]. A collection of test devices was developed for neutron imaging that can be used to quantify pixel and voxel size, resolution of the imaging system, and beam divergence.…”