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A new type of high performance and compact neutron collimator can be manufactured from Gd- or B-doped microchannel plates (MCPs). Structures only a few mm thick have very narrow rocking curves and high out-of-angle rejection ratios, as observed previously with a cold neutron beam. We present the results of measurements with a collimated (L/D ratio ~ 280 : 1) thermal neutron beam. MCP collimators doped with 3 mole % of [sup.nat][Gd.sub.2][O.sub.3] as well as doped with 10 mole % of [sup.10][B.sub.2][O.sub.3] were calibrated for transmission versus tilt angle. The MCPs used in this study were only 0.6 and 0.8 mm thick with ~ 8.5 [micro]m circular pores on 11.5 [micro]m centers. All the measured rocking curves agree well with the theoretically predicted performance. Both experimental and modeling results indicate that very efficient MCP collimators (with < 0.1[degrees] wide rocking curves and a rejection ratio exceeding [10.sup.3]) can be built with the existing technology. The possibility to manufacture collimators with very large L/D ratios exceeding 1000:1 is also discussed for the case of unetched MCPs. The peak transmission of such devices with very sharp rocking curves will be limited to ~ 40 % by the transmission of the undoped glass. Application of MCP collimators for scatter rejection in neutron radiography is also considered in terms of possible image distortions, which are shown to occur only for the systems with detector spatial resolution better than 20 [micro]m FWHM. Index Terms--Collimators, neutron optics, neutron scattering.

Detectors with microchannel plates (MCPs) are currently widely used in photon and charged particle detection with high spatial (~10/[micro]m) and temporal ( The same MCPs can be used as very efficient and compact thermal neutron collimators. In this paper, we compare the efficiency of circular- and square-pore MCP collimators with the help of our model, the validity of which has already been verified by our experimental measurements reported last year. The rocking curve of 5-mm and 2.5-mm thick MCPs doped with 3 mole % of [sup.nat][Gd.sub.2][O.sub.3] is predicted to be only [+ or -] 0.1[degrees] and [+ or -] 0.3[degree] wide, respectively, for both geometries. A very compact device with high thermal neutron detection efficiency and angular sensitivity can be built by combining an MCP neutron detector with an MCP collimator. Index Terms--High spatial resolution, neutron detection, neutron optics, position sensitive detectors.

In most neutron scattering experiments and in boron neutron capture therapy, the angular spread of the neutron beam is defined by the quality of the neutron collimator. A typical collimator consists of a large number of parallel plates coated with neutron absorbing material, and at present these plates are at least few centimeters in length. In order to obtain collimation in both vertical and horizontal planes, two orthogonally aligned collimators are installed in the neutron beam. We present a new type of high performance neutron collimator made with Gd-doped microchannel plates (MCPs). Such collimators are only few millimeters thick and the rocking curve is expected to be even sharper than that of conventional 0.5[degrees] collimators. While collimation is performed in two perpendicular planes simultaneously, the geometry of these new collimators can be changed so that the degree of collimation in each direction is controlled independently. The modeling of the proposed collimator indicates that for the existing MCP technology the rocking curve can be made as sharp as 0.2[degrees] FWHM, which can be further improved by current developments in the MCP technology. The preliminary experimental evaluation of our first very thin (only 0.6 mm) MCP collimators confirms the accuracy of our numerical model. Index Terms--Collimators, neutron optics.