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![[Figure 3]](ge5109fig3mag.jpg)
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Figure 3
(a) A 3D depiction of the hybrid multiple CB 18-pinhole-collimation option available on the VSANS instrument. The beams are kept separate by a set of 13 pinhole masks roughly equally spaced within the collimation vessel (only three are shown). Between the last two masks before the sample are a stack of focusing lenses and gravity-canceling prisms for each beam. The beams converge at the beamstop in front of the high-resolution detector. (b) shows the partial horizontal cross section of the 13 masks used in the 18-beam CB collimation system. The beam-defining first and last apertures are 6.0 and 10.6 mm diameter, respectively. The vertical black lines denote absorbing sections of the masks. The first and last mask sizes are used for beam profile size determination. The intermediate masks block cross-talk between channels. The second to last mask fronts the lens stack. Three converging beams (blue central lines) are shown which converge at the detector located 47.2 m from the first mask. Solid lines are drawn from the center of the channels while dashed lines are drawn from the upper and lower edges. The red line shows a cross-talk ray which is blocked by masks 5, 6, 7, 8 and 9. The intermediate masks' circular openings are oversized by 5–20% to allow for mask misalignment and changes in neutron trajectory caused by gravity. (c) shows an equivalent system, but without lens focusing, providing the same beam size of 12.3 mm diameter at the detector using beam-defining first and last apertures that are 5.52 and 2.91 mm diameter, respectively. To cover the equivalent sample area with the smaller sample aperture requires 10 × 21 = 210 beams. None of the intermediate mask openings are oversized. Only mask 8 blocks the potential red cross-talk ray between channels. This system would require more than the 13 masks shown to entirely eliminate cross-talk and has additional losses from potential mask misalignment and gravity distortion of the neutron path since the mask openings do not have the oversizing that is allowed by the focusing lenses. |
![[Figure 3]](ge5109fig3.jpg)
 | JOURNAL OF APPLIED CRYSTALLOGRAPHY |
ISSN: 1600-5767
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