10-Boron based neutron detector, our alternative for 3-Helium filled PSD counter tubes!

The Jalousie neutron detector has been developed by CDT to serve as alternative for classical 3-He position sensitive detector tubes (PSD). It is as such thought to resolve today´s 3-He availability crisis for neutron scattering instruments. The neutron converting material is 10-Boron and replaces 3-He. The comparatively small overall detection efficiency of an individual layer is enhanced by tilting the layer towards the incoming neutron path, thus increasing the effective absorption depth. Additionally, eight to twelve such boron layers are arranged along any neutron path to further enhance the overall detection efficiency.  A Jalousie detector system comprises many lamella shaped individual modules, where each makes up an enclosed multi wire proportional chamber with two anode planes and four cathode planes that carry the converter layers.  Several such lamellae, when stacked and tilted with respect to the neutron paths, may be arranged to cover square meter sized planes, or alternatively a cylindrical surface to enclose a scattering sample. The design depicted has been realized for the powder diffractometer POWTEX at FRM II, where, once in operation, an overall area of 9 sqm will be covered. Spatial resolution is 5 mm (FWHM) and may be altered through design parameters. The POWTEX lamella length was chosen to be 1,8m and includes a concentric orientation of the readout channels towards the scattering centre.

The Jalousie Endcap Detector is a special, segmented Jalousie configuration designed to cover the cylinder endcaps avoiding blind areas. The circular endcap disk is covered by 30 segment units of 12° each. Each segment comprises several subunits, each of which contains several Jalousie cassettes. The converter layers are oriented radially, sandwiching an array of Anode wires. The Anode wires are roughly directed towards the scattering center, a configuration that avoids blind areas entirly.     

Optional enhancement of resolution to sub mm (FWHM) transverse to converter layers: Sub mm resolution with Jalousie may be feasable if the anodes are exposed to one converter layer only. In this case the area of the cathode strip projected onto the entrance window determines spatial resolution. For POWTEX with the standard geometry of dual converter layers spatial resolution is determined by the spacing between the layers.

Along the converter layers however resolution is for both configurations is related to the width of the voxel and can be tuned to about 5 mm FWHM.  

Jalousie 21.08.18.PDF

Flyer Endcap Detector