A radial oscillating collimator for small position sensitive detectors

2014 A radial oscillating collimator built for reducing background and parasitic scattering from the sample environment on the diffractometer D2 at the ILL is described in this paper. First results are presented. Revue Phys. Appl. 19 (1984) 799-800 SEPTEMBRE 1984, 1 Most of diffraction experiments on diffractometers using position sensitive detectors (PSD) require sample environments (fumace, cryostat, etc.) which produce parasitic scattering. Moreover, the air on the way of the direct beam gives rise to an additional background The first solution was the use of high, low or room temperature devices mounted with a vanadium cylinder near the sample and a large vacuum chamber around. The vanadium only contributes to the background, and the scattering from the material of the chamber (usually Al) crossed by the direct beam is catched by cadmium sheets located in well-chosen areas inside (Fig.1 a). The vacuum avoids air scattering. This simple solution which is independent of the size of the detector has unfortunately some disadvantages : 1) background from the vanadium, 2) not available for special sample environments (very high temperature, pressure cells, cryomagnet) which are more and more required, 3) particular sample environment devices which cannot be used on other instruments. Therefore an other solution must be found to overcome those difficulties. In the same context, Soller collimators have been used in diffraction instruments (with single detectors) for some decades to limit the irradiated sample volume viewed by the detector and reduce the detection of off-centre parasitic scattering. In the case of PSD, a development at the ILL, the Radial Oscillating Collimator (ROC) is a diffracted beam collimator of revised geometry, designed to suppress off-sample parasitic scattering without perturbing the sample scattering or modifying the resoFig. 1. a) Sketch of the previous solution. b) Sketch of the ROC solution. Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/rphysap:01984001909079900