Detectors

Si(Li) solid state detector
High Resolution X-Ray Camera
Wide-area X-Ray Diffraction Camera

Si(Li) solid state detector

A Si(Li) detector (GRESHAM) of 30 mm² active area and 3.5 mm active thickness with an 8 micron thick Be window is used to detect the characteristic X-ray line intensities generated in the excited micro-spot of the sample. The solid state detector is placed at 90° to the incident X-ray beam and within the storage ring plane (photon polarization plane) in order to minimise the intensity of the scattered peaks in the spectra. A CANBERRA 9660 digital signal processor and a CANBERRA 556A AIM is used to collect the X-ray spectra. The detector itself is placed onto motorised translation stages, allowing for micron-sized optimisation of the detection position. By raster scanning the sample in the focused beam the 2 dimensional X-ray intensity maps of the sample can be registered. The optimum step-size is determined by the size of the focused beam. The typical measurement time/pixel is in the 1-10 s range depending on the thickness and composition of the being analysed sample.
In usual analysis conditions the detector is operated with a minimum air path of ~1cm between the sample and the Be entrance window. As a guide, the approximate detector efficiency as a function of the photon energy to be detected is shown in the following graph.

Interchangeable external collimator assemblies allow the angular acceptance of the detector to be adapted to the requirements of a particular experiment and limit the number of extraneous photons entering the detector.

High Resolution X-ray Camera

This camera is used for both alignment of the microprobe and radiographic imaging of samples with full-field illumination. X-rays impinging on a thin phosphor screen are converted to visible light and imaged using visible light magnifying optics onto a peltier cooled 14-bit dynamic range CCD camera (Sensicam). The X-ray resolution of the camera is ~1µm with a field width of ~0.6mm. Images are acquired into a digital frame-grabber on a PC. Image acquisition (including control of the on-chip integration time) can be fully controlled via the beamline control software for synchronisation with sample scanning.

Wide-area X-ray Diffraction Camera

This camera (Photonic Science) is used for acquisition of Wide or Small angle X-ray Scattering data for structural/diffraction studies. X-rays are converted to visible light by a ~70mm diameter phosphor screen. Light is transferred via a tapered fibre optic bundle to a slow read-out (~20s) peltier-cooled CCD chip giving 16bit dynamic range. The camera is interfaced to a frame grabber card in a PC and is fully controllable from the beamline control software.