Time and position dependent artefacts in X-ray spectra from a Si(Li) detector

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Abstract
The background levels in X-ray spectra from a Si(Li) detector have been studied in two different ways. First, an increasingly larger area of the detector was irradiated and significant changes in the resulting spectra were observed. Secondly, the detector was scanned across a diagonal and the detection efficiency was measured. Both methods showed that the active area as given by the manufacturer was significantly larger than that which could be irradiated without degradation of X-ray spectra. Furthermore, it is shown that the detector performance changed drastically with the time since the bias was applied. Artefacts and a general increase in the background reduced the usable detector area with 20% after twelve hours. In a normal analysis this gives rise to an increase in detection limits of up to 65% for an aerosol sample as compared to the detection limits when bias just has been applied.