X-GEF Contamination and Effects

X-GEF Contamination and Effects, Version 1.0, November 1998

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Creation of this Report is a work in progress...


1. Introduction

There is clear data that the SSD and the PSPC windows are very slowly being coated with a hydrocarbon in the X-GEF vacuum. For the SSD window this is roughly equivalent to a 1 micron thickness of polyimide accumulated per year; for the PSPC window the accumulation is of order 0.4 micron of polyimide equivalent per year. This should not to first-order change the measured grating efficiencies because of the sample-divided-by-reference measurement technique; however, to a lesser extent these efficiency changes may influence the fitting process and resulting measurements.

2. SSD Window Contamination

A clear indication of contamination build-up on the SSD window is seen in the X-GEF SSD data. Plots over time of the ratio of SSD count rate to the SMD count rate for X-GEF lines show a clear trend and energy dependence, Figure cont.1 . The energy dependence of the change in the spectral response, Figure cont.2, is reasonably modelled as a partially covering (60%) of an absorbing layer (e.g., 3 um of Polyimide accumulated in 2 years). In comparison, the SMD detector appears stable in response, Figure cont.3, and can be treated as an accurate measure of the source spectrum.

3. PSPC Window Contamination

4. To-Do

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