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Annealing is the process whereby the RHESSI detectors are heated to approximately 100 degrees Celsius for a week or so in order to remove damage to the crystal structure of the germanium detectors caused mainly by high energy particles. This radiation damage is a particular problem for RHESSI because its detectors are unshielded and it passes through the South Atlantic Anomaly, where fluxes of trapped high-energy particles are enhanced due to the reduced geomagnetic field in this region.

Annealing has occurred during the following time period(s):


Start Date

Time (UT) End Date Time (UT) Comments
1 2007 November 5 07:00 2007 November 27 20:00
2 2010 March 16 00:30 2010 May 01 01:50 RHESSI's Anneal Adventure
3 2012 January 17 03:00 2012 February 22 14:50

The list of Anneal and Offpoint times shows when solar observations were not being made.

Another anneal will probably occur in 2014. It will be the last anneal before laboratory tests have shown that the detectors do not become segmented when the high voltage is reapplied. This means that each detector may no longer become electrically separated into front and rear segments and hence will act as one large detector. This will result in higher X-ray background count rates, degraded energy resolution, and the inability to make gamma-ray measurements during periods of intense X-ray fluxes. The data will still allow X-ray imaging and spectroscopy to be carried out with little, if any, loss in angular resolution at energies between ~10 keV and several hundred keV. Also, experience with Detectors #2 and 4 that did not segment after the last anneal shows that segmentation becomes possible after some time as radiation damage builds up again.

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