Subject: Xe line calibration Dear All, I've been buried in RAW data trying to determine the relative positions of the Xe line in the detector spectra to the calibration spectral lines. This is so that we can include changing (aging) values of these spectral line positions in the keywords of JMXi-SPAG-MOD, such that the relative changes in the detector vs. calibration area lines can be taken into account during the gain correction. This has been made necessary by the fact that the heavily irradiated areas of the detector (calibration zones) are aging differently to the rest of the detector. Here are the results for JEM-X1. http://www.dsri.dk/~oxborrow/sdast/sdast_forum.html/CAOjmx1.XeLines.ps.tar Figure jemx1RawChannels.ps shows the raw found ADC channels for the four calibration spectra and for Xe determined from detector spectra (binned ADC channels for entire science windows). For each of the calibration spectra, the average position during a half day when gain is constant has been found. For Xe the average ADC channel for all the available science windows during that half day is used. Source 1 (Fe): black; source 2 (Cd): red; source 3 (Fe): blue; source 4 (Cd): green; Xe: yellow. Figure jmx1ChannelRatios.ps shows the ratio of Xe to each of the calibration sources for each half-day period. This is where we can see the differential gain aging of the detector: there is a slow but definite trend upward in the ratios which currently translates into a slow drift of the Xe line up from 30keV in our corrected (keV) spectra. By including the values of the channels of the Cd/Fe peaks and Xe peak in the keywords for JMXi-SPAG-MOD for each of 9 operational epochs, this drift will be corrected in the final spectra. Source 1 (Fe): red; source 2 (Cd): source 3 (Fe): green; source 4 (Cd): blue. There is some systematic variation in this data depending on the quality of the Xe peak in the detector spectra. Where the Xe peak falls close to the instrumental upper cutoff, the peak is always found too low. Values used in the IMOD group are only taken for revolutions where the Xe peak sits on a good spectral plateau. It should also be noted that the data for source 4 shows most scatter, and that this calibration source is not used for gain correction since it falls on a dead anode and is somewhat unstable. Source 1 (black points) seems to show the expected gain aging behaviour: rapid burn-in during the earliest revolutions; a halt in gain aging while the unit is unused; a slow but steady increase in gain aging after the unit has been re-activated. Figure jemx1ChanRatioAverages presents the same data as above, but averaged over all four calibration sources. Black line shows i=1..4, and red line shows Xe/ i=1..4. Again the steady increase in the differential aging of the detector plate is clearly seen. A thorough physical explanation of this differential aging - microstrip ion drift versus radiation damage versus other unknown forms of aging - might make an interesting article for some instrumentation journal. Now that all the bugs are ironed out of my idl programs, and I've learnt how to find good detector spectra, let's hope things go a little quicker with JEM-X2. Best wishes, Carol Anne DANISH NATIONAL SPACE CENTER Dr. Carol Anne Oxborrow Email: oxborrow@dnsc.dk Homepage: http://www.dsri.dk/~oxborrow Telephone (direct): +45 35 32 57 33 Telephone (secretary): +45 35 32 57 01 Fax: +45 35 36 24 75 ------------------- The Danish National Space Center (DNSC) is a new research center under the Ministry of Science, Technology and Innovation. The center is the result of the Danish Space Research Institute merging with a part of the National Survey and Cadastre. Read more about the Danish National Space Center at: www.spacecenter.dk E-mail: office@spacecenter.dk