Rad-test interested folks,           5/7/2001

  I've made some progress on investigating the "anomalies" seen in the
XGEF radiation exposure tests and have updated plots on the internal
page: file:/nfs/cxc/h3/dd/text/VSG/Rad_anal/rad_anal.html
The current list of anomalies is appended here as well.

  Of 17 anomalies noticed in the ratios of after/before tests of the
12 gratings, 9 have been checked out and 8 (mostly 2nd and
zeroth-order efficiency) are to be investigated.

  Some first-order efficiency changes seen in MEG and HEG gratings at
our lowest test energy, 0.93 keV from a Cu-L line, were investigated.
Three (perhaps 4) gratings showed 10%-ish changes at this energy and
over the 5 test regions of each grating.  Improving the fitting of the
HEG data (which starts to resolve the two lines in the Cu-L blend)
reduced the effect somewhat.
  Because all 5 regions of the grating-under-test are referenced to a
single reference measurement, an error in the reference measurement
will show up as a common offset for the five measured regions. Effects
like this feel like the most reasonalble explanation of the 0.93 keV
changes.
  If, however, all three of the gratings showing this effect were to
have been radiation exposed, then I would allow that this could be the
result of the exposure.  Note that in this (unlikely) case the level
of the effect, ~10%, is still small compared to the few per cent per
year which ongoing Chandra flight HETG calibration seeks to achieve.

  I will continue to focus my efforts on finishing this analysis
and hope to complete it in the next week or so.

  - Dan

rad_anom.010507.txt:
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 Anomalies seen in the Plots created by rad_compare
     updated 5/7/01 dd

   -------------------
   Key:  
    ** - anomaly not yet explained or investigated
    OK - anomaly is explained
    !! - anomaly is or could be a "real" measurement change
    :) - no unexplained anomalies
   -------------------

MA1025  (010301/001207)
 OK - zero jump at 0.93 keV (high zo Chi2)
       4/4-OK: SSD/fitting problem, reanalyzed, lowered Chi2
 ** - first second-order point consistantly ~12% low in all regions

MA1026  (010301/00111)
 :)

MB1148  (010302/001117)
 !! - zero-order change at MB1148m4 +15% at 0.93 keV
       4/4 data look alright, real change or just stat fluke?
 OK - first-order 0.93 keV 10% high in m4 and all regions
 !!    5/4 Conclude that it's probably either:
            i) some ref/PSPC thing common to '1148 and '1158 ( and also
               showing up in some HEG tests...)
                 OR
           ii) it may be a rad effect that BOTH '1148 and '1158 experienced,
               if they were both rad-exposed.

MB1158  (010302/001117)
 OK - second order Chi2 large - poor fitting of small signals
       4/4 exclude poor fits/measurements
 :)

MA1022  (010307/001116)
 :)

ME1409  (010307/001127)
 ** - large second-order Chi2 in one region

HC2214  (010308/001101)
 OK - large second-order Chi2
       5/7 3 regions OK, 2 regions CHi2 < 6.0.
 :)

HC2259  (010308/001101)
 OK - minus 20% change in first-order 0.93 keV m=+1 effic in p8,
 !!   other regions too
       5/4 improved HEG Cu-L line fitting and effect is more like
           only -10% averaged over the five regions.  Unfortunately
           we don't have the 001101 m=+1 Cu-L measurements for HC2214
           which was tested at the same time as '2259...
           This effect feels like the MB1148 problem of Cu-L
           measurement systematic effects...
       5/7 The HX220 ratios are within 3% for 001101 and 010308,
           so most of the 10% effect is from the grating... and
           counting uncertainty of few per cent.
 ** - second-order large change in region m8 at one energy    

HB2104  (010309/001113)
 ** - first-order in p4 region looks 5-10% low over all energies --
      this is isolated to one test region of the grating --
      don't see anything like this in other gratings/regions,
      what's the cause?
 ** - large zero-order Chi2, 5% drop in effic at 1.25 keV
 ** - large second-order Chi2

HE2426  (010309/001115)
 OK - large second-order Chi2 in m8 (Al-K +1 order)
       5/7 re-analysis reduced the Chi2.
 :)

HE2412  (010312/001115)
 OK - large zero-order Chi2: 5% drop in effic at 1.25 keV
       5/7 OK: looks statistical...
 :)

HF2517  (010312/001114)
 OK - first-orders at 0.93 keV: one higher, one lower by ~15%.
 !!    5/4 re-analysis reduced the effect a little... a la '2259.
       5/7 The reference measurements are only 4% different, so
           it appears to be mostly in the grating...
 ** - large zero-order Chi2: ~5% increase in effic at 1.25 keV
 ** - second-order Chi2 at one energy in m8 region

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