Last revision January 16, 2001

  Calibration Line Change for Spectroscopy Detector 1

TJD 10526 = March 19, 1997
TJD 10527 = March 20, 1997

Because an artifact in the spectrum in Spectroscopy Detector 1 (SD 1)
near the 511 keV line, which gradually became stronger and interfered
with the use of the line for spectral calibration purposes, the line
that was used for calibration was changed at the beginning of TJD
10527 from the 511 keV line to a line or group of lines at 191 keV
for SD 1 only.

Therefore, for SD 1, the 511 keV line was used from the beginning of
the mission (effectively TJD 8367) through the end of TJD 10526, and
the 191 keV line was used from the beginning of TJD 10527 through the
end of the mission (effectively TJD 11690).  Note that the gain itself
was not changed at this time.

According to an attribution (comments in IDL code) by W. Paciesas to
R. Preece (1997), the linear channel number for the 191 keV line
can be converted to the equivalent channel number for the 511 keV line
by the formula:
   chan num 511 = 2.528 * (chan num 191) - 8.3
and the uncertainty or error in the channel number of the peak is
given by the formula:
   error chan num 511 = 2.528 * (error chan num 191)

For all other Spectroscopy Detectors (SDs 0,2,3,4,5,6,7), the 511 keV
line was used for spectral calibration during the entire mission.

(Incidentally, the 511 keV line was used for spectral calibration of
the Large Area Detectors (LADs) during the entire mission.)