
Date: Tue, 2 Dec 2003 11:54:11 +0100 (MET)
From: Carol Anne Oxborrow <oxborrow@dsri.dk>
Subject: JMX2: Gain resolution (SVR)
To: njw
Mime-Version: 1.0

kaere NJW,

her er den lidt redigerede version af figuren om den gennemsnitelige energi
resolution per revolution. Og et par figurer til med bemaerkninger som kan
bruges in SVR - hvis du vil!

Caption: Figure jemx2.gain.resol.ps
 shows the average relative energy resolution of JEM-X2
for the Cd-109 22 KeV  line as determined from the calibration spectra from
each of the four anode segments of the detector, averaged over one revolution.
Black is source 1; red is source 2; blue is source 3; green is source 4.

The figure clearly shows how the outer segments of the detector both began
the mission with very poor energ resolution, probably due to unstable anode
strips that have since either died completely or stabilised in their
behaviour. Despite this `burning in' process, anode 4 still is considerably
poorer than the other 3 sources, probably due to a known dead anode running
directly through the spectral calibration area. For this reason source 4 is
not used for gain determination and event correction. The other anode
segments, especially the inner ones (2 and 3) show gain resolutions as good
as or better than the predicted resolution of 10% ( 47% / (sqrt 22) ).
However, a slow degradation in the gain resolution is also apparent for all
four anode segments, suggesting that cosmic ray exposure is having an
effect on the quench gas and/or microstrip plate. Whatever the cause of this
slow loss of resolution, it clearly affects the entire detector uniformly.
Presumably, this deterioration has the same cause as the steady gain increase
in the JEM-X2 unit that has been apparent since the beginning of the mission.

Figure jemx2.all.gain.ps shows the value of the onboard energy channel of the
peak of the Cd-109 22 KeV lines for the four calibration spectra. Black is
source 1; red is source 2; blue is source 3; green is source 4. The steady
increase in detector gain is clearly apparent. The sudden drops in peak
channel value show where the high voltage supply to the microstrip plate has
been lowered to keep the gain within the range used for pre-flight
calibration.

It is clear from the figure that the gain increase, like the resolution
decrease, affects the detector plate uniformly. We can also see that the
rate of increase is related to the level of the high voltage supply on the
plate. The gain increases more slowly as the HV is decreased.
This raises the possiblity that the two effects are related to the presence
of the high voltage, and that JEM-X1 which has been largely switched off
since revolution 45, may be undamaged and can be expected to perform much as
it did during pre-flight calibration when it is finally switched on again.

Figure jemx1.gain.all.ps shows the onboard peak channels for the four
calibration sources of JEM-X1. Black is source 1 (Fe-55, 6 KeV); red is source
2 (Cd-109, 22 KeV); blue is source 3 (Fe-55, 6 KeV); green is source 4
(Cd-109, 22 KeV). 

In the earliest revolutions there is a clear gain increase,
which seems to decrease with time despite the constant HV value and
this seems to have stopped by revolutions 39 to 45. The revolution 102 data
suggests a gain increase for the cadmium sources but not for the Fe sources,
so it is difficult to  judge what is going on here. In general however, the
strong steady gain increase seen in JEM-X2 is not seen in the JEM-X1 unit.
Similarly, available data from JEM-X1 does not show any clear sign of a steady
deterioration of the energy resolution. 

Keep up the good work,

Carol Anne


.DANISH.SPACE.RESEARCH.INSTITUTE.DANISH.SPACE.RESEARCH.INSTITUTE.DANISH.
Dr. Carol Anne Oxborrow
Email: oxborrow@dsri.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