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The 1st record of the CB data type id unchanged and the 2nd has the
following layout:
Bytes
Content
0-63
SHF key of Gain measurements time.
64-127
SHF key of start time of applicability of gain
drift parameters.
128-159
Gain drifts, units are per day*106.
160-191
Digital Ag's at time of gain measurement.
For a description if the above parameters and how to apply them see
Express No. 6, p.25. Note that the gain measurements currently in the
CCF were made on 1984 day 86 (SHF=133574400) and that there is no
evidence for any Xenon gain changes.
The layout of data type DS is as follows:
Record
Contents
1
Argon counter A, configuration (a)
spectrum
2
Argon counter A, configuration (b)
spectrum
3
Argon counter B, configuration (a)
spectrum
4
Argon counter B, configuration (b)
spectrum
.
.
.
.
17
Argon half1 configuration (a)
spectrum
18
Argon half1 configuration (b)
spectrum
19
Argon half2 configuration (a)
spectrum
20
Argon half2 configuration (b)
spectrum
21-40
The same for Xenon
Note that each record contains data for 128 channels. In order to
obtain spectra in cts/sec/bin the values stored in the CCF must be
multiplied by 10-5. Note that there are no data in the
records appropriate to configuration (a) since this is not normally
used. Uncertainties are not included in this data type pending
investigation of the systematic errors associated with the spectra.
Each of the spectra represent the difference in background counting
rate obtained when a detector is fully offset in the +ve direction
compared with that obtained when it is co-aligned. See Express No.5
p.48 for a detailed description of background subtraction techniques
and difference spectra. These difference spectra should be
subtracted from a background spectrum obtained in a fully
positive offset configuration and added to a background
spectrum obtained in a fully negative configuration prior to
subtraction of the background spectrum from an aligned spectrum to
obtain the source spectrum.
Note also that an error was introduced into some recently produced
CCF's. Two of the configuration (b) Argon detector C resolution
coefficients had become transposed. to check if this is the case on a
particular CCF compare the configuration values (a) and (b). If they
differ, then the configuration (b) values are wrong! Current CCF's
(identified by a time of SHF=152634849) are correct and also include a
better estimate of the detector D Argon gain drift parameters
determined in the recent Crab Nebula calibration.