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MKIII OPERATOR'S MANUAL
100
Position 7 allows simultaneous observation through slits 3 and 5. Dark count-corrected counts are
stored in the BASIC F() array (refer to the Preliminary Data Reduction document for details). The
following algorithm is used to derive a value for instrument deadtime:
Assume Poisson statistics:
τ
⋅
−
⋅
=
0
0
N
e
N
N
⎟
⎠
⎞
⎜
⎝
⎛
⋅
=
N
N
N
e
0
0
log
1
τ
where:
N
o
is the true count-rate (counts/sec),
N is the observed count-rate,
τ
is the deadtime (sec). (The BASIC variable T1 is used for
τ
.)
1. As a first approximation set the true (unknown) count-rates equal to the observed count-
rates:
3
3
F
F
←
ʹ′
5
5
F
F
←
ʹ′
2. Compute an estimate for deadtime:
7
3
5
3
log
1
F
F
F
F
F
e
ʹ′
+
ʹ′
⋅
ʹ′
+
ʹ′
←
τ
3. Revise the estimates for the true count-rates:
τ
⋅ʹ′
⋅
←
ʹ′
3
3
3
F
e
F
F
τ
⋅
ʹ′
⋅
←
ʹ′
5
5
5
F
e
F
F
4. Iterate steps 2 and 3 until the value for T1 converges.
Deadtime measurements are made at both high and moderate light intensity levels by using two
different neutral-density filter settings (positions 0, 1 for Filterwheel #2); five measurements are
taken at the higher intensity, ten at the lower intensity.
Method:
The command DT is issued.
Following the usual five minute lamp warm-up, and a further 10 minutes for test to run, results will
be printed in a format similar to the following:
FILTER #1/1 AND FILTER #2/0
GMT
DEADTIME
191054
4.94288936E-08
191119
4.81299056E-08
191143
4.93662915E-08
191208
4.91343971E-08
191233
4.84666031E-08
48.705
±
.6
APPENDIX F FACTORY TESTS
Содержание Brewer Mk III
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