Kipp&Zonen Brewer MkIII - Manual (Page 103)

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