Thermo Scientific SAM12, Manual

Page: 114 / 176

Technical Description - Physics Issue: 1.0
6-10 SAM12 User Manual Thermo Fisher Scientific
Residual Contamination is assumed to exist where the
following formula is satisfied:
( )
⎟⎟
⎠
⎞
⎜⎜
⎝
⎛
≥ −
MON
sum
RCC
sum
T
B
N B
RCC
C
where
C
RCC
is the average count rate during the Residual Contamination
Count period.
N
RCC
is the RCC threshold variable (see Params 1 (page 5-8) ).
The default setting for N
RCC
is 7.0
σ
and should never be set to a
less that the sum of the probabilities of detection and false alarm (
P+F).
In the event of residual contamination being detected, the SAM
will enter an “Out of Service” state and monitoring will not be
possible (see
Notes regarding Residual Contamination Check
(page 5-60) ). The doors will lock if the option is fitted.
Intervention by a password holder will be required to terminate
the fault status (see
Instrument Contaminated (page 5-61) ).
The Calibration technique (see
Calibration Menu (page 5-19) )
uses flash (10 second) background and source counts to
automatically calculate the count time for the user. The
Calibration Accuracy and the associated confidence level is set
in Params 3 menu (see
Params 3 (page 5-11) ).
The count confidence level has a default setting of 3
σ
(99.7%)
which is a generally accepted Confidence level that produces
acceptable count times.
Then Calibration Count Time,
where N
conf
= 3 (Count Confidence Level of 99.7%)
n = Flash background Count (cps)
b = Flash Background Count (cps)
A = Calibration Accuracy (ratio e.g. 5% = 0.05)
The calculated count time is rounded up to the nearest whole
second and T is limited to 10,000 seconds.
Note that when CCM (see CCM
Menu (page 5-30) ) is installed,
during a
60
Co calibration, both
the CCM channel and all the detectors are calibrated at the
same time. This may lead to slightly extended counting times
due to the lower CCM channel efficiency.
Isotope gamma efficiencies
The following data were obtained during type testing in a stable
7-10
μ
R/h (0.07-0.1
μ
Sv/h) Background using pant-sources in
Automatic Calculation of
Calibration Monitoring
Time
( )
( )
( )
s Sec
b n A
nb n
N T
conf
'
2
2
2
−
+
=