Thermo Scientific SAM12, Manual

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Technical Description - Physics Issue: 1.0
6-4 SAM12 User Manual Thermo Fisher Scientific
C
cps
Contamination Alarm Count-rate (cps)
is the
count-rate at which the user requires the alarm to be
triggered. It is equivalent to the Contamination
Alarm Level set by the user modified by the system
Efficiency Correction Factor (E).
C
effect
Effective Alarm Count rate (cps)
is the effective
net count rate at which the SAM normal alarm is
triggered. The Contamination Alarm Count rate is
modified to take account of the monitoring time,
background statistical fluctuation and user
programmed Probability of Detection. This ensures
the Alarm set point reflects the measurement
certainty required. The current Effective Alarm
count rate may be viewed in
Information (page 5-
16) . The Ceffect calculation is detailed in
Contamination Alarm (page 6-8) .
F
Probability of False Alarm (
σ
)
is the probability
that a false alarm does not occur during a measuring
sequence. The value of F in terms of sigma is set in
Params 2 (page 5-10) , where the associated
probability is shown alongside in parentheses. The
value is usually set as high as possible, so that false
alarms do not occur, e.g. one false alarm in a
hundred measurements is a probability of 99% (2.4
σ
), see Table 3- Probability - Sigma and % (page 6-
12) .
P
Probability of Detection (
σ
)
is the probability that
exactly one Alarm Level of contamination will
cause an alarm. The value of P in terms of sigma is
set in
Params 2 (page 5-10) , where the associated
probability is shown alongside in parenthesis. The
minimum allowable probability is 50% (zero
sigma). Increasingly higher probabilities become
increasingly subject to other parameters,
particularly background level. The interrelationship
will be discussed in the Calculation stages.
E
Efficiency Correction Factor
is the system
efficiency (summed efficiency for all detectors) to
the nuclide (Enuc) or mixture of nuclides (Emix)
being monitored. E is given by the contamination
count rate in a given time and divided by the
activity. E is determined by calibrating with a
known radionuclide source, as detailed in
Calibration for Other Nuclides (page 10-3) .