Thermo Scientific SAM12, Manual

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Technical Description - Physics Issue: 1.0
6-6 SAM12 User Manual Thermo Fisher Scientific
M is the Detector Changing Background variable (see Params 1
(page 5-8) ). The default value for M is 7. It is not recommended
that M should be set below 4.0 σ .
All four or six detector counts show a N
σ
change from their
relevant stored averages in the same direction:
[ ]
av a av
B N C B
≥ −
where
B
av
is the rolling average for any one detector.
C
a
is the counts registered in the last one second background
update.
N is the Gross Changing Background variable (see Params 1 (page
5-8) ). It is not recommended that N should be set below 3.0
σ
.
The former expression detects gross changes in any single
channel, while the latter guards against significant drift in all
channels.
After every successful 10 second background update, the
average background for each channel is updated. The four or
six average backgrounds are then summed and a new
monitoring time is re-calculated as follows:
Act Act cps
Z E C C
. .
=
where Act is one of the units below
Z
Act
is the corresponding multiplier
Units Unit Multiplier Z
Act
Bq 1
kBq 1000
Dpm 0.01666
pCi 0.037
nCi 37
μ Ci 3.7E4
mCi 3.7E7
Ci 3.7E10
T
cal
found by solving:
In practice, the software solves this expression using a
numerical substitution for T
cal
and iterative binary search
technique. The value of T
cal
which provides the solution is then
Calculation of the
Monitoring Time (T
cal
)
⎟⎟
⎠
⎞
⎜⎜
⎝
⎛
+ + +
+
+ + =
+
cal B cal
cps eff
B
eff
cal
eff
B
eff
cps
T t
P F
T
C B
t
B
P
T
B
t
B
F C
1 1
) (
4
1
2