PCM-2 Manual.pdf - Voss Associates

High Voltage
Geometry Factor
Alpha & Beta
Channels Active
Alpha Threshold
Beta Threshold
Alpha & Beta
Efficiencies
Alpha & Beta RDAs
Alpha & Beta
High Fail
Alpha & Beta
Low Fail
Alpha & Beta
Weig ht Factors
The detector voltage may be adjusted in steps of approximately ten volts.
Background count rates are multiplied by this factor before being used to test for
detector sensitivity. This converts average background count rates into count rate
per unit area in order to compensate for differences in detector size. This is used
only for channel sensitivity calculation.
Detector(s) marked as inactive will not be used in any computations. This may be
done to keep the instrument operating if one detector fails.
Particles which cause the detector to produce a pulse exceeding this voltage will
be counted as alpha particles. Lower amplitudes register as betas.
Particles which produce pulses below this amplitude will not be counted as either
alpha or beta.
The ratio of counts per disintegration expressed as a percentage.
Contamination of this activity level will be detected with a probability equal to the
system RDA confidence level.
Detectors which show background levels above these limits will be considered too
noisy or contaminated to use, and will remove the instrument from service.
Detectors with backgrounds below these levels are assumed to have failed. The
instrument will not count if this occurs.
This parameter controls the speed with which the computed average background
rate will follow changes in actual background count rates. The weight factors
smooth statistical fluctuations in background measurements by synthesizing an
exponential moving-average. Increasing the weighting factor will enhance the
smooting function at the expense of extending the time constant associated with
recognizing step changes in the real average background count rate. The formula
for computing the weighted average background count rate is:
fRoid x WF) + R new
R bkg = WF+l
Where: R bkg = The new computed average background count rate
R o1d =
The previous computed average background count rate
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I-'CML.MAN/ Hev A/April I ~~b