PCM-2 Manual.pdf - Voss Associates

High Voltage
Geometry Factor
Alpha & Beta
Channels Active
Alpha Threshold
Beta Threshold
Alpha & Beta
Efficiencies
Alpha & Beta
High Fail
Alpha & Beta
Low Fail
Alpha & Beta
Weight Factors
The detector voltage may be adjusted in steps of approximately ten volts not to
exceed 1750 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 rates
per unit area in order to compensate for differences in detector size. This is used
only for channel sensitivity test calculations.
Detector(s) marked as inactive are not 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 are
counted as alpha particles. Lower amplitude pulses are registered 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.
Detectors which show background levels above these limits are 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
rates 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:
iliald x WF) + R llew
R bkg = WF + 1
Where:
R blcg = The new computed average background count rate
Raid = The previous computed average background count rate
WF= Weight Factor
5-8
PCM2.MAN/ Rev A/April 1995