Ludlum Measurements 334A, Руководство по эксплуатации

Страница: 21 / 60

Model 334A Operations Manual
Ludlum Measurements, Inc 12 January 2021
There are either zero, one or two alpha isotopes-of-interest, plus the Po-218, Po-214 and
Po-212 radon-progeny peaks. In radon mode, a peak marker for Po-210 will also appear.
The lower reference line(s) on the spectrum coincide with the isotope(s)-of-interest.
Configuration Settings
The four fields on the top of the Alpha Energy dialog each correspond to one of the four
configuration settings. The parameters for Gain, Threshold, Offset and Scale, determine the
view of the alpha spectrum on the display. These configuration settings affect the location,
width, spacing and offset of alpha peaks on the spectrum. The threshold, gain and scale
should not have to be adjusted from factory settings, so
only the offset may have to be
changed based on the elevation of the instrument’s location.
The instrument is initially calibrated at 5100 feet. Alpha calibration is altitude dependent, so
it is important that this is taken note of. The values for these four settings are stored
permanently on the Multi Channel Analyzer board, and changing any of them will save the
new values over the old values. The user can read the following descriptions of the four
parameters to get a better understanding of how the Alpha spectrum is displayed:
Gain
— (Range 1 to 31) This value controls the amplitude of pulses coming from the
detector. Increasing the gain broadens isotope peaks, shifts them to the right, and
spreads individual peaks further apart. As the Gain is increased, the peak(s) can be
shifted completely off the right end of the spectrum display. Shifting to the next
Scale will bring the peaks back into view on the spectrum. Also, as Gain is increased,
the noise amplitude will increase proportionally, requiring a compensating increase in
Threshold level. Gain should not normally be changed from the factory setting.
Threshold
— (Range 1 to 31) This value controls the amplitude threshold that
pulses must exceed to be measured. It should be set just above the level where the
amplifier noise is first observed. Default Threshold is 9. Less than 9 disables the threshold.
Offset
— (Range 0 to 255, in 8 channel increments) Increases in this value shift the
256-channel spectrum the defined number of channels to the left. The Offset is
elevation-dependent and may need to be adjusted by the user in increments of 8.
Offset is related to the Scale setting by controlling the 256-channel window on the
scaled discriminator output. If the Scale is zero, the Offset will allow the output of
any consecutive 256 channels, from discriminator channel 1 to channel 512. If the
Scale is one, Offset will allow the display of any 512-channels over the 1024-channel
discriminator range (binned down to 256 spectrum channels). If the Scale is two, the
Offset has no effect and the entire 1024-channel discriminator output is compressed
4::1 to the 256-channel spectrum.
Default Offset is set at factory calibration.
Scale
— (Range 0 to 2) This value controls the binning or compression of the 1024-
channel discriminator output into the 256-channel spectrum value. A value of zero
results in no compression. A value of one is a 2::1 compression, binning 512
channels of the discriminator output into 256 spectrum channels. A value of two is a
4::1 compression, binning all 1024 channels of the discriminator output into 256
spectrum channels. Default Scale is 1 and should not normally be changed.