UltraLo-1800 Alpha Particle Counter
XIA LLC
Page 67
CounterMeasure to process it as a pulse. If that level is low, CounterMeasure will trigger on the noise
inherent in the system, and this will produce quite a few triggers. Fortunately this is very easy to
diagnose, as you can simply check the
A large increase in Noise events is also possible for various other reasons, including loose
connections between high-voltage nodes. This typically only occurs if the counter has been moved or
otherwise vibrated. If you have excess noise events with adequate thresholds, please contact XIA
support at
8.
Non-Alpha Events
As was mentioned previously, mechanical vibrations are capable of causing erroneous events to
appear in measurements (see
for more information on mechanical vibrations). The computed
energy and risetime of those events will sometimes fall within the typical energy and risetime bands
occupied by our various classifications, but most often they won’t. Vibrations are easy to spot because
the traces oscillate wildly and they rarely look like alpha pulses.
Occasionally the counter will see events whose origin is purely electronic (see Figure VII-9). It’s not
entirely clear what causes these events, but static charge buildup on insulators, especially when the
insulator is the sample, is a prime suspect (see
). These events are, in our experience, never
categorized as alphas, but usually as Negative Charges or Noises. If you’re seeing a very large number of
them and you’re not measuring an insulator, contact XIA at
9.
Large Drop in Emissivity During a Run
The most likely cause for a large drop in emissivity over the course of run is contamination from
for more information on how to tell if radon is present on your samples.
Figure VII-9: One type of noise event.