UltraLo-1800 Alpha Particle Counter
XIA LLC
Page 63
collected. In that case it will display the error shown in Figure VII-4b. For more information on debugging
large amounts of noise, see
3.
Noise on Traces
The most common cause of traces with excess noise on them (see Figure VII-6) is electrical noise.
This can come from a variety of sources, but a few are more common than others. One potential source
is a noisy ground connection, which can happen if the ground connection to the UltraLo is shared with
other large machinery, especially large electrical switches. It is very important to make sure that the
UltraLo is connected to a quiet ground. If you start seeing noise suddenly, a change in the ground
environment may have occurred. Try a different outlet and consult your facilities managers to see if
something has changed in the electrical system.
There is also a possibility that noise can be generated internally. If the counter has been moved
recently, connections may have loosened. If you suspect this is the case, contact XIA at
and we will assist you with debugging.
4.
Excessively High Sample Emissivity
If a sample has a higher emissivity than you expected, there are a few things to check. First, look at
the emissivity versus time plot, if there’s a large decrease throughout the run it’s possible you had radon
contamination (see
). In that case, measure the sample again and the measurement should be
accurate. If there’s no transient activity, check the analysis panel to see if there’s an excess number of
events. If there is, see
for more troubleshooting tips. If everything about the run looks
normal but its emissivity is higher than expected, it’s likely that the sample is simply more radioactive
than expected.
5.
No Alphas
If no alphas show up during a run, but there are other events, there are a few different things that
could be happening.
a)
Moisture
The most likely reason for not seeing any alphas while other events are occurring is that the
moisture in the counter is too high. Water atoms in otherwise pure gas have the effect of increasing the
drift velocity of electrons. This reduces the measured risetime and energy of alpha events, causing them
to be misclassified (the effect is most apparent with risetime, and the events with low risetimes are
Figure VII-6: Noise trace.
