All valves close automatically when the detector is lifted off the
bracket; this stops the gas supply and keeps the P10 gas in the
counting chamber.
The operation life after filling or flushing is at least 8 hours with
a loss in efficiency of less than 5 %. See also Figure 7.8 which
shows the efficiency of a counter tube filled with P10 gas over
the course of 3 days.
Efficacy of the P10 flow-through counter tube as a function
of time.
The following diagram shows the efficiency after a counter tube
filling with P10 gas, for alpha and also for beta sources, as a
function of the time. The average loss in efficiency for beta
sources is 0.1% / h. The average loss in efficiency for alpha
sources is 0.05 % / h.
The diagram illustrates that measurements over 8 hours are
easily possible with one counter tube filling with less than 5%
loss in efficiency.
Figure 7.8: Efficiency of a counter tube filled with P10 gas
as a function of time
Commissioning of the alpha-beta detector with P10 gas supply
1. First, unscrew the valve opener (counter-clockwise) from
one of the two valves of the P10 flow-through counter tube.
The valve opener, a screw with a borehole, ensures that no
over- or under-pressure builds up in the detector during
transport which may damage the detector foil. Keep the
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