Berthold LB 134, Руководство пользователя

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LB 134 Design and Mode of Operation of the LB134
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1.5 Background measurement
The background, the normal environmental radiation, is meas-
ured in cps. It is automatically subtracted from sample meas-
urements. Gross and raw data values can be displayed on the
screen simultaneously. The background measurement can be
started automatically after switching on the device. The back-
ground should be re-measured every now and then; for sample
measurements requiring a high accuracy, we recommend to
measure the background directly before carrying out the sample
measurement. Since the size of the background and the asso-
ciated measurement time affect the accuracy of a sample
measurement, the background should always be determined
using a long measurement time, e.g. 1 hour or more. The size
of the background itself depends on the detector and the shield-
ing. If you know that radioactive sources are present in the
measurement environment, you should change the location for
the sample measurements and, of course, for the background
measurement.
1.6 Various Averaging Methods
The LB 134 features the following measurement modes:
a)
Search Mode to quickly search for contamination,
doserates or activities. In this measurement mode, the de-
vice is very sensitive to different radiation activities and
shows changes very quickly.
b) The
Ratemeter mode does not react as fast to differences
in activity, but is more accurate. In the ratemeter mode one
can work with a common time constant or the statistical ac-
curacy. In the second case, the device calculates every
second a dynamic time constant from the entered accuracy
and the actual count rate which ensures that the measured
value reaches this accuracy. If count rate jumps occur, this
will not be true directly, but after a certain averaging time,
when the count rate is reasonably stable, the actual accu-
racy will approach the entered value. The measurement
time determines when measured values are stored or
transmitted. The number of cycles indicates how often
measured values are stored. The ratemeter has a dynamic
component that ensures that the displayed value tracks the
real value as quickly as possible if fast activity changes oc-
cur. Since some detectors such as Geiger-Müller counter
tubes may occasionally generate interference pulses out-
side the Gaussian statistics, an additional software burst fil-
ter has been added to avoid unrealistic activity jumps.