Two different methods are available to average the statistical
fluctuations in count rates. For searching of hidden radioactivity:
a ratemeter mode, where the average value traces the actual
rates somewhat delayed; for single sample measurements: a
counter/timer function where the counts are added up over a
fixed preset measuring time and divided by the elapsed meas-
uring time after background correction.
Counts per second (cps)
In the simplest case, the LB 134 measures the radiation activity
in counts per second. Since the number of counts detected per
second is subject to statistical fluctuations, e.g. the above-
mentioned ongoing averaging (ratemeter) is carried out so that
the displayed value is matched to the count rate and the dis-
played measured value is less and less subject to statistical
fluctuations within a short measurement time.
Calculated unit of measurement in contamination
measurements
The simultaneous determination of alpha and beta contamina-
tion in two measuring channels is a rather complicated meas-
urement method with this device and therefore has to be treat-
ed in more detail. The results of measurements with other
probes are always obtained in a very similar way, but in most
cases only through one measuring channel, e.g. dose rate
probes, Tritium probe or NaI crystal probe.
So, if the contamination is to be measured in Bq/cm² (i.e. activi-
ties per unit area), the count rate has to be converted to area
activities. The conversion factor is different for each nuclide.
The individual factors are stored in the device. In each case,
therefore, the nuclide or nuclide mixture to be measured must
be set on the device prior to measurement. One can set an al-
pha nuclide for the alpha channel and a nuclide with beta or
gamma radiation for the beta-gamma channel. The radiation
types are distinguished in the course of the measurement. The
measurement is performed at the same time.
This does not mean, however, that the LB 134 is capable of
measuring these nuclides selectively; rather, the monitor treats
contamination (i.e. the measured count rate) as if it were
caused by the respective radionuclide.
The conversion is based on calibration factors determined for
each nuclide. They are not only dependent on
- type of radiation,
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