The statistics of the measurement are very important to the
determination of changes in dose rate. Basically, any radiation
measurement has statistical variation associated with the
measurement, due to the random nature of the gamma photons
being measured. The more noise in the measurement, the longer one
must average the signal for a given confidence level.
To illustrate this concept, Figure 9 shows data taken from the HPIC
and a cylindrical GM counter. The “calibration” of each of these
detectors may be the same, but the amount of time required to
achieve a given statistical accuracy is quite different.
In this example, the field increased from 8 uR/h to 15 uR/h, but with
the GM output, it is much less clear what actually happened during
this period.
Figure 9 Statistical Response
One of the strengths of the HPIC is the angular response to incident
photons. This is due to the spherical design of the detector as
compared with cylindrical detectors that do not have 4 symmetry.
The directional characteristics are primarily due to the detector, but
are also affected by the packaging and internal components of the
sensor. Refer to the datasheet for specifications.
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