EPD/HB/40521/000
ISSUE 5
EPD TECHNICAL HANDBOOK Page 54
seconds below 1mSv/h. Due to limitations in the processing and memory available,
this time constant cannot be reduced when rapid changes are observed, and the
Hp(0.07)/h dose rate is approximated as the sum of Hp(10)/h and the beta dose rate.
This approximation means that at low gamma energies (below 50 keV) the
Hp(0.07)/h dose rate typically under-responds by up to 25% in comparison to the
Hp(0.07) dose response. However, above 25 keV the dose rate response remains
within ±30% accuracy criteria.
Peak Dose Rate
The highest dose rate calculated by the EPD since this value was last cleared is
termed the peak dose rate. The peak dose rates and the times at which these peak
rates occur are recorded and can be displayed on the LCD or read over the IR
communications link.
Note: Peak dose rate times are stored to 1 second resolution.
4.6.6 Counts
The EPD has four internal counters:
♦ HG: Hard Gamma
♦ SG: Soft Gamma
♦ FB: Full Beta
♦ BC: Beta Compensating
These record the pulses output by each of the radiation detectors.
The EPD calculates the Hp(10) and Hp(0.07) doses by weighted summing (ratios set
during calibration) of the counts received on the four detector channels.
Counts can only be read via the IR communications link, although the least significant
digits are visible on the internal counts display ( section 3.5 ).
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