ELECTRONIC PERSONAL DOSEMETER HANDBOOK
EPD/HB/40521/000
INTRODUCTION
ISSUE 5
Thermo
Page
3
1.3
Brief Functional Description
The EPD is a highly sophisticated device sensitive to gamma and X-rays
(photons), and beta radiation (energetic electrons) in the following energy range:
gamma, X-rays
:
15 keV to 10 MeV
Beta radiation:
250 keV to 1.5 MeV (mean energy)
A full list of radiological characteristics and specifications can be found in Appendix
A to this Handbook.
Radiation detected by the three silicon diode detectors is combined to give the
following dose equivalents (as defined by ICRU Document 47):
(i)
Hp(10) personal dose equivalent at a depth of 10mm of tissue (‘penetrating’,
‘deep’ or ‘whole body’ dose).
(ii) Hp(0.07) personal dose equivalent at a depth of 0.07 mm of tissue
(‘superficial’, ‘shallow’ or ‘skin’ dose).
The EPD calculates both the accumulated dose and the dose rate for Hp(10) and
Hp(0.07). These, and other data, are stored in an internal store (EEPROM) within
the EPD. A button in the EPD case allows the user to retrieve this data from store,
select a range of displays, acknowledge alarms and perform user control
functions. Data is displayed to the user on a LCD display on the top of the EPD
(see Figure 2.1). To minimise the loss of data from battery or other failure, data is
saved to secure memory within the EPD every 15 minutes.
Data is written to and read from the EPD via an integral infra-red communications
interface. The Thermo supplied
EasyEPD2
program reads and writes data to the
EPD via the Infra-red communications link and displays the data in a PC window.
Thermo also produces a range of Access Control Systems for use with the EPD.
Dose is accumulated separately in the EPD in three stores:
Dose
,
Total Dose
and
ADS Dose
. The use of several stores allows dose to be recorded over differing
periods, for example the
Dose
store may be used for each job or task performed
(and reset after each ), whilst the
Total Dose
records the total or aggregate dose
from all the jobs or tasks performed.
ADS Dose
is a password-protected dose
store intended for ‘legal dosimetry’ applications. Note that audible alarms are given
if either the accumulated dose or dose rates exceed programmable threshold
levels. Dose alarms are raised against the
Dose
store only.
The EPD is a sealed unit and is splash-proof. The unit will withstand short periods
of immersion in water but is not designed for prolonged immersion under pressure.
General maintenance is confined to:
