Operating Manual

211210
Personal protection equipment
Pendosismeter (PDM)
The PDM consists of a quartz fibre electrometer and a simple optic lens system housed in a
fountain pen type holder, see figure 2-19.
A small charging unit is used to electrically charge the fibre, which can then be viewed
through the lens.
The fibre is set on the zero mark of the calibrated scale as initial setting for the work period.
Any radiation will cause the charge to leak away through its ionising effect and the fibre will
move across the scale. The amount of radiation received can be read off the calibrated scale.
This type of instrument is excellent for personal protection as it is small, inexpensive and
reasonably robust. It can be easily read and records the total amount of radiation received
for the work period with an accuracy of ±10 %.
Thermoluminescent dose meter (TLD badge)
The TLD meter consists of an aluminium plate with circular apertures. Two of these contain
luminescent crystals. Figure 3-19 shows an open TLD-meter and the plate with crystals next
to it. The right side of the
illustration shows the same
meter, now closed. When the
meter is read only one crystal is
used to determine the monthly
dose. The other one is spare
and, if necessary, can be read to
determine the cumulative dose.
The TLD meter is sensitive to X-
and gamma radiation of 30 keV
and higher. The dose measuring
range is large and runs from
0.04 mSv to 100 mSv with an
accuracy of ±5 %.
The instrument measures
60 x 40 x 10 mm and is conve-
nient to wear
19.6 Radiation measurement and recording instruments
From what has been said before, it follows that establishing the presence of ionising radia-
tion and measuring its level is of paramount importance. Since ionising radiation cannot be
detected by the senses, detectors and measuring equipment are used. There are various
instruments with which the radiographer can measure or register radiation.
The most common measuring instruments are:
1. Dose rate meters
2. Scintillation counters
The most common instruments for personal protection are:
3. Pendosismeter (PDM)
4. Thermoluminescent badge (TLD)
5. Film badge
Radiation measuring instruments
Dose rate meters
A portable Geiger-Müller counter of 7 x 15 x 4 cm, see
figure 1-19, is the most commonly used instrument for
measuring dose rate, but the more accurate and more
expensive ionisation chamber is used as radiation
monitor as well. Both instruments measure the electric
current that is produced by ionisation.
The radiation level can be read instantly off a micro-
ampere meter with a μSv/h or mSv/h calibrated scale.
Some radiation monitors give an audible signal when
a pre-set dose is exceeded.
The instruments are used by personnel working with
radioactive material or X-ray equipment, to determine
the safe distance and the dose rate of for instance
10 μSv/h at the safety barrier. A GM-counter has a
measuring range from 1 μSv/h to 2 mSv/h.
Scintillation counter
This is an accurate and multifunctional instrument to measure and analyse radiation.
The incidence of ionising radiation on a Sodium-iodine crystal is converted into weak light
flashes, which are amplified into electric pulses by an integrated photo-multiplier.
By measuring amplitude and number of these electric pulses, energy and intensity (dose
rate) of the radiation can be determined.
These instruments are predominantly used for scientific purposes.
Fig.1-19. Geiger-Müller counter
Fig. 2-19. Pendosis meter
Fig. 3-19. Open TLD meter Closed TLD meter