PROCEEDINGS OF THE 7 INTERNATIONAL ... - Fizika

O. Klepalov et al. / Medical Physics in the Baltic States 7 (2009) 83 - 85
2. Personal dosimetry system
The TLDs most commonly used in medical applications
are LiF:Mg,Ti, LiF:Mg,Cu,P and Li2B4O7:Mn, because
of their tissue equivalence. Other TLDs, which are used
because of their high sensitivity, are CaSO4:Dy,
Al2O3:C and CaF2:Mn.
TLDs are available in various forms (e.g. powder, chips,
rods and ribbons).
A basic TLD reader system consists of a planchet for
placing and heating the TLD, a PMT to detect the
thermoluminescence light emission and convert it into
an electrical signal linearly proportional to the detected
photon fluence and an electrometer for recording the
PMT signal as a charge or current. A basic schematic
diagram of a TLD reader is shown in Fig. 1. TLDsystem
which is used at Ignalina NPP is presented in
Fig.2.
Fig.1. TLD reader.
Fig.2. Schematic diagram of the TLD system "RADOS"
in Ignalina NPP.
External exposure of personnel in the reference year
was controlled once a month using thermoluminescent
dosimeters.
84
Control of the externel exposure of personnel working
under hazardous conditions was performed using both:
thermoluminescent and electronic RAD dosimeters at
the same time. The staff was allowed to work in a
controlled area, presuming a dose of 0.2 mSv per day if,
the difference between the collected individual dose and
annual dose limit did not exceed 5.0 mSv after the work.
If the difference between the collected individual dose
and the annual dose level did not exceed 3.0 mSv, the
staff was allowed to work under hazardous conditions,
accounting 0.05 mSv per day.
In 2008 individual dosimetric control was carried out
for 3599 workers. 2320 workers of the NPP staff and
1279 workers from contractor's organization staff (CO).
3. Results
The average individual dose of 0.91 mSv was estimated
to CО + INPP personnel in 2008: 0.96 mSv for NPP
personnel and 0.83 mSv for the personnel from contract
organizations (Fig.3). Maximum individual dose for
INPP staff was 18.09 mSv, maximum dose to sole
worker from the contractor organization was 19.98
mSv.
Data on the number of investigated workers and
received collective doses are provided: for 2008 - in
Table1; for the whole period of operation of Ignalina
NPP –in Fig.4.
1. Table. 2008 Ignalina NPP and contractor's
organization personnel irradiance indicators.