Dosimetry/Poster presentation
Havlik, Ernst; et al.
High dose values due to contaminated badges
High dose values due to contaminated badges
Havlik, Ernst1; Copty Atallah2
1)
Center for Medical Physics and Biomedical Engineering,
Medical University of Vienna, AUSTRIA
2)
Magistrate Division 39 – Testing Monitoring and Certification Body of the City of Vienna
PTPA – Laboratory for Radiation Protection, Vienna, AUSTRIA
Abstract
In some cases extraordinary high monthly radiation doses have been determined by the
PTPA for radiation workers of the Department of Nuclear Medicine of the General
Hospital Vienna. These values only could be explained to be caused by contaminations
of the cover of the dosimeters (badges). These incidents were the motive for the
presented study, with the aim to find out the amount of radioactivity sufficient to
produce a monthly dose of 1.67 mSv, derived from the maximum permissible annual
dose (20 mSv).
For this reason 50 badges (UD-802A) have been contaminated systematically with
calibrated radioactive solutions, using a 10µL-pipette. The drops have been placed on
the resin cover above one of the four TL phosphors respectively in order to consider
different spots of possible contaminations. The badges have been shielded by lead to
avoid irradiating each other. They were stored for one month at most and evaluated
afterwards. The procedure was performed with the nuclides F-18, P-32, Tc-99m, In-
111, I-123, I-125 and I-131. In order to consider different times of contamination the
results of the measurements were converted for 2, 14 and 30 days respectively before
the evaluations.
As a result just low amounts of radioactivity are causing relative high doses. Due to the
radionuclide and – for nuclides of longer half lives in addition due to the moment when
a contamination occurred – the values differ significantly. Our study shows, that
possible contaminations of the badges can be considered to be the reason for
conspicuous high evaluated doses.
Introduction
In some cases extraordinary high monthly radiation doses have been determined by the
PTPA for radiation workers of the Department of Nuclear Medicine of the General
Hospital of Vienna. These values only could be explained to be caused by
contaminations of the cover of the dosimeters (badges). The incidents were the motive
for the presented study, with the aim to find out the amount of radioactivity sufficient to
produce a monthly dose of 1.67 mSv, derived from the maximum permissible annual
dose (20 mSv) [1].
Proceedings of Third European IRPA Congress 2010 June 14−18, Helsinki, Finland
1
Dosimetry/Poster presentation
Havlik, Ernst; et al.
High dose values due to contaminated badges
Material and Method
Thermoluminescence dosimeters (TL-badges; Panasonic UD-802A) were contaminated
systematically with calibrated radioactive solutions, using a 10µL-pipette. The drops
were placed on the resin cover above one of the four TL phosphors respectively, in
order to consider different spots of possible contaminations. The procedure was
performed altogether more than 300 times, with the nuclides F-18, P-32, Tc-99m, In-
111, I-123, I-125 and I-131.
The contaminated dosimeters were covered with 2mm lead to avoid exposure towards
each other. In the case of P-32 a cylindrical shielding of 8mm acryl with an additional
cover of 1mm lead was used. The dosimeters thereafter were stored for a month at
most, at a place with low radiation background before they were evaluated by the
PTPA.
Fig. 1: Cross section through a TL-dosimeter, with resin jacket
Fig. 2: TL-dosimeter Panasonic UD-802A [2]
Proceedings of Third European IRPA Congress 2010 June 14−18, Helsinki, Finland
2
Dosimetry/Poster presentation
Havlik, Ernst; et al.
High dose values due to contaminated badges
Fig. 3: Efficiancy curves of the four TL phosphors between the diverse filters [2]
Results
The results are summarized in the tables 1 to 7. They are corrected for radiation
background and are normalized to an activity of 1 MBq (column 2). In order to consider
different times of contamination before the time of evaluation the results of the
measurements have been converted for 2, 14 and 30 days. The activities, sufficient to
cause 1.67 mSv (A1.67) are listed in column 3 to 5 of the tables. The respective
irradiation times are indicated in parentheses.
Meaning of the terms in the first column of the tables:
“phosphor #1”: contamination over the first Phosphor; mean of 7 values
(just as for “Phosphor #2” to “Phosphor #4”)
“Ph. 1-4, mean”: mean of the values “Phosphor #1” to “Phosphor #4”
“Ph. 1-4, uniform: uniform distributed contamination over the four Phosphors (singular
values)
Proceedings of Third European IRPA Congress 2010 June 14−18, Helsinki, Finland
3
Dosimetry/Poster presentation
Havlik, Ernst; et al.
High dose values due to contaminated badges
Table 1: Contaminations with fluorine-18
F-18 mSv/MBq (3d) A1.67 (2d) A1.67 (14d) A1.67 (30d)
Phosphor #1 763.3 2.10 2.10 2.10
Phosphor #2 20.1 79.50 79.50 79.50
Phosphor #3 96.9 16.51 16.51 16.51
Phosphor #4 10.3 155.11 155.11 155.11
Ph. 1-4, mean 222.7 7.19 7.19 7.19
Ph. 1-4, uniform 56.1 28.50 28.50 28.50
Table 2: Contaminations with phosphorus-32
P-32 mSv/MBq (22d) A1.67 (2d) A1.67 (14d) A1.67 (30d)
Phosphor #1 20372.8 0.56 0.10 0.07
Phosphor #2 39510.7 0.29 0.05 0.03
Phosphor #3 1307.2 8.68 1.63 1.05
Phosphor #4 30.7 369.75 69.42 44.60
Ph. 1-4, mean 15305.3 0.74 0.14 0.09
Ph. 1-4, uniform 10786.6 1.05 0.20 0.13
Table 3: Contaminations with technetium-99m
Tc-99m mSv/MBq (14d) A1.67 (2d) A1.67 (14d) A1.67 (30d)
Phosphor #1 30.8 52.2 52.0 52.0
Phosphor #2 23.9 67.3 67.0 67.0
Phosphor #3 5.1 313.5 312.2 312.2
Phosphor #4 1.8 890.4 886.8 886.8
Ph. 1-4, mean 15.4 104.3 103.9 103.9
Ph. 1-4, uniform 10.0 160.3 159.7 159.7
Table 4: Contaminations with indium-111
In-111 mSv/MBq (28d) A1.67 (2d) A1.67 (14d) A1.67 (30d)
Phosphor #1 173.5 23.64 9.50 9.22
Phosphor #2 425.8 9.63 3.87 3.76
Phosphor #3 1477.0 2.78 1.12 1.08
Phosphor #4 313.5 13.08 5.26 5.10
Ph. 1-4, mean 597.5 6.87 2.76 2.68
Ph. 1-4, uniform 769.8 5.33 2.14 2.08
Proceedings of Third European IRPA Congress 2010 June 14−18, Helsinki, Finland
4
Dosimetry/Poster presentation
Havlik, Ernst; et al.
High dose values due to contaminated badges
Table 5: Contaminations with iodine-123
I-123 mSv/MBq (11d) A1.67 (2d) A1.67 (14d) A1.67 (30d)
Phosphor #1 13.5 129.09 118.76 118.76
Phosphor #2 50.6 34.39 31.64 31.64
Phosphor #3 296.9 5.86 5.39 5.39
Phosphor #4 9.4 185.04 170.23 170.23
Ph. 1-4, mean 92.6 18.79 17.28 17.28
Ph. 1-4, uniform 79.2 21.95 20.20 20.20
Table 6: Contaminations with iodine-125
I-125 mSv/MBq (45d) A1.67 (2d) A1.67 (14d) A1.67 (30d)
Phosphor #1 1087.5 26.13 4.00 2.04
Phosphor #2 3573.6 7.95 1.22 0.62
Phosphor #3 12962.5 2.19 0.34 0.17
Phosphor #4 2740.3 10.37 1.59 0.81
Ph. 1-4, mean 5091.0 5.58 0.85 0.44
Ph. 1-4, uniform 6740.3 4.22 0.64 0.33
Table 7: Contaminations with iodine-131
I-131 mSv/MBq (11.7d) A1.67 (2d) A1.67 (14d) A1.67 (30d)
Phosphor #1 5652.7 1.14 0.26 0.19
Phosphor #2 356.0 18.04 4.07 3.09
Phosphor #3 527.7 12.17 2.75 2.08
Phosphor #4 186.0 34.52 7.80 5.91
Ph. 1-4, mean 1680.6 3.82 0.86 0.65
Ph. 1-4, uniform 3652.7 1.76 0.40 0.30
Proceedings of Third European IRPA Congress 2010 June 14−18, Helsinki, Finland
5
Dosimetry/Poster presentation
Havlik, Ernst; et al.
High dose values due to contaminated badges
1000
100
10
A1.67 in kBq
0,1
0,01
F-18 P-32 Tc-99m In-111 I-123 I-125 I-131
2d 14d 30d
Fig. 4: A1.67 = “Contamination-activity”, sufficient to cause 1.67 mSv
the days represent the time between contamination and evaluation
Discussion
Just low amounts of radioactivity are causing relative high doses. Contaminations with
less than 1 kBq of the nuclides P-32, I-125 or I-131 are sufficient to exceed the
maximum permissible monthly dose. Compared to these nuclides, about 100 kBq of Tc-
99m are necessary to reach this dose.
For nuclides with longer half-lives (P-32, I-125, I-131) the values differ significantly,
depending on the moment of contamination. As expected this does not apply to nuclides
with short half-lives (F-18, Tc-99m, I-123).
The evaluated doses depend on the radiation energy, on the half-life of the radionuclide
and consequently on the cumulated activity à (number of decays during the irradiation
time). For example à for an irradiation time of 14 days for P-32 is about hundred times
higher than that for F-18. Due to the position of the contamination on the dosimeter the
doses differ from 1:8.5 (In-111) to 1:1.300 (P-32). The mean values “Ph. 1-4, mean”,
written in bold letters, are the most evident results. In most cases they are similar to the
values “Ph. uniform”.
Proceedings of Third European IRPA Congress 2010 June 14−18, Helsinki, Finland
6
Dosimetry/Poster presentation
Havlik, Ernst; et al.
High dose values due to contaminated badges
The doses for P-32 seem to be surprisingly high, but are explainable with the relative
long half-life and with the fact, that the Phosphors #1 und #2 are within the range of the
beta radiation and that adjacent phosphors can be reached by the slanting rays.
Furthermore, the results are due to the evaluation algorithm for the TL-dosimeters,
generally intended for uniform external irradiation rather than for contaminations.
Conclusion
Our study shows, that contaminations of personal dosimeters with low amounts of
radioactivity should be considered to be the reason for conspicuous high evaluated
doses.
References
[1] Allgemeine Strahlenschutzverordnung, BGBl II 191/2006, Austria
[2] Technical information, Matsushita Electric Trading Co., Ltd., Osaka, Japan
Proceedings of Third European IRPA Congress 2010 June 14−18, Helsinki, Finland
