Proceedings of the 2003 International Radon Symposium - Volume I1
American Association of Radon Scientists and Technologists, Inc.
October 5 - 8,2003
MEASUREMENT OF RADON EXHALATION RATE FROM INDIAN GRANITE
TILES
Sundar, S. Bala; Ajoy, K.C; Dhanasekaran, A., Gajendiran, V & Santhanam, R.

S. Bala Sundar. K.C. Aiov, A. Dhanasekaran. V. Gaiendiran, and R. Santhanam
Radiation Safety Section, Radiological Safety Division,
Indira Gandhi Centre for Atomic Research, Kalpakkam-603 102, Tamil Nadu, India.

ABSTRACT
Measurement of radon exhalation rate from different varieties of granite tiles
quarried from various parts of India has been carried out. Seventeen varieties of widely
exported granite tiles of dimensions 5 x 5 x 2.5 cm have been tested. Five samples were
received for each variety. The samples were exposed for 24 hours in a leak tight mild
steel chamber. Gas samples were then collected using Lucas cell and counted for alpha
activity to evaluate, using standard procedure, the concentration of radon from which,
radon exhalation rate was estimated. Powder samples of the tiles were subjected to
gamma spectral analysis. The results obtained are presented and discussed.
Key words : radon, granite, Lucas cell
Corresponding author: S.Bala Sundar email : sbs^?.iecar.ernet.in

INTRODUCTION

Human beings have always been exposed to ionizing radiation from various
natural sources of radiation and one of the major routes of internal exposures is through
inhalation of radioactivity present in the atmosphere. The three primordial radionuclides,
viz, ^K, ^U and 2 3 2 ~ hthat are present in the building materials in varying
concentrations cause both internal and external exposures to the residents. External
238"
exposure is caused by the gamma radiation from '*OK and the daughter products of
and ^ ~ h . It is known that as a result of inhalation of ^ ~ n ,a daughter product of decay
chain of ^u, and its daughter products, the equivalent dose to the entire lung is 20 %
and 45 % higher than the equivalent dose in other tissues.

Proceedings of the 2003 International Radon Symposium - Volume I1
American Association of Radon Scientists and Technologists, Inc.
October 5 - 8,2003
Soil, natural gas, water, construction materials are some of the sources of radon.
From the epidemiological study made on the mortality rate among uranium and nonuranium miners, the correlation between cumulative exposure to the short-lived radon
daughters and the excess incidence of lung cancer has vividly demonstrated the existence
of a positive relation (Ahemed,J.U.,1992). For this reason, an assessment of radon,
exhaling from building materials assumes significance.
Several studies have been undertaken to evaluate the radon exhalation rate from
building materials (Maged and Borhem, 1997; Abu-Jarad et al 1980). The Austrian
Standard ONORM S 5200 has proposed that a type of building material is considered
acceptable if in a room the annual effective dose does not exceed 2.5 mSv (Steger.F et
al. 1999).
Granite is a form of igneous rock, which is composed primarily of Quartz,
Alkalie, and Felspar. India stands third in export of granite stone and first in granite stone
production. In this paper, the results of radon exhalation measurements of different
varieties of granites mined in southern parts of India are presented. These results are of
general interest since granites are globally used as building, ornamental and monumental
materials especially due to its elegant look, durability and scratch resistant properties.
MATERIALS AND METHODS

Seventeen varieties of granite tile samples of dimensions 5 x 5 x 2.5 cm each
weighing about 120 - 150 g were collected. Five samples were received for each variety.
Of these, two samples were crushed and sieved through one mm sieve and preserved for
gamma spectral analysis and remaining three tiles were used for exhalation rate
measurements.
(I) Radon exhalation measurements:

Lucas cells (Scintillation cells) were used for the estimation of radon exhalation
rate (RER) from these materials (Somalai J. et al, IRPA, Poffijin A. et al, 1983). A
cylindrical shaped of mild-steel container was fabricated for carrying out the
measurement. The container was 10 cm in diameter with an internal volume 750 cc.
Nozzles fitted with valves were provided for collecting samples with the Lucas cells.
The back diffusion process and leak rate , which hamper the exhalation
measurement results, are significant for the sampling time more than 30 hours (Stranden,
1983). Hence, the residence time of the sample in the container was restricted to about 24

Proceedings of the 2003 International Radon Symposium - Volume I1
American Association of Radon Scientists and Technologists, Inc.
October 5 - 8,2003
hours, to minimize back diffusion. The ratio of volumes of the container and sample was
more than 10, which further reduced the probability of back diffusion (Hafez.A.F, 2001).
In order to establish the leak rate of the container, a separate study was carried out. The
chambers were pressurized upto 1.2 kg/cm2 and sealed. The reduction in pressure was
continuously monitored for about a month. A graph was plotted with the pressure against
time (Fig 1). It was observed that the leak rate was 0.5% by volume per day.

The samples were kept in the containers and sealed. After allowing a growth time
of 24 hours, gas samples were collected from the container in Lucas cell of volume 150
ml. After a delay of three hours to allow radon gas to attain equilibrium with its
daughters, the Lucas cells were counted using a PM tube assembly. The efficiency of the
counting system used in the study was 70%. From the counts, the concentration of radon
gas collected in the Lucas cell was estimated using the following equation (Jha, et al,

200 1 ):

cy.

Q

=

......................
3EV e'" ( 1- e'?lT)

Where,

Q is the radon concentration (Bq m"3)
C is the net counts in T seconds

A is the decay constant of radon (s")

(1)

Proceedings of the 2003 International Radon Symposium - Volume I1
American Association of Radon Scientists and Technologists, Inc.
October 5 - 8,2003

E is the efficiency of the counting system (fraction)
V is the volume of the Lucas cell (m3)
t is the counting delay (s)
As stated above, it may be noted that radon is in equilibrium with its daughters; for the
decay of each radon atom there will be simultaneous disintegration of its two daughters
and hence the factor 3 is used in the equation.
From the sample surface area and residence time in the container, radon
exhalation rate was calculated using the equation given below.

Q Vem \
E

-

----------------

(2)

A (1- e^)
Where,
E is the radon exhalation rate (Bq m'2h-')
Q is the concentration of radon (Bq m'3)

Vcm is the effective volume of the container (m3)

1 is the decay constant of radon (h-')
A is the surface area of the sample (m2)
T

is the growth time (h)

The MDA for the exhalation rate for the above experimental conditions was estimated to
be 0.10 Bq mV2h-'.

Proceedings of the 2003 International Radon Symposium - Volume I1
American Association of Radon Scientists and Technologists, Inc.
October 5 - 8,2003

(II) Gamma spectral analysis

-

The crushed samples were homogenized and dried in an oven at 100 1 lo0 C for
about 24 hours. The samples were then filled

in standard 250 ml air tight PVC

containers. The containers were sealed hermetically and externally using a adhesive tape
and kept aside for about 30 days. This will ensure the equilibrium between

*

Ra and its

daughters.

The containers were subjected to gamma ray spectral analysis using 3" x 3" NaI
(TI) detector. The detector is shielded on all the four sides as well as at the top portion by
15-cm thick lead. Aluminum, cadmium and copper sheets in that order (graded lining) are
also provided in between the lead shield and the detector so as to decrease the intensity of
characteristic X-rays emitted by the high atomic number shield materials. 95% of
background reduction is achieved by this arrangement. This system is situated in a
nuclear counting facility, which is constructed using soil with low natural radioactivity.
The system was calibrated using IAEA reference standards similar in geometry as that of
the sample containers.
Each sample was counted for 20000 sec and the natural primordial radionuclides
present in the tiles were identified. For the quantification, the peaks corresponding to

Proceedings of the 2003 International Radon Symposium - Volume I1
American Association of Radon Scientists and Technologists, Inc.
October 5 - 8,2003
1.46 MeV (Â¥"'K)1.76 MeV ('"~i) and 2.61 MeV (""~1)were considered in arriving at
the activity levels of OK,

238",

226

Ra and ^ ~ hrespectively. The activity of each

radionuclide in the sample was determined using the total net counts under the selected
photo peaks after subtracting appropriate background counts and applying appropriate
factors for photo peak efficiency and weight of the sample. The MDA (30) for each
radionuclide was established from the background radiation spectrum for a counting time
of 20000 sec and the values were 8.5, 1 and 13.25 ~~k~~ for ^U ( ^ ~ a ) , ^ ~ hand ^K
respectively.

RESULTS AND DISCUSSION
To estimate the leak rate of the chamber, plot between pressure and
number of days is given Fig. 1. The average volumetric leak rate was calculated using the
formula (V.Barashko et.al, 2002).

Where
Q is average volumetric flow rate in cm3m"

* H is initial and final pressure difference in bar

* B is initial and final atmospheric pressure change during
observation in bar
V is the volume of the chamber in cm3
~t is the time of observation in min
The volumetric leak rate was calculated to be 4.2k0.33 cm3d'l
The radon concentration inside the container varied from 60 to 485 ~ ~ m The
' ~ .
exhalation rate of the tiles varied from 0.24 Â 0.01 to 2.07 Â 0.07 Bq m^h" which are
tabulated in Table I .
Out of seventeen samples 11 were havin ^ ~ hcontent above 1 ~ ~ k ~10" ' ,
samples were having 2 3 8 content
~
above 8.5 Bqkg' ? and all the samples were having '"K.

Proceedings of the 2003 International Radon Symposium - Volume 11
American Association of Radon Scientists and Technologists, Inc.
October 5 - 8,2003
The activity concentration of the primordial radionuclides in the tiles are given table.2
The ^ ~ hconcentration varied from 17± to 212± Bqkg"', 2 3 8 ~ ( 2 2 6 concentration
~a)
~ the
' ' 4 0 concentration
~
varied from 132 Â 5 to
varied from
17 ± to 195±~ ~ k and
2 1 16Â9 ~ ~ k ~ - ' ,
In order to compare the specific activities of the radionuclides, a common index is
required to obtain the sum of activities. The index, which is called the radium equivalent
activity ,for the samples, was calculated using the formula (Beretka and Mathew, 1985).

where, AK,Apa and A n are the activities of Potassium, Radium and Thorium
respectively, in Bq kg"'. This formula is based on the estimation that 370 Bq kg"' of
"'~a, 259 Bq kg" of * " ~ hor 48 10 Bq kg" of "K produce the same gamma dose rate.
The radium equivalent for the tested samples varied from 10 to 563 Bqkgm'.
Fig 2 gives the correlation between radon exhalation rate and uranium content of
the tile. An exponential fitting was done which yielded equation with a correlation
coefficient 0.9469 given below.

E (Bq m'2h" ) = 0.107 * Exp (-0.0 147 * X)

(5)

' 'calculated
.
where X is uranium activity concentration of the sample in ~ ~ k ~The
values using the above equation and the measured values are given in table 3. The
variation between calculated and experimental values of radon exhalation rate may be
attributed to the inadequacy of the number of samples with detectable uranium content
and also to the fact that the porosity and the density of the samples, which influence the
radon exhalation rate, were not normalized for the plot.
CONCLUSION
Out of seventeen samples nine samples were found to have higher thorium
content upto a maximum of 10 times the uranium content. Due to this, estimation of
thoron exhalation rate also assumes importance. Attempts are being made to study the
thoron exhalation too.
Six samples showed radon exhalation rate above detectable level and these values
are in good agreement with the reported values for Indian granite tiles (Mentazul I.
Choudhury, JRNC,1998, Al Jarallah, 2001). There exists a good correlation between the
uranium content of the sample and radon exhalation rate. This implies that there exists a
possibility to use the concentration of 238 u ( ^ R ~ ) as an indicator for the extent of radon
exhalation.

Proceedings of the 2003 International Radon Symposium - Volume I1
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October 5 - 8,2003

REFERENCE
Abu-Jarad F., Frem1in.J.H. and Bull.R.,1980. A study of radon emitted from building
materials using plastic alpha track detectors. Physics of Medical Biology 25, pp.
683-694.
Ahemed.J.U. (1992) Regulatory Approach Toward Controlling Exposure to Radon in
Dwellings, Radiation protection and Dosimetry vol.45, pp 745-750.
Al Jarallah, 2001. Radon exhalation from granites used in Saudi Arabia Journal of
Environmental Research 53, pp 9 1-98.
Barashko.V, Dolinsky.S, Ignatenko.M, K0rytov.A and Procofiev.0, 2002. EMU CSC
systems chamber leak rate measurements, internal report, university of Florida.
Beretka J. and Mathew P.J, 1985. Natural radioactivity of Australian building materials,
industrial wastes and by products. Health Physics 48, pp.87-95,
Erling Stranden, (1.983). Assessment Of The Radiological Impact Of Using Fly Ash In
Cement, Health Physics vol. 44 no.2, pp 145 - 153.
Hafez.A.F, Hussein.A.S. and Rasheed.N.M., 2001. A study of radon and thoron release
from Egyptian building materials using polymeric nuclear track detectors.
Applied Radiation and Isotopes.54, pp 291-298.
Jha.S, Khan A.H, Mishra U.C. (2001), A Study Of The Technologically Modified
Sources Of Radon And Its Environmental Impacts In An Indian U Mineralized
Belt. Journal of Environmental Radioactivity Vol53, pp no. 183 - 197.
Maged.A.F. and Borham.E., 1997. A study of the radon emitted from various building
materials using alpha track detectors. Radiation Measurements 28, pp 61 3-6 17.
Mentazul I. Choudhury,(1998) Concentration Of Radio Nuclides In Building And
Ceramic Materials Of Bungladesh And Evaluation Of Radiation Hazard. Jrnl.
Radioanalytical and Nuclear Chemistry, vol23 1,
Poffijin A., Bourgoignie.R, Marijns.R, Uyttenhove.J, JanssensA and. Jac0bs.R (1984);
Laboratory measurements of radon exhalation and diffusion, Radiation Protection
Dosimetry, vol7, p 77-79.

Proceedings of the 2003 International Radon Symposium - Volume I1
American Association of Radon Scientists and Technologists, Inc.
October 5 - 8,2003
Somalai.J, . Nemeth Cs, Kanyar.B, K0vacs.J; Variations of Radon Emanation of CoalSlags with the Burning Temperature, Proceedings of IRPA 10.
Steger F. And Grun K.(1999),Proceedings of Radon in the Living Environment, Athens,
Greece.

Proceedings of the 2003 International Radon Symposium - Volume I1
American Association of Radon Scientists and Technologists, Inc.
October 5 - 8,2003

0
0

5

10

15

20

25

30

MIMBKR OF DAYS

FIG1 GRAPH SHOWING PRESSURE DECREASE WITH TIME

35

Proceedings of the 2003 International Radon Symposium - Volume I1
American Association of Radon Scientists and Technologists, Inc.
October 5 - 8,2003

ow

50.00

150.00

100.w

200.00

U-238 (Bafkg)

FIG.2. CORRELEATION BETWEEN URANIUM CONTENT AND
EXHALTION RATE OF THE SAMPLES

250.00

Proceedings of the 2003 International Radon Symposium - Volume I1
American Association of Radon Scientists and Technologists, Inc.
October 5 - 8,2003
TABLE 1 RADON EXHALATION RATE (RER) OF GRANITE TILES

SAMPLE CODE

RER (Bq m^h")

S7

€0 0
S8
€0.

S9
<o. 10
S10
0.10
Sll
€0 0
S12
€0 0
S 13
0.10
S14

€0.
S 15
0.10

S 16
€0.
S17
<0.10

Proceedings of the 2003 International Radon Symposium - Volume I1
American Association of Radon Scientists and Technologists, Inc.
October 5 - 8,2003

TABLE 2 NATURAL RADIOACTIVITY CONCENTRATION PRESENT IN THE TILES

SAMPLE
CODE
S1

^ ~ h
238 U ( ^ ~ a )
~ ~ k g ' ~ ~ k g '
74±
195±

4

0

~

~
~
k
989±1

Ra e!,
~ Bqkg
"
377

Proceedings o f the 2003 International Radon Symposium - Volume I I
American Association of Radon Scientists and Technologists, Inc.
October 5 - 8,2003

TABLE 3 COMPARISON OF RADON EXHALATION RATES

SAMPLE
CODE

"8

w226~a)

RER (Bq m-'h")
ERROR

B

'

EXPERIMENTAL CALCULATED

Proceedings of the 2003 International Radon Symposium - Volume I1
American Association of Radon Scientists and Technologists, Inc.
October 5 - 8,2003
INVESTIGATION AND REDUCTION OF PERSONNEL RADON EXPOSURE LEVELS
IN BAVARIAN WATER SUPPLY FACILITIES

M. Trautmannsheimer, S. KOrner

Bavarian Environmental Protection Agency,
D-86 177 Augsburg, Germany

ABSTRACT
Water supply facilities in Bavaria (Germany) were investigated with regard to radon
concentrations in groundwater and indoor air as well as radon exposure to the staff
working in these buildings.
500 water supply facilities were asked to take a groundwater sample and expose several
track-etch detectors in order to obtain the mean room concentration of the main staff
work places. In addition, the personnel had to wear a track-etch detector during the time
they spent in the supply facilities.
About ten percent of the process controllers in the East Bavarian crystalline region are
subjected to an annual effective dose of more than 20 mSv.
The management of supply facilities where process controllers were subjected to very
high annual radon levels were asked to take remedial action. In one specific case, these
measures reduced the annual effective dose of a process controller from 100 mSv to
about 6 mSv.

INTRODUCTION
Exposure to radon is normally the main contributory factor to the annual effective
radiation dose of the population. Apart from the level of radon exposure in housing, there
are some work places where increased exposure can be expected. Especially high radon
activity concentrations have been measured in mines [I], visitor caves [2,3], radon spas
[4,5] and water supply facilities [6-101. Therefore in May 1996, the European
Commission passed the Council Directive 96129lEuratom [I I], laying down the basic
safety standards for the protection of the health of workers and the general public against
the dangers arising from ionizing radiation. The annual recommended upper limit for
natural radiation for a worker is 20 mSv. This basic safety standards concerning radon
exposure at work places are implemented in the revised German radiation protection
regulation [ I 21 became effective in August 2001.
In 1995, the Bavarian State Ministry for State Development and Environmental Affairs
set up a research project to study the level of radon exposure to which the staff of the
Bavarian water supply facilities were subjected. Bavaria is the largest and most southern
state of the 16 states of the Federal Republic of Germany. After various preliminary
investigations a questionnaire was sent to all 2,600 Bavarian water supply facilities.

Proceedings of the 2003 International Radon Symposium - Volume 11
American Association of Radon Scientists and Technologists, Inc.
October 5 - 8,2003
Process controllers, supervisors and cleaning staff were asked to provide information
about the type of facility, the number of buildings, water extraction and ventilation in
their supply facilities. They were also asked to answer questions about their typical work
processes and the length of time spent in the potable water reservoirs and in the water
purification buildings. About 50 percent of the water supply facilities returned the
questionnaire containing data of 1,000 employees and 9,000 buildings. From this data it
was calculated, that approx. 4,500 persons work in about 20,000 buildings for the
Bavarian water supply facilities [13]. These persons stay in the supply buildings for
regular inspections and cleaning of the potable water reservoirs, water purification units
and collecting galleries. The average duration of stay in the water purification for backwashing is about 2 hours per week. Back-washing is a special working process to clean
the filter material of the water purification systems and is normally the major
contributory factor to the length of time spent by the process controller in these work
places. In addition to this regular stay, the elevated reservoirs have to be cleaned
thoroughly about once a year. The cleaning is often done by special staff or external
companies.
Bavaria, which has an area of 70,600 km', can be partitioned into ten main geological
regions according to the geological formations and the main aquifers. Taking into
account the results of the radon soil gas measurements [I41 and the information of the
mean uranium and radium contents in the ground, the ten regions can be classified
according to their "radon potential". The highest potential is assigned to the East
Bavarian region (no. 5) and region no. 10 with its mainly granite substructure (Fig. 1).

RADON MEASUREMENTS METHODS IN WATER SUPPLY FACILITIES
From each region, a total number of more than 500 water supply facilities proportional to
the size of the region was selected for radon (Rn-222) measurements. The processing
plant workers were asked to take a 1 litre ground water sample in a radon tight PET
bottle. For the sampling, a water hose was fixed at a tap of the raw water pipe and pushed
down to the base of the bottle in order to fill the bottle very slowly and without
turbulence. Preliminary experiments revealed that the loss of radon gas during this filling
procedure is negligible [ I 51. The process controllers were advised to fill the bottle
completely in order to avoid leaving an air space. After filling, the sample was
immediately sent to the gamma spectroscopy lab at the
Bavarian Environmental Protection Agency for analysis. To obtain the activity
concentration of Rn-222 for the analysis, the gamma lines of Bi-214 and Pb-214 were
used. Since no sample is measured earlier than one day after sampling, these nuclides are
in virtually radioactive equilibrium with Rn-222 during the measurement and therefore
they should have the same activity as Rn-222. Several track-etch detectors were sent by
mail to the water supply facilities. They were exposed for a period of two weeks in order
to get the mean room concentration of the main working places of the staff. In addition,
the processing plant worker had to wear a personal track-etch detector for two months,
which was fixed to his clothes, during his stay in the supply facilities. From the recorded

Proceedings of the 2003 International Radon Symposium - Volume I1
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measurements, his individual, effective dose was estimated. When not in use, the
personal detector was stored near a reference detector at a place with low radon
concentration. An instruction sheet was enclosed to aid the selection of a suitable storage
place. Sites such as car garages, car boots or well ventilated areas such as rooms with
constantly open windows, office rooms outside the supply facilities and roofed balconies
were recommended. In spite of the fact that track-etch detectors cannot be switched off,
the exposure resulting purely from the stay in the water supply facilities can be calculated
by the exposure of the reference detector and the protocol of the duration of stay. From
the results of these two month measurements the annual dose of the processing plant
worker was estimated. Track-etch detectors were used for measuring the indoor radon
concentration levels and the radon exposure levels of the personnel. These track-etch
detectors, about 3,000 in number, were obtained and evaluated by the GSF - National
Research Centre for Environment and Health, Neuherberg, Germany. These are CR39
type detector foils in a diffusion chamber [16,17]. The system was also successfully
tested for short time exposure measured in minutes. It is insensitive to thoron. The
measuring error (2-sigma standard deviation) is about 25 % and almost unaffected by the
recorded exposure. Much larger errors can occur by the calculation of the personal
exposure of the processing plant workers. In order to keep the error level below 30%, the
average radon concentration at the storage place must be below 200 Bq m'3.
Concentration can be checked by the exposure of the reference detector. About 10% of
the measurements with personal detectors had to be repeated because of poor measuring
precision. In this case, the processing plant worker was advised by telephone how to find
a better storage place.

RESULTS FROM RADON MEASUREMENTS
The results of about 550 measurements of raw water samples from the whole of Bavaria
are shown in Fig. 2. The process controllers were asked to take a raw water sample from
the incoming water in a water purification unit or potable water reservoir. Generally, this
water is a mixture taken from several springs and wells. Due to operational reasons, the
amount of water from the various springs and wells can vary. Therefore, the radon
concentration in the raw water can also show time variations. As expected, region 5
shows an increased average radon concentration in the raw water samples. Due to the
small area of region 10 with its granite substructure, most supply facilities in this region
obtain their water from aquifers outside the area. The raw water concentrations in these
supply facilities are therefore similar to the concentrations in the other non-granite
regions.
Around 1,250 measurements were taken in order to obtain information about the indoor
concentrations in the water supply facilities (Fig. 3). As not every room in the buildings
could be supplied with an track-etch detector, the process controllers were asked to place
the detectors mainly in potable water reservoirs, water purification units and rooms
where staff spent long periods of time. In all regions, there are some rooms with
concentrations higher than 3 kBq m-3 . Taking into account that the normal annual

Proceedings of the 2003 International Radon Symposium - Volume I1
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working time is 2,000 h per year, indoor air concentrations of more than 3 kBq m ' can
lead to an effective dose above the limit of 20 mSv per year. Region no. 5 revealed the
highest concentrations and therefore the median is significantly higher than that of the
other regions. Indoor radon gas concentrations of up to 1200 kBq m ' were observed.
Some higher values in region no. 10 may be caused mainly by radon transported directly
from the air into the ground soil and thus into the collecting galleries of one supply
facility via cracks and holes in the concrete foundations. The main purpose of this
research project was to obtain information about the annual radon exposure levels of the
staff in the Bavarian water supply facilities. About 500 measurements were taken over a
period of 2 months. From these data, a linear estimate of the annual exposures was made.
Under "normal conditions" (equilibrium factor of about 0.4, unattached fraction of about
5 to 10%) an exposure of 2 and 6 MBq h rnv3is equivalent to an effective dose of 6 and
20 mSv, respectively [18], In accordance with the regulations of the Council Directive
96/29/Euratom, continuous supervision of persons with annual exposure levels of
between 6 and 20 mSv is recommended. An effective dose above the limit of 20 mSv per
year is, according to the directive, not allowed. Fig. 4 shows the estimated percentage of
personnel subjected to an effective dose above these limits. In all geological regions,
exposure levels of over 6 mSv per year can occur. About 10% of the staff in the granite
region of East Bavaria (region no. 5), and in the rest of Bavaria about 2% of the staff are
subjected to exposure levels of over 20 mSv per year.

Proceedings of the 2003 International Radon Symposium - Volume II
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October 5 - 8,2003

EFFECTIVE MEANS TO REDUCE STAFF EXPOSURE
Due to very high radon activity concentrations and annual exposure of process controllers
remedial actions were undertaken in an East Bavarian water supply facility
Fichtelgebirge). The radon activity concentration in the round water is about 900 Bq L'
and indoor concentrations of up to 50,000 Bq m"? were measured in the water
purification building. Besides the filter basins, this building contains a laboratory,
workshop, restroom, storage room and a control centre (Fig. 5). Therefore the amount of
time spent by the controller in this building is relatively high and a annual radon
exposure of 110 mSv was estimated. The exposure of the process controller was
measured with personal track-etch detectors changed and evaluated every month. In order
to reduce the radon exposure of the process controlers a ventilation system and a glass
wall between the filter basins and the control centre was installed. The ventilation system
is normally operated at half power. If the process controller has to inspect the filter basin
room, he raises the ventilation power to 100 percent 15 minutes before he enters the
room. These effective means reduced the annual radon exposure of the process controller
to about 6 mSv (Fig. 6). The increase of the exposure in April after the structural
alterations is due to the cleaning and painting of the filter basins. This service and
maintenance has to be performed about every five years.

CONCLUSION
Prediction of the radon exposure levels of the staff without measurements is very difficult
because exposure levels are influenced by 1 .) radon concentration in the untreated ground
(raw) water, 2.) characteristics of the buildings and work processes such as ventilation of
the rooms, fraction of room volume to water surface of the basins, water flow through the
basins, turbulent filling of the basins (cascades), enhanced radon production by special
work processes (back-washing, filling times of the reservoirs), 3.) length of time spent in
the water supply facilities.
In general, the most reliable method to evaluate radon exposure of the staff in a water
supply facility, is to use personal track-etch detectors or electronic devices small enough
for the staff to carry comfortably on their person. The calculation of exposure levels from
the different indoor air concentrations and from the time spent in these areas is very
approximate. Due to frequent and short stays in different buildings, the exact recording of
the time spent in these places is usually too difficult for the personnel to carry out. An
estimate of the time they spend in these areas given by the personnel involved, is also
likely to be inaccurate. In addition, the radon concentration levels while the process
controller is in the building can be different from the measured average concentration
because the ventilation and the radon production rate (special work processes) are
influenced by the process controller.
In all geological regions, exposure levels over 6 mSv per year can occur. In the granite
region in East Bavaria about 10 % of the staff of region no.5 and in the rest of Bavaria

Proceedings of the 2003 International Radon Symposium - Volume I1
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about 2% of the staff of all regions except no. 5 workers are subjected to exposure levels
of over 20 mSv per year.
To reduce the exposure levels, it is very important to provide detailed information for the
water supply facilities, because there are usually simple ways in which to minimise the
time spent in the buildings. Other effective means to reduce the exposure levels of the
staff are optimisation of the ventilation or air-conditioning systems, separation of
frequently used working places from basins or water purification systems and the
avoidance of turbulence whilst filling the basins.
Acknowledgements - This work was supported by the Bavarian State Ministry for State
Development and Environmental Affairs.

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Proceedings of the 2003 International Radon Symposium - Volume I1
American Association of Radon Scientists and Technologists, Inc.
October 5 - 8,2003
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Trautmannsheimer M, Schindlmeier W, Borner K. Radon concentration
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Proceedings of the 2003 International Radon Symposium - Volume I1
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Fig. 1: The ten main geological regions of Bavaria. The regions with the highest
"geogenic radon potential" are region no. 5 and region no. 1 0.
Rock types of the regions: new red sandstone (1); shell limestone, Keuper (2); franconian
Keuper (3); upper Jurassic, Dogger, Cretaceous (4); granite, gneiss (5,lO); ejection
material of the Ries meteorite (6); sediment rocks, molasses (7); young moraine (8);
Trias, Jura, Tertiary (9).

Proceedings of the 2003 International Radon Symposium - Volume 11
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Iaverage

median

region

Fig. 2: Mean radon activity concentration in ground water in the different geological
regions of Bavaria.

Iaverage

median

region

Proceedings of the 2003 International Radon Symposium - Volume I1
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Fig. 3: Mean radon indoor activity concentration in the Bavarian water supply facilities
(averaged over each geological region).

Proceedings of the 2003 International Radon Symposium - Volume I I
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percentage

Ipercentage > 20 mSv1a

percentage > 6 mSv/a and < 20 mSv/a
201

region

Fig. 4: Effective annual dose distribution amongst the Bavarian water supply facility
personnel. This effective dose is from radon exposure during working time in the supply
facilities.

ventilation

9
<^

<^

2
2^

-Ct-

^
<ta
<t^

^

dividing glass

restroom

workshop

I

storage room

Proceedings o f the 2003 International Radon Symposium - Volume I1
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before structural alterations

after structural alterations

mSv

20

I

annual effective dose
ca. I10 mSv

I

annual effective dose
without filter basin cleaning
ca. 6 mSv

cleaning of filter basins

Fig. 5: Ground view of a water purification building of a supply facility in the East
Bavarian region.
Fig. 6: Monthly effective dose of a process controller before and after structural
alterations in the water purification building.