Indian Journal of Pure & Applied Physics
Vol. 44, April 2006, pp. 287-291
Assessment of radon-222 concentrations and exhalation rates of rocks and
building materials
A M El-Arabi, A Abbady, N K Ahmed, R Michel*, A H El-Kamel** & A G E Abbady
Physics Department, Faculty of Science Qena, South Valley University, Egypt
*Institute of the Radiation Protection and Radioecology, Hanover University, Germany
**Physics Department, Faculty of Science, Assiut University, Egypt
Received 14 March 2005; revised 22 November 2005; accepted 31 January 2006
One hundred samples were collected from two regions (Bir El-Sid and Wady El-Gemal ) in the Nile Valley. It contain
various types of igneous and metamorphic rock samples (acidic dykes, intermediate dykes, basic dykes, serpentinite,
metagabbro, menalge). Another set of samples were collected from different regions of Germany. Samples were analyzed
and the concentrations in Bq/kg dry weight of radium were determined by gamma-ray spectrometry using hyper-pure
germanium (HPGe) detector. A direct method is used to measure 222Rn emanated from the samples, which was analyzed in
laboratory using the portable radon monitor Prassi. 222Rn activity concentrations (Bq/m3) were in the range from 36.1± 2 to
96.4 ± 6, 17.8 ± 3 to 73.6 ± 4 and 18.0 ± 2 to 188.1± 15 Bq/m3 for samples collected from Bir Elsid, Wadi El-Gemal and
samples from Germany respectively. The corresponding values of exhalation rates were from 0.0012 to 0.004, 0.005 to
0.015 and 0.007 to 0.0069 Bq/gs for these areas respectively.
Keywords: Radon, Building materials, Exhalation rates
IPC Code: H01J65/08
1 Introduction
In the last ten years, there have been many studies
aimed at detecting a correlation between the incidence
of lung cancer and exposure to radon in dwelling.
Some of these have shown positive correlation, but
many have not1,2 . The radon exhalation properties of
porous materials both naturally occurring like soil and
rocks and man-made, like mining wastes and many
building materials have been investigated8,9. Most of
these studies have been geographical correlation
studies. These involve selecting two or more areas,
some of high and others of low, and average
concentration of radon in dwellings.
Although the basic theory of radon exhalation-or
release of radon from materials-is the same whether
the radon comes from the soil or from a slab of
building material some features of the exhalation
process are usually very different in the two cases. In
the case of exhalation from the soil, one is naturally
limited to measure the exhalation from a very small
part of the exhaling surface although the sample can
be considered to extend indefinitely in the exhalation
direction. If the measurements do not change the
exhalation process scaling up results obtained for one
small area to larger areas is only a question of
homogeneity of the soil as far as radioactivity,
porosity, permeability etc is concerned. Similar
methods have also been applied in the case of
building materials10.
The greatest fraction of the natural radiation
exposure in humans results from inhalation of the
short-lived decay products of radon, which occur in
the free atmosphere and higher concentrations in the
room air of buildings. Radon and its decay products in
air are known carcinogens, and a proportion of indoor
radon comes from building materials.
2 Experimental Details
In the present work, a simple method is used for
the measurement of radon-222 in laboratory. The rock
and building materials samples were analyzed in the
laboratory with the portable radon monitor PRASSI.
This monitor is suitable for radon gas continuous or
grabs sampling measurements with scintillation cell
technique. It consists basically of 1.83 1 cell coated
with zinc sulphide activated with silver [ZnS(Ag)]
coupled to a low-gain-drift photomultiplier. The
sample air is pre-filtered before reaching the
measurement chamber and the sampling flow rate is
electrically regulated to compensate for filter clog-up.
The measurement is performed in a closed loop
circuit as shown in Fig. 1.
INDIAN J PURE & APPL PHYS, VOL 44, APRIL 2006
288
.... (3)
located in the Pan-African basement of Egypt. The
area covers about 96 km2 of crystalline basement
rocks of Egypt. The second area is Wady El-Gemal
located at the Red Sea some 220 km east of Kom
Ombo in the Nile Valley. It contains various types of
rocks, acidic dykes, intermediate dykes, basic dykes,
serpentinite, metagabbro, menalge. Another set of
igneous and metamorphic rock samples was collected
from different regions of Germany.
The PRASSI Mod.5S has a built-in detector
suitable for measurements of radon concentrations
based on a broadly-accepted technique. It consists of a
1.83-liter cell coated with zinc-sulphide activated with
silver ZnS(Ag) coupled with a low-gain-drift
photomultiplier. The cell characteristics provide the
detection of very low radon concentration levels in
the sampled air. The instrument has two operating
modes: continuous and grab sampling. In the
continuous mode, air is allowed to circulate in the
measuring cell at a constant rate, electronically
regulated to 3 L/min. PRASSI measures the counts in
a preset time and at preset intervals, from which the
radon concentration in Bq/m3 or pCi/l is then
determined. A key feature of the PRASSI is the
ability to compensate for the count rate due to radon
daughters adherent to the cell walls. The resulting
count rate is, therefore, strictly proportional to the
concentration of radon gas only. In the grab sampling
mode, air is flushed into the measuring cell for some
minutes, which is then closed by two electric valves.
After a preset time (normally 2.5 h), repeated
counting periods had been performed with the
sampled air. This method confers very high sensitivity
to the system, which turns out to be extremely useful
in particular applications, such as measurements of
radon in solids or rocks performed with suitable
probes or measurements of radon in water with the aid
of suitable de-gassing devices.
where R is the activity concentration in (Bq/m3), c is
the exhalation rate in (Bq /gs), λ is the decay constant
in (= 2.1 × 10-6 s-1) and Vd is the dead-space volume (=
0.00075 m3)
It follows, however from the theory and it has been
documented experimentally9 that c will decrease as N
increases because of back diffusion. The decrease in c
depends upon the properties of the material and upon
the ratio of the sample volume to the dead space
volume.
One hundred samples were collected from two
regions. The first is the Bir El-Sid area, which is
3 Results and Discussion
Fifty-four samples from different rock types were
collected from Wadi El-Gemal area as follows: 16
dyke, 22 ophiolit (Serpintinite, Metagabbro,
Menalge), 10 granite and 6 amphibolites rocks. From
radon concentration, results measured by PRASSI, the
exhalation rates (Bq.g-1s-1) can be calculated for acid,
intermediate and basic dyke rocks from Wadi ElGemal. The minimum value 22±8.1 found in basic
dykes where the maximum value 141.2±2.7 was
found in the acid dykes. The average values of radon222 activity concentration in acid, intermediate and
Fig. 1— Samples measurement set-up
The exhalations of radon from the samples were
determined by studying the growth of radon activity
in the bottle containing the samples of materials.
Let us consider a sample with the volume Vb
enclosed in a container with a deadspace volume Vd .
If the total exhalation rate (number of atoms per unit
time) of the sample is c, the radon concentration
(number of atoms per unit volume) N will grow with
the time t according to the equation
dN / dt = ( c / Vd) - λ N
... (1)
In Eq. (1), it is assumed that radon atoms are
removed from the container only by radioactive
decay. If furthermore, c is assumed to be constant and
independent of N (free exhalation rate). Equation (1)
has the solution:
N = (c / λ Vd) (1 - e -λt )
... (2)
or, expressed as activity (concentration).
R = (c / Vd) ( 1 - e -λt )
ARABI et al.: ASSESSMENT OF RADON-222 CONCENTRATIONS
basic dykes (Bq.m-3) are 75.5 ± 5.4, 349.2± 3.8 and
28.1 ± 5.7, respectively.
In ophiolit rocks it was found that the minimum
value 10.8 ± 3.6 in serpintinite where the maximum
value 59.4 ± 5.4 in the menalge. The average values
of radon-222 activity concentration (Bq.m-3) in
serpintinite, metagabbro and menalge are 21.2±3,
28.2±2.6 and 45.6± 6.2, respectively.
The values of radon concentration level (Bq.m-3)
for granite rocks vary from 39.7±2.8 to 89±5.5 with
average 73.6±4.2. The corresponding values of
amphipolite were 10.8±3.6 to 32.3±3.7 with average
value 17.8±3.1. The highest values of radon
concentration were found in acid and granite rocks,
while the lowest value was found in amphipolite
rocks. The variation of concentration value of radon
and exhalation rates from 17.8±3.1 to 75.5±5.4
(Bq.m-3) and 0.0005 to 0.0027 Bq.g-1s-1 in all samples
rocks in Wadi El-Gemal as presented in Table 1.
The measured concentration and exhalation rate of
radon in rocks collected from Bir El-Sid area are
shown in Table 2. In dyke rocks, the minimum values
24.8±1.4 Bq.m-3, 0.0008 Bq.g-1s-1 found in dolerite,
while the maximum values 87.1±2.1 Bq.m-3, .0032
Bq.g-1s-1are found in felsite with mean values 28.9±2.9,
36.1±2, 63.7±4.3 and 57.3±3.7 (Bq.m-3) for dolerite,
diorite, lamprophyre and felsite respectively. As a
Table 1—Mean activity concentration and exhalation rates of Rn222 in different rocks from Wadi El-Gemal area
Rn-222
Exhalation rate
Type of rock
Bq m
Bq.g-1s-1
granite
serpentinite
meragabbro
menalge
acid dyke
interm. dyke
basic dyke
amphibolite
73.6 ±4.2
21.2 ±3
28.2 ±2.6
45.6 ±6.2
75.5±5.4
49.2±3.8
28.1±5.7
17.8 ±3.1
0.0025
0.0007
0.0009
0.0016
0.0027
0.0018
0.0010
0.0005
-3
Table 2—Mean activity concentration and exhalation rate of Rn222 in different rocks from Bir El-Sid area
289
general trend, the low values are found in dolerite and
the highest values are found in felsite, which are due to
the variation of these radium content. For Fawakher
granitioide, the minimum values 32.8±4.5 Bq.m-3,
0.0015 Bq/gs found in quartz diorite, while the
maximum values 113±18.4 Bq.m-3, 0.0052 Bq.g-1s-1 are
found in granite. The average values of radon-222
activity concentration (Bq.m-3) in quartz diorite,
granodiorite and granite are 33.5±3.7, 72.8±2 and,
96.4±6.6 respectively. In serpentinite the minimum and
maximum values of radon are 25.6±2.2, 50.4±5.8
(Bq.m-3) with mean value of 40.7±3.2.
The average values of radon concentration varied
from 28.9±2.9 to 96.4±6.6 and exhalation rates from
0.0012 to 0.0040. As a general trend, the low values
are found in dolerite and the highest values are found
in granite, which are due to the variation of their
radium content.
The last series of experiments have been carried
out to measure the concentration of radon and
exhalation rates of some type rock and building
materials in Germany, the mean calculated values are
given in Table 3. Minimum concentrations of radon
were 18±1.9 (Bq.m-3) for amphibolites and maximum
value were 188.4±15 (Bq.m-3) for granite group. Also
the minimum exhalation rates of radon were 0.0007
for amphibolites and the maximum values were
00.0069 for granite rocks.
The classifications and coding legends of the
building material samples in Table 4 denote to: G1
(granite type Rosa point from Spain), G2 (Silver
Cloud from North-America), G3 ( Rojo Sevilla from
Venezuela), G4 (Bianco Cistal from Spain), G5
(Indian Stars Galaxy), G6 (Giallo California. from
Brazil ), G7 (Kashmir White from India), RB (Red
Brick from Hannover), Ce (Portland Cement from
Hanover) and GV (Gravel from Hanover). These
samples are used as building materials in Germany.
Table 3—Radon activity concentration and exhalation rate in
rocks from different areas. Germany using PRASSI
Type of rock
Rn-222
Bq m-3
Exhalation rate
Bq.g-1s-1
Type of rock
Rn-222 concentration
Bq m-3
Exhalation Bq.g-1s-1
felsite
lamprophyer
diorite
dolerite
granite
q-diorite
granodiorite
serpintinite
57.3±3.7
63.7±4.3
36.1±2
28.9±2.9
96.4±6.6
33.5±3.7
72.8±2
40.7±3.2
0.0024
0.0030
0.0024
0.0012
0.0040
0.0012
0.0031
0.0017
granite
serpentinite
metagabbro
acid dyke
lamprophyer
diorite
dolerite
amphibolite
188.1±15
25.1±6.2
54.4±2.9
84±8.2
102 ± 8.6
39.8±3.1
40.5±3.2
18±1.9
0.0069
0.0010
0.0018
0.0032
0.0045
0.0014
0.0013
0.0007
INDIAN J PURE & APPL PHYS, VOL 44, APRIL 2006
290
Table 4—Radon-222 activity concentration and exhalation rate
for selected building materials used in Hanover City, Germany
using PRASSI
Sample Type
Rn-222 Bq m-3
Exhalation rate Bq.g-1s-1
G1
G2
G3
G4
G5
G6
G7
RB
Ce
GV
203.7±33.1
175.2±14.2
250±16
238.5±7.9
92.1±8.1
234.8±59.5
212.7±8.3
82.8±4.2
65.4±11.6
56 ±7
0.0007
0.0008
0.0011
0.0006
0.0002
0.0006
0.0006
0.0003
0.0002
0.0002
The values of radon concentration level (Bq.m-3) in
building materials were from minimum value 24±5.2
measured in sand to maximum value 250±16
measured in granite. Except granite rocks, it is evident
that sand as building material has the lowest value of
concentration and exhalation compared with red
bricks, which has the highest values. Building
materials have internal properties that affect the
recoil, transport and exhalation of radon in a complex
manner12. These intrinsic properties of materials
include radium content and its distribution within the
material size of the mineral grains that compose the
material size distribution, configuration of the pore
Fig.2⎯Mean activity concentration (Bq/m3) and exhalation rates (Bq/gs) in the areas under consideration
ARABI et al.: ASSESSMENT OF RADON-222 CONCENTRATIONS
291
Table 5—Average values of radon activity concentration (Bq.m-3) and radon exhalation rates (Bq/gs) for different rock types in the areas
under investigation
Type of rock
granite
serpentinite
metagabbro
acid dyke
lamprophyer
diorite
dolerite
amphibolite
Bir El-Sid
Exh. (Bq.g-1s-1)
Con. (Bq.m-3)
96.4±6.6
0.0040
40.7±3.2
0.0017
……..
…….
57.3±3.7
0.0024
63.7±4.3
0.0030
36.1±2
0.0024
28.9±2.9
0.0012
…….
…….
Wadi El-Gemal
Con. (Bq.m-3)
Exh. (Bq.g-1s-1)
73.6 ±4.2
0.0025
21.2 ±3
0.0007
28.2 ±2.6
0.0009
75.5±5.4
0.0027
49.2±3.8
0.0018
…….
…….
28.1±5.7
0.0010
17.8 ±3.1
0.0005
system and the composition of the fluid within the
pores. The complex interaction of these properties is
that a building material may have a high radium
content and a high porosity but may have a low
exhalation of radon due to a predominance of small
pores and a low probability of radon entrainment
because of the absence of water in the pores.
A summary of the average values of radon
concentration (Bq.m-3) and exhalation (Bq.g-1s-1) from
the rocks of different regions are presented in Table 5.
These values are shown in Fig. 2. Considering the
values of maximum and minimum, it can be noticed
that these are corresponding to maximum and
minimum values of radium content. Comparing
between the results of different regions, it is evident
that the samples of granite and acid dyke rocks show
the maximum values of concentration and exhalation
rate, while the values of basic dykes and amphibolites
are the minimum. A result, which can be accepted
owing to the correlation between Rn-222 and Ra-226.
Information on the rock types and distribution of
lithologic units and other geological features are of
primary importance in radon assessment. Lithological
and mineralogical descriptions not only indicate the
possible uranium content but also aid in the
predication of general radon emanation. For instance
rock types with natural high uranium are most likely
to cause indoor radon problems.
4 Conclusions
The samples of granite and acid dyke rock show
the maximum values of concentration and exhalation
rates of radon. While the minimum values are due to
basic dykes and amphibolites. The radon level
(Bq.m-3) in building materials was from minimum
24±5.2 for sand to maximum value 250±16 for
granite. Except for granite rocks, it is evident that
sand has the lowest values of content compared with
Germany
Con. (Bq.m-3)
Exh. (Bq.g-1s-1)
188.1±15
0.0069
25.1±6.2
0.0010
54.4±2.9
0.0018
84±8.2
0.0032
102 ± 8.6
0.0045
39.8±3.1
0.0014
40.5±3.2
0.0013
18±1.9
0.0007
red bricks. Other factors which could influence
significantly radon indoors are certain natural
building materials, as has been gamma absorbed dose
rates in air and radon concentration13. In future, the
number of measurements in high radon areas will be
increased and detailed studies on radon sources, entry
pathways, etc., will be performed. In this context, the
involvement of laboratories at district level is
particularly important.
References
1
2
3
4
5
6
7
8
9
10
11
12
13
Samet J M, J Nat Cancer Inst, 81 (1989) 745.
Stidlely C A & Samet J M, Health Phys, 65 (3) (1993) 234.
Harley N H & Pasternak B S, Health Phys, 40(1981) 307.
US NCRP Report No. 78, Evaluation of Occupational &
Environmental Exposures to Radon & Radon daughters,
Bethesda, MD (1984).
ICRP publication 50, Lung cancer risk from indoor
exposures to radon daughters, Annals of the ICRP, 17 (1)
(1987).
U S National Research Council Report BEIR IV, Health risks
of radon & other internally deposited alpha-emitters,
(National Academy Press, Washington DC) 1988.
Jacobi W, Proceeding of the International Conf on Radiation
effects & protection (Mito, Ibaraki, Japan), March 18-22,
(1992).
Krisuk E M, Tarasov S I, Shamov N I, Shalak E P &
Gomelsky L G, Research Institute for Radiation Hygiene,
Leningrad (1971).
Jonassen N & J P McLaughlin, The Natural Radiation
Environment III Vol 2, Symp Proc (Edited by Gesell T F &
Lowder W M Houston, TX, 23-28 April 1978, NTIS, CONF780422, pp 1211-1224 (1980).
E Stranden, Health Phys, 37(2(l979)) 242.
W M Lowder, Miller K M, & Porstendörfer J, Radiation
protection, fifth international symposium on the natural
radiation environment commission of the European
communities. rlando: Academic Press (1993).
Colle R, Rubin R J, Knab L I & Hutchinson J m R, National
Bureau of standards technical note 1139 (Washington, DC,
GPO) (1981).
G Campos Venuti, Risica S, A Antonini, Borio R, Gobbi G &
Leogrande M P, Sci Total Environ, 43(1985) 373.