Appl. Radial. Isot. Vol. 43, No. 7, pp. 937-938, 1992 ht. J. Radial. Appl. Instrum. Part A Pergamon Press Ltd. Printed in Great Britain 0883-2889/92 $5.00 + 0.00
Measurement of Radon/Thoron and Its Daughter Nuclides in Room Air RAFEAH SUPPIAN, S. VEGANDRAJ and S. KANDAIYA* School of Physics, University of Sains Malaysia, 11800Penang, Malaysia (Received
26 November
1991)
Introduction The general public receives the highest share of its annual average radiation exposure from natural sources. A worldwide significant increase in exposure comes from radium and its decay products. Prime sources for radon in the environment and in houses are subsoil and building materials. The concentration of radon/thoron decay products in the air is dependent on the concentration of aerosols or dust particles. The presence of radomthoron and its daughter nuclides can be detected by pumping air through a membrane (Thomsen, 1982; Lamb, 1989). The concentration of radionuclides can then be determined using an alpha (x) counter. In our biophysics laboratory, among samples kept in plastic bags are stored in Room I (Fig. 1). Among is a general term to denote byproducts obtained when tintailings are processed into tin ores. The byproducts are heavy minerals such as monazite, zircon and struverite, which contain both the uranium-238 and thorium-232 radioactive series (Hu and Kandaiya, 1985). Radon/thoron gas and its radionuclides in the air were analysed in the various rooms in the biophysics laboratory. The vacuum pump was used to collect the air samples on soft tissue paper.
for 3, 5, 10, 15, 20, 25 and 30 min, and counted on the alpha scintillation counter for 2min. The counts were corrected for background counts. Figure 2 shows that the relationship between counts and running time is linear. The sampling method is then used to compare the radionuclide air concentration in the various rooms in the laboratory (Fig. I) for a pumping time of 15 min. The air flow meter showed that the sucking rate of the vacuum cleaner was 0.68 m3/min. With the counting efficiency of the alpha counter from the standard americium source known to be 0.58, the radionuclide concentration can then be determined. Table 1 shows the radionuclide concentrations in air in the various rooms. Room 6, which is located in the basement, has the highest radionuclide concentration whilst Room 7, which is the corridor outside the biophysics laboratory, has the lowest concentration. The decay of radonithoron daughter nuclides was studied by monitoring the radiation from the tissue over a period of a few hours. The decay curve obtained showed that the sample had a half-life of less than 45 min. This could be a compound effect of the half-lives of the daughter nuclides in the radon/thoron decay. The diurnal variation of the radionuclides in two rooms, i.e. Room 1 and Room 6, were analysed. The windows in the laboratory are kept closed as the laboratory is cooled by
r----I
4
2
1
-
’
1
5 1 7
T
1
t
I
2 - Neutron
3 - Ge(Li) 4 - Store
for staff
II
I
1 - Room with low activity includes amang samples source
sources
which
room
room
activity
6 - Neutron
generator
7 - Corridor
outside
measurement
placed the
in the
biophysics
room
basement laboratory
Fig. 1. Plan of Biophysics Laboratory. 937
also
room
5 - Environmental
*Author for correspondence.
Steps
---
3
Room technical
The running time of the vacuum cleaner affects the concentration of radionuclides collected on the tissues, Samples were taken in succession and at the same location
f ‘-i=
_---
Experimental
Results and Discussion
I
6
--
I
A number of initial trials showed that the soft tissues was ,a good membrane. The data obtained were reproducible. The membrane was placed across the collection pipe of a ‘vacuum cleaner and air from the room was sucked through mt.The contaminated dust particles that adhered to the tissue #werethen counted on an alpha scintillation counter. The ,fetection efficiency of the counter was calibrated with a tandard surface-plated americium-241 source. The rate of air sucked into the pump was measured with an air-flow meter. The concentration of radionuclides in the ;tir in the various rooms was determined. The diurnal 1ariation in the radionuclides in two specific rooms was also analysed.
7
938
Technical
Note
1200 1000
-
:_
800
-
s; z
600
-
2 0
400
-
200
-
Table 2. Diurnal
variation Activity
v)
0
I
I
I
I
I
I
I
I
4
0
12
16
20
24
26
32
Pumping
Fig. 2. Counts
time
(min)
vs pumping
time.
a central air-conditioning system. However, this system is switched off at 4 p.m. and on at 9 a.m. The data obtained are shown in Table 2. A dramatic decrease in counts was observed when the rooms were ventilated, i.e. when the air-conditioning system Table
I. Radionuclide concentration air in the various locations
ROOlll
Activity
(Bqim?)
I
I .62
2 3 4 5 6 1
1.41 0.99 I .x9 I .04 5.55 0.26
in
in two locations (Bq@)
Room
Time: 9.00 am.
12.00 p.m.
2.00 p.m.
4.00 pm.
I 6
2.23 6.78
I.17 5.75
1.14 5.21
0.96 4.46
was switched on. However, Room 6, which is located in the basement, has poorer ventilation than Room 1, which is located on the ground floor. Since Room 6 is in the basement, radon from the soil will diffuse not only from the floor but also from the four walls. The pumping system with an alpha counter is a simple system for analysing radon/thoron and its daughter nuelides. These diurnal variations have to be recognised when assessing human exposure.
Summary Pumping air through a soft tissue which acts as a membrane is a relatively easy and quick method to collect and measure radomthoron and its daughter nuclides in air. Analysis of the activity of the radionuclides can be calculated using an alpha counter which has been calibrated. In this method the activity of radon/thoron cannot be separated from the activity of radionuclides already present in the aerosol or dust particles.
References Hu S. J. and Kandaiya S. (1985) Health Phys. 49, 1003. Lamb N. (1989) Phys. Educ. 24, 175. Thomson P. (1982) Hong Kong Sci. Teach. J. 10, 106 (1982).
Measurement of Radon/Thoron and Its Daughter Nuclides in Room Air RAFEAH SUPPIAN, S. VEGANDRAJ and S. KANDAIYA* School of Physics, University of Sains Malaysia, 11800Penang, Malaysia (Received
26 November
1991)
Introduction The general public receives the highest share of its annual average radiation exposure from natural sources. A worldwide significant increase in exposure comes from radium and its decay products. Prime sources for radon in the environment and in houses are subsoil and building materials. The concentration of radon/thoron decay products in the air is dependent on the concentration of aerosols or dust particles. The presence of radomthoron and its daughter nuclides can be detected by pumping air through a membrane (Thomsen, 1982; Lamb, 1989). The concentration of radionuclides can then be determined using an alpha (x) counter. In our biophysics laboratory, among samples kept in plastic bags are stored in Room I (Fig. 1). Among is a general term to denote byproducts obtained when tintailings are processed into tin ores. The byproducts are heavy minerals such as monazite, zircon and struverite, which contain both the uranium-238 and thorium-232 radioactive series (Hu and Kandaiya, 1985). Radon/thoron gas and its radionuclides in the air were analysed in the various rooms in the biophysics laboratory. The vacuum pump was used to collect the air samples on soft tissue paper.
for 3, 5, 10, 15, 20, 25 and 30 min, and counted on the alpha scintillation counter for 2min. The counts were corrected for background counts. Figure 2 shows that the relationship between counts and running time is linear. The sampling method is then used to compare the radionuclide air concentration in the various rooms in the laboratory (Fig. I) for a pumping time of 15 min. The air flow meter showed that the sucking rate of the vacuum cleaner was 0.68 m3/min. With the counting efficiency of the alpha counter from the standard americium source known to be 0.58, the radionuclide concentration can then be determined. Table 1 shows the radionuclide concentrations in air in the various rooms. Room 6, which is located in the basement, has the highest radionuclide concentration whilst Room 7, which is the corridor outside the biophysics laboratory, has the lowest concentration. The decay of radonithoron daughter nuclides was studied by monitoring the radiation from the tissue over a period of a few hours. The decay curve obtained showed that the sample had a half-life of less than 45 min. This could be a compound effect of the half-lives of the daughter nuclides in the radon/thoron decay. The diurnal variation of the radionuclides in two rooms, i.e. Room 1 and Room 6, were analysed. The windows in the laboratory are kept closed as the laboratory is cooled by
r----I
4
2
1
-
’
1
5 1 7
T
1
t
I
2 - Neutron
3 - Ge(Li) 4 - Store
for staff
II
I
1 - Room with low activity includes amang samples source
sources
which
room
room
activity
6 - Neutron
generator
7 - Corridor
outside
measurement
placed the
in the
biophysics
room
basement laboratory
Fig. 1. Plan of Biophysics Laboratory. 937
also
room
5 - Environmental
*Author for correspondence.
Steps
---
3
Room technical
The running time of the vacuum cleaner affects the concentration of radionuclides collected on the tissues, Samples were taken in succession and at the same location
f ‘-i=
_---
Experimental
Results and Discussion
I
6
--
I
A number of initial trials showed that the soft tissues was ,a good membrane. The data obtained were reproducible. The membrane was placed across the collection pipe of a ‘vacuum cleaner and air from the room was sucked through mt.The contaminated dust particles that adhered to the tissue #werethen counted on an alpha scintillation counter. The ,fetection efficiency of the counter was calibrated with a tandard surface-plated americium-241 source. The rate of air sucked into the pump was measured with an air-flow meter. The concentration of radionuclides in the ;tir in the various rooms was determined. The diurnal 1ariation in the radionuclides in two specific rooms was also analysed.
7
938
Technical
Note
1200 1000
-
:_
800
-
s; z
600
-
2 0
400
-
200
-
Table 2. Diurnal
variation Activity
v)
0
I
I
I
I
I
I
I
I
4
0
12
16
20
24
26
32
Pumping
Fig. 2. Counts
time
(min)
vs pumping
time.
a central air-conditioning system. However, this system is switched off at 4 p.m. and on at 9 a.m. The data obtained are shown in Table 2. A dramatic decrease in counts was observed when the rooms were ventilated, i.e. when the air-conditioning system Table
I. Radionuclide concentration air in the various locations
ROOlll
Activity
(Bqim?)
I
I .62
2 3 4 5 6 1
1.41 0.99 I .x9 I .04 5.55 0.26
in
in two locations (Bq@)
Room
Time: 9.00 am.
12.00 p.m.
2.00 p.m.
4.00 pm.
I 6
2.23 6.78
I.17 5.75
1.14 5.21
0.96 4.46
was switched on. However, Room 6, which is located in the basement, has poorer ventilation than Room 1, which is located on the ground floor. Since Room 6 is in the basement, radon from the soil will diffuse not only from the floor but also from the four walls. The pumping system with an alpha counter is a simple system for analysing radon/thoron and its daughter nuelides. These diurnal variations have to be recognised when assessing human exposure.
Summary Pumping air through a soft tissue which acts as a membrane is a relatively easy and quick method to collect and measure radomthoron and its daughter nuclides in air. Analysis of the activity of the radionuclides can be calculated using an alpha counter which has been calibrated. In this method the activity of radon/thoron cannot be separated from the activity of radionuclides already present in the aerosol or dust particles.
References Hu S. J. and Kandaiya S. (1985) Health Phys. 49, 1003. Lamb N. (1989) Phys. Educ. 24, 175. Thomson P. (1982) Hong Kong Sci. Teach. J. 10, 106 (1982).
