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Natural radiation exposure due to radon
and thoron indoors in the mining and ore bearing regions of Cameroon: from
measurement, inhalation dose assessment to a national radon plan
SAÏDOU1, Shinji TOKONAMI2, Masahiro HOSODA2
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Nuclear Technology Section, Institute of Geological and Mining Research, Cameroon
Institute of Radiation Emergency Medicine, Hirosaki University, Japan
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The Ninth International Symposium on Naturally Occurring Radioactive Material
23-27 September 2019 - Denver, Colorado, USA
Outline
❖Introduction
❖Material and methods▪RADUET detectors (Rn and Tn)
▪Thoron progeny monitors (TnP)
❖Results▪ Indoor Rn, Tn, TnP and inhalation dose
▪Achievements of CMR9009
❖Conclusion and perspectives
Introduction• Since 2005 several research
studies of natural radiation exposure to the public wereperformed in the following areas:– Uranium bearing region of Poli
– Uranium and thorium bearingregion of Lolodorf
– Gold mining region of East Cameroon
– Bauxite bearing region of South Adamawa
– Oil bearing Bakassi Peninsula
– Yaounde and Douala cities
• Focus on radon indoors since 2012 using Electrets ionization chambers and Raduet detectors from 2014
• Most of the study areas are mining or ore bearing areas.
Material and methods
Metasomatite uranium deposit of Kitongo: 10 000- 25 000 tU
at a grade of 0.05-0.1%
Status: Exploration (UDEPO, 2016)
Material and methods
House built on a high naturalradiation area at Bikoue (Mvengue) Lolodorf (August 2016)
Intrusive uranium deposit of Lolodorf: 1 000-2 500 tU
at a grade of 0.05-0.1%
Status: Exploration (UDEPO, 2016)
Material and methodsStudy area Number of Raduet
detectors deployed
Number of TnP
monitors deployed
Uranium bearing
region of Poli
100 40
Thorium bearing
region of Lolodorf
220 170
Gold mining areas of
Betare Oya
50 50
Douala city 70 70
Total 450 330
Material and methods
Study areas Inhabited areas
Uranium bearing region of Poli Fignole, Gompou, Gode, Poli,
Kitongo
Thorium bearing region of Lolodorf Awanda, Akongo, Ngombas, Bikoue,
Lolodorf, Kribi, Logbatindi, Eseka
Gold mining areas of Betare Oya Betare Oya, Mali
Douala city Douala I, Douala II, Douala III
Detectors collected after 2-3 months and sent back to Hirosaki
University in Japan for analysis.
Material and methods
Radon, thoron and progeny indoors
Material and methods
Microscope method Image-J method
Results
Study area Radionuclide Mean concentration
(Bq.m-3)
Range (Bq.m-3)
Poli 222Rn 82 46-143
220Rn 94 18-238
Lolodorf 222Rn 97 27-937
220Rn 160 6-700
Betare Oya 222Rn 133 88-282
220Rn 92 4-383
Douala 222Rn 139 31-436
220Rn 80 4-246
Rn and Tn concentrations
Results
Study area Rn>100
Bq.m-3 (%)
Tn>100
Bq.m-3 (%)
Rn>300
Bq.m-3 (%)
Tn>300
Bq.m-3 (%)
Poli 20 42 0 0
Lolodorf 47 54 1 10
Betare-Oya 76 25 3 3
Douala city 27 27 0 0
Reference Levels : 100 and 300 Bq.m-3
Results
Reference Level (RL)=100 Bq.m-3
• 43% of houses have Rn > RL
• 37% of houses have Tn > RL
Reference Level (RL)=300 Bq.m-3
• 1% of houses have Rn > RL
• 3.3% of houses have Tn > RL
Results
• When setting a reference level, various national factors such as the distribution of radon, the number of existing homes with high radon concentrations, the arithmetic mean indoor radon level and the prevalence of smoking should be taken into consideration.
• The lower the national reference level, the more the overall population risk from radon exposure would be mitigated.
Results
Study area Mean EETC
(Bq.m-3)
Range
(Bq.m-3)
Mean Equilibrium
Factor
Range
Poli 6.4 4-9 0.08 0.01-0.3
Lolodorf 10.3 0.4-36 0.1 0.01-0.6
Betare Oya 6 0.6-19 0.1 0.01-0.5
Douala city 4.6 1.5-13 0.07 0.02-0.3
Equilibrium Equivalent Thoron Concentrations (EETC)
❑ The world mean value of the Equilibrium Factor for thoron (FTn=EETC/Tn)
given by UNSCEAR is 0.02.
❑ High Equilibrium Factor leads to high corresponding inhalation dose.
ResultsInhalation dose due to radon and thoron
Study area Mean Rn
inhal. dose
(mSv.yr-1)
Range
(mSv.y-1)
Mean Tn
inhal. dose
(mSv.y-1)
Range
(mSv.y-1)
Mean
contribution
of Tn (%)
Range
(%)
Poli 1.5 0.9-2.6 1.8 0.34-6.2 49 12-67
Lolodorf 2 0.53-18.5 2.2 0.08-7.9 53 3-80
Betare Oya 2.5 1.7-5.3 2 0.13-4 31 7-70
Douala city 2.6 0.6-9 1 0.3-2.9 26 7-60
❑ World average value for radon+thoron (UNSCEAR): 1.26 mSv.y-1 (0.2-10)
❑ Uranium bearing region of Poli: 3.3 mSv.y-1 (1.3-8.8)
❑ Uranium and thorium bearing region of Lolodorf: 4.4 mSv.y-1 (0.7-26.5)
❑ RL=300 Bq.m-3 corresponds to, in terms of effective dose, approximately 10
mSv year for radon.
Results
❖The average contribution of thoron to the total
inhalation dose is 40% in the studied areas of
Cameroon.
❖Thus thoron can not be neglected in dose assessment
to avoid biased results in radio-epidemiological
studies.
❖Thus it would be advisable to define reference level
for Tn at the international scale or combine reference
level for radon and thoron
Results1. Saïdou et al. (2014). Indoor radon measurements in the uranium regions of Poli and Lolodorf, Cameroon.
Journal of Environmental Radioactivity 136, 36-40.
2. Saïdou et al. (2015). Natural Radiation Exposure of the Public in the oil-bearing Bakassi Peninsula,
Cameroon. Radioprotection, Vol 50, 35-41.
3. Saïdou et al. (2015). Radon-Thoron discriminative measurements in the high natural radiation areas of
Southwestern Cameroon. Journal of Environmental Radioactivity 150, 242-246.
4. Saïdou et al. Comparative study of natural radiation exposure in three uranium and oil regions of
Cameroon. Radioprotection, DOI: 10.1051/radiopro/2015017
5. Saïdou et al. (2016) Natural Radiation Survey in the uranium and thorium bearing regions of Cameroon.
Radiation Environment and Medicine.
6. Ndjana Nkoulou II et al. (2019). Simultaneous indoor radon, thoron and thoron progeny measurements in
Bétaré-Oya gold mining areas, Eastern Cameroon. Radiation Protection Dosimetry, 1-11.
7. Saïdouet al. (2019). Natural radiation exposure to the public in mining and ore bearing regions of
Cameroon. Radiation Protection Dosimetry.
8. Takoukam et al. (2019). Simultaneous measurements of indoor radon and thoron and inhalation dose
assessment in Douala City, Cameroon. Isotopes in Environmental and Health Studies.
9. Saïdou et al. (2019). Natural radiation exposure to the public in the uranium bearing region of Poli,
Cameroon: from radioactivity measurements to external and inhalation dose assessment. Journal of
Geochemical Exploration.
10. Oumar Bobbo et al. (2019). Occupational natural radiation exposure at the uranium deposit of Kitongo,
Cameroon. Radioisotopes.
11. Bineng et al. Equilibrium factor influence on internal dose estimation due to indoor radon, thoron and
progeny: case of the uranium and thorium bearing region of Lolodorf, Cameroon. Under review. Journal of
Environmental Radioactivity.
Results
❑A project (CMR9009) dealing with
Establishing a national radon plan for
controlling public exposure due to radon
indoors was elaborated and submitted to IAEA
in 2016.
❑Accepted for funding within the frame of TC
between Cameroon and IAEA, the project will
run from 2018 to 2019.
❑The project effectively started in March 2018.
CMR9009 kick-off meeting
in Yaounde, 20-22 March, 2018
Achievements of CMR9009
Inputs Achievements
Training of personnel on radon 3 staff (01 SV+02 FE) trained in Spain and
Hungary
Procurement of 2000 Radtrack detectors 1500 detectors delivered
Procurement of Radon Calibration System
- ATMOS12 and Alphaguard radon
monitors with the necessary
accessories
- Radon source
- Chamber + pre-chamber with
accessories
To be delivered shortly
Procurement of an in-situ gamma spectrometer
and radon-risk equipment
Ongoing
Organization of a National Training Course on
Regulatory control of public exposure to radon
in dwelling and in workplaces
Effective
• Drafting Regulation on radon
• Definition of Reference Levels
• Drafting National Radon Action Plan
Ongoing
Radon measurements campaign Ongoing (440 Radtrak deployed)
Radon deployment plan
Conclusion and perspectives
❑Radon and Thoron exposure occurs in Cameroon
❑Reference levels should be defined for radon.Thoron should not be disregarded.
❑Extensive radon indoors and geogenic radonmeasurements should be effective to establishradon-risk mapping of Cameroon
❑Regulation on radon and the National RadonAction Plan should be effective in Cameroon
❑Government should fund the implementation ofthe National Radon Action Plan
Acknowledgments
❑Hirosaki University, Japan
❑International Atomic Energy Agency (IAEA)
❑Ministry of Scientific Research and Innovation, Cameroon
❑UNESCO-SIDA
❑University of Lausanne, Switzerland
❑University of Douala, Cameroon
❑University of Yaounde I, Cameroon
Thank you for your kind
attention