Transcript Applications of Nuclear Science in Environmental Studies
Applications of Nuclear Science in Environmental Studies
Ehsan Ullah Khan
Director Research Center for Emerging Sciences, Engineering and Technology ( C E SET )
Former Professor of Physics & Chairman, Department of Physics, GU.
Former Professor of Physics & Dean Faculty of Sciences, CIIT Former Professor of Physics & Dean Faculty of Sciences, IIU Deputy Chief Scientist, PINSTECH
Environment and Radiation Types of Radiation (i) Ionizing Radiation
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Ionizing radiation is composed of particles that individually carry enough energy to ionize an atom or molecule without raising the bulk material to ionization temperature.
Ionizing Radiation is generated through nuclear reactions either from an artificial or natural source such as cosmic rays, alpha, beta and gamma rays, X-rays, neutrons, and in general any charged particle moving at relativistic speeds.
(ii) Non-Ionizing Radiation
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Non-ionizing radiation refers to any type of electromagnetic radiation that does not carry enough energy per quantum to ionize atoms or molecules. Instead, of producing charged ions when passing through matter, the electromagnetic radiation has sufficient energy only for excitation. Nevertheless, different biological effects are observed for different types of non-ionizing radiation.
Near Ultraviolet , Visible light, Infrared, Micro and Radia Waves and low-frequency RF (longwave) are all examples of non-ionizing radiation
Types of Radio-nuclides Present in the Environment (i) Primordial Radionuclides That RNs that are present since the creation of earth and having long half-lives, e.g. 210 Pb , 226 Ra (ii) Cosmogenic Radionuclides That RNs that are produced in the upper atmosphere as a result of cosmic rays interaction with light particles (carbon, Nitrogen and Oxygen), e.g. 7 Be , 22 Na, 32 P, 32 S (iii) Anthropogenic Radionuclides That RNs that are produced as a result of man-made activities such as nuclear fuel fabrication, enrichment, nuclear power generation, nuclear accidents etc., e.g. 137 Cs , 134 Cs, 131 I, 90 Sr etc.
1. Radon
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Radon is an invisible, colorless, odorless, tasteless radioactive gas created during the natural breakdown of uranium in rocks and soils It is one of the heaviest substances that remains a gas under normal conditions and is considered to be a health hazard causing cancer It has three isotopes, namely, 222 R ( 238 U), 220 Rn ( 232 isotopes Th) and 219 Rn ( 235 U). 222 Rn has longer half life (3.84 days) than the other two
Radon in Buildings
There are two main sources for the radon in home's indoor air: the soil and the water supply
Health Hazard
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Breathing air that contains radon can cause lung cancer Risk of lung cancer from breathing radon in the air is much greater than risk of stomach cancer from swallowing water with radon in it Most of risk from radon in water comes from radon released into the air when water is used for showering and other household purposes Radon in home's water is not usually a problem when the water source is surface water. A radon problem is more likely when the source is groundwater (e.g., a private well or a public water supply system that uses groundwater)
Radon Measuring Techniques There are two techniques used for Rn measurements Passive Technique
(Alpha sensitive plastics) Accumulates the alpha radiation over certain time period (months) to give average Rn concentration Active Technique (Pylon and RAD-7 Detectors) Gives instantaneous value of Rn in air (also in water as well as in soils)
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Radon Survey in Pakistan Rn Survey has been carried out in:
Various divisions of Punjab including Bahawalpur, Lahore, Gujranwala and Rawalpindi Divisions Various districts in KPK including D.I. Khan, Peshawar, Charsadda, Mardan, Hazara and Swabi Parts of FATA, AJK and Islamabad are also surveyed There is lack of radon data from different provinces of the country, specially Sind and Baluchistan
Radon Levels in Pakistan
o o
The results obtained so far show that there is no area in Pakistan that has higher level of Rn than Permissible level of Indoor radon (4 pCi/l or148 Bq/m earth quack areas 3 ). The level has not crossed the limit even in However, there is a need to prepare Rn Map of Pakistan like of USA & UK
Scientific Uses of Rn Studies
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Because of radon's rapid loss to air and comparatively rapid decay, radon is used in hydrologic research that studies the interaction between ground water and streams. Any significant concentration of radon in a stream is a good indicator that there are local inputs of ground water Radon is also used in the dating of oil containing soils because radon has a high affinity of oil-like substances
Scientific Uses of Rn Studies
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Radon soil-concentration has been used in to map buried close-subsurface geological faults because concentrations are generally higher over the faults. Similarly, it has found some limited use in geothermal prospecting Some researchers have also looked at elevated soil-gas radon concentrations, or rapid changes in soil or groundwater radon concentrations, as a predictor for earthquakes . Results have been generally unconvincing
2 (a). Radioactivity in Drinking Water Neutron activation technique:
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Water samples are dried on Nuclear Track Detectors, exposed to known fluence of thermal neutrons at reactors. The number of fission events are then co-related to the concentration of radio nuclide
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This study has been carried out at a very limited scale. Extended work is required to have a comprehensive survey
2 (b). Radioactivity in Material used in construction
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226
Ra,
232
Th, and
40
K are easily detected in building materials using NaI Detector
Bricks, stones and other flooring materials is crushed dry and gamma spectrum taken This study has been carried out in very limited area and in limited building materials Studies so far in Pakistan has not shown any abnormal results
3. Measurement of
137
Cs in Soil
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The major source of 137 Cs in the atmosphere is atmospheric nuclear explosions that were conducted by developed countries from 1940 to 1960
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Among this huge amount ~ 90 % was released by atmospheric testing, 6 % by the Chernobyl accident and nearly 4 % is released by nuclear fuel processing facilities
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The site with deposition or erosion can be identified only if a reference site has been identified near the study
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A reference site has been identified in Lehri Park, on GT Road near Jhelum for the first time in Pakistan
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Hence ground is set for 137 Cs based soil erosion studies in Potohar region
Soil Measurements
2000 1800 1600 1400 1200 1000 800 600 400 200 (A) Open Land Soil 1000 2000 3000 4000 5000 6000 210 Pb Inventory (Bq/m 2 ) 7000 1600 1400 1200 1000 800 600 400 200 2000 (B) Wood Land Soil 3000 4000 5000 6000 210 Pb Inventory (Bq/m 2 ) 7000 210 Pb Vs 137 Cs inventories in soil samples from open land (A) and Woodland (B) sites. In both plots, in general with a very few exceptions, linearly proportional.
210 Pb Vs 137 Cs inventories are
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Soil Measurements
7500 6000 4500 3000 150 100 50 0 (A) 2000 1900 900 600 300 0 (B) Altitude (ft) Altitude (ft) 210 Pb (A) and 137 Cs (B) inventories in soil samples from study sites of different altitudes.
210 Pb shows decreasing while 137 Cs depicts increasing trend with altitude.
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70 60 50 40 30 20 10 0 (A) a
210 Pb in Open Land 210 Pb in Woodland
15 12 3 0 9 6 (B) a
137 137 Cs in Open Land Cs in Woodland
b c Depth in soil d b c Depth in soil d 210 open land (A) and Woodland (B) sites with increasing depth in soil.
210 Pb and Pb Exc.
137 Cs concentrations in soil samples from is decreasing But 137 Cs is showing a decreasing trend with depth in soils.
4. Nuclear Aerosols as Atmospheric Tracers
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Some of the objectives are to study: Cloud scavenging and precipitation Processes Aerosols transit, deposition velocities and residence time in the troposphere The air-water exchange rate Aerosol traps above the above ground vegetation Soil erosion Deposition patterns of air-borne contaminants
Main Uses are:
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Tracing of the atmospheric processes Climate change prediction
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Atmospheric dating:
e.g., dating of earthquake eruption of earth releasing radon using 210 Pb
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Better use of hydrological cycle
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Aerosols and Related Processes
Aerosol package NCAR CAM4, Xiahong Liu
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(a)
Rain Collector and Met Instruments
(b)
A
Background Spectrum
B
Pb-210 46.5 keV Pb-214 295 keV Pb-214 352 keV Cs-137 662 keV Air Sample Spectrum K-40 1460 keV
(477 keV)
Part 1: Air Measurements
Map of Pakistan showing the wind directions on a sampling day obtained from GrADS software (a) The overall view of wind directions over Pakistan (b) the magnified view at the sampling point (c) The colours in the arrow shows wind speed.
Part 1: Air Measurements Measured Monthly Mean Concentrations 0.40
0.35
0.30
0.25
0.20
0.15
0.10
0.05
Regime I
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Regime II 210 Pb Experimental Linear fit Upper 95% CL Lower 95% CL Regime III
40 60 80 100 120 140 Monthly Rain [mm] 4.5
4.0
3.5
3.0
2.5
2.0
1.5
20 7 Be
Experimental Data9D UCL LCL
Regime I Regime II 40 60 80 100 Monthly Rain [mm] 120 140 Monthly concentrations (mBq m -3 ) of and 210 Pb 7 Be in air samples against the amount of rainfall.
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0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
Measured Seasonal Concentrations 210 Pb 2 1 0 4 3 6 5 Part 1: Air Measurements 7 Be Seasonal concentrations (mBq m -3 ) of 210 Pb and 7 Be in air samples.
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3 2 1 Part 1: Air Measurements Measured Concentrations and NFLL-FHL Air Masses 0.4
0.3
0.2
0.1
0.0
Concentrations of 7 Be (mBq m -3 ) and percentages of NFLL-FHL air masses in air samples. The error bars are the standard deviation of 7 Be and 210 Pb concentration at each bin.
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0.6
0.5
0.4
0.3
0.2
0.1
0.0
Part 1: Air Measurements Concentrations of aerosols and Percent Pressure 6 5 1 0 4 3 2 Concentrations of 210 High-Low pressures in air samples. The error bars are the standard deviation of Pb and 210 7 Be (mBq m Pb and 7 -3 ) and percentages of Be concentration at each bin.
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Part 1: Air Measurements Determination of residence time of aerosols
Statistics of the 210 Pb, 214 Pb and 7 Be concentrations (mBq m -3 ) and mean residence time of aerosol over Islamabad.
Radionuclide 210 Pb 214 Pb 7 Be Min.
0.056
200.56
0.772
1 st 0.172
385.35
2.321
Quartiles Median 0.246
554.37
2.977
3 rd 0.390
875.77
3.672
Max.
0.761
1371 6.847
Mean (µ) 0.284
631.06
3.171
Uncertainty (σ) 0.012
155.47
0.084
MRT (days) 5.29±0.91
7.18±0.97
110 100 90 80 70 60 50 40 30 20 10 0 Part 2: Precipitation Measurements Concentrations of 210 Pb (a) Open Rain Samples 15 10 5 0 40 35 30 25 20 (b) Throughfall Samples Sampling Month/Year Sampling Month/Year Concentrations of 210 Pb in (a) open rain and (b) throughfall samples during the sampling period. Straight horizontal lines show respective mean values.
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2000 1800 1600 1400 1200 1000 800 600 400 200 0 Part 2: Precipitation Measurements
Concentrations of
7
Be
(a) Open Rain Samples 1200 (b) Throughfall Samples 1000 800 600 400 200 0 Sampling Month/Year Sampling Month/Year Concentrations of 7 Be in (a) open rain and (b) throughfall samples during the sampling period. Straight horizontal lines show respective mean values.
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Part 2: Precipitation Measurements Concentrations of radionuclides and precipitation 100 (a) Open Rain Samples 2000 (b) Open Rain Samples 80 Regime I Regime II 1600 Regime I Regime II 60 1200 40 800 20 400 0 0 100 200 300 Monthly Rainfall (mm) 400 0 0 100 200 300 Monthly Rainfall (mm) Results of concentrations of (a) 210 Pb and (b) versus monthly amount of precipitation.
7 Be radionuclides 400
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50 Part 2: Precipitation Measurements
Accumulated Concentrations of
210
Pb
(a) Open Rain Samples (b) Throughfall Samples 25 40 20 30 15 20 10 10 5 0 Autumn Winter Spring Summer Season 0 Autumn Winter Spring Summer Season Accumulated concentrations of 210 Pb in (a) open rain and (b) throughfall samples for different seasons.
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1200 Part 2: Precipitation Measurements
Accumulated Concentrations of
7
Be
(a) Open Rain Samples 1200 (b) Throughfall Samples 1000 1000 800 800 600 600 400 400 200 200 0 Autumn Winter Spring Summer 0 Season Autumn Winter Spring Summer Season Accumulated concentrations of 7 Be in (a) open rain and (b) throughfall samples for different seasons.
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Part 2: Precipitation Measurements 10 (a) Activity Ratios of 210 Pb and 7 Be aerosols 25 (b) 20 15 1 10
Rain-Temp
5 0.1
100 1000 Altitude [m] (a) Measured activity ratios of 210 Pb and activity ratios. (b) Activity ratios of different altitudes around the globe.
210 7 Be aerosols. Dashed line shows the situation when activities of both aerosols are equal whereas solid line is the mean value of all measured Pb and 7 Be aerosols for
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Part 2: Precipitation Measurements
Mean Annual Rainfalls and Temps at Murree
2400 (a) 2000 1600 1200 800 400 Grand average 21 (b) 18 15 0 1960 1970 1980 1990 Year 2000 2010 12 1980 1984 1988 1992 1996 2000 2004 2008 Year Mean annual rain, at Murree, for the period of 1960-2009 and (b) mean maximum temperature for the period of 1980-2008.
Conclusion
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A number of Scientific groups in various R&D centers and universities in Pakistan have been using Nuclear radiations for environmental Studies.
Most of the Rn survey has been done using low cost Nuclear Track Detection Technique There are very limited instruments available, particularly N-type HPGe detectors for gamma spectroscopy in the country There is a need to develop Rn map of Pakistan through collaborative efforts
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Coordinated efforts are needed to promote the culture of cooperation and readiness to extend access to limited equipment available at various fortunate locations
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The life cycle of atmospheric aerosols is complex. Most atmospheric aerosols eventually drop to the ground or get washed down with the rain. However, some particles ascend to the highest levels of the atmosphere, stay for a very long time and travel long distances
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Since these particles know no borders, international cooperation is essential in any measures designed to control them.