IAEA Natural Terrestrial Radiation Day 3 – Lecture 7 Sources of Radiation 1.
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Transcript of IAEA Natural Terrestrial Radiation Day 3 – Lecture 7 Sources of Radiation 1.
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Natural Terrestrial Radiation
Day 3 – Lecture 7
Sources of Radiation
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OBJECTIVE
To discuss about the natural terrestrial radiation, radioactive decay chains, important radionuclides, radon and its significance, NORM, TENORM and NARM
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Content
Terrestrial decay chains
Important radionuclides
Radon and its health significance
NORM
TENORM
NARM
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Radioactivity in Nature
Primordial – existing since the creation of the Earth
Cosmogenic – formed as a result of cosmic ray interactions
Human produced – enhanced or formed due to human actions
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Primordial Nuclides
Nuclide Half-life Natural Activity235U 7.04 x 108 yr 0.711% of all natural
uranium238U 4.47 x 109 yr 99.275% of all
natural U; 0.5 to4.7 ppm total U in common rocks
232Th 1.41 x 1010 yr 1.6 to 20 ppm in common rocks
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Nuclide Half-life Natural Activity226Ra 1,600 yr 16 Bq/kg in limestone and
48 Bq/kg in igneous rock
222Rn 3.82 days Noble gas; average annual air concentrations in US range from 0.6 to 28 Bq/m3
40K 1.28 x 109 yr 0.037 to 1.1 Bq/g in soil
Primordial Nuclides
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Background Radiation
There are three decay “chains” that occur in nature:
the uranium series, beginning with 238U the thorium series, which originates with 232Th the actinium series, which originates with 235U
Once upon a time there was also a neptunium series, which originated with 241Pu, that has a half-life of only 14 years. The only remaining member of this series is 209Bi with a half-life of 2E18 years.
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238U Decay Chain
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Natural Radioactivity in Soil
Element*Assumed Activity**
Mass of Element* Activity
Uranium 25 Bq/kg 2,200 kg 31 GBq
Thorium 40 Bq/kg 12,000 kg
52 GBq
Potassium-40
400 Bq/kg 2,000 kg 500 GBq
Radium 48 Bq/kg 1.7 g 63 GBq
Radon 10 kBq/m3 11 g 7.4 GBq* Potassium-40 is a radionuclide ** per kg of soil
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Natural Radioactivity inBuilding Materials (mBq/g)
Material Uranium Thorium Potassium
Granite 63 8 1184
Sandstone 6 7 414
Concrete 31 8.5 89
Wallboard 14 12 89
Gypsum 186 66 5.9
Clay Brick 111 44 666
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Natural Radioactivityin the Oceans
Nuclide*Assumed Activity Pacific Atlantic All Oceans
Uranium 33 mBq/L 22 EBq 11 EBq 41 EBq
40K 11 Bq/L 7400 EBq 3300 EBq 14000 EBq
3H 0.6 mBq/L 370 PBq 190 PBq 740 PBq
14C 5 mBq/L 3 EBq 1.5 EBq 6.7 EBq
87Rb 1.1 Bq/L 700 EBq 330 EBq 1300 EBq
*Uranium is an element
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Background Radiation - Radon
Radon is a noble gas (also called “inert”).
Radon is chemically like other members of this group of the periodic table, namely He, Ne, Ar, Kr, and Xe, gas. The noble gases do not readily form compounds due to their stable electron shell configuration. With the exception of helium, they all have 8 electrons in their outer shell (ns2np6 for you chemists in the audience).
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Background Radiation - Radon
The average dose from radon-222 (222Rn) is approximately 2000 Sv per year. Radon is an alpha emitter. Many of the radon decay products are also alpha emitters.
Radon is produced from the radioactive decay of 238U an isotope of uranium which is naturally present in the environment. In fact, in some areas of the western US, the concentration of natural uranium is high enough that is it mined to provide a source of uranium for reactors.
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Production of 222Rnby Decay of 238U
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Background Radiation - Radon
Just as helium can diffuse through a balloon, radon can diffuse through the soil and foundations of homes. The diffusion is greater when the soil has low moisture content.
Radon is a radiological hazard because the decay products are alpha emitters. Since they are formed by emission of alpha particles, the resulting decay products have an electrostatic charge and are attracted to particulates in the air. These may become deposited in the lung. These particles then decay by alpha emission, which results in a dose to the lung.
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Radon Diffusion Through Soil
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Radon Transport Into Homes
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Background Radiation - Radon
The concern is really not with the radioactive decay of radon, but with the radon progeny (also called “daughter products”), that are produced when radon decays. Since radon decays by alpha emission, the radon “daughters” have a ++ charge and so are electrostatically attached to particulates in the air. These decay products are also radioactive, and many decay by alpha particle emission.
The alpha particle energy delivers a dose to the lung where the particles are deposited. The dose to the lung is attributed to the development of lung cancer for uranium miners (hence the regulatory limits for radon and radon daughter concentrations).
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Relative Risk from Radon
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Radionuclides Foundin Your Body
Nuclide*Total Mass of
Nuclide Found in the Body
Total Activity of Nuclide Found in
the Body
Daily Intake of Nuclides
Uranium 90 g 30 pCi (1.1 Bq) 1.9 g
Thorium 30 g 3 pCi (0.11 Bq) 3 g
40K 17 mg 120 nCi (4.4 kBq) 0.39 mg
Radium 31 pg 30 pCi (1.1 Bq) 2.3 pg
14C 95 g 0.4 Ci (15 kBq) 1.8 g
*Uranium, Thorium and Radium are elements
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Natural Radiation Exposure Around the World
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Effective Dose Equivalent to a Member of the Population of the United States
Source
Average AnnualEffective Dose Equivalent Sv mrem
Inhaled (radon and decay products) 2000 200
Other Internally Deposited Radionuclides
390 39
Terrestrial Radiation 280 28
Cosmic Radiation 27 3
Cosmogenic Radioactivity 10 1
Rounded Total from Natural Sources 3000 300
Rounded Total from Artificial Sources 600 60
Total 3600 360
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Natural Sources2.4 mSv (79%)
Others× 0.005 mSv (<1%)
Medical Exposures0.64 mSv (21%)
Per Capita Annual Dose – UNSCEAR 2008
×Others include Fallout, Nuclear Power Production, Occupational exposures etc.
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Per Capita Annual Doses from Natural Sources – UNSCEAR 2008
Radon Inhalation1.15 mSv (48%)
Cosmic Radiation0.39 mSv (16%)
Ingestion 0.29 mSv (12%)
Thoron Inhalation0.1 mSv (4%)
External GammaRadiation0.48 mSv (20%)
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NORM and NARM
NORM Naturally Occurring Radioactive Material
TENORM Naturally Occurring Radioactive Material enhanced by
processing is called TENORM NARM Naturally Occurring and
Accelerator-Produced Radioactive Material
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Summary
Natural terrestrial radiation was discussed
Important radionuclides and their distribution was discussed
Radon in particular and its significance was discussed
NORM, TENORM and NARM were defined
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Where to Get More Information
Cember, H., Johnson, T. E, Introduction to Health Physics, 4th Edition, McGraw-Hill, New York (2009)
UNSCEAR, Sources and Effects of Ionizing Radiation, 2008 Report to the General Assembly with Scientific Annexes, United Nations, New York, 2008
International Atomic Energy Agency, Postgraduate Educational Course in Radiation Protection and the Safety of Radiation Sources(PGEC), Training Course Series 18, IAEA, Vienna (2002)