1.3 naturally occurring radioactive material (norm)
TRANSCRIPT
NPRE 441, Principles of Radiation Protection
Chapter 1: Radioactivity
1.3 Naturally Occurring Radioactive Material (NORM)
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An Overview of Radiation Exposure to US Population
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NPRE 441, Principles of Radiation Protection
Chapter 1: Radioactivity
Naturally Occurring Radioactivity
Radioactivity of building materials
An example of environmental radiation
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NPRE 441, Principles of Radiation Protection
Chapter 1: Radioactivity
• The existence of the radioactive gas in the three series is one of the chiefreasons for the presence of naturally occurring environmental radioactivity.
Naturally Occurring Radioactivity
• The probable atmospheric radon concentration is on the order of 2x10‐6 Bq/mL.Significant increase in background radiation level can be expected in the case ofrain fall.
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Chapter 1: Radioactivity
Terrestrial NORM consists of radioactive material that comes out of the Earth’s crustand mantle, and where human activity results in increased radiological exposure.The materials may be original (such as uranium and thorium) or decay productsthereof, forming part of characteristic decay chain series, or potassium‐40. The twomost important chains providing nuclides of significance in NORM are the thoriumseries and the uranium series.
Terrestrial NORM
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Chapter 1: Radioactivity
http://www.world‐nuclear.org/info/inf30.html258
Chapter 1: Radioactivity
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NPRE 441, Principles of Radiation Protection
Chapter 1: Radioactivity
Naturally Occurring Radioactivity
Radioactivity of building materials
An example of environmental radiation
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NPRE 441, Principles of Radiation Protection
Chapter 1: Radioactivity
• All of the heavy elements (Z>83) found in nature are radioactive and decay byalpha and beta emission. 209
83Bi is the only stable nuclide with an atomicnumber greater than that of lead (Z=82).
Terrestrial NORM
• All of the naturally occurring heavy radionuclides belong to one of the threeseries, the uranium series, the thorium series and the actinium series.
• Several other elements, outside the uranium, actinium and thorium series, arealso found to have radioactive isotopes, such as 40K, 87Rb etc.
• Other naturally occurring radionuclides are of cosmogenic origin. Only thoseproduced as a results of cosmic ray interactions with constituents of theatmosphere results in any mentionable exposure to man: 3H, 7Be, 14C and 22Na.
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Chapter 1: Radioactivity
Common characteristics of radioactive series:• The first member of each series is very long‐lived – 232Th: 1.391010 years, 238U:
4.51109 years and 235U: 7.13108 years.
The Indoor Radon Problem
Actinon called is and series actiniumin appears
Thoron called is and series in thorium appears
Radon called is and series uraniumin appears
21986
22086
22286
Rn
Rn
Rn
series actiniumin appears
series in thorium appears
series uraniumin appears
20782
20882
20682
Pb
Pb
Pb
• All three naturally occurring series each has a gaseous member.
Artificially created radioactive series, such as the neptunium series has nogaseous member.
• The end product of all three naturally occurring radioactive series is lead.
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Chapter 1: Radioactivity
All three isotopes of radon has radioactive daughters, so they are all potentiallyhazardous.
Naturally Occurring Radioactivity– Other Isotopes of Radon
seconds 4T U,from :(Actinon)
seconds 56T Th,from :(Thoron)
3.81daysT U,from :(Radon)
23521986
23222086
23822286
Rn
Rn
Rn
The health concerns of these isotopes are determined by two factors:• The rate of production from their parent nuclides.• The probability of decay before get airborne.
The contributions from the daughters of 220Rn and 219Rn to internal exposure areusually negligible compared with that from 222Rn.
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Chapter 1: Radioactivity
Radon gas in the environment:
• The noble gas 222Ra produced in the uranium series can becomeairborne before decaying.
Naturally Occurring Radioactivity– Radon and Radon Daughters
• The soil and concrete in building material contribute to the presence ofindoor radon.
• Some of the daughters of radon atoms in air are absorbed onto micron‐or submicron aerosols or dust particles. Others remain in the air asessentially free ions and other forms.
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Chapter 1: Radioactivity
Naturally Occurring Radioactivity– Radon and Radon Daughters
Sources of indoor radon in a typical house265
NPRE 441, Principles of Radiation Protection
Chapter 1: Radioactivity
• Airborne radon itself poses little health hazard. It is not retained in significantamounts by the body.
• The health hazard is closely related to the short‐lived daughters of radon.
Naturally Occurring Radioactivity– Health Concerns of Radon Gas
particles
particles
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Chapter 1: Radioactivity
The WHO predicts that “The risk of lung cancer increased by 8% per 100 Bq/m3 increase in measured radon concentration (95% confidence interval).” (from the WHO Indoor Radon Handbook)
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Chapter 1: Radioactivity
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Chapter 1: Radioactivity
Example of Secular Equilibrium
From <<Radiation Protection and Dosimetry>>, by Michael Stabin.
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Chapter 1: Radioactivity
From this relationship,
one can see that1. As the time goes by, e‐tdecreases and QB approaches QA.At equilibrium, we have
BA QQand
2. Since A has a relatively long half life, QA may be considered as aconstant. So the total activity converges to a constant.
Secular Equilibrium: TA >> TB (λA << λB)
TA >> TB
7TB
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Chapter 1: Radioactivity
The radon problem, is that of alpha‐particle irradiation of sensitive lung tissues bythe short‐lived daughter of radon and the associated risk of lung cancer.
Naturally Occurring Radioactivity– Radon and Radon Daughters
For example, An alpha particle emitted by 214Po deposits 7.69MeV within ~70m.In comparison, an 1MeV beta particle emitted by 214Bi deposits its energy over adistance of ~4000 m.
Indoor radon is the second leading cause for lung cancer in the US, only aftersmoking.
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Cosmogenic Radioactivity
• Cosmogenic NORM is formed as a result of interactions between certaingases in the Earth’s atmosphere and cosmic rays.
• The production of cosmogenic radionuclides is an ongoing process and asteady state has been established. The radionuclides are produced at thesame rate as they decay.
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Chapter 1: Radioactivity
Examples of Cosmogenic Radioactivity – 14C• Carbon‐14 is produced in the atmosphere by thermal neutrons absorbed by
nitrogen atoms. When cosmic rays enter the atmosphere, they undergo varioustransformations, including the production of neutrons. The resulting neutrons (1n)participate in the following reaction:
1n + 14N → 14C + 1H
• Carbon‐14 decay through the following scheme (half‐life: 5730 years)
• The carbon‐14 dating technique?
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Chapter 1: Radioactivity
Examples of Cosmogenic Radioactivity – 3H• The production of cosmogenic radionuclides is an ongoing process and a
steady state has been established. The radionuclides are produced at thesame rate as they decay.
• Tritium occurs naturally due to cosmic rays interacting with atmosphericgases. In the most important reaction for natural tritium production, a fastneutron (greater than 4MeV) interacts with atmospheric nitrogen:
14N + n→ 12C + 3H
• Tritium is produced in nuclear reactors by neutron activation of lithium‐6:
6Li + n→ 4He ( 2.05 MeV ) + 3H ( 2.75 MeV )
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Examples of Cosmogenic Radioactivity – 3H
• Tritium decays through beta emission and releases 18.6 keV of energy in theprocess.
3H→ 3He + e− + νanti
• The electron has an average kinetic energy of 5.7 keV, while the remaining energyis carried off by the nearly undetectable electron and antineutrino.
• The low‐energy beta radiation from tritium cannot penetrate human skin, sotritium is only dangerous if inhaled, ingested, or—if it is in water molecules, as withtritiated water—absorbed through pores in the skin. Its low energy also createsdifficulty detecting tritium labelled compounds except by using liquid scintillationcounting.
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Chapter 1: Radioactivity
Examples of Cosmogenic Radioactivity – 14C• Carbon‐14 is produced in the atmosphere by thermal neutrons absorbed by
nitrogen atoms. When cosmic rays enter the atmosphere, they undergo varioustransformations, including the production of neutrons. The resulting neutrons (1n)participate in the following reaction:
1n + 14N → 14C + 1H
• Carbon‐14 decay through the following scheme (half‐life: 5730 years)
• The carbon‐14 dating technique?
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Radiocarbon (14C) formation and decay
1 14 14 10 7 6 1n N C H
‐formed by interaction of cosmic ray spallation products with stable N gas
14 146 7C N Q
‐radiocarbon subsequently decays by β‐ decay back to 14N with a half‐life of 5730y
Radiocarbon dating was first explored by W.R. Libby (1946), who later won the Nobel Prize. Most published dates still use the “Libby” half‐life of 5568y to enable comparison of 14C dates.
The activity of radiocarbon in the atmosphere represents a balance of its production, its decay, and its uptake by the biosphere, weathering, etc.
Which of these threethings might change
through time,and why? 278
Convention:The atmosphericradiocarbonanomaly with respect to a standardis defined as D14C
14 12
1414 12
/1 *1000
/spl
std
C CC
C C
Atmospheric radiocarbon variability through time
‐addition of isotopically lightfossil fuel C to atmosphere
‐solar activity changes
Note:the D14C is 0during 1890,b/c that’sthe activity of theoxalic acid standard
time
But how did somebodyconstruct this curve?
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data from:corals (bright red)lake varves (green)marine varves (blue)speleothems (orange)tree rings (black)
The Radiocarbon Calibration Curve (atmospheric 14C history)Principle: compare radiocarbon dates with independent dates examples of independent dating: tree‐ring counting, coral U‐Th dates, varve counting,
correlation of climate signals in varves with ice core
Hughen et al., 2004
So was atmospheric14C larger or
smaller at 20k (LGM)than today?
Observation:radiocarbon datesare consistently younger than calendar ages
time
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Chapter 1: Radioactivity
• The coal industry (mining and combustion)• The oil and gas industry (production)• Metal mining and smelting
• Mineral sands (rare earth minerals, titanium and zirconium).• Fertilizer (phosphate) industry • Building industry
• Recycling
Industries Producing NORM
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Chapter 1: Radioactivity
Industries Producing NORM
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Chapter 1: Radioactivity
Industries Producing NORM
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Chapter 1: Radioactivity
Industries Producing NORM
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