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Chapter 8. Radioactive isotopes and Their Applications 1.Introduction 2.Production of Radioisotopes 3.Some Commonly Used Radionuclides 4.Tracer Applications.

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Presentation on theme: "Chapter 8. Radioactive isotopes and Their Applications 1.Introduction 2.Production of Radioisotopes 3.Some Commonly Used Radionuclides 4.Tracer Applications."— Presentation transcript:

1 Chapter 8. Radioactive isotopes and Their Applications 1.Introduction 2.Production of Radioisotopes 3.Some Commonly Used Radionuclides 4.Tracer Applications 5.Thickness Gauging 6.Radioisotope Dating 7.Radioisotope Applications in Space Exploration

2 Produce Select suitable nuclides Radioactive nuclei Nuclear reactoracceleratorgenerator

3 4.1 Radioisotopes are ideal tracers( The use of some easily detected material to tag or label some bulk material allows the bulk material to be followed as it moves through some complex process. Fluorescent dyes, stable isotopes, radioisotopes … Why radioisotopes?

4 The amount of tagging material needed If a sample contains N atoms of the radionuclide, the observed count rate (CR) is ε: detection efficiency To detect the presence of the radionuclide tag, this count rate must be greater than some minimum count rate CR min which is above the background count rate. Then the minimum number of radioactive atoms in the sample needed to detect the presence of the radionuclide is If the atomic weight of the radionuclide is A, the minimum mass of radionuclides in the sample is

5 A typically gamma-ray detector efficiency is ε ~ 0.1 and a minimum count rate is CR min ~ 30 min -1 = 0.5 s -1 Thus, for 14 C (T 1/2 = 5730 y = 1.18 x s), the minimum detectable mass of 14 C in a sample is: few atoms are needed! How about 32 P (T 1/2 = d) ? P is often used in plant studies to follow the uptake of phosphorus by plants.

6 6 4.2 Medical Applications Radioisotopes with short half-lives are used in nuclear medicine because they have the same chemistry in the body as the nonradioactive atoms. in the organs of the body, they give off radiation that exposes a photographic plate (scan) giving an image of an organ. Thyroid scan

7 4.3 Leak Detection To find the location of a leak in a shallowly buried pipe without excavation This use of radionuclide tracers to find leaks or flow paths has wide applications : (1)finding the location of leaks in oil-well casings, (2)determining the tightness of abandoned slate quarries for the temporary storage of oil, (3)Locating the positions of freon leaks in refrigeration coils, (4)finding leaks in heat exchanger piping, (5)locating leaks in engine seals.

8 Underground pipe leaks Tracer will be added to the liquid in the pipe Detector is moved along the pipe The count rate will increase as there is large amount of water The radioactive source will be a short half-life γ emitter

9 4.4 Other applications Pipeline Interfaces Flow Patterns Flow Rate Measurements Surface Temperature Measurements Oil from different producers is often carried in the same pipeline. measuring the spatial distribution of the activity concentration (1) ocean current movements, (2) atmospheric dispersion of airborne pollutants, (3) flow of glass lubricants in the hot extrusion of stainless steel, (4) dispersion of sand along beaches, (5) mixing of pollutant discharges into receiving bodies or water, and (6) gas flow through a complex filtration system. measurements of the activity concentrations of a radioactive tag in the fluid medium The time required for the radionuclide (and the flowing material) to travel to a downstream location is given by the time for the activity to reach a maximum at the downstream location. krypton atoms are only released at certain high temperatures. remaining 85 Kr kryptonated surface

10 Thickness gauging by radiation transmission Thickness gauging by backscatter transmission 5. Thickness gauging Thickness gauging using stimulated fluorescence

11 Thickness control The manufacture of aluminium foil β emitter is placed above the foil and a detector below it Some β particle will penetrate the foil and the amount of radiation is monitored by the computer The computer will send a signal to the roller to make the gap smaller or bigger based on the count rate

12 Chapter 8. Radioactive isotopes and Their Applications 1.Introduction 2.Production of Radioisotopes 3.Some Commonly Used Radionuclides 4.Tracer Applications 5.Thickness gauging 6.Radioisotope Dating 7.Radioisotope Applications in Space Exploration

13 Carbon dating Carbon has 3 isotopes: 12 C – stable 13 C – stable 12 C: 13 C = : C – radioactive Abundance: 6.1 Radiocarbon dating principles By observing how much of a long-lived naturally occurring radionuclide in a sample has decayed, it is possible to infer the age of the sample.

14 RadiocarbonForms: in the upper atmosphere in the upper atmosphere Decays: t ½ = 5730 yr. Living Tissue 14 C/ 12 C, Tissue ratio same as atmospheric ratio Dead Tissue 14 C/ 12 C< 14 C/ 12 C tissueatmosphere

15 Measured Constant Calculated ??? Clock starts when one dies

16 N ( t ) = N(0)exp(-λt) we never know N(0). the initial ratio N(0)/N S of the radionuclide and some stable isotope of the same element can be estimated with reliability This ratio also decays with the same radioactive decay law as the radionuclide It is usually easier to measure the specific activity of 14C in a sample, i.e., A 14 per gram of carbon

17 As a consequence, 14 C is no longer in equilibrium with its atmospheric production rate. However, before humans upset this ancient equilibrium, the ratio of 14C to all carbon atoms in the environment was about, a value that has remained constant for the last several tens of thousand years. It is usually easier to measure the specific activity of 14C in a sample, i.e., A 14 per gram of carbon. This specific activity is proportional to the N 14 /N C ratio,

18 What is the age of an archaeological sample of charcoal from an ancient fire that has a A 14 (t)/g(C) ratio of 1.2 pCi/g of carbon?

19 Radiocarbon Measurements and Reporting Radiocarbon dates are determined by measuring the ratio of 14 C to 12 C in a sample, relative to a standard, usually in an accelerator mass spectrometer. standard = oxalic acid that represents activity of 1890 wood 14C ages are reported as 14 C years BP, where BP is 1950

20 First 14 C date: wood from tomb of Zoser (Djoser), 3rd Dynasty Egyptian king (July 12, 1948). Historic age: 4650±75 BP Radiocarbon age: 3979±350 BP Second 14 C date: wood from Hellenistic coffin Historic age: 2300±200 BP Radiocarbon age: (C-?) Modern! Fake! First Curve of Knowns: 6 data points (using seven samples) spanning AD 600 to 2700 BC. Half life used: 5720± 47 years Carbon-14 dating lends itself to age determination of carbon- containing objects that are between 1,000 and 40,000 years old

21 21 The Shroud of Turin Credit: The Image Works Reputed as the burial cloth of Jesus Christ. C-14 dating by 3 independent labs report the Cloth originated during the Medieval times, between A.D

22 22 Mummified remains found frozen in the Italian Alps At least 5000 years old By carbon-14 dating In 1991,hikers discovered the body of a prehistoric hunter that had been entombed in glacial ice until the ice recently moved and melted. pathologists also examined his well-preserved remains, he died from a fatal wound in the backmost likely delivered during his prolonged struggle with at least two other prehistoric hunters.

23 data from: corals (bright red) lake varves (green) marine varves (blue) speleothems (orange) tree rings (black) The Radiocarbon Calibration Curve (atmospheric 14 C history) Principle : compare radiocarbon dates with independent dates Examples of independent dating: tree-ring counting, coral dates, varve counting, correlation of climate signals in varves with ice core Hughen et al., 2004 equiline Observation : radiocarbon dates are consistently younger than calendar ages time

24 Source of Error in 14 C dating 1.Variations in geomagnetic flux. Geomagnetic field strength partly controls 14 C production in the atmosphere because of attenuation affects on the cosmic flux with increasing magnetic field strength. 2.Modulation of the cosmic-ray flux by increased solar activity (e.g., solar flares) leads to attenuation of the cosmic-ray flux. 3.Influence of the ocean reservoir. Any change in exchange rate between ocean reservoir and atmospheric reservoir will affect the level of 14 C in the atmosphere. 4.Industrial revolution (ratio of 14 C to stable carbon decreased because of burning fossil fuels) and bomb effects ( 14 C to stable carbon increased because of increased neutron production from detonation of nuclear bombs in the atmosphere) have made modern organic samples unsuitable for as reference samples.

25 Radioactive elements Not all elements are radioactive. Those are the most useful for geologic dating are: U-238Half-life = 4.5 By the age of the earth K-40Half-life = 1.25 By rocks Also, Sm-147, Rb 87, Th-232, U-235

26 The blocking temperature is the temperature above which a mineral or rock no longer behaves as a closed system and the parent/daughter ratios may be altered from that due to pure radioactive disintegration. This can result in resetting the isotopic clock and/or give what are called discordant dates. These types of problems have given opponents of the radiometric dating of the Earth ammunition to attack the 4.5 By age geologists cite. Blocking temperatures for some common minerals and decay series.

27 Fig. 5.9 Fission tracks in an apatite crystal. They are produced when an atom of U-238 disintegrates emitting an alpha particle, a Helium nucleus (He-4). This massive atomic particle causes massive structural damage in the crystal that can be revealed by etching. The number of tracks in a given area is proportional to the age of the mineral. (Why not just use the U-238 to Pb-206 method directly in such cases?)

28 7. Radioisotope Applications in Space Exploration Radioisotope Thermoelectric Generator (RTG) if two dissimilar metals were joined at two locations that were maintained at different temperatures, an electric current would flow in a loop In an RTG, the decay of a radioisotope fuel provides heat to the hot junction, while the other junction uses radiation heat transfer to outer space to maintain itself as the cold junction high degree of reliability

29 an RTG loaded with 1 kilogram of plutonium (238) dioxide fuel would generate between 21 and 29 watts of electric power for the spacecraft. After five years of travel through space, this plutonium-fueled RTG would still have approximately 96 percent of its original thermal power level available for the generation to electric power

30 Applications Summary

31 Alternative Technologies

32 Disposal and Recycling

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34 Chapter 8. Radioactive isotopes and Their Applications 1.Introduction 2.Production of Radioisotopes 3.Some Commonly Used Radionuclides 4.Tracer Applications 5.Thickness Gauging 6.Radioisotope Dating 7.Radioisotope Applications in Space Exploration

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