Chapter 19 Radioactivity and Nuclear Chemistry PDF

Chapter 19 Radioactivity and Nuclear Chemistry The Chalk River Laboratories, ON  The Learning Goals Students will be able to Understand major types of radioactivity, including α decay, β decay, γ ray emission, positron emission and electron capture; write nu...

Chapter 19 Radioactivity and Nuclear Chemistry The Chalk River Laboratories, ON  The Learning Goals Students will be able to Understand major types of radioactivity, including α decay, β decay, γ ray emission, positron emission and electron capture; write nuclear equations of each type of radioactivity; Understand the concept of the Valley of Stability; predict the stability and types of radioactivity of given isotopes; Learn measurements of radioactivity, kinetics of radioactive decay and radiometric dating. Understand nuclear fission and nuclear fusion, and calculate energy associated with nuclear reactions based on mass defect and nuclear binding energy; Learn the safety effects of radiation, and major applications of radioactivity in medicine and energy. 2  Biomedical Imaging & Electromagnetic Spectrum Isotopes For Nuclear Medicine mechanical wave 3 BMC Medical Imaging 2005(5)1471  The Discovery of Radioactivity Antoine-Henri Becquerel (1852- 1908) designed an experiment to test if phosphorescent minerals also gave off X-rays. He discovered in 1896 that certain minerals with uranium, even without exposure to outside light, were constantly producing energy rays that could penetrate matter. He called them uranic rays, which is not related to phosphorescence. 4  The Curies Marie Curie (1867-1934) discovered the rays were also emitted from elements other than uranium. She also discovered new elements by detecting their rays  radium named for its green phosphorescence  polonium named for her homeland Becquerel, Marie and Pierre Curie were awarded Nobel Prize in physics in 1903, for the discovery of radioactivity. 5 Electroscope  What Is Radioactivity? Radioactivity is the release of tiny, high- energy particles or gamma rays from an atom Particles are ejected from the nucleus 6  Types of Radioactive Decay Ernest Rutherford discovered three types of rays  alpha () rays 4 have a charge of +2 c.u. and a mass of 4 amu 2 He what we now know to be helium nucleus  beta () rays 0e have a charge of −1 c.u. and negligible mass –1 electron-like  gamma (rays 0γ form of light energy (not a particle like and) 0 In addition, some unstable nuclei emit positrons  like a positively charged electron Some unstable nuclei will undergo electron capture  a low energy electron is pulled into the nucleus 7 Rutherford’s Experiment ++++++++++++    -------------- Ernest Rutherford, 30 August 1871 – 19 October 1937 A New Zealand-born British chemist and physicist, known as the father of nuclear physics Nobel Prize in Chemistry (1908) McGill University (1898-1907), University of Manchester 8  Properties of Radioactivity Radioactive rays can ionize matter cause uncharged matter to become charged basis of Geiger Counter and electroscope Radioactive rays have high energy Radioactive rays can penetrate matter Radioactive rays cause phosphorescent chemicals to glow basis of scintillation counter 9 Electroscope Penetrating Ability of Radioactive Rays    0.01 mm 1 mm 100 mm Pieces of Lead 10  Nuclear Medicine Changes in the structure of the nucleus are used in many ways in medicine Nuclear radiation can be used to visualize or test structures in your body to see if they are operating properly (Diagnosis) e.g. labeling atoms so their intake and output can be monitored Nuclear radiation can also be used to treat diseases because the radiation is ionizing, allowing it to attack unhealthy tissue (Therapy) 11  Facts About the Nucleus Very small volume compared to volume of the atom Essentially entire mass of atom Very dense Composed of electron protons and neutrons that are tightly held together the particles that make up the nucleus are called nucleons 12  Facts About the Nucleus Every atom of an element has the same number of protons atomic number (Z) Atoms of the same elements can have different numbers of neutrons isotopes different atomic masses Isotopes are identified by their mass number (A) mass number = number of protons + neutrons 13  Facts About the Nucleus The number of neutrons is calculated by subtracting the atomic number (Z) from the mass number (A) The nucleus of an isotope is called a nuclide less than 10% of the known nuclides are non- radioactive, most are radionuclides Each nuclide is identified by a symbol Element – Mass Number = X – A He – 4 4 2 He Xiao-An ZHANG 14  Radioactivity Radioactive nuclei spontaneously decompose into smaller nuclei  radioactive decay  we say that radioactive nuclei are unstable  decomposing involves the nuclide emitting a particle and/or energy The parent nuclide is the nucleus that is undergoing radioactive decay The daughter nuclide is the new nucleus that is made All nuclides with 84 (polonium) or more protons (Z  84) are radioactive 15 Important Atomic Symbols 16  Transmutation During the radioactive process, atoms of one element are changed into atoms of a different element – transmutation  showing that Dalton’s Atomic Theory is not valid all the time, only for chemical reactions For one type of element to change into another, the number of protons (Z) in the nucleus must change! 17  Chemical Processes vs Nuclear Processes Chemical Reactions Nuclear Reactions Change in (valence) electron. Change in particles in configuration. nucleus (protons, neutrons). All elements remain Elements may be converted unchanged. from one to another. Release or absorb much Release or absorb immense smaller amounts of energy. amounts of energy Rates of reaction depend on Rates of reaction usually are factors such as concentration, not influenced by external pressure, temperature, and factors catalysts, etc. 18  Nuclear Equations We describe nuclear processes with nuclear equations Use the symbol of the nuclide to represent the nucleus The atomic numbers (Z) and mass numbers (A) are conserved  use this fact to predict the daughter nuclide if you know parent and emitted particle Uranium Thorium 19  Alpha Emission An  particle contains 2 protons and 2 neutrons helium nucleus Most ionizing, but least penetrating of the types of radioactivity Loss of an alpha particle means atomic number (Z) decreases by 2 mass number (A) decreases by 4 222 88 Ra 4 2 He  218 86 Rn Radium Radon 20 Alpha Decay 21  Beta Emission A  particle is like an electron moving much faster than  produced from the nucleus About 10 times more penetrating than , but only about half the ionizing ability When an atom loses a  particle its atomic number increases by 1 mass number remains the same In beta decay, a neutron changes into a proton Thorium Protactinium 22 Beta Decay 23  Gamma Emission Gamma () rays are high energy photons of light No loss of particles from the nucleus No change in the composition of the nucleus  same atomic number and mass number Least ionizing, but most penetrating Generally occurs after the nucleus undergoes some other type of decay and the remaining particles rearrange 24  Positron Emission Positron has a charge of +1 c.u. and negligible mass anti-electron Similar to beta particles in their ionizing and penetrating ability When an atom loses a positron from the nucleus, its mass number remains the same atomic number decreases by 1 Positrons result from a proton changing into a neutron 25 Positron Emission 26  Electron Capture Occurs when an inner orbital electron is pulled into the nucleus No particle emission, but atom changes same result as positron emission Proton combines with the electron to make a neutron mass number stays the same atomic number decreases by one 27 Particle Changes 28 29  Nuclear Equations In the nuclear equation, mass numbers and atomic numbers are conserved We can use this fact to determine the identity of a daughter nuclide if we know the parent and mode of decay 30 Example 19.2b: Write the nuclear equation for positron emission from K–40 1. Write the nuclide symbols for both the starting radionuclide and the particle 31 Examle 19.2b: Write the nuclear equation for positron emission from K–40 2. Set up the equation emitted particles are products captured particles are reactants 32 Example 19.2b: Write the nuclear equation for positron emission from K–40 3. Determine the mass number and atomic number of the missing nuclide mass and atomic numbers are conserved 33 Example 19.2b: Write the nuclear equation for positron emission from K–40 4. Identify and determine the symbol of the element from the atomic number 34 Practice – Write a nuclear equation for each of the following alpha emission from U–238 beta emission from Ne–24 positron emission from N–13 electron capture by Be–7 35 What Causes Nuclei to Decompose? The particles in the nucleus are held together by a very strong attractive force only found in the nucleus called the strong force acts only over very short distances (fm, 10−15 m) The neutrons play an important role in stabilizing the nucleus, as they add to the strong force, but don’t repel each other like the protons do 37  N/Z Ratio The ratio of neutrons : protons is an important measure of the stability of the nucleus If the N/Z ratio is too high, neutrons are converted to protons via  decay If the N/Z ratio is too low, protons are converted to neutrons via positron emission or electron capture or via  decay – though not as efficiently in changing N/Z, but significantly causing decrease of both A and Z. 38 Valley of Stability for Z = 1  20, stable N/Z ≈ 1 for Z = 20  40, stable N/Z approaches 1.25 for Z = 40  80, stable N/Z approaches 1.5 for Z > 83, there are no stable nuclei 39  Example 19.3b: Predict the kind of radioactive decay that Mg−22 undergoes Mg–22  Z = 12  N = 22 – 12 = 10 N/Z = 10/12 = 0.83 From Z = 1  20, stable nuclei have N/Z ≈ 1 Because Mg–22 N/Z is low, it should convert p+ into n0, therefore it will undergo positron emission or electron capture 40  Practice – Predict whether Kr–85 is stable or radioactive. If radioactive, predict the mode of radioactive decay and the daughter nuclide. 41  Magic Numbers Besides the N/Z ratio, the actual numbers of protons and neutrons affects stability Most stable nuclei have even numbers of protons (Z) and neutrons (N) Only a few have odd numbers of protons and neutrons (tendency of pair together) If the total number of nucleons adds to a magic number, the nucleus is more stable  same principle as stability of the noble gas electron configuration  most stable when N or Z = 2, 8, 20, 28, 50, 82; and N = 126 43  Decay Series In nature, often one radioactive nuclide changes into another radioactive nuclide  i.e. the daughter nuclide is also radioactive All of the radioactive nuclides that are produced one after the other until a stable nuclide is made is called a decay series To determine the stable nuclide at the end of the series without writing it all out 1. count the number of  and  decays 2. from the mass no. subtract 4 for each  decay 3. from the atomic no. subtract 2 for each  decay and add 1 for each  44  U-238 Decay Series         or    or other     combinations       45  Detecting Radioactivity To detect something, you need to identify what it does Radioactive rays can expose light-protected photographic film We may use photographic film to detect the presence of radioactive rays – film badge dosimeters 46  Detecting Radioactivity, cont’d Radioactive rays cause air to become ionized An electroscope detects radiation by its ability to penetrate the flask and ionize the air inside A Geiger-Müller counter works by counting electrons generated when Ar gas atoms are ionized by radioactive rays 47  Detecting Radioactivity , cont’d Radioactive rays cause certain chemicals (such as NaI or CsI) to give off a flash of light when they strike the chemical A scintillation counter is able to count the number of flashes per minute https://en.wikipedia.org/wiki/Scintillation_counter 48  Natural Radioactivity There are small amounts of radioactive minerals in the air, ground, and water Even in the food you eat! The radiation you are exposed to from natural sources is called background radiation 49  Kinetics of Radioactive Decay The rate of a reaction is the change in the number of reactant or product molecules ( ) per unit time ( ) Rate = ∆N/∆t First order kinetic rate laws (temperature independent) Rate: ∆N/∆t = kN (see Chapter 13, Chemical Kinetics)  N = number of radioactive nuclei  k: rate constant. different for each radioactive “isotope”; Each radionuclide has a constant half-life (t1/2): the length of time to lose half its radioactivity, a constant independent of the number of radioactive nuclei (N). The larger the rate constant, the faster the nuclei decay, the shorter the half-life (the sample is hotter). 50  Kinetics of Radioactive Decay First order rate: ∆N/∆t = kN Rewrite in differential form (infinitesimally small change): Integrate both sides: Solve the integrals: Let N0 is the initial value of at =0: N0 Final integrated rate law: Nt = N 0 51  The Integrated Rate Law Based on the integrated rate law: Nt= N0 At half-life (t1/2), Nt / N0 = ½. 52 Pattern for Radioactive Decay 53  Half-Lives of Various Nuclides Type of Nuclide Half-Life Decay Th–232 1.4 x 1010 yr alpha U–238 4.5 x 109 yr alpha C–14 5730 yr beta Rn–220 55.6 sec alpha Th–219 1.05 x 10–6 sec alpha 54 Example19.4: If you have a 1.35 mg sample of Pu–236, which has a half-life of 2.86 yr, calculate the mass that will remain after 5.00 years Given: mass Pu–236 = 1.35 mg, t = 5.00 yr, t1/2 = 2.86 yr Find: mass remaining, mg Conceptual t1/2 k + m0, t mt Plan: Relationships: Solve: Check: units are correct, the magnitude makes because since it is less than ½ the original mass for longer than 1 half-life 55 Practice—Radon–222 is a gas that is suspected of causing lung cancer as it leaks into houses. It is produced by uranium decay. Assuming no loss or gain from leakage, if there is 10.24 g of Rn–222 in the house today, how much will there be in 5.4 weeks? ( Rn–222 half-life is 3.8 Days) 56  Radiometric Dating The change in the amount of radioactivity of a particular radionuclide is predictable and not affected by environmental factors By measuring and comparing the amount of a parent radioactive isotope and its stable daughter we can determine the age of the object by using the half-life and the previous equations Mineral (geological) dating compare the amount of U-238 to Pb-206 (plumbum or lead) in volcanic rocks and meteorites dates the Earth to between 4.0 and 4.5 billion yrs. old compare amount of K-40 to Ar-40 58  Radiocarbon Dating All things that are alive or were once alive contain carbon Three isotopes of carbon exist in nature, one of which, C–14, is radioactive C–14 radioactive with half-life = 5730 yrs 14 14 0 C N + e  6 7 –1 We would normally expect a radioisotope with this relatively short half-life to have disappeared long ago, but atmospheric chemistry keeps producing C–14 at nearly the same rate it decays 14 1 14 1 N + n C + H 7 0 6 1 59  Radiocarbon Dating While still living, C–14/C–12 is constant because the organism replenishes its supply of carbon CO2 in air ultimate source of all C in organism Once the organism dies the C–14/C–12 ratio decreases By measuring the C–14/C–12 ratio in a once living artifact and comparing it to the C–14/C–12 ratio in a living organism, we can tell how long ago the organism was alive The limit for this technique is 50,000 years old about 9 half-lives, after which radioactivity from C–14 will be below the background radiation 60  Radiocarbon Dating % C-14 (compared to living Object’s Age (in years) organism) 100% 0 90% 870 80% 1850 60% 4220 50% 5730 40% 7580 25% 11,500 10% 19,000 5% 24,800 1% 38,100 61 Measure the Age of Artifacts, Fossils, Trees… The Dead Sea Scrolls are 2000- year-old biblical manuscripts. Western bristlecone pine trees can Their age was determined by live > 5000 years. We can use annual radiocarbon dating. rings in tree trunks to calibrate the timescale for radiocarbon dating. 62 Example 19.5: An ancient skull gives 4.50 disintegrations per second per gram of carbon (dis/min∙gC). If a living organism gives 15.3 dis/min∙gC, how old is the skull? Given: ratet = 4.50 dis/min∙gC; ratet0 = 15.3 dis/min∙gC; t1/2 Find: time, yr Conceptual t1/2 k + rate0, ratet t Plan: Relationships: Solve: Check: units are correct, the magnitude makes sense because it is less than 2 half-lives 63 Practice – Archeologists have dated a civilization to 15,600 yrs ago. If a living sample gives 20.0 counts per minute per gram C, what would be the number of counts per minute per gram C for a rice grain found at the site? 64  Nonradioactive Nuclear Changes A few nuclei are so unstable that if their nucleus is hit just right by a neutron, the large nucleus splits into two smaller nuclei — this is called fission Small nuclei can be accelerated to such a degree that they overcome their charge repulsion and smash together to make a larger nucleus - this is called fusion Both fission & fusion may release Lise Meitner (1878-1968) determined that U-235 can enormous amounts of energy undergo nuclear fission with Otto Hahn and Fritz  fusion could releases more energy per Strassmann. But Nobel Prize gram than fission in Chemistry 1944 was 66 awarded to Otto Hahn only.  Fission Reaction 235 92 U Nuclear fission first reported in January 6, 1939 67  Fission Chain Reaction A chain reaction occurs when a reactant that initiates the process is also a product of the process in the fission process it is the neutrons so you only need a small amount of neutrons to start the chain Many of the neutrons produced in fission are either ejected from the uranium before they hit another U- 235 or are absorbed by the surrounding U-238 Minimum amount of fissionable isotope needed to sustain the chain reaction is called the critical mass 68  Fission Chain Reaction 69  On July 16, 1945, tested in the New Mexico desert, and in August 06, used in Hiroshima 70 and then Nagasaki.  Fissionable Material Fissionable isotopes include U–235 (uranium), Pu–239, and Pu–240 (plutonium) Natural uranium is less than 1% U–235 rest mostly U–238 not enough U–235 to sustain chain reaction To produce fissionable uranium, the natural uranium must be enriched in U–235 to about 7% for “weapons grade” to about 3% for reactor grade 71  Nuclear Power Nuclear reactors use fission to generate electricity about 15 % of electricity in Canada, ~50 % in Ontario (16 reactors) about 20% of U.S. electricity uses the fission of U–235 to produce heat The heat boils water, turning it to steam The steam turns a turbine, generating electricity Pickering- nuclear- generating- station 72  Nuclear Power Plants vs. Coal-Burning Power Plants Use about 50 kg of Use about 2 million kg fuel to generate of fuel to generate enough electricity for 1 enough electricity for 1 million people/d million people/d No air pollution Produce NO2 and SOx that add to acid rain Produce CO2 that adds to the greenhouse effect 73  Pressurized Light Water Reactor Design used in United States (GE, Westinghouse) Water is both the coolant and moderator Water in core kept under pressure to keep it from boiling Fuel is enriched uranium subcritical Containment dome of concrete 74  Nuclear Power Plants - Core The fissionable material is stored in long tubes, called fuel rods, arranged in a matrix subcritical Between the fuel rods are control rods made of neutron-absorbing material B and/or Cd neutrons needed to sustain the chain reaction The rods are placed in a material to slow down the ejected neutrons, called a moderator allows chain reaction to occur below critical mass 75 Nuclear Reactor 76  Concerns about Nuclear Power Core melt-down Waste disposal  waste highly radioactive  reprocessing, underground storage?  Federal High Level Radioactive Waste Storage Facility at Yucca Mountain, Chernobyl (now Ukraine) Nevada reactor core exploded Transporting waste in1986 due to over-heat. How do we deal with nuclear power plants that are no longer safe to operate?  Yankee Rowe in Massachusetts The Fukushima Daiichi nuclear disaster (福島第一原子力発電所 事故) due to earthquake, March 77 11, 2011 Where Does the Fission Energy Come from? During nuclear fission, some of the mass of the nucleus is converted into energy:  E = mc2 235 + 1n 140 92 U 0 56 Ba + 93 Kr + 3 1 n 36 0 78  Converting Mass to Energy Mass lost = 236.05258 u – 235.86769 u = 0.18489 u×1.66054 x 10–27 kg u–1 = 3.0702×10–28 kg Energy Produced (E) = mc2 = 3.0702×10–28 kg x (2.9979×108 m s–1)2 = 2.7593×10–11 J per 235U atom Each mole of U–235 that fissions produces about 1.7 x 1013 J of energy a very exothermic chemical reaction produces 106 J per mole 79 Mass Defect and Nuclear Binding Energy When a nucleus forms, some of the mass of the separate nucleons is converted into energy The difference in mass between the separate nucleons and the combined nucleus is called the mass defect 2 11 H  2 01 n  42 He m 80  Nuclear Binding Energy The energy that is released due to mass defect when the nucleus forms is called the binding energy. Nuclear physicists often use electron volt (eV) or megaelectron volt (MeV) as unit for binding energy:  1 MeV = 1.602 x 10−13 J  1 u (or amu) of mass defect = 931.5 MeV He nuclear binding energy: Nuclear binding energy per nucleon: The greater the binding energy per nucleon, the more stable the nucleus is. 81 82  Example19.7: Calculate the mass defect and nuclear binding energy per nucleon (in MeV) for C–16, a radioactive isotope of carbon with a mass of 16.014701 amu Given: mass C-16 = 16.01470 amu, mass p+ = 1.00783 amu, mass n0 = 1.00866 amu Find: mass defect in amu, binding energy per nucleon in MeV Conceptual mass mp+, mn0, mC-16 binding energy Plan: defect Relationships: Solve: 83 Practice – Calculate the binding energy per nucleon in Fe–56 84  Nuclear Fusion Fusion is the combining of light nuclei to make a heavier, more stable nuclide The Sun uses the fusion of hydrogen isotopes to make helium as a power source Requires high input of energy to initiate the process  because need to overcome repulsion of positive nuclei Produces 10x the energy per gram as fission No radioactive byproducts Unfortunately, the only currently working application is the H-bomb 86 Fusion 87  Tokamak Fusion Reactor [The DIII-D National Fusion Facility is a Department of Energy user facility, operated by General Atomics under cooperative agreement DE-FC02-04ER54698; Image Courtesy of General Atomics. © 2017 General Atomics.] 88  Making New Elements: Artificial Transmutation High energy particles can be smashed into target nuclei, resulting in the production of new nuclei The particles may be radiation from another radionuclide, or charged particles that are accelerated  Rutherford made O–17 by bombarding N–14 with alpha rays from radium  Cf–244 (Californium) is made by bombarding U–238 with C–12 in a particle accelerator 89  Artificial Transmutation Bombardment of one nucleus with another causing new atoms to be made can also bombard with neutrons Reaction done in a particle accelerator linear cyclotron Tc-97 is made by bombarding Mo-96 with deuterium, releasing a neutron 90  Linear Accelerator +- + - +- + - +- + - +- + - +- + - +- + - +- + - +- + - +- + - +- + - +- + - +- + + + source target 91 Linear Accelerator Cyclotron - Wikipedia 92  Cyclotron target source 93  Practice – Predict the other daughter nuclide and write a nuclear equation for each of the following bombarding Ni–60 with a proton to make Co–57 bombarding N–14 with a neutron to make C–12 bombarding Cf–250 with B–11 producing 4 neutrons 94  Biological Effects of Radiation Radiation has high energy, energy enough to knock electrons from molecules and break bonds ionizing radiation Energy transferred to cells can damage biological molecules and cause malfunction of the cell 96  Acute Effects of Radiation High levels of radiation over a short period of time kill large numbers of cells from a nuclear blast or exposed reactor core Rapid dividing cells, such as immune cells or intestinal lining cells, are more susceptible to radiation, causing weakened immune system and lower ability to absorb nutrients from food may result in death, usually from infection 97  Chronic Effects Low doses of radiation over a period of time show an increased risk for the development of cancer radiation damages DNA that may not get repaired properly Low doses over time may damage reproductive organs, which may lead to sterilization Damage to the DNA in reproductive cells may lead to genetic defects in offspring 98  Measuring Radiation Exposure Number of decay events: 1 becquerel (Bq) = 1 event/second Absorbed dose gray (Gy) measures the amount of energy absorbed: 1 Gy = 1 J/kg body tissue Both do not account for the degree of biological damage. Equivalent dose: 99  Factors that Determine the Biological Effects of Radiation 1. The more energy the radiation has, the larger its effect can be 2. The better the ionizing radiation penetrates human tissue, the deeper effect it can have  Gamma >> Beta > Alpha 3. The more ionizing the radiation, the larger the effect of the radiation  Alpha > Beta > Gamma 4. The radioactive half-life of the radionuclide 5. The biological half-life of the element 6. The physical state of the radioactive material 100  Biological Effects of Radiation Effects of Instantaneous Radiation Exposure 101  Medical Uses of Radioisotopes, Treatment – Radiotherapy Cancer treatment  cancer cells more sensitive to radiation than healthy cells – use radiation to kill cancer cells without doing significant damage  brachytherapy  place radioisotope directly at site of cancer  teletherapy  use gamma radiation from Co–60 outside to penetrate inside  radiopharmaceutical therapy  use radioisotopes that concentrate in one area of the body 102  Radiotherapy Teletherapy Brachytherapy Gamma Ray 103  Medical Uses of Radioisotopes, Diagnosis Radiotracers certain organs absorb most or all of a particular molecules You use radioisotope tagged molecule and a counter or detector to measure or image the target tagged = radioisotope that can then be detected and measured use radioisotope with a short half-life use radioisotope that is low ionizing beta or gamma 104 Common Radiotracers for Medical Applications 105  SPECT Single Photon Emission Computed Tomography (SPECT) requires a gamma- emitting radionuclide. 99mTc → 99Tc + γ A γ -camera can intercept the γ –ray to create a 2D image; For 3D recording, single or multiple γ – cameras rotate around the object and acquires projections from (equally spaced) angular intervals; 3D image can be created using an iterative reconstruction technique. The radioisotope can be attached to a special radioligand for targeting purpose. 99mTc-exametazime 106 HMPAO (Ceretec, GE)  Bone Scans (Tc-99m Bisphosphonates) 99mTc MDP (aka 99mTc-Methyl Diphosphonate, Technicium [99mTc]Medronate, 99mTc-Methylene 107 diphosphonate)  PET – Positron Emission Tomography Certain radionuclides emit positrons. When a positron meets an electron, they annihilate each other. This annihilation results in a generation of two gamma rays. The gamma rays travel in opposite directions. The energy of these gamma rays is 511 KeV. PET Imaging is based on detection of these gamma rays. Angew. Chem. Int. Ed. 2008(47)8998  PET Systems Event Detection Several gamma-detector rings surround the patient. When one of these detects a photon, a detector opposite to it, looks for a match. Time window for the search is a few nanosecs. If such a coincidence is detected, a line is drawn between the detectors. When done, there will be areas of overlapping lines LOR – Line of Response indicating regions of radioactivity.  Medical Uses of Radioisotopes, Diagnosis PET scan positron emission tomography F–18 tagged glucose F–18 is a positron emitter brain scan and function FDG: fluorodeoxyglucose (18F) 110 Nonmedical Uses of Radioactive Isotopes Smoke detectors  Am–241  smoke blocks ionized air, breaks circuit Insect control  sterilize males Food preservation Radioactive tracers  follow progress of a “tagged” atom in a reaction Chemical analysis  neutron activation analysis 111