Nuclear Chemistry

1. Nuclear Chemistry

2. History of Nuclear Chemistry • Henri Becquerel – in 1896 he found that uranium ore gave off invisible radiation. This was an accidental discovery using photographic film wrapped in light proof paper with a piece of fluorescent uranium salt. The film showed an image proving that something given off by the salt, rather than light, caused the image. • Marie Curie and her husband, in 1898, discovered the new radioactive elements they named polonium and radium.

3. Becquereland the Curies were awarded the 1903 Physics Nobel Prize Marie Curie died as a result of complications due to exposure to radiation http://nobelprize.org/physics/laureates/1903/becquerel-bio.html http://www.accessexcellence.org/AE/AEC/CC/historical_background.html

4. Nuclear Chemistry • Understanding Radioactivity and Radioactive Decay • Figuring Out Half-Lives • Tracing the Effects of Radiation • The Basics of Nuclear Fission • Looking at Nuclear Fusion

5. It all starts with the Atom • Nuclear Chemistry refers to changes that occur in the dense central core of the atom containing protons (+) and neutrons (0) • Atoms of the same element with different numbers of neutrons are called isotopes. Many elements have several isotopic forms http://www.lbl.gov/abc/Basic.html

6. 239 92 Nuclide – name given to the unstable nucleus of a radioactive atom How many protons and neutrons are found in an atom of uranium-239? U Atomic number = protons There are 92 protons Mass number = sum of protons and neutrons 239 – 92 = 147 There are 147 neutrons

7. Radioactivity and Radioactive Decay • Radioactivity is the spontaneous decay of an unstable nucleus • An unstable nucleus may break apart into two or more other particles with the release of energy • Transmutation is the change which occurs when one element is changed into another as a result of an alteration in the nucleus (number of protons changes)

8. You can predict particles of radioactive decay by balancing nuclear reactions • Reactions are represented as follows: • Reactants  Products • Reactants are substances you start with • Products are substances being formed • The reaction arrow indicates that a reaction has taken place http://www.lbl.gov/abc/Basic.html

9. 35Cl + 1n X? + 1H 17 0 1 For a nuclear reaction to be balanced, the sum of all the atomic numbers on the left side of the reaction arrow must equal the sum of all the atomic numbers on the right side of the arrow. The same is true for the mass numbers. In the above example, an isotope of Chlorine (Cl-35) is bombarded by a neutron. You observe that an isotope of hydrogen (H-1) is created along with another isotope that you need to identify.

10. 35Cl + 1n X? + 1H 17 0 16 1 • To figure out the unknown isotope (X) you need to balance the equation. The sum of the atomic numbers on the left is 17 (17 + 0), so you want the sum of atomic numbers on the right to be 17 also. You already have an atomic number of 1 on the right, so the atomic number of the unknown is 17-1 = 16. • 35Cl + 1n ?X + 1H17 0 16 1

11. 35Cl + 1n ?X + 1H 17 0 16 1 • Now look at the mass numbers in the equation. The sum of the mass numbers on the left is 36 (35 + 1), and you want the sum of the mass numbers on the right to equal 36, too. Right now there is a mass number of 1 on the right; 36 – 1 = 35, so that’s the mass number of the unknown isotope. You can now determine that the unknown isotope is sulfur (atomic #16), and the balanced equation looks like this: • 35Cl + 1n 35S + 1H17 0 16 1

12. Transmutation • This example represents a nucleartransmutation, the conversion of one element into another. Nuclear transmutation is a process human beings control. S-35 is an isotope that doesn’t exist in nature – it is a manmade isotope. • Alchemy – age old attempt to turn common metals into gold http://www.bayerus.com/msms/fun/pages/periodic/gold/

13. Natural Radioactive Decay • Certain isotopes are unstable. Their nucleus breaks apart, undergoing nuclear decay. • The nucleus has all the positively charged protons tightly packed together in an extremely small space with all the protons repelling each other. • All elements with 84 or more protons are unstable. • Other isotopes with fewer than 84 protons can be radioactive if the neutron / proton ratio is too high. If the isotope is “neutron rich” it is unstable. That’s why some isotopes of an element are stable and others are radioactive.

14. Naturally occurring radioactive isotopes can decay in the following ways: • Alpha particle emission - α • Beta particle emission - β • Gamma radiation emission - γ Less common types of radioactive decay: • Positron emission • Electron capture

15. Alpha Emission • An alpha particle is the positive nucleus of a He atom, and is represented as 4He. It is actually a He2+ ion – Helium ion with no electrons. • Normally an alpha particle given off picks up two electrons quickly and becomes a neutral helium atom. (electrons are easy to pick up or lose) • Radon-222 is an example of an isotope that undergoes alpha emission as follows: • 222Rn  218Po + 4He 2 86 84 2 alpha particle

16. Beta Emission • Isotopes with high neutron / proton ratio undergo beta emission. • In beta emission, a neutron decays into a proton and an electron. • The atomic number increases by 1, and a beta particle is given off. • Iodine-131 which is used in the detection and treatment of thyroid cancer, is a beta particle emitter: • 131I  131Xe + 0e 53 54 -1 beta particle

17. Gamma Emission • Alpha and beta particles have the characteristics of matter. They have definite masses and volumes. • Because there is no mass change associated with gamma emission, it is referred to as gamma radiation emission, and is similar to x-rays (high energy, short wavelength electromagnetic radiation). • Gamma radiation emission often accompanies both alpha and beta emission, but is not usually shown in a balanced nuclear reaction. • Some isotopes give off large amounts of gamma radiation such as Cobalt-60, which is used in the radiation treatment of cancer. Gamma rays are focused on the tumor, destroying cells.

18. A problem with gamma radiation: http://www.hulklibrary.com/hulk/home/home.asp http://www.hulkmovie.com/cast/ericbana.htm

19. Positron Emission • Positron emission occurs with some manmade radioactive isotopes. • A positron is an electron with a positive charge. • When a proton decays a neutron and a positron are formed and the positron is emitted from the nucleus. • Potassium-40 is an example of a positron emitter: • 40K  40Ar + 0e 19 18 +1 positron

20. http://kazza.cia.com.au/images/website/startrek-enterpr.jpg Antimatter • Do you watch “Star Trek?” • A positron is a tiny bit of antimatter. • When a positron comes in contact with an electron, both particles are destroyed with the release of energy. • Fortunately, not many positrons are produced, so we don’t have to go around dodging explosions.

21. Electron Capture • Electron capture is a rare type of nuclear decay in which an electron from the innermost energy level (1s) is captured by the nucleus. • This electron combines with a proton becoming a neutron. • The following equation shows the electron capture of Polonium-204: • 204Po + 0e  204Bi + x-rays With the 1s orbital vacant, electrons drop down releasing energy – x-rays 84 -1 83

22. Half-Lives and Radioactive Dating • It takes a certain amount of time for half the atoms in a sample of radioactive material to decay. It then takes the same amount of time for half the remaining radioactive atoms to decay, and the same amount of time for half of those remaining radioactive atoms to decay, and so on… • The amount of time it takes for one half of a sample to decay is called the half life of the isotope and is given the symbol: t ½ • The decay of a radioactive isotope is exponential

23. Radioactive Decay

24. Carbon-14 Radioactive Decay

25. Half-Lives of some Radioactive Isotopes

26. Radioactive Dating • Carbon-14 is absorbed by plants from carbon dioxide in the atmosphere and enters the food chain. • As long as an organism is alive, the amount of C-14 remains constant. • C-14 begins to decrease at a predictable rate when an organism dies. (t ½ of C-14 is 5,730 years) • Radioactive dating using C-14 has been used to determine the age of skeletons found at archeological sites. • For nonliving substances, scientists use other isotopes, such as potassium-40.

27. Safe Handling • Knowing about half-lives allows scientists to know when a sample of a radioactive material is safe to handle. • The rule is that a sample is safe when its radioactivity has dropped below detection limits. This usually occurs at 10 half lives. • If radioactive iodine-131 (t ½ = 8 days) is injected into the body to treat thyroid cancer, it will be “gone” in 10 half lives or 80 days.

28. Measuring Radiation • Curie (Ci) – used to measure radioactivity • 1 Ci = 3.7 X 1010 disintegrations per second • Radiation Absorbed Dose (rad) – the amount of energy absorbed per gram • Radiation Equivalent for Man (rem) – used to estimate radiation effects on the body

29. Detecting Radiation • Geiger Counter – gas filled metal tube that when exposed to radiation causes a current to flow creating an audible click from a built in speaker. • Scintillation Counter – uses a specially coated phosphorous surface to detect radiation. Radiation striking the surface causes bright flashes of light, or scintillations. • Film badge – worn by people who work near radiation sources. It is several layers of photographic film covered with black, light proof paper. Radiation exposure will cause a darkening of the film.

30. Geiger counter http://www-istp.gsfc.nasa.gov/Education/wgeiger.html Film Badges http://www.orau.org/ptp/collection/dosimeters/keleketmetalfilmbadge.htm

31. Average Yearly Human Exposure Maximum recommended dose per year: 500 millirems

32. Ability of Various Types of Radiation Penetrating

33. Biological Effects of Radiation • Radiation can have two basic effects on the body: • It can destroy cells with heat • It can ionize and fragment cells leading to damage, destruction or mutation

34. http://www.gensuikin.org/english/photo.html

35. Nuclear Fission • In the 1930’s scientists discovered that some nuclear reactions can be initiated and controlled. • This is usually accomplished by bombarding a large isotope with a second, smaller one – commonly a neutron. • The collision causes the larger isotope to break apart into two or more elements. • This is known as nuclear fission. • These types of reactions release a lot of energy.

36. The first atomic bomb was dropped on Hiroshima, Japan, on August 6, 1945. Two pieces of a fissionable isotope are kept apart until it’s time for the bomb to explode. Conventional explosives force the two pieces together to cause a chain reaction releasing a tremendous amount of energy instantaneously. http://www.gensuikin.org/english/photo.html Atomic Bombs

37. Fission Chain Reaction http://www.euronuclear.org/info/encyclopedia/chainreaction.htm

38. FISSION REACTIONS http://www.visionlearning.com/library/module_viewer.php?mid=59&l=&c3=

39. Energy from Nuclear Fission • After a fission reaction, the mass of the reactants is less that the original mass of the products. • The loss of matter during the nuclear reaction is called the mass defect. • The missing matter is converted into energy. • The amount of energy produced can be calculated with the following equation: • E = mc2 • m is the “missing mass” • c is the speed of light

40. Nuclear Power Plants – Controlled Energy Release • A nuclear power plant produces heat through controlled nuclear fission to boil water, which, in turn, is used to make steam to turn a turbine attached to a generator that produces electricity. • Conventional power plants burn coal, oil or gas, producing air pollution. • Potential accidents, and radioactive wastes are problems associated with nuclear power plants. • Large amounts of radioactive isotopes produced by nuclear power plants have to be kept safe and undisturbed for thousands of years.

41. Nuclear Reactor http://reactor.engr.wisc.edu/power.html

42. Nuclear Power Plants http://www.nrc.gov/info-finder/reactor/ Glen Rose, TX Approximately 50 miles from Ft. Worth

43. Nuclear Power Plants - Accidents • Three Mile Island – In 1979 at the Three Mile Island Plant in Pennsylvania, a combination of operator error and equipment failure caused a loss of reactor core coolant leading to a partial meltdown and the release of a small amount of radioactive gas. There was no loss of life or injury to plant personnel or the general population. • Chernobyl, Ukraine – In 1986, human error and poor reactor design contributed to a tremendous overheating of the reactor core, causing it to rupture. Two explosions and a fire resulted, blowing apart the core and scattering nuclear material into the atmosphere. A small amount of the material traveled to Europe and Asia. Hundreds of people died; many others were sick from radiation poisoning and developed cancer. The area is still uninhabitable. The reactor is encased in concrete, and must remain undisturbed for hundreds of years.

44. Chernobyl http://www.spaceman.ca/gallery/chernobyl/Chernopik http://www.answers.com/topic/chernobyl-accident

45. Nuclear Fusion – Hope for the Future • In fusion, lighter nuclei are fused into a heavier nucleus, releasing large amounts of energy. • The fusion process is the reaction that powers the sun. • Controlled release of energy from a fusion reaction could produce an unlimited supply of energy that has no wastes or contaminants to harm the atmosphere.

46. Nuclear Fusion http://www.lbl.gov/abc/Basic.html

47. Problems in achieving fusion: • Temperature – the fusion process requires an extremely high activation energy. The heat required would be 40,000,000 K. This is hotter than the sun! • Time – the nuclei must be held together close enough and for long enough at an extremely high temperature for the reaction to start – about 1 second. • Containment – the best ceramics developed for the space program would vaporize when exposed to this high temperature.

48. Hydrogen Bomb • In the Hydrogen bomb the explosion of a nuclear fission charge (atomic bomb) produces the temperature and density so fusion can occur. This fusion results in a sudden release of a large amount of energy that produces an even bigger explosion. http://encarta.msn.com/encyclopedia_761557090/Hydrogen_Bomb.html

49. FUSION REACTIONS http://www.visionlearning.com/library/module_viewer.php?mid=59&l=&c3=

50. Something to Remember • Radioactive dating is not…. • Taking an x-ray technician to the movies