Nuclear Chemistry Text Chapter 18 - PowerPoint PPT Presentation

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Nuclear Chemistry Text Chapter 18

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  1. Nuclear ChemistryText Chapter 18 Tomotherapy machine for radiation treatment of cancer at Johns Hopkins Glow in the Dark Stars Nuclear Submarine

  2. Nuclear ChemistryWhat does nuclear refer to? • Nucleus • Protons & neutrons (nucleons). • Overall positive charge.*** • Strong force holds nucleons together. • Neutrons space positive charges and add stability. Who discovered the very dense, positive nucleus?

  3. Isotopes • Same atm #(protons) but diff # of neutrons (diff atomic mass). • Most isotopes are stable but many are unstable. • If unstable, the neutrons can’t balance all protons and the nucleus spontaneously decays, emitting radiation and/or particles (radioactivity). • Radioactive isotopes are called radioisotopes.

  4. Predicting Nuclear Stability • Stability of isotopes is based on the ratio of neutrons and protons in its nucleus. • Low atomic #’s(<20) stable atoms have a ratio of neutrons/protons=1. • High atomic #’s stable atoms have ratio of neutrons/protons=1.5. • Above atomic #83, no atoms are stable. How shown on Ref Tables?

  5. Radioactivity or Radioactive Decay • Process by which an unstable nucleus emits particles and/or radiant energy. • If emitted particles are protons, what will happen? • The atomic # is altered and one element is changed to another due to the nuclear change (transmutation).

  6. Emanations:emission of particles and/or energy from nucleus • Types of Emanations differ from each other in mass, charge, penetrating power and ionizing power. • Reference Table O.

  7. Alpha decay () • Alpha particle (helium nucleus) is given off as a result of nuclear disintegration. • High energy, relative velocity. • Shielding: stopped by thickness of a sheet of paper, skin

  8. Beta decay (-) A neutron is converted to a proton by emitting an electron. • Beta particle (high speed electron) is given off as the result of nuclear disintegration. • High velocity, low energy. • Beta particles have virtually no mass. • Shielding: stopped by 1cm of aluminum, average thickness of book.

  9. Gamma Radiation () • Gamma rays are similar to high energy x-rays. • Travel @ speed of light like all other forms of electromagnetic energy. • Do not have charge or mass. Type of radiation (photons) , not particles. • Shielding: 13cm of lead

  10. Positron decay(+) • Positrons are given off as result of nuclear disintegration. • Positrons are antiparticles of electrons. • When a positron hits an e-, they annihilate each other, forming 2 gamma rays (high penetration and high ionizing power). A proton is converted to a neutron.

  11. Separating , , and  emissions Geiger Counters are used to measure radioactivity. • Gamma rays and alpha and beta particles can be separated using an electric or magnetic field. Review

  12. Radioactivity Equations • Notice that the sum of the mass numbers (superscripts) on both sides of equation are equal (226=222+4). Why? • Law of Conservation of Mass • The sum of the atomic numbers (subscripts) on both sides of equation are also equal (88=86+2). Why? • Law of Conservation of Charge

  13. Balancing Radioactivity Equations • Use both Reference Table O & (PT). • If the atomic number changes, remember the identity of the element changes. • What 2 quantities must be balanced? #1 #2 The breakdown of Co60 in cancer radiation therapy.

  14. More Balancing of Radioactivity Equations • First use Reference Table N to determine the decay mode. • Continue and finish similar to other problems. Radioactive Orchestra

  15. ArtificialRadioactivity • Elements can be made radioactive by bombarding their nuclei with high energy particles. • Use particle accelerators. • Most elements from 93 and up (transuranium elements) were created with the use of particle accelerators. CERN Particle Accelerator in France & Switzerland + ___

  16. NuclearReactions • Mass is converted to energy. • Think E=mc2. • Produce tremendous amounts of energy!!! • 2 Types: Fission and Fusion Nuclear explosion at sea

  17. Nuclear Fission • Type of nuclear rxn. • Splitting of nucleus of a large atom into two or more fragments. • Produces additional neutrons and a lot of energy. • *Think binary fission or fissure. (splitting)

  18. ChainReactions • Each nucleus emits 3 neutrons that can cause the fission of another radioactive nucleus and so on. • Continues until a stable compound forms. • Ex: Atomic Bomb. • Nuclear reactors can control fission chain reactions and convert released energy into electric power.

  19. Parts of a NuclearReactor • Fuel (U235 & Pu239) • Moderator(slow down speed of neutrons, H2O, Be or graphite) • Control Rods(absorb neutrons, B & Cd) • Coolants(lowers temp,H2O) • Shielding(protects the reactor and people from radiation, steel or concrete)

  20. NuclearFusion • Two nuclei unite to form a heavier nucleus with release of enormous amounts of energy. • High temps and High pressures are necessary. • Occurs in the Sun and stars and the Hydrogen Bomb. • Think Unite, Fusion. 1st aerial test of H-bomb makes Bikini Atoll unlivable

  21. Differences Fission:splitting Fusion: uniting Fusion releases much more energy than fission. Fission produces radioactive waste, fusion only produces He. Similarities Both release a lot of energy. Both convert mass into energy. Compare & Contrast Fission andFusion

  22. Half-lives • Each radioisotope has a specific mode and rate of decay (half-life). • Ref Table N • Half-life is the time required for one-half of the nuclei of a given sample of an isotope to disintegrate.

  23. Half-life Problems can be used to find the following 4: • Fraction of radioisotope remaining (left) • Half-life • Initial amount (original amount) of radioisotope • Age of sample containing radioisotope (Radioactive Dating) Decay animation

  24. Benefits of Radioisotopes • Tracers • Medical Diagnosis or Treatment • Radiation of food • Radioactive Dating • Nuclear Power • Industrial Measurement • Industrial Applications

  25. Tracers • Radioisotopes can be used to follow the course (trace/track) of a chemical or biological reaction. • This is one way scientists learn about the many steps involved in reactions. • For example, C-14 has been used as a tracer to learn the steps of respiration (Kreb’s cycle)

  26. Medical Diagnosis & Treatment • Isotopes with very short half-lives and which will be quickly eliminated from the body are used in detecting and treating diseases. • Has created field of medicine called “Nuclear Medicine.” A PET scan using radiotracers to identify heart disease

  27. Medical Diagnosis & Treatment Examples • Tc-99 is used for pinpointing brain tumors and bone scans. • Radium and Cobalt-60 are used to attack cancer. • I-131 is used for diagnosis and treatment of thyroid disorders. A CT scan of the brain using Tc-99

  28. Irradiation of Food • Radiation kills bacteria, molds and yeast. It permits food to be stored for a longer time. Symbol for Irradiated Food

  29. Radioactive Dating • Comparing the ratio of radioactive to stable isotopes in a rock sample can give the age of the rock or geologic formation (mountains, etc.) (ie: U-238 to Pb-206 • Ratio of C-14:C-12 can be used to find age of organic materials.

  30. Nuclear Power • Nuclear reactors are used to produce electrical energy or electricity.

  31. Industrial Measurement • A beam of subatomic particles (α,β, or γ) is blocked by a certain thickness of metal. Measuring the fraction of the beam that is blocked gives a precise measurement of the thickness of the metal.

  32. Industrial Applications • A variety of radioisotopes are used in everyday applications. • Am-251 is used in smoke detectors. • The neutron activation analysis method can be used to detect artwork forgeries.

  33. Risks of Radioisotopes • Biological Damage • Long Term Storage • Accidents • Pollution Uranium Implosion Little Boy and Plutonium Implosion Fat Man

  34. Biological Damage • Radiation exposure can damage or destroy cells of organisms. Examples are burns, cataracts, cancer, etc. • When reproductive cells are damaged, the damage is passed on to offspring. Radiation burns from A-bomb in Hiroshima

  35. Long Term Storage Yucca Mtn. Storage Project • Fission products from nuclear reactors are very radioactive and dangerous. • These products must be stored in special containers underground for hundreds of thousands of years until radioactively decayed.

  36. Accidents • Nuclear reactor accidents can cause fuel and wastes to escape and harm the environment and biosphere. • Example: Chernobyl, Ukraine (1986) in the former USSR. Uncontrolled chain reaction and fire allowed winds to spread radioactivity across Europe. Chernobyl Meltdown Solidified

  37. Pollution • Traces of radioactive materials are present in air, water, food and soil either naturally or released by human activities. People can be harmed if there is too much radioactive material.