Nuclear Chemistry Text Chapter 18 Tomotherapy machine for
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Nuclear Chemistry Text Chapter 18 Tomotherapy machine for radiation treatment of cancer at Johns Hopkins Glow in the Dark Stars Nuclear Submarine
Nuclear Chemistry What 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?
• 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. Isotopes
• 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? Predicting Nuclear Stability
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).
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.
• 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 Alpha decay ( )
Beta decay ( -) • Beta particle (high speed electron) is given off A neutron is as the result of nuclear disintegration. converted to a • High velocity, low energy. proton by emitting • Beta particles have virtually no mass. an electron. • Shielding: stopped by 1 cm of aluminum, average thickness of book.
Gamma • Gamma rays are similar to high energy x-rays. Radiation ( ) • Travel @ speed of light like all other forms of electromagnetic energy. • Do not have charge or mass. Type of radiation (photons) , not particles. • Shielding: 13 cm of lead
• Positrons are given off as result of nuclear disintegration. Positron • 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. decay( +)
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
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
Balancing Radioactivity Use both Reference Table O & (PT). Equations • • If the atomic number changes, remember the identity of the element changes. • What 2 quantities must be balanced? #1 #2 The breakdown of Co 60 in cancer radiation therapy.
More Balancing of Radioactivity Equations • First use Reference Table N to determine the decay mode. • Continue and finish similar to other problems. Radioactive Orchestra
• 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. Artificial Radioactivity CERN Particle Accelerator in France & Switzerland + ___
• Mass is converted to energy. • Think E=mc 2. • Produce tremendous amounts of energy!!! • 2 Types: Fission and Fusion Nuclear explosion at sea Nuclear Reactions
• 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) Nuclear Fission
• 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. Chain Reactions
Parts • Fuel (U 235 & Pu 239) • Moderator (slow down speed of neutrons, H 2 O, Be or graphite) • Control Rods (absorb neutrons, B & Cd) • Coolants (lowers temp, H 2 O) • Shielding (protects the reactor and people from radiation, steel or concrete) of a Nuclear Reactor
• 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. Nuclear Fusion 1 st aerial test of H-bomb makes Bikini Atoll unlivable
Compare & Contrast Fission and Fusion • Similarities • Differences • Both release a lot of energy. • Both convert mass into energy. • Fission: splitting Fusion: uniting • Fusion releases much more energy than fission. • Fission produces radioactive waste, fusion only produces He.
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.
1. Half-life Problems can be used to find the following 4: Fraction of radioisotope remaining (left) 2. Half-life 3. Initial amount (original amount) of radioisotope 4. Age of sample containing radioisotope (Radioactive Dating) Decay animation
Benefits of Radioisotopes • • Tracers Medical Diagnosis or Treatment Radiation of food Radioactive Dating Nuclear Power Industrial Measurement Industrial Applications
• 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) Tracers
• Medical Diagnosis & Isotopes with very Treatment 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
Medical Diagnosis & Treatment Examples A CT scan of the brain using Tc-99 • 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.
Irradiation of Food • Radiation kills bacteria, molds and yeast. It permits food to be stored for a longer time. Symbol for Irradiated Food
• 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. Radioactive Dating
Nuclear Power • Nuclear reactors are used to produce electrical energy or electricity.
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.
• 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. Industrial Applications
Risks of Radioisotopes • • Biological Damage Long Term Storage Accidents Pollution Uranium Implosion Little Boy and Plutonium Implosion Fat Man
• 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. Biological Damage Radiation burns from -bomb in Hiroshima A
Yucca Mtn. Storage Project Long Term Storage • 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.
• 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. Accidents Chernobyl Meltdown Solidified
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.
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