Transcript Chapter
Chapter 22 Nuclear Reactions Nuclear Rxns Nuclear reaction-a reaction that involves a change in an atom’s nucleus. Therefore, an atom of one element changes into an atom of another element. Nuclear Rxns Nuclide (Nucleus of an atom) Contains nucleons(protons and neutrons) Chemical vs. Nuclear Rxns. Chemical Rxns Nuclear Rxns Occur when bonds are broken and formed Occur Atoms remain unchanged, just rearranges Atoms Involve only outer electrons May Associated Associated with small energy changes when nuclei emit particles and/or rays are often converted into atoms of another element. involve p, n with large energy changes Radiation Radiation-The rays and particles that are emitted by radioactive materials. Alpha Radiation Alpha radiation-radiation deflected towards the negatively charged plate and gives off alpha particles Alpha particles, He or α : 2p, 2n so +2 charge, largest mass (4 amu) Beta Radiation Beta radiation-radiation deflected towards the positively charged plate and gives off beta particles (electrons). Beta particles, β or e: 1e so -1 charge, mass is between alpha and gamma particles Gamma Radiation Gamma radiation-radiation deflected towards no plate and gives off gamma rays Gamma rays, γ : no mass and no charge, usually occupied by α and β decay. Nuclear Rxns (1) Rn → N + He C + e β decay (3) U → α decay (2) Ra → γ decay Th + He + 2γ Types of Radiation (Memorize) Consists Alpha Beta Gamma Charge Mass Stopped w/ symbol Types of Radiation Positron emission-radioactive decay that involves the emission of a positron from a nucleus (antimatter) Positron-particle with the same mass as the electron but opposite charge • Symbol: Types of Radiation Electron Capture- nucleus of an atom draws in a surrounding electron and an X-ray photon is emitted Symbol: Nuclear Reactions Nuclear Rxn- a rxn that changes the nucleus Transmutation-a change in the identity of the nucleus, change in # of protons in nucleus. Nuclear Stability Mass defect – diff. between mass of an atom and sum of masses for p, n, e. Why loss of mass? Caused by conversion of mass to energy upon formation of nucleus Nuclear Binding energy – energy released upon formation of nucleus Nuclear Stability The smaller stable nuclides have a neutron-proton of 1:1 to the larger nuclides of 1.5:1. If the nuclei ratio falls above/below the band of stability, the nuclides will undergo decay until they are within the band of stability. Radioactive decay Radioactive decay-spontaneous disintegration of an unstable nucleus to a smaller nucleus by giving off nuclear radiation. Radioactive nuclide- unstable nucleus that will undergo radioactive decay Nuclear Rxns Identify the product that balances the following nuclear rxns. 1. 212Po → 4He + ____ 2. 230Th → _____ + 3. 238U + 4He 4. 27Al + 1n 4He → ____ + 1n → 24Na + ____ Radioactive decay Alpha Emission 210Po 206Pb + ____ Beta Emission 14C 14N + ____ Electron Capture (reverse of beta) 106Ag + _____ 106Pd Positron emission 11C → 11B + _____ Half-life Half-Life- t1/2 - the time required for half the atoms of a radioactive element to decay into another element. Fluorine-21 has a half life,t1/2, of 5 seconds 1000 atoms F-21500 atoms F-21 250 atoms F-21 1(whole amt) ½ left ¼ left 100 g F-21 50 g F-21 25 g F-21 Half-Life Problems Formulas: To determine the number of half-lives that past: #half-lives past = total time t1/2 To determine amount remaining: Amount remaining = (Initial amt)1 n 2 n= # of half lives past Half-Life Problems 1. If the radioactive sample of I-131 was 18.5g, what amt is left after 32 days? (t1/2 = 8 days) Half-Life Problems 2.Iron-59 is used in medicine to diagnosis blood circulation disorders. The half-life of iron-59 is 44.5 days. How much of a 2.000 mg sample will remain after 133.5 days? Half-Life Problems 3. If gallium-68 has a half-life of 68.3 minutes, how much of a 10.0 mg sample is left after two half-lives? Half-Life 4. After 15 days only 2 grams remain of a sample that has a half life of 5 days. How many grams were in the original amount? 5. What is the half life of K-42 if a 750 gram sample decays to 93.75 grams in 24 hours? 6. The half-life of carbon-14 is 5715 years. A sample has only ¼ of its original amount. What is the age of the sample? Decay Series Decay Series-a series of radioactive nuclides produced by successive radioactive decay until a stable nuclide is reached Decay Series Questions Use pg. 814 Write the four nuclear equations of the uranium-238 decay series. What stable nuclide does U-238 finally become? How long is the half life of U-238? U-238 U-238 is found in small amounts in soil and rock, particularly, shale and granite. Rn is one of the daughter nuclide of U238(parent nuclide) decay. Rn is a radioactive gas that can be a health hazard trapped in homes from cracks and holes in foundation. It can cause lung cancer and birth defects. Ra-226, Po-210, Pb-210 are found in cigarettes and the lungs of smokers. Induced Transmutation Induced Transmutation- bombardment of stable nuclei with charged and uncharged particles. This process is used to make radioactive nuclides not found nature, like our newly discovered elements. Induced Transmutation 1. Write a balanced nuclear equation for the induced transmutation of aluminum27 into phosphorus-30 by alpha particle bombardment. A neutron is emitted from the aluminum atom. Induced Transmutation 2. Write the balanced nuclear equation for the induced transmutation of aluminum-27 into sodium-24 by neutron bombardment. An alpha particle is released in the rxn. Induced Transmutation What element would be formed in the following nuclear rxn? 3. 242Cm + 4He ______ + 1n Nuclear Radiation Radiation Exposure Rem-a unit used to measure radiation damage to human tissue like x-rays… (Complete personal radiation wkst) Nuclear Radiation Radiation Detection Geiger Muller counters -measures electrical pulses on gas ionized by radiation Film badges Scintillation counter Geiger Counter Applications of Nuclear Radiation Radiochemical Dating: 14C t1/2 0e + 14N = 5715 yrs Living organisms absorb 14C through food. This C-14 is a constant amt. When the organism dies, there is no new absorption of C-14. The C-14 decays to N-14. By measuring the amount of C14 the age may be approximated. Applications of Nuclear Radiation Radioactive Nuclides in Medicine Radioactive tracers are radioactive atoms incorporated into substances so they can be followed by radiation detectors. Ex. Tc-99 used to detect bone cancer, I-131 to detect thyroid problems Applications of Nuclear Radiation Radioactive Nuclides in Agriculture Radioactive tracers are used to determine effectiveness of fertilizers. Cobalt-60 is used to irradiate food, to kill bacteria and insects. It is also used to kill cancer cells. Nuclear Waste 1. Produced from nuclear power plants, nuclear weapons manufacturing, medical research,… 2. Containment on nuclear waste from nuclear power plants is on-site and off-site disposal. Nuclear Waste *3. Each nuclear reactor has large pools of water where spent uranium fuel rods can be stored. 4. When the pools are filled, they are sealed in concrete and steel dry casks then moved to permanent storage facilities. There are 77 disposal sites in the US. Nuclear Fission Nuclear Fission Nuclear Fission- splitting a larger nucleus to smaller intermediate nuclides Nuclear Reactors use controlled fission reactions to produced energy by this rxn: Parts of Nuclear Reactor Chain rxn-self propagating rxn Fuel- U-235 Moderator-slows down high speed neutrons to CONTINUE chain rxn; uses water, Be, or C(graphite) Control Rods -absorbs neutrons, thereby controlling rate of fission rxn; made of Cd Parts of Nuclear Reactor Coolant-water to remove heat to turbines to generate electricity Containment structure(shielding)structure built around reactor to hold in radiation from escaping in case of an accident; server feet thick concrete. Recent Nuclear Accidents 1986 Chernobyl power plant in Soviet Union-Complete meltdown of core 1979 Three Mile Island, USApartial meltdown Nuclear Fusion Nuclear Fusion-small nuclei join to form larger nuclei Ex. sun and stars fusion releases 20X more energy per gram than fission Uses: hydrogen bomb and in future fusion power plants Fusion Reactors Disadvantages of fusion reactors Huge input of energy needed to start process A temperature of 200 million K needed to sustain rxn. Fusion Reactors Advantages of fusion reactors: Readily available hydrogen from water Nonradioactive products Can stop rxn by dropping temp. Can produce inexhaustible supply of energy