2 Review: Elements and Isotopes What are elements defined by?What are isotopes?What is the difference between a stable and a radioactive isotope?
3 Radioisotopesexperience radioactive decay (the loss of alpha or beta particles over time)Result: atoms of one element physically change into another element.Eg Carbon-14 decays to Nitrogen-14 by loss of negative beta particlesRadioactive half life= the amount of time it takes for 50% of the radioactive isotope in a substance to decay.radioactive decay (the loss of alpha or beta particles over time)Alpha particles are two protons and two neutronsBeta particles are high energy electronsRadioisotopes can also give off gamma radiation: high energy light (sources include radio waves, light waves, and x-rays)
4 Practice:Plutonium-239 has a half-life of 24,000 years. How much of a 4 gram sample will remain after 96,000 years?1g0.5g0.25g0.125g0.625g
5 Dating with radioactive isotopes Carbon-14 can be used to estimate the age of plant and animal remainsAll living things utilize C-14 and incorporate it into their tissuesAfter death, C-14 changes into N-14Geologists can determine the age of a set of remains by comparing the ratio of C-14 to N-14Carbon dating is useful for remains between 1,000 and 50,000 years old
6 Geological dating with Uranium Uranium-238 is a very common radioisotope that decays to a stable isotope of leadIt has a half life of 4.5 billion yearsThis is very useful for dating rock formations that are billions of years oldEg if there are equal parts lead and uranium in a rock, it is 4.5 billion years old
7 The discovery of radioactive atoms 1896 uranium radiation observed1898 radiation consists of high energy particles1919 N nuclei hit with alpha particles turned into O1938 First fission reaction1896 a French physicist discovered that uranium containing minerals spontaneously & continuously gave off energy (radiation)1898 a British physicist showed radiation to consist of high energy particlesIn 1919 same British guy bombarded N nuclei with alpha particles and turned it into OIn 1938 German scientists hit uranium with neutrons, splitting U into barium and krypton, and lots of energy…FISSION!This led to a realization of the potential power of fission and a subsequent race for a bomb and energy development (Einstein came to US during WWII to warn of impending German innovation)
8 Nuclear rxns vs combustion Atoms do not change; are rearrangedMass of reactants = mass of productsEnergy is released as heat when bonds breakNucleic changes result in element transformationsSmall of amount of matter releases large amounts of energy…less mass in productsCombustion (fossil fuels):atoms do not change, they are rearranged.The mass of the reactants is equal to the mass of the products.Energy is given off as heat when chemical bonds are broken.Nuclear reaction:Changes occur within the nuclei of atoms.Atoms actually transform into atoms of another element.Small amounts of matter are transformed into large amounts of energy.
9 Types of nuclear reactions FissionFusionFission: larger atoms are split into 2 smaller atoms of different elements (this is the type of reaction used to create commercial energy and atomic bombs)Fusion: 2 smaller atoms combine to make one larger atom of a different element (this is what powers the sun and stars)In both reactions the end product mass is less than the mass of the starting material. The remainder is converted to energy.Fission produces 2-3 million times more energy than combustion of fossil fuels.
10 NUCLEAR ENERGYNuclear power plants use U-235, a radioactive isotope of uranium.MiningEnrichmentFuel assemblyMined uranium oxide consists of about 99.3% non-fissionable uranium-238 and 0.7% fissionable uranium-235.The concentration of uranium-235 is increased through an enrichment process (removing some of the U-238) to result in 97% U-238 oxide and 3% U-235 oxide fuel.Enrichment is very energy intensive, but the energy payoff is even greaterAfter enrichment, U-235 is transformed into uranium dioxide to form small fuel pelletsThese pellets are placed into fuel rods, which in turn are grouped into fuel assemblies (~100 rods), of which there may be 1000s per reactor core
11 Nuclear power plant2/3 of reactors in the US are PWRs; 1/3 are BWR
12 NUCLEAR WASTEAfter three or four years in a reactor, spent fuel rods are removed and stored in a deep pool of water contained in a steel-lined concrete container for 10 years.
13 NUCLEAR WASTEAfter spent fuel rods are cooled considerably (10 years), they are moved to dry-storage containers made of steel or concrete.Long-term storage (10, ,000yrs) until radioactivity falls to safe levels. Spent fuel rods are dangerous to human health for 10 or more half lives.
14 Math PracticeAfter 100 million years, only 1/32 of the original amount of a particular radioactive waste will remain. The half-life of this radioactive waste is how many million years?a b c d e. 50You have 180g of a radioactive substance. It has a half-life of 265 yrs. After 1,325 yrs, what mass remains?B (5 half-lives)5.625g (5 half-lives…265y-->90g, 530y-->45g, 795y-->22.5, 1060y-->11.25g, 1325y-->5.625g)
15 Nuclear waste Low level High level Radioactive solids, liquids, or gases that give off small amounts of ionizing radiationSources include power plants, hospitals, research labs, and industriesLow Level Radioactive Waste Policy Act 1980 & 1985All states must be responsible for disposal of non-defense related waste produced w/in their borders.High levelRadioactive solids, liquids, or gases that initially give off large amounts of ionizing radiationSources include anything that was inside the reactor core (metals, water, gases, spent fuel)High level= not safe for 10,000-milion years
16 Nuclear Waste Policy Act 1982 Stated that there must be a permanent site for storing high level waste by 1998That was not met; postponed to 2010 at earliest1987 Congress identified Yucca Mountain in Nevada as the best potential siteIn 2002 it was officially approved by CongressRescinded by Obama in 2009Feasibility studies were carried out for over a decade
17 NUCLEAR ENERGYScientists disagree about the best methods for long-term storage of high-level radioactive waste:Bury it deep underground.Shoot it into space.Bury it in the Antarctic ice sheet.Bury it in the deep-ocean floor that is geologically stable.Change it into harmless or less harmful isotopes.
18 The risks of nuclear energy MeltdownAcute radiation syndromeDaily radiation for workers (carcinogenic over time)Radiation into groundwater from stored wasteSmall scale persistent radiation to nearby communitiesMeltdown: this is when the actual metal around the reactor core melts from the heat of fission; radiation is emitted into the atmosphere in one large doseAcute radiation syndrome= too many body cells are killed by the radiation dose to be repaired.
19 Radiation and healthWe are exposed to natural (background radiation) and artificial radiation every day300 millirems per year from space/the atmosphere, the soil (radon), foods we eat (radioactive potassium)60 millirems from manmade radiation (radiowaves, hospitals, industries, housing materials, microwaves, cell phones, tobacco, television, smoke detectors, etc.)10,000 mrem’s on average by Chernobyl workers.Radiation is often ionizing, which is very disruptive to living cellsChronic exposure to radiation can lead to cancer and thyroid problems
20 In 1995, the World Bank said nuclear power is too costly and risky. In 2006, it was found that several U.S. reactors were leaking radioactive tritium into groundwater.Figure 16-19