L I D E. Chapter 8 Nuclear Chemistry. Radiation. Tragedy. Chemistry in Focus 3rd edition Tro

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1 Chemistry in Focus rd edition Tro Chapter 8 Nuclear Chemistry Radiation The emission of energetic particles The study of it and the processes that produce it is called nuclear chemistry. Unlike the chemistry we have studied to this point, nuclear chemistry often results in one element changing into another one. Tragedy April 6, 986, : am V.. enin nuclear power plant Chernobyl, UR xplosions in reactor immediate deaths, 0 hospitalizations, countless exposures to high level radiation The aftermath continues to this day.

2 Ordinary chemistry Atomic and molecular changes involving electrons Attainment of the stable octet configuration Nuclear chemistry Atomic changes involving the nuclei Nuclei emit energetic particles we call radiation 5 6 Becquerel iscovered that his paper-wrapped photographic plate was exposed by uranium-containing crystals Which disproved his hypothesis linking the exposure to UV light and phosphorescence But it revealed a brand new phenomenon which he termed the emission of uranic rays Curie iscovered two new emitters of uranic rays, one was a new element (polonium) ince the rays were not unique to uranium, a new term radioactivity

3 7 Radioactivity Characterized by Rutherford The result of nuclear instability 8 Alpha Radiation Composed of two protons and two neutrons Represented by the symbol for a helium nucleus High ionizing power ow penetrating power 9

4 0 Beta Radiation An energetic electron represented by the symbol (beta particle symbol here) maller than alpha particles, so more penetrating But this also means less ionizing power n beta decay, a neutron converts to a proton, emitting an electron and increasing the atomic number by. Gamma Radiation An energetic photon emitted by an atomic nucleus Represented by the symbol γ Gamma rays are electromagnetic radiation, not matter. Highest penetrating power, lowest ionizing power

5 5 Half-ife The time required for half of the nuclei in a sample to decay General idea: f nuclei emit particles to form lighter elements, they might also absorb particles to form heavier elements. The result would be a synthetic element. Half-ife Nuclear Fission

6 6 7 8 Fermi hoped to make a synthetic element with atomic number 9. He detected beta emission following his neutron bombardment of uranium. ubsequent experiments by Hahn, Meitner, and trassman seemed to confirm Fermi s work. Puzzling vidence Just before the outbreak of WW, Hahn, Meitner, and trassman reported that no heavier element was detected, rather two lighter ones. Previous nuclear processes had always been incremental. Contradicting all previous experiments in nuclear physics, they proposed a model for the fission of uranium atoms on absorption of neutrons. arge amounts of energy were also emitted during fission.

7 9 0 Weeks later, U-5 fission was proposed as the basis for both a chain reaction and a bomb of inconceivable power. The Manhattan Project Could Nazi Germany develop a fission bomb? Albert instein communicated this possibility to President Roosevelt. The largest scientific endeavor of its time, the race to beat Germany to the atomic bomb was code named Manhattan Project. nrico Fermi and eo zilard constructed the first nuclear reactor at the University of Chicago; they achieved a self-sustaining controlled fission reaction lasting.5 minutes.

8 Critical Mass esser masses of fissionable material will not undergo self-sustaining fission; too many neutrons are lost to the surroundings instead of being absorbed by other U-5 nuclei. After the successful controlled reaction, the goal became the construction of a device where fission would spiral out of control. Collection and synthesis of fissionable fuel (U-5 and Pu-9) were pursued at Oak Ridge, TN and Hanford, WA. J. Robert Oppenheimer directed bomb design at os Alamos, NM. Two designs were constructed and a successful test carried out on July 6, 95. Two atomic bombs (one uranium and one plutonium) were dropped on Japan only weeks later.

9 5 6 7 Nuclear Power Bombs are designed such that fission escalates to produce an explosion. Nuclear reactors are designed to produce a controlled fission reaction. Uranium rods are interspersed with control rods of neutron-absorbing material, usually boron or cadmium. Heat of fission boils water to produce steam which turns the turbine to produce electricity. Nuclear vs. Coal-burning Power Plants Nuclear Uses 00 lb. of fuel per day Produces enough electricity for a city of million people oes not produce air pollution, greenhouse gases, or acid rain Problems include waste disposal and accidents Coal-burning Uses 5 million lb. of fuel to produce an equivalent amount of energy

10 8 9 0 Waste isposal Uranium oxide pellet fuel assemblies are replaced with fresh fuel every 8 months. Most spent fuel is currently stored on site. 98 Nuclear Waste Policy Act stablished a program to build an underground nuclear waste repository Yucca Mountain, NV is the controversial site of this much-delayed project. Nuclear Accidents Nuclear power plants cannot detonate like nuclear explosions. nriched uranium at % U-5 vs. 90% U- 5 Three Mile sland March 8, 979 Chernobyl April 6, 986 uperior power plant design in the U.. has meant no accidental nuclear deaths, nevertheless public support for nuclear power is chilly.

11 Mass efect Mass defect is the difference between the experimentally measured mass of an atom, and the sum of the masses of individually measured protons, neutrons, and electrons. The missing mass was converted to energy when elements form from constituent protons and neutrons. This energy is related to the mass defect by instein s equation = mc. Nuclear Binding nergy instein s equation = mc, represents the energy that holds a nucleus together. The highest values for this binding energy are for elements with mass numbers close to 56. The products have higher binding energy than the reactants; it follows that the products weigh less. The missing mass is converted to energy according to = mc. This difference in binding energy is the source of the energy liberated in fission.

12 5 6 Fusion ike fission reactions, the products of fusion have higher nuclear binding energies, so energy is released. Fusion releases ten times more energy per gram than fission. Fusion is responsible for the sun s energy and is the basis of modern nuclear weapons. Controlled Fusion Advantages Potential for an almost limitless source of energy for society ess radioactive waste products Naturally occurring deuterium in water isadvantages/obstacles High temperatures required and a lack of materials available to contain them Current production methods consume more power than they produce. Radiation and Human ife Radiation can destroy biological molecules. ow-level alpha emitters present little danger externally but, once ingested, have access to internal organs. anger is usually overstated by the popular press.

13 7 8 9 Measuring xposure rem most common unit for measuring human exposure xposure, on average, per year, is / rem Possible ffects The human body can repair itself and suffer no adverse effects. Abnormal growth can begin that leads to cancerous tumors. amage of intestinal lining leads to radiation sickness, hampering the intake of nutrients and water. amage to the immune system allows infection to go unchecked. Genetic defects in offspring have occurred in laboratory animals.

14 0 Radon Radon is the single greatest source of human radiation exposure. Naturally occurring uranium deposits in the earth lead to the collection of radon in residential basements. ignificance of radon as a health threat is controversial. Carbon ating Carbon- is made in the upper atmosphere: p. 5 equation here The half-life of C- is 570 years. evels of C- in carbon-based artifacts are compared to modern levels as an age signature.

15 5 The Age of the arth U-8 is used to measure longer periods of time. t decays to lead with a half-life of.5 X 0 9 years. ead levels in artifacts are used as an age signature. Nuclear Medicine iagnosis Radioactive elements (like technetium-99m) will concentrate in specific areas of interest in the body. Gamma emitters will expose photographic film, allowing images of organs to be recorded. Therapy Radiation can destroy cancerous tumors. Minimizing exposure of healthy tissue is a challenge.