Amerol nuclear chemistry talks about .pptx

this is a nuclear activity

1. APPLICATIONS OF NUCLEAR CHEMISTRY SAHRIMA M. AMEROL

2. Nuclear chemistry is the study of the chemical and physical properties of elements as influenced by changes in the structure of the atomic nucleus. Modern nuclear chemistry, sometimes referred to as radiochemistry, has become very interdisciplinary in its applications, ranging from the study of the formation of the elements in the universe to the design of radioactive drugs for diagnostic medicine. In fact, the chemical techniques pioneered by nuclear chemists have become so important that biologists, geologists, and physicists use nuclear chemistry as ordinary tools of their disciplines. While the common perception is that nuclear chemistry involves only the study of radioactive nuclei, advances in modern mass spectrometry instrumentation has made chemical studies using stable, nonradioactive isotopes increasingly important.

3. RADIOISOTOPES Isotopes are atoms of the same element with the same number of protons but different numbers of neutrons . The decay of unstable isotopes is a spontaneous process that takes place all the time . All elements have one or more isotopes that are unstable and that decay to produce other elements . These isotopes may be natural or they may be artificial . Many elements have at least one radioactive isotope , or radioisotope , that occurs naturally.

4. HALF-LIFE The half-life of a radioactive isotope is the time it takes for one half of a sample of that isotope to decay . Rubidium ( Rb ) has two naturally occurring isotopes. It consists of 72.15 % rubidium-85 and 27.85 % rubidium-87. The 85 Rb isotope is perfectly stable, but 87 Rb is radioactive, giving off a beta particle and decaying to strontium-87:  

5. HALF-LIFE Tin ( Sn ) also has a naturally occurring radioactive isotope , tin-124. It accounts for 6.01% of naturally occurring tin and decays to produce beta particles and antimony. Examples of natural radioactive isotopes: Rubidium-87 Tin-24 The half-life of rubidium-87 is 6 x 10 10 (60 billion years). This means that in 60 billion years , one half of the 87 Rb in a particular sample would be gone.

6. HALF-LIFE

7. HALF-LIFE Sample Problem The half-life of mercury-95 is 31 hours. If you start with a sample of 5.00 g of pure mercury-195, how much of it will still be present after 93 hours?

8. HALF-LIFE You know that one half of the sample is changed for each half-life that passes. Therefore , you can calculate the amount of time that has passed, and the initial mass. You must first calculate the number of half-lives that will have passed in 93 hours. Then divide the mass of the sample in half for each half-life that has passed. The result will give you the total amount of sample that remains unchanged after 93 hours. After 93 hours, three half-lives will have passed (93÷31=3). Therefore, the initial mass of 5.00 g will have been divided in half three times . After 93 hours, or three half-lives, 0.625 g of mercury-195 will be present in the sample. The answer is reasonable because it indicates that a small (but nonzero) amount of the original sample still remains unchanged after 93 hour or three half-lives.

9. RADIOCARBON DATING One of the best known radioactive isotopes is carbon-14 which decays to produce nitrogen-14 and beta particles. The half-life of carbon is 5730 years. Carbon-14 is produced in the Earth’s atmosphere by the action of cosmic rays on ordinary atmospheric region (nitrogen-14). Cosmic rays are streams of high-energy charged particles from outer space that collide with atoms in the Earth’s upper atmosphere.

10. RADIOCARBON DATING What makes carbon-14 such an important isotope? Carbon dioxide is an essential part of the process of photosynthesis in plants. Photosynthesis is the process by which green plants use the sun’s energy to convert carbon dioxide and water into sugars and starches . The sugars and starches, in return, are food for animals that eat the plants and exhale carbon dioxide. Because this cycle exposes plants and animals to a constant source of carbon-14, the amount of this isotope in living plants and animals is constant. The emission of beta particles is likewise constant as the isotope decays.

11. NUCLEAR BOMBARDMENT REACTIONS An unstable nucleus is radioactive, which means that it undergoes a spontaneous nuclear reaction to become more stable. Do you think that a stable, nonradioactive nucleus can ever become unstable? The answer is yes. One way to make a stable nucleus unstable is with nuclear bombardment reaction . In a nuclear bombardment reaction, an atom is bombarded with a stream of particles such as alpha particles. When a few of this particles strike their target ₋ the atom’s nucleus ₋ particle and nucleus combine to form a new nucleus.

12. NUCLEAR BOMBARDMENT REACTIONS Ernest Rutherford - first scientist to identify a nuclear bombardment reaction. In 1919, he observed that when a high speed alpha particle strikes a nitrogen-14 nucleus, oxygen-17 and hydrogen-1 are produced:  

13. NUCLEAR BOMBARDMENT REACTIONS Scientists have developed a variety of devices to accelerate alpha particles and other particles to the speeds needed to collide with a nucleus . These devices , sometimes called “atom smashers",formally called particle accelerators . Cyclotron Synchotron Bevatron Linac (short for Linear Accelarator )

14. NUCLEAR BOMBARDMENT REACTIONS CYCLOTRON LINEAR ACCELERATOR

15. NUCLEAR BOMBARDMENT REACTIONS Not all nuclear bombardment reactions require particles to be accelerated to such high speeds. In 1934, Enrico Fermi (1901-1954) reasoned that because neutrons are neutral, they would not need to be accelerated to collide with a nucleus. By bombarding atoms with neutrons, scientists have created more than 1500 artificial radioactive isotopes. For example, a neutron bombardment reaction turns molybdenum-98 into a radioactive technecium-99, an isotope that physicians use to detect brain tumors and to examine other human body organs . Here is the nuclear equation for the production of technicium-99 :  

16. NUCLEAR BOMBARDMENT REACTIONS Sample Problem The neutron bombardment of calcium-40 produces potassium-40 and possibly another particle as a byproduct. Write the nuclear equation for this reaction . You know that when the calcium-40 is bombarded with neutrons, potassium-40 and possibly another particle are produced. You are asked to write the nuclear equation for this reaction. If a particle is formed as a byproduct, it will have a nonzero mass number and atomic numbers on each side of the equation . Write the symbols for calcium-40 and the neutron on the left side of the equation. Write the symbols for potassium-40 and the unknown particle on the right side of the equation. You already know the mass numbers of calcium-40 and potassium-40. You can find their atomic numbers in the periodic table. The symbol for a neutron is .  

17. NUCLEAR BOMBARDMENT REACTIONS According to the periodic table, the atomic number of calcium is 20 and the atomic number of potassium is 19. You now have enough information to write a preliminary nuclear equation: where represents the unknown particle. To identify the particle, first balance the mass numbers on each side of the equation: 40 + 1 = 40 + 1, so the mass number of the particle is 1. Then balance the atomic numbers: 20 + 0 – 19 + 1 so the atomic number of the particle is also 1. This means that the unknown particle is a hydrogen-1 nucleus. The complete nuclear reaction is  

18. BIOLOGICAL EFFECTS OF RADIATION Units of Radiation Becquerel ₋ SI unit of radioactivity, named after Henri Becquerel. Curie ( Ci ) ₋ more widely used unit of radioactivity, named after Pierre and Marie Curie, the discoverers of radium . One curie of radiation = number of nuclear disintegrations per second from 1 gram of radium

19. BIOLOGICAL EFFECTS OF RADIATION Rem unit most often used to measure radiation exposure in humans, named after Wilhelm Roentgen, the discoverer of X-rays. short for roentgen equivalent for man includes both the amount of energy transferred by the radiation and the sensitivity of the body to that type of radiation. a dose of 150 rem would cause the same amount of damage no matter what kind of radiation is involved or what part of the body is exposed . very high doses of radiation ₋ well above 1000 rem – are always fatal and doses below 1000 rem may eventually be fatal. Doses below 150 rem are generally not fatal but can cause serious tissue damage.

20. MEASURING RADIATION DOSES Dosimeter measures the total amount of radiation that a person has received most dosimeters take advantage of the fact that photographic film is sensitive to radiation the film is covered by a layer of material such as paper or plastic that prevents light from reaching the film but allows radiation to pass through. a badge-type dosimeter is commonly worn by people who might be exposed to radiation, such as nuclear power plant workers. After use, the film is slipped out of the dosimeter and developed. The extent of darkening on the developed film can be translated into a measure of the total amount of radiation actually received by the person.

21. EFFECTS OF RADIATION ON LIVING TISSUE How does radiation damage living tissue ? Highly penetrating radiation, particularly gamma radiation, follows an essentially straight path through living tissue. The radiation has enough energy to strip electrons from molecules, forming ions through the process of ionization. This radiation is called ionizing radiation . These ions – and high-energy fragments of molecules called free radicals also formed by ionizing radiation – are so reactive that they easily disrupt living cells. This can lead to the destruction of tissues, particularly those in which cells multiply rapidly, such as blood-forming tissues and lymph nodes. Leukemia, which is characterized by excessive growth of white blood cells and swollen lymph nodes, is probably the most common cancer caused by radiation. Ironically, both Marie Curie and her daughter Irene died of leukemia, probably as a result of long exposure to radiation.

22. TYPES OF RADIATION DAMAGE Radiation damage may affect an organism directly or it may affect the organism’s offspring. Somatic damage - damage to the organism that received the radiation directly. It affects only body cells. Examples: Burns and rashes on the skin, cataracts in the eyes, and a wide range of cancers. Genetic damage - damage that affects reproductive cells . It may result in the birth of deformed offspring.

23. DETECTION OF RADIATION Geiger Counter - depends on the ionizing ability of radiation, is the most common instrument for detecting radiation. It consists of a hollow cylinder with a wire in the center.

24. BENEFICIAL USES OF RADIOISOTOPES In spite of the hazards of radiation, radioisotopes have many beneficial applications in medicine, agriculture, and industry . Radiotracers - sometimes referred to as radioactive labels - are used to follow a specific substance as it moves through a natural system . In 1977, Rosalyn Yalow received the Nobel Prize for the development of a technique called radioimmunoassay, which is a sensitive method of using radiotracers in the human body.

25. BENEFICIAL USES OF RADIOISOTOPES Cancer Treatment Cancer is a disease in which abnormal cells in the body are produced at a rate far beyond the rate for normal cells. The mass of cancerous tissue resulting from this runaway growth is called a tumor . It is particularly suitable for radiation therapy because the fast-growing cancer cells are more susceptible to high-energy radiation such as gamma rays than are the healthy cells. Thyroid cancer can be treated with iodine-131 because almost all the iodine in the body is taken up by the thyroid. Iridium-192 is used to treat some cancers. Small “seeds” with iridium-192 at the center have a platinum metal coating to ensure that the radioactive iridium will not escape and spread throughout the body. Cobalt-60 is an example of a radioactive source that is used externally. It produces a beam of gamma rays that is applied to the cancerous tissue.

26. BENEFICIAL USES OF RADIOISOTOPES Food Preservation The ability of radiation to damage organisms has been used to preserve certain foods, particularly sensitive fruits such as strawberries.

27. HARNESSING THE NUCLEUS Nuclear Fission In the late 1930s, the largest known nucleus was the nucleus of a uranium atom, which has 92 protons. In the hope of making a larger nucleus, Enrico Fermi and his colleagues bombarded uranium with neutrons. Fermi thought that a nuclear bombardment reaction would produce a heavier isotope of uranium which would then decay into an atom with more protons. Fermi was indeed correct. Uranium-239, which decays to neptunium-239 :  

28. HARNESSING THE NUCLEUS Nuclear Fission 1938 - German scientists Otto Hahn (1879-1968) a nd Fritz Strassman (1902-1980) attempted to repeat Fermi’s experiment. To their dismay, they discovered barium among their products. At first they thought that barium might be an impurity. But barium is not a particularly common element and they had no idea how barium had found its way into their experiment. Hahn wrote a letter about this puzzle to his former colleagues Lisa Meitner (1878-1968). Meitner was living in Sweden where she had emigrated to escape German anti-Semitism. It was Meitner who grasped the significance of barium among the products. She came to the bold conclusion that a uranium nucleus had split during the reaction, producing a barium nucleus as one of its products. She also recognized that the nuclei produced in this reaction would violently repel each other beacause of their large positive charges, which meant that a single uranium atom was a source of tremendous energy.

29. HARNESSING THE NUCLEUS Nuclear Fission Meitner’s ideas proved to be correct. Later investigations showed that neutron bombardment could split one of uranium’s less abundant isotopes. Uranium-235, into two smaller nuclei, one of which is a barium nucleus. Here is the nuclear equation for this reaction: In a nuclear fission reaction, a large nucleus is split into two smaller nuclei approximately equal mass.  

30. Energy and “Missing” Mass Today. Fission reactions are used to provide what is commonly called nuclear power. In a nuclear reactor, the fission of 4.5 grams of uranium-235 will satisfy the average person’s energy needs for an entire year. In comparison, about 15 tons of coal would have to be burned to provide the same amount of energy . WHERE DOES ALL THIS ENERGY COME FROM ? The answer involves all the “missing” mass in nuclear fission reactions. Intriguingly, the total mass of the products in a fission reaction is slightly less than the mass of the starting materials. In other words, the law of conservation of matter does not apply to fission reactions! So what happens to the missing mass? The answer is that the missing mass is converted into energy. The amount of energy released can be calculated from a famous equation derived by Albert Einstein . E = mc 2

31. Energy and “Missing” Mass One fission reaction produces enough neutrons to start three more fission reactions, each of which in turn produces the neutrons needed to start three more reactions, and so on, in a series of fission reactions. This continuous series of fission reactions is called a nuclear chain reaction . Once started, a nuclear chain reaction can escalate rapidly. An atomic bomb is designed to produce a “runaway” chain reaction creating an incredibly powerful explosion .

32. NUCLEAR REACTORS Could a nuclear power plant ever explode like an atomic bomb, you might be wondering? The answer is no, it cannot. The fuel rods in nuclear reactor contain too little uranium-235 to sustain a runaway chain reaction. Reactors are further regulated by control rods that absorb neutrons and thus regulate the speed of the nuclear chain reaction.

33. NUCLEAR REACTORS Most of the concern about nuclear power plants is with the highly radioactive waste materials that are formed as a result of the fission process. However, several incidents at nuclear power plants have raised questions about the basic safety of these plants. 1979 – the cooling system of the reactor at Three Mile Island, Pennsylvania, lost water due to operator error. As a result, heat generated in the fuel rods by the decay of radioactive isotopes could not be dissipated, raising concern that the melting point of the fuel would be reached and a “meltdown” would occur. Fortunately, coolant water was restored and the meltdown was prevented.

34. NUCLEAR REACTORS The reactor in Chernobyl, Ukraine, used graphite as a moderator to slow down neutrons. Although it is normally very difficult to ignite, once graphite is burning it can reach very high temperatures and is extremely difficult to extinguish. In 1986, excessive heat within the Chernobyl reactor, again a result of operator error ignited the graphite and the fire that resulted burned for days. Many firefighters later died as a result of exposure to radiation . The reactor was completely destroyed, allowing tremendous amounts of radiation to be released into the atmosphere and carried on the winds to many parts of Europe. Thousands of fatal cancers in humans exposed to the radiation are eventually expected as a result of the Chernobyl accident.

35. NUCLEAR WASTE DISPOSAL As a nuclear reactor operates, radioactive fission products build up in the fuel rods as the fissionable material is used up. About one fourth of all the fuel rods must be replaced every year, representing several hundred tons of highly radioactive material to dispose of. Disposal of this radioactive waste is a major problem . Burial appear to be the best solution to the problem, but there is no agreement as to where the radioactivity wastes can be safely buried. A reprocessing program, in which the uranium fuel left in the rods is extracted for reuse, leaving only the fission products in the rods for disposal, might be a desirable alternative. Until a substantially risk-free method of nuclear waste disposal can be found, however, it seems that nuclear power will remain a controversial source of energy for our rapidly growing population.

36. NUCLEAR FUSION In a nuclear fusion reaction, two small nuclei join to form a large nucleus . Fusion reaction in which two isotopes of hydrogen combine to form helium : Like a fission reaction, a fusion reaction converts some of the mass of the original nuclei into energy – a great deal of energy. Unfortunately, fusion reactions are difficult to produce and control. In order for 2 atoms to fuse. their nuclei must come together. That goal is strongly resisted, first by the repulsion of the atom negatively charged electron clouds and then by the repulsion between the positively charged nuclei.  

37. NUCLEAR FUSION Stripping off the electrons at very high temperatures solves the problem. The resulting “sea” of bare nuclei is called a plasma. These bare nuclei must then be forced together to allow a fusion reaction to take place. If 2 nuclei are to overcome the force of repulsion so that they can combine in a fusion reaction, they must be moving very fast. To reach the speeds required, the nuclei must be heated to an extremely high temperature – about 40 million kelvins! Because of these high temperatures, nuclear fusion reactions are often called thermonuclear reactions. Thermonuclear reactions are also the source of the destructive power of a hydrogen bomb.

38. FUSION RESEARCH In the future, fusion reactions may be an important source of energy. A fusion reaction using hydrogen – an abundant element – as fuel would release more energy per gram of fuel than does a fission reaction. Furthermore, the products of a fusion reaction are not radioactive. However, the controlled use of fusion is still in the experimental stage because the high temperatures required are hard to achieve and maintain. Several research groups are attempting to produce a sustained and controlled fusion reaction.

39. THE COLD FUSION CONTROVERSY The excitement surrounding the quest for almost limitless energy has occassionally resulted in hasty reporting of results and intense controversies. The most striking demonstration of this is “cold fusion”. In 1989, Stanley Pons and Martin Fleishman , two chemists working at the University of Utah, reported at a nuclear fusion reaction that could be performed under ordinary laboratory condition . Pons and Fleishman’s “cold fusion” reaction was very simple – basically, the electrolysis of water to yield hydrogen and oxygen. The water they used, however, was not ordinary H 2 O. Instead, Pons and Fleishman used deuterium oxide, or heavy water ( 2 H 2 O). In addition, the reaction used palladium as the cathode, the electrode at which deuterium gas would be liberated. Two pieces of evidence were reported to support the occurrence of cold fusion. Much more heat was liberated than was possible by the ordinary chemical reaction and helium , an impossible product of the ordinary reaction was detected.

40. THE COLD FUSION CONTROVERSY The Utah chemists proposed that before the deuterium atoms could combine to form deuterium gas, they were absorbed into the palladium cathode. The deuterium atoms were packed so tightly within the palladium that they reportedly underwent a fusion reaction as follows : The chemists claimed that the extra energy detected in the reaction was the energy given off in the fusion reaction and the helium detected was the product of the reaction above. The announcement of cold fusion caused a massive furor, not only among scientists but also among politicians and ordinary citizens. Enormous amounts of money were appropriated for additional cold fusion research. As more and more negative results have been reported, however, the dream of using cold fusion as a source of cheap, unlimited energy has receded.  

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