Nuclear Chemistry. Opal reactor ANSTO. Production of materials.

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1 Nuclear Chemistry Opal reactor ANSTO Production of materials Atoms contain protons and neutrons in a nucleus surrounded by electrons in energy level shells. Isotopes of an element are atoms of that element containing the same number of protons but different numbers of neutrons. 2010

2 Isotopes are named by their mass number. Distinguish between stable and radioactive isotopes and describe the conditions under which a nucleus is unstable Isotopes of the same element have the same atomic number (Z) but a different mass number (A). eg 235 U, 238 U have Z = 92 Only 279 of about 2000 known isotopes are stable. In a stable isotope nucleus, the protons and neutrons are in a low energy level and are unable to emit radioactivity. Radioactive isotopes are unstable. They emit radiation as they spontaneously release energy. This is called radioactive decay. An unstable isotope is called a radioactive isotope or radioisotope. The zone of stability 2005 question 1 Plot number of neutrons (A-Z=N) against number of protons (Z) Ratio N/Z of 1:1 up to Z=20 Ratio N/Z of 3:2 at Z=80 1. If N/Z ratio is too high or too low the isotope is unstable. Unstable isotopes lie outside the Zone of Stability (grey) in the blue area or beyond 2. Elements with Z>83 are unstable and radioactive

3 2009 question question 3 Which of the following is an important factor in predicting the nuclear stability of an isotope? (A)Atomic radius (B) Nuclear radius (C) The ratio of neutrons to protons (D)The ratio of electrons to protons 2002 Radioisotopes can emit 3 types of radiation 1. If the ratio of the number of neutrons (N) to the number of protons (atomic number,z) is too high i.e. (N:Z) >1 or too low the isotope is unstable. 2. Elements with an atomic number of Z>83 are also unstable and radioactive Sheet of paper 0.5mm sheet of Pb 5cm thickness of Pb or 15cm of concrete How do they behave in an electric field?

4 Modes of Radioactive decay neutrons atomic number mass number Neutron proton + electron Remember, the atomic number (Z) determines what element it is Balancing equations for nuclear reactions Formation of tritium in a nuclear reactor: Z = 28 α-particle Formation of cobalt-60 in a nuclear reactor: Because cobalt-60 has a neutron to proton ratio of 1.22 that is somewhat too high for the isotope with atomic number 27 to be stable - it lowers its neutron to proton ratio by emitting a beta particle (and gamma radiation) γ-particle β-particle

5 The decay series of U α-decay Unstable β-decay stable An isotope will continue to decay until it becomes stable remember two reasons! Give both an eample of alpha decay and beta decay. What is an alpha and beta particle? Eplain how the atomic number and mass number change as a result of alpha and beta decay. Why is Pb now considered stable? Half-Lives of Radioisotopes Not eplicitly mentioned in the syllabus but this is a crucial concept in nuclear chemistry time taken for half the radioactive nuclei in a sample to decay

6 A fission reaction chamber Describe how commercial radioisotopes are produced This is an eample is only one of many possible results of nuclear fission. 6 new isotopes formed! And lots of neutrons Nuclear reactions (a) atomic bombs (b) nuclear reactor All neutrons released can initiate further fission reactions All but one of the emitted neutrons are captured so that a steady controlled reaction proceeds

7 A light water nuclear reactor so, in summary. When the uranium nucleus breaks up into two nuclei, many different possible isotopes can form (eg Rb, Cs, Kr, Ba). Differences in chemical properties of the elements produced can be used to chemically separate the different radioisotopes. Any U-235 that has not undergone fission can be separated and recycled into new fuel rods. The high-speed neutrons emitted can be used to bombard atoms of various elements to produce useful neutron rich isotopes. Describe how transuranic isotopes are produced Transuranic elements are elements with an atomic number (Z) greater than 92, the atomic number of uranium. Eample: Neptunium & plutonium are generated by bombarding U-238 with neutrons (to form U-239) followed by subsequent beta decay. Transuranic elements from atomic number 96 and up are all made by accelerating a small positive nucleus (such as He, B or C) in a charged particle accelerator to collide with a heavy nucleus (often of a previously made transuranic element) target. 93, Np Neptuniam named after Neptune 94, Pu Plutonu named after Pluto 95, Am Americium where first produced! 96, Cm Curium after Curie s 97, Bk Berkelium city where University of California is located, Berkeley 98, Cf Califorium state where University of California is located 99, Es Einsteinium after Albert Einstein 100, Fm Fermium after physicist Enrico Fermi (chain reaction) 101, Md Mendelevium after russian chemist Mendeleyev (periodic table) 102, No Nobelium 103, Lr Lawrencium after Ernest Lawrence (cyclotron) 104, Rf Rutherfordium after Ernest Rutherford (atomic nucleus concept) 105, Db Dubnium Also called hahnium 106, Sg Seaborgium after Glenn Seaborg (chemist) 107, Bh Bohrium after Danish Physicist Neils Bohr (atom) 108, Hs Hassium after German Bundesland 109, Mt Meitnerium ater German physicist Lise Meitner (fission) 110, Ds Darmstadtium after Darmstadt, Germany 111, Rg Roentgenium after Wilhelm Roentgen (X-ray) The eistence of elements up Z = 116 has also been confirmed

8 Commercial radioisotopes produced by fission reactions Bombard an isotope (eg U-235) with a high speed neutron from an accelerator. Give an eample of two commercial radioistopes produced eg Ba, Kr Fission reactions also produce ecess neutrons that need to be controlled. How are neutrons controlled? describe a nuclear reactor, control rods Define a transuranic element atomic number >92. Do not occur naturally as they are unstable. Can be made by bombarding U238 with neutrons which then undergo beta decay Can also be made by bombarding element with a small positive nucleus (He, B, or C) using a particle accelerator Define a transuranic element atomic number >92. Do not occur naturally as they are unstable. Discuss fission reactions, nuclear reactors and the need to control the reaction Can be made by bombarding U238 with neutrons which then undergo beta decay Can also be made by bombarding element with a small positive nucleus (He, B, or C) using a particle accelerator Identify instruments and processes that can be used to detect radiation Geiger-Müller counter Remember: High energy radiation that causes ionisation of atoms is called ionising radiation and is potentially harmful to living things. 1. Most radioactive emissions are ionising radiation and are usually detected by a Geiger-Müller counter 2. Low energy radiation that is too weak to ionise atoms is called non-ionising radiation and can be detected by a scintillation counter. 3. Vapour trails occur in cold supersaturated vapour of water or alcohol in cloud chambers 4. Radiation causes photographic film/plates to become eposed

9 Identify ONE use of a named radioisotope in (A) industry AND (B) medicine INDUSTRY 1. Sodium 24, leak detector in pipes, short half life 2. Caesium 137, irradiation of food/medical supplies 3. Cobalt 60, thickness guage MEDICINE 1. Cobalt 60, cancer treatment 2. Technetium 99m, medical tracer 3. Fluorine 18, PET scans Summarise the Use, Benefits and Problems - know their chemical properties Radioisotopes: their role in society today (PDF)

10 Describe the way in which the industrial and medical radioisotopes are used and eplain their use in terms of their chemical properties 2004 TYPES OF QUESTIONS TO CONSIDER 1. Type/s of radiation emitted: good or bad? 2. High or Low energy radiation? 3. Penetrating power? 4. How is the radiation detected? 5. What is the half life? Good or bad? 6. Is it easily disposed of? 7. What does the radioisotope target? Many to choose from ONLY LEARN ONE for industry (and one for medical use) Know the correct mass number Know benefits and problems Name and describe properties for a radioisotope from (i) industry and (ii) from medicine Show link between the described properties and their use Describe the benefits and problems of their use on society / Provide a judgement PLAN YOUR ANSWER provide a logical progression to your answer; use correct scientific principles and ideas

11 Concepts to Understand Concepts to Understand continued Key Terms: radioactivity, isotopes, radioisotope, fission, unstable nuclei, transuranic elements, ionising radiation Characteristics of three common radioactive emissions: α, β, γ How various forms of decay affect the mass number (A) and atomic number (Z) How the neutron / proton ratio correlates with nuclear stability and decay mode Monitoring radioactive emissions: Geiger-Müller counters, scintillation counters, photographic film and cloud chambers How radioisotopes are produced commercially Transuranic elements and their production Applications of radioisotopes in industry AND medicine Learn how to assess benefits and problems associated with industrial and medicinal applications of radioisotopes.