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The quest for the heaviest elements

The quest for the heaviest elements. Dr David Jenkins University of York. Overview. (Nuclear) Physics (Nuclear) Chemistry History of the 20th Century Psychology, what motivates us? The Curse of Heavy Elements Fraud in science and how we respond…. What is an element?.

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The quest for the heaviest elements

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  1. The quest for the heaviest elements Dr David Jenkins University of York

  2. Overview • (Nuclear) Physics • (Nuclear) Chemistry • History of the 20th Century • Psychology, what motivates us? • The Curse of Heavy Elements • Fraud in science and how we respond…

  3. What is an element?

  4. Rutherford - father of Nuclear Physics All science is either physics or stamp collecting

  5. Chadwick and the neutron • Chadwick discovered a very penetrating form or radiation in 1932 • He called the particle emitted the neutron as it interacted as if it had no electric charge

  6. What is an isotope? • Isotopes have the same number of protons • Different numbers of neutrons • They are chemically almost identical • The physical properties are slightly different • Tin has the most (10) stable isotopes from 112Sn to 124Sn

  7. Radioactivity • Radioactivity is a random, statistical process • We define a characteristic halflife in which 50% of a sample would have decayed • An estimated halflife can be established on the strength of just one observed event!

  8. Alpha decay • Least penetrating radiation • Stopped by sheet of paper • Polonium (element 84) and radium (element 86) discovered from Pitchblende (natural decays from uranium)

  9. Beta decay • Beta decay is a natural tendency to avoid excess of protons/neutrons • Beta decay changes from one element to another • The beta particles (electrons or positrons) are stopped by a thin sheet of metal

  10. Glenn Seaborg • The great nuclear chemist • Led work at Lawrence Berkeley National Laboratory in California

  11. Medical isotopes discovered by Seaborg • 59Fe - diagnosis of blood • 60Co - radiotherapy • 131I - thyroid diagnosis and treatment • 99Tc - diagnostic • 137Cs - radiotherapy

  12. Cockcroft and Walton • In 1932, Cockcroft and Walton split the atom by accelerating protons into lithium and splitting into two alpha particles • They built the first particle accelerator to do this

  13. Accelerators • Accelerators increase the kinetic energy (velocity) of charged particles • At sufficient energy, the particles can overcome the Coulomb repulsion and fuse with a target nucleus • The probability for such fusion is called “cross-section”

  14. First transuranic elements:Neptunium (93) and Plutonium (94) These elements were first produced by bombarding 238U with deutrerons with Berkeley cyclotron in 1941 By such means, large amounts of material could be made and the chemistry studied in detail At the peak of cold war, perhaps 300000kg of plutonium was stockpiled

  15. False start - 1930’s • Once they knew how to produce neutrons they thought about bombarding uranium to produce heavier elements • People used chemistry to separate the “new” elements • They found they could not separate them from well-known lighter elements despite them being radioactive • Why?

  16. Bombarding plutonium gives:Americium (95), Curium (96) Some heroic and patient chemistry was needed Separation relied on using knowledge of chemical analogue

  17. Bombarding Am and Cm gives:Berkelium (97) and Californium (98)

  18. Einsteinium (99) and Fermium (100) • These elements were identified chemically from the fallout of the first thermonuclear bomb ‘Mike’ • Einsteinium is the last element of which micrograms exist • Fermium is produced by capturing no less than 17 neutrons onto uranium • Fermium fissions very quickly and so no further progress can be made with adding neutrons • This is the end of classical “nuclear chemistry”

  19. Heavy ions • To reach heavier elements, beams of heavy ions were needed e.g. C, N, O • Such accelerators started to come on line about 1957 • The baton passed to the Nobel Institute in Stockholm

  20. Nobelium (102) • The first claim was made by Nobel Institute and called the element Nobelium • This became “Nobelievium” when Berkeley failed to find it • It took several years and very careful work to identify the alpha decay of No • The Berkeley group confused isotope 254 with 252 • The Dubna group showed that they were in error • Despite everything, the Nobelium name was allowed to remain

  21. Cold War “As a young man I was called obstinate but now I am called insistent"

  22. Where is the next magic shell gap?

  23. What’s in a name? • IUPAC regulates the recognition of superheavy elements • They insist that identification is made at more than one laboratory • They specify the names which are allowed

  24. False Start II:Are they in the earth?The curse of heavy elements http://www.halos.com/

  25. Heavier ions and higher sensitivityRecoil separators

  26. GSI

  27. Germany takes up the mantle

  28. False Start III:Ninovium - the element that never was… • In 2001, to great acclaim researchers at Berkeley announced the discovery of element 118 • Two years and a long enquiry later, the announcement was retracted…

  29. From Russia with 48Ca … Russia plays the game with key advantages: Dedicated facility - long running times 48Ca beam obtained from reactors Actinide targets e.g. Pu, Cm

  30. Modern periodic table

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