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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

The quest for the heaviest elements

Dr David Jenkins

University of York

overview
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…
rutherford father of nuclear physics
Rutherford - father of Nuclear Physics

All science is either physics or stamp collecting

chadwick and the neutron
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
what is an isotope
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
radioactivity
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!
alpha decay
Alpha decay
  • Least penetrating radiation
  • Stopped by sheet of paper
  • Polonium (element 84) and radium (element 86) discovered from Pitchblende (natural decays from uranium)
beta decay
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
glenn seaborg
Glenn Seaborg
  • The great nuclear chemist
  • Led work at Lawrence Berkeley National Laboratory in California
medical isotopes discovered by seaborg
Medical isotopes discovered by Seaborg
  • 59Fe - diagnosis of blood
  • 60Co - radiotherapy
  • 131I - thyroid diagnosis and treatment
  • 99Tc - diagnostic
  • 137Cs - radiotherapy
cockcroft and walton
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
accelerators
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”
first transuranic elements neptunium 93 and plutonium 94
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

false start 1930 s
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?
bombarding plutonium gives americium 95 curium 96
Bombarding plutonium gives:Americium (95), Curium (96)

Some heroic and patient chemistry was needed

Separation relied on using knowledge of chemical analogue

einsteinium 99 and fermium 100
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”
heavy ions
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
nobelium 102
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
cold war
Cold War

“As a young man I was called obstinate but now I am called insistent"

what s in a name
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
false start iii ninovium the element that never was
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…
from russia with 48 ca
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