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The quest for the heaviest elements
The quest for the heaviest elements
Dr David Jenkins
University of York
Dr David Jenkins
University of York
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OverviewOverview
(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…
(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…
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What is an element?What is an element?
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Rutherford - father of Nuclear PhysicsRutherford - father of Nuclear Physics
All science is either physics or stamp collectingAll science is either physics or stamp collecting
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Chadwick and the neutronChadwick 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
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
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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
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
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RadioactivityRadioactivity
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!
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!
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Alpha decayAlpha decay
Least penetrating radiation Stopped by sheet of paper
Least penetrating radiation Stopped by sheet of paper
Polonium (element 84) and radium (element 86) discovered from Pitchblende (natural decays from uranium)
Polonium (element 84) and radium (element 86) discovered from Pitchblende (natural decays from uranium)
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Beta decayBeta 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
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
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Glenn SeaborgGlenn Seaborg The great nuclear chemist Led work at Lawrence Berkeley National Laboratory in California
The great nuclear chemist Led work at Lawrence Berkeley National Laboratory in California
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Medical isotopes discovered by SeaborgMedical isotopes discovered by Seaborg
59Fe - diagnosis of blood 60Co - radiotherapy 131I - thyroid diagnosis and treatment 99Tc - diagnostic 137Cs - radiotherapy
59Fe - diagnosis of blood 60Co - radiotherapy 131I - thyroid diagnosis and treatment 99Tc - diagnostic 137Cs - radiotherapy
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Cockcroft and WaltonCockcroft 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
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
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AcceleratorsAccelerators
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”
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”
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First transuranic elements:Neptunium (93) and Plutonium (94)
First transuranic elements:Neptunium (93) and Plutonium (94)
These elements were first produced by bombarding These elements were first produced by bombarding 238238U with U with deutrerons with Berkeley cyclotron in 1941deutrerons with Berkeley cyclotron in 1941
By such means, large amounts of material could be made and the By such means, large amounts of material could be made and the chemistry studied in detailchemistry studied in detail
At the peak of cold war, perhaps 300000kg of plutonium was stockpiledAt the peak of cold war, perhaps 300000kg of plutonium was stockpiled
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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?
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?
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Bombarding plutonium gives:Americium (95), Curium (96)
Bombarding plutonium gives:Americium (95), Curium (96)
Some heroic and patient chemistry was neededSome heroic and patient chemistry was needed
Separation relied on using knowledge of chemical analogueSeparation relied on using knowledge of chemical analogue
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Bombarding Am and Cm gives:Berkelium (97) and Californium (98)
Bombarding Am and Cm gives:Berkelium (97) and Californium (98)
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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”
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”
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Heavy ionsHeavy 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
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
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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
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
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Cold WarCold War
““As a young man I was called obstinate but As a young man I was called obstinate but now I am called insistent"now I am called insistent"
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Where is the next magic shell gap?Where is the next magic shell gap?
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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
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
Atomic number
Berkeley Dubna IUPAC
104 Rutherfordium Kurchatovium Rutherfordium
105 Hahnium Nielsbohrium Dubnium
106 Seaborgium Seaborgium
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False Start II:Are they in the earth?The curse of heavy elements
False Start II:Are they in the earth?The curse of heavy elements
http://www.halos.com/
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Heavier ions and higher sensitivity Recoil separators
Heavier ions and higher sensitivity Recoil separators
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GSIGSI
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Germany takes up the mantleGermany takes up the mantle
Atomic number
Name Symbol Discovery
107 Bohrium Bh 1981
108 Hassium Hs 1984
109 Meitneirium Mt 1982
110 Darmstadtium Ds 1994
111 Roentgenium Rg 1994
112 No name 1996
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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…
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…
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From Russia with 48Ca …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
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Modern periodic tableModern periodic table