The quest for the heaviest elements

The quest for the heaviest elements

Dr David Jenkins

University of York

Dr David Jenkins

University of York

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…

What is an element?What is an element?

Rutherford - father of Nuclear PhysicsRutherford - father of Nuclear Physics

All science is either physics or stamp collectingAll science is either physics or stamp collecting

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

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

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!

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)

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

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

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

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

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”

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

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?

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

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

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

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”

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

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

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"

Where is the next magic shell gap?Where is the next magic shell gap?

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

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/

Heavier ions and higher sensitivity Recoil separators

Heavier ions and higher sensitivity Recoil separators

GSIGSI

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

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…

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

Modern periodic tableModern periodic table