Transmutation, Nuclear Fission and Fusion

Nuclear Transformations

• Nuclear Transformations: Changing one element into another by particle bombardment

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Nuclear Transformations

• Rutherford: 1919 First to discover nuclear transformation

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How is this different from radioactivity?•Not a natural occurrence•Can be controlled – stopped or started•Two reactants instead of one•Uses bombardment by a lighter particle

Nuclear Transformation

• Irene Curie and Frederick Joliot– Were the 1st to create an artificial radioactive

isotope– 14 years after Rutherford

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Nuclear Transformation

• How was it done?– Both sets of scientists used alpha particles

• They bombarded a larger nucleus with a smaller particle.

– Both the nucleus and alpha particle were positive so they repelled each other. • Very high energies needed to accomplish

transformation. – A particle accelerator was used to accelerate the

particles to the required speeds.

Accomplishing Nuclear Transformation• Neutrons also used. Why would they

be easier? – They are neutral and not repelled so they

are absorbed easier.– This is the method used to extend the

periodic table.

Creating Synthetic Isotopes

• Synthetic isotopes are made by using particle accelerators – Prior to 1940, the heaviest known element

was Uranium• Since 1940, many transuranium elements have

been produced from nuclear transformations.

– Get to name them after anything you want • Countries or scientists are common

Writing Equations

• Write equations showing the neutron formation of Americium

• Bombard (react) Pu-240 with a neutron.• Take the product from ‘a’ and have it

undergo beta decay.

• Show the gamma decay of Am-243.• Show the alpha decay of Am-243.

NUCLEAR FISSION AND FUSION

Nuclear Energy

• Two types of nuclear processes that release energy:– Fusion: combining two light nuclei to form

a heavier nucleus– Fission: splitting a heavy nucleus into two

nuclei with smaller mass numbers

Nuclear Fission

•Was discovered in the late 1930s–A Uranium-235 nucleus was spilt into two lighter elements during neutron bombardment:

•The fission of 1 mole of U-235 releases 26 million times as much energy as the combustion as 1 mol of methane

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Nuclear Fission

• Besides the product nuclides, neutrons are also produced

Nuclear Fission

– Each fission event will produce neutrons that can collide with even more U-235 nuclei

– Because each fission event produces neutrons, we call it a chain reaction

Nuclear Fission

• For the fission to be self-sustaining at least ONE neutron from each fission event must go on to split another nucleus– If less than one neutron causes a fission event,

– If exactly one neutron from each fission event causes ANOTHER fission event, the process sustains itself and is said to be

– If more than one neutron from each fission event causes another fission event, the process escalates and the heat build-up causes an explosion

(AKA: Ka-Boom)

critical

the process dies out

Nuclear Fission• During WWII, the US carried out a research

effort called the Manhattan Project– The goal was to build a bomb based on the

principles of nuclear fission– This project produced the first fission bomb

• Used on Hiroshima and Nagasaki in 1945

– The bomb operates by rapidly escalating fission events that produce an explosion!

Oak Ridge, Tennessee.  60,000 workers worked for three years to separate 2 kilograms of uranium-235 from uranium-238 for the Manhattan Project

The other Energy Source: Nuclear Fusion• Combining two light nuclei to create

one heavier nucleus– Produces even more energy than fission

• Occurs in stars - including our sun– Fusion of protons to form helium

Fusion

•Efforts are underway to develop a feasible fusion process

–There is a ready availability of light nuclides•Deuterium( ) is in seawater

–Can serve as fuel for fusion reactions

•Initiating fusion is much more intensive than initiating fission

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Fusion

• Forces binding nucleons together only work at very small distances– Getting protons close requires lots of

energy

• Must be shot at each other– This is because the protons repel each

other, so the repelling forces must be overcome with spee

Fusion• Need temperatures of 40 million Kelvin

– Product of fusion is plasma, which is hard to contain

– Scientists are studying two types of systems to produce the extremely high temperatures required:• High powered lasers• Heating by electric currents (magnets)