Transmutation, Nuclear Fission and Fusion

Nuclear Transformations Nuclear Transformations: Changing one element into another by particle bombardment α N O H

Nuclear Transformations Rutherford: 1919  First to discover nuclear transformation 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 1 st to create an artificial radioactive isotope –14 years after Rutherford

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

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

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)