Transmutation, Nuclear Fission and Fusion

Transmutation, Nuclear Fission and Fusion

Nuclear Transformations • Nuclear Transformations: Changing one element into another by particle bombardment α O N 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 1st 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 milliontimes 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 • the process dies out critical • (AKA: Ka-Boom)

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)

Transmutation, Nuclear Fission and Fusion