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Radioactivity- A2 physics

Dave Jones

on 28 April 2010

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Transcript of Radioactivity

Atomic Structure
Radioactive decay
Half life
Squash Court Science
Marie Curie
Atomic bomb
Los Alamos
nuclear power
Radio therapy
carbon dating
Marie Curie's Notebooks
The first X-ray was taken in January 1896 by William Roentgen, showing his wife, Berthea's hand and wedding ring. In the early days of x-rays, before they knew how harmful they were, it was fashionable to display full body x-rays of yourself in your home or for newly married women to send an x-ray of their hand and wedding ring to friends to show that they were married.
bananas and potassium rich foods
On 26th April 1986 one of four nuclear reactors at Chernobyl Power station in Ukraine overheated and exploded. 56 direct deaths have been attributed to the disaster and another 6000 deaths from cancer have also been linked to the explosion. These figures include the firefighters who went to the nuclear plant to attempt to control the subsequent fire, without proper protection from radiation.
As an energy source nuclear power is very efficient. Nuclear fission of uranium or plutonium is used to provide energy to heat water, create steam and ultimatly turn the turbines that give us electricity. On the whole this is a relativley cheap and efficient way of producing electricity but protesters always point out the extreme dangers if something goes wrong such as at Chernobyl or 3 mile island.
Nuclear Disasters
Three Mile Island
In 1979 a cooling malfunction at 3 Mile Island nuclear power plant caused part of the second reactor to melt. Radioactive gas was given off a few days later but fortunatly the level was low enough that it was not harmful.
With the discovery of radioactivity and nuclear fission just before the outbreak of world war two the race was on to see which side would be the first to develop and make a nuclear bomb.
Some of America's finest physicists, including Feynman,Fermi, Hans Bethe descended on Los Alamos to help the war effort. They succeeded in amking a working atomic bomb which the americans dropped in 1945 on Hiroshima and Nagasaki ending world war two.
On 6th August 1945 American planes dropped an atomic bomb on the Japanese town of Hiroshima and one on Nagasaki a few days later. The death toll is estimated to be around 140000.
Discovered natural radioactivity from uranium when looking for a connection between x-rays and phosphorescence. Received half the nobel prize for physics in 1903.
After Becquerels discovery of radioactivity, Marie Curie, along with her husband Pierre continued to study radioactivity eventually discovering polonium and radium.
When J.J. Thomson discovered the electron in 1987, he modelled the atom as a 'cloud' of positive charge with negative electrons in it.
Plum Pudding Model
Rutherfords Model
In 1909 Geiger and Marsden, under the direction of Rutherford, fired alpha particles at a very thin sheet of gold foil. They dicovered that:
the majority went straight through
Approximatly 1 in 100 were deflected less than 90 degrees
1 in 2000 were reflected back towards the emittor.
From this Rutherford realised that an atom is mostly empty space with most of the mass centred in the nucleus, which has a positive charge and the electrons orbit this.
Current Model
In 1932 James Chadwick discovered the neutron, completing the atom. The presence of the neutron in the nucleus helps explain how the protons remain so close together without repeling.
The notebooks used by Marie Curie are still radioactive. As radium 226 has a half life of 1622 years, they will continue to emit radiation for along time to come.
Oklo in Gabon, Africa is a natural reactor. A layer of uranium ore in the ground changes naturally from U238 to U234, emmitting alpha particles.
A Natural Reactor
Although alpha particles cannot penetrate the skin, if they get inside you they can have very serious effects. The particles ionise nearby atoms, scrambling the DNA sequence. This can turn the cells cancerous.
Beta particles are not as strongly ionising as alpha particles so only do about 1/20 of the damage. However they can pass through skin so are more likely to get inside you.
Gamma rays hardly ionise atoms at all. However if they are absorbed by atoms the atoms gain energy and give out other particles.
Whilst working on the atonic bomb at Los Alamos during the war Harry Daghlian accidently exposed himself to radiation. He suffered radiation burns, like this one to his hand, and died 25 days later.
Today, all workers who come into contact with radioactive sources are required to wear a film badge that measures their exposure to radiation. If this gets too high then the workers are not allowed to work near radioactive sources anymore. They also have regular health check ups.
Why do atoms decay?
Atoms of larger elements are often unstable. They emit particles in an attempt to become more stable. The most stable element is iron, which is the most abundant element in the universe.
What is emitted
helium nuclei-2 protons and 2 neutrons
high speed electrons
Ray- photon
When are they emitted
If the nucleus contains too many protons which causes excessive repulsion in the nucleus.
If the neutron to proton ratio is too great in the nucleus.
Nucleus has to much energy
polonium 360, radium 226
cobalt 60
tritium (hydrogen 3), carbon 14
cosmic rays
cosmic rays
In November 2006 Alexander Litvinenko, an ex russian spy, died from radioactive poisoning. It is thought that his food was laced with polonium 210. This gives off alpha particles which are the most ionising and affect DNA in cells in the body but is hard to detect as it does not pass through the skin.
Disclaimer: The author does not condone the use of radioactivity as a poison and accepts no responsibility for the actions of those reading this poster.
The 'half life' of a radioactive isotope is defined as the time taken for half the atoms in a sample to decay into a different isotope.
When a living thing dies it stops absorbing carbon. However carbon 14 continues to decay into carbon 12. As archeologists know that carbon 14 has a half life of 5700 years, they can date an object by how much carbon 14 remains.
Doctors use beams of radiation to stop tumours from growing.
A radioactive isotope is absorbed. Detection devices can then be used to see where it ends up in the body.
Rutherford worked as a professor at Manchester university. He had his students do experiments and record the measurements. From these results he built his theories on atomic structure and radioactivity.
James Chadwick
Chadwick was working as a student under Rutherford when he discovered the neutron.
Geiger worked with Ernest Marsden on Rutherford's gold leaf experiment. He later went on to help develop the geiger-muller tube for detecting radiation.
The first nuclear reactor was built in 1942 in a squash court at the university of Chicago. by Enrico Fermi. Safety was a big concern and men were employed to stand with axes ready to cut the ropes that held a big lead block over the reactor that would seal it in. These axe men later went on to develop cancer from the high radiation levels they were exposed to.
The accident occurred when engineers on the evening shift began an experiment with the cooling pump system. The control rods were lowered t oreduce the output, but when the output dropped too much they were raised again and the automatic shutdown was disabled. When the power reached 12% the experiment began but then the power levels surged, causing the reactor to begin to overheat, and the coolant to turn to steam. The emergency button was pressed and the control rods were reinserted but this caused the reactivity to intensify in the lower core. This caused the fuel pellets to explode, blowing off the roof which ingnited a fire which burned for 9 days.
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