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Free to try, no credit card required1. The atomic number versus the atomis mass (3)
2. The helium nucleus versus the hydrogen nucleus (2)
3. The assumption that when beryllium is hit with alpha particles, that the radiation emitted is gamma rays. (4)
1. Alpha particles were shot at beryllium and knowcked out its neutrons.
2. "New particles" or the supposed gamma rays were blasted into the paraffin.
3. Protons from the paraffin were detected.
The Discovery of the Neutron
The atomic number of an element is the number of protons in one atom. The atomic mass is the mass of the nucleus of a particular atom. The mass of a proton was already known at this point, and it was also known that the protons were in the nucleus of an atom. However, when calculating the mass of all the protons using the atomic number and the known mass of one proton, the atomic mass always turned out to be higher.
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Suspicions...
In an experiment done by Bothe and Becker, beryllium was hit with alpha particles, and there was a resulting radiation assumed to be gamma rays. When the Joliot-Curies let this radiation hit paraffin wax, protons were blasted out the other end. For the radiation to be comprised of gamma rays, it would have to be peculiarly potent. Chadwick was not convinced.
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After experimentation, it was shown that a helium nucleus exerts double the electric force on an electron as did one of hydrogen. This was explained with the reasoning that helium has two protons while hydrogen only has one (since it is the lightest atom). Thus, helium would have two electrons and two protons, making a helium atom have a mass twice as large as one of hydrogen (one electron and one proton). In rality, helium atoms have a mass about four times as large as a hydrogen atom. Chadwick speculated that if two new particles that have a mass very similar to a proton and are electrically neutral were present, this relation would be fulfilled.
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First Experiment:
1. Mass of neutron
2. Initial velocity of neutron
3. Final velocity of neutron
Second experiment:
4. Final velocity in the new collision
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Neutrons and protons are thought to be made up of even smaller particles called quarks. Up quarks have a positive charge, and down quarks have a negative charge.
Unknowns
Bibliography
1. Experimental Diagram
Significance (4)
The discovery of the neutron was very significant. Besides for clearing up all of the discrepancies shown in my "Suspicions" slide, it was also helpful in nuclear aspects.
In a system of equations, to solve for every variable, one must have as many unknowns as equations. Chadwick did this by doing the same experiment twice, but with different elements. These were hydrogen and nitrogen gas (in the detection chamber).
From his experiments, Chadwick gleaned information that he could put toward definative equations.
The Trinity bomb explosion was the first atomic bomb test (4).
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As it turns out, a lone neutron is not stable. It decays because one of its quarks changes, so it becomes either a proton, an electron, or a light particle called a neutrino.
2. Experimental Information
Equations (2)
James Chadwick (6)
3. Experimental Information
4. Experimental Information
5. Quark Picture
“Chadwick’s Experiment to Discover the Neutrons.” ThinkQuest. Oracle, n.d. Web. 3 Oct. 2010. <http://library.thinkquest.org/C001124/gather/aexp.html>.
6. Portrait of J. Chadwick
7. Video of the Bomb Testing
8. Experimental Video
9. Explanation of the helium atom Suspicion
The Nuclear Bomb
Equations
Neutrons, unlike protons, can penetrate through atoms without repulsion. They can even be made to stop within the nucleus of another atom. These qualities make them very useful to nuclear physicists. During WWII, this idea helped with the construction of nuclear weapons. Chadwick also helped with a demonstration of a particle accelerator in Liverpool needing only a few kilos of uranium to create a nuclear bomb.
First Experiment:
1. Conservation of momentum
2. No loss of kinetic energy
Second experiment:
3. Conservation of momentum in new collision
4. No loss of kinetic energy in the new collision
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It was thought that something with a neutral charge would puncture the paraffin because something with a charge would be electrically deflected in various directions. Also, there would be no reduction in speed for this reason as well. Thus, the neutrons would be able to smack the protons out of the paraffin wax.
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The neutrons from the beryllium knocked out the protons from the wax. The protons were then detected. The speed of the protons suggested the similar mass of the neutrons.
Experimentation (4)
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