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James Chadwick

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Luke Lemons

on 18 September 2013

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Transcript of James Chadwick

James Chadwick
Working at Cambridge in 1920, James Chadwick' and his mentor, Ernest Rutherford, were able to prove the existence of the proton, yet found a problem when the atomic number was less than the atomic mass.

If electrons have nearly no mass and protons do have a mass.
How is it possible that the number of protons in an atom, is less
than the atomic mass if electrons and protons are the only
molecules in an atom?

Well it must be that there is another molecule in an atom that is undetectable because it has no charge. I'll call it a neutron!
Rutherford did first suggest the IDEA of the neutron yet there was
no test or evidence that could back up his theory
And Chadwick did not dedicate his studies to purely proving the neutrons existence. Instead he traveled to Europe and began studying radiation with different scientists.
While in Europe, a groups of famous scientists were shooting alpha rays at an element called beryllium. The waves shot back with a neutral radiation that could penetrate 200 milliliters of lead. Yet protons could only penetrate less than one millimeter of lead.

Walther Bothe
Irene Joliot-Curie
Frederic Joliot
Some scientists claimed that it was just high-energy gamma rays
Chadwick said that it couldn't be gamma rays, there wasn't enough energy. So he decided to test if it could be his mentors theoretical neutron particle
In 1932, Chadwick put Beryllium in a chamber with Polonium which shot alpha rays at it
Beryllium emitted neutral radiation waves which Chadwick lined up to hit targets
When the targets were hit, electrically charged atoms flew off the target
Chadwick calculated the speed of
the atoms for numerous different
targets and came to the conclusion
that gamma ray could not explain
the atoms speed; therefore, it must
be neutrons.
To prove the particle truly was a neutron, Chadwick found it's mass by canceling every other factor in his experiment.

He found the neutron to be 1.0067 times the mass of the proton.
Chadwick had discovered the neutron and modestly released his findings in a book called "Possible Existence of a Neutron".

He then re-imagined what the atom looked like with his neutron, replacing his mentor, Rutherford's, atom.
In 1935 Chadwick won the Nobel Prize in Physics for his work with radiation and discovery of the neutron
Because of Chadwick's discovery many future scientists like Einstein and Cockcroft were able to blast atoms' nuclei with neutrons (they called them "neutron bullets") which lead to the splitting of atoms.
James Chadwick and John Cockcroft
The End
"James Chadwick - Biographical". Nobelprize.org. Nobel Media AB 2013. Web. 16 Sep 2013. <http://www.nobelprize.org/nobel_prizes/physics/laureates/1935/chadwick-bio.html>

"The Atom Timeline." Timetoast. 16 Sept. 2013 <http://www.timetoast.com/timelines/the-atom-timeline>.

PBS. PBS. 16 Sept. 2013 <http://www.pbs.org/wgbh/aso/databank/entries/dp32ne.html>.

"Award Ceremony Speech." Nobel Prize in Physics 1935. 16 Sept. 2013 <http://www.nobelprize.org/nobel_prizes/physics/laureates/1935/press.html>.

"James Chadwick - Biographical." James Chadwick - Biographical. 16 Sept. 2013 <http://www.nobelprize.org/nobel_prizes/physics/laureates/1935/chadwick-bio.html>.

"UCSB Science Line Sqtest." UCSB Science Line Sqtest. N.p., n.d. Web. 18 Sept. 2013. <http://scienceline.ucsb.edu/getkey.php?key=1>.

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