31st December 2013
A Level Chemistry: James Chadwick and the Discovery of the Neutron
Who he was:
· James Chadwick was born in Cheshire on the 20th of October 1891
· He studied physics at the Victoria University of Manchester, where the department was headed by Ernest Rutherford.
· In 1919 Rutherford became the director of the Cavendish Laboratory at the University of Cambridge; Chadwick then joined him a few months later.
Leading up to his discovery:
· In his research at Cambridge Chadwick continually probed the atomic nucleus. In 1925, the concept of spin (the angular momentum carried by subatomic particles) allowed physicists to finally explain the Zeeman effect (splitting a spectral line into several components in the presence of a static magnetic field), but also created unexplainable anomalies.
· At Cambridge, while Chadwick continued to study radiation, Walter Bother and Herbert Becker used polonium to bombard beryllium, producing an unusual form of radiation. This to Chadwick was evidence of his hypothesis of the neutron.
What he already knew about the atom:
· The electron was discovered in 1897 by J.J Thompson.
· Rutherford discovered the proton.
· Before Chadwick’s discovery scientists believed that an atom only consisted of electrons and protons.
· At the time physicists believed that the atomic number of an atom was equal to the proton number, however this gave it the right mass and charge but the wrong spin.
What he did:
· He devised a simple experiment that consisted of a cylinder containing a polonium source and beryllium target. The polonium source emits alpha radiation which then hits the beryllium target, releasing neutrons. The neutrons then collide with the paraffin wax, triggering the release of protons which can be detected by the oscilloscope in the ionisation chamber.This occurrence proved to be inconsistent with what would happen if the same wax were bombarded with gamma radiation.
What he found out:
· After conducting the experiment Chadwick realised that the energy of the ejected protons could be explained if the neutral particle had a mass similar to that of a proton.
· He discovered that the neutron was found to measure slightly heavier than the proton with a mass of 1840 electrons and with a neutral charge. The proton and neutron together were called the nucleus.
What conclusions he drew from his results:
· Although scientists knew that atoms of a particular element have the same number of protons they discovered that some these atoms have slightly different masses. They concluded that the variations in mass result from the number of neutrons in the nucleus of the atom. Atoms of an element having the same atomic number but different atomic masses were called isotopes of that element.
· James Chadwick was born in Cheshire on the 20th of October 1891
· He studied physics at the Victoria University of Manchester, where the department was headed by Ernest Rutherford.
· In 1919 Rutherford became the director of the Cavendish Laboratory at the University of Cambridge; Chadwick then joined him a few months later.
Leading up to his discovery:
· In his research at Cambridge Chadwick continually probed the atomic nucleus. In 1925, the concept of spin (the angular momentum carried by subatomic particles) allowed physicists to finally explain the Zeeman effect (splitting a spectral line into several components in the presence of a static magnetic field), but also created unexplainable anomalies.
· At Cambridge, while Chadwick continued to study radiation, Walter Bother and Herbert Becker used polonium to bombard beryllium, producing an unusual form of radiation. This to Chadwick was evidence of his hypothesis of the neutron.
What he already knew about the atom:
· The electron was discovered in 1897 by J.J Thompson.
· Rutherford discovered the proton.
· Before Chadwick’s discovery scientists believed that an atom only consisted of electrons and protons.
· At the time physicists believed that the atomic number of an atom was equal to the proton number, however this gave it the right mass and charge but the wrong spin.
What he did:
· He devised a simple experiment that consisted of a cylinder containing a polonium source and beryllium target. The polonium source emits alpha radiation which then hits the beryllium target, releasing neutrons. The neutrons then collide with the paraffin wax, triggering the release of protons which can be detected by the oscilloscope in the ionisation chamber.This occurrence proved to be inconsistent with what would happen if the same wax were bombarded with gamma radiation.
What he found out:
· After conducting the experiment Chadwick realised that the energy of the ejected protons could be explained if the neutral particle had a mass similar to that of a proton.
· He discovered that the neutron was found to measure slightly heavier than the proton with a mass of 1840 electrons and with a neutral charge. The proton and neutron together were called the nucleus.
What conclusions he drew from his results:
· Although scientists knew that atoms of a particular element have the same number of protons they discovered that some these atoms have slightly different masses. They concluded that the variations in mass result from the number of neutrons in the nucleus of the atom. Atoms of an element having the same atomic number but different atomic masses were called isotopes of that element.
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