This not only changed our view of the nucleus, but also provided a new, relatively inexpensive means of probing the nucleus. Because the neutron was relatively massive but neutral, it was scarcely affected by the cloud of electrons surrounding the nucleus or by the positive electrical barrier of the nucleus itself; thus it could penetrate the nucleus of any element. Consult Nature magazine for the original Letter to the Editor by James Chadwick regarding the "possible existence of a neutron," published February 27, Frank A.
Settle Washington and Lee University. Courtesy of the American Institute of Physics left , Lord Rutherford at Cambridge right Twelve years earlier, Lord Ernest Rutherford, a pioneer in atomic structure, had postulated the existence of a neutral particle, with the approximate mass of a proton, that could result from the capture of an electron by a proton. Chadwick's Apparatus The search was over. Contributors Frank A.
Chadwick went on to work on other projects, but kept thinking about the problem. Around , several researchers, including German physicist Walter Bothe and his student Becker had begun bombarding beryllium with alpha particles from a polonium source and studying the radiation emitted by the beryllium as a result. Some scientists thought this highly penetrating radiation emitted by the beryllium consisted of high energy photons.
Chadwick had noticed some odd features of this radiation, and began to think it might instead consist of neutral particles such as those Rutherford had proposed. They found that this radiation knocked loose protons from hydrogen atoms in that target, and those protons recoiled with very high velocity. In , he tried similar experiments himself, and became convinced that the radiation ejected by the beryllium was in fact a neutral particle about the mass of a proton.
He also tried other targets in addition to the paraffin wax, including helium, nitrogen, and lithium, which helped him determine that the mass of the new particle was just slightly more than the mass of the proton. Chadwick also noted that because the neutrons had no charge, they penetrated much further into a target than protons would.
By it had been established that the newly discovered neutron was in fact a new fundamental particle, not a proton and an electron bound together as Rutherford had originally suggested. Scientists soon realized that the newly discovered neutron, as an uncharged but fairly massive particle, could be used to probe other nuclei. As an enemy alien, Chadwick was interned by the Germans, but allowed to set up a laboratory in the stables of his civilian internee camp outside Berlin.
He remained there throughout the war, doing his research, before returning to Britain in Working again with Rutherford, who had by this time moved to Cambridge University, Chadwick helped his mentor achieve the first artificial nuclear transformation. In he was elected a Fellow of the Royal Society.
In , Chadwick made a fundamental discovery in the domain of nuclear science: he proved the existence of neutrons — elementary particles devoid of any electrical charge. In contrast with the helium nuclei alpha rays which are charged, and therefore repelled by the considerable electrical forces present in the nuclei of heavy atoms, this new tool in atomic disintegration need not overcome any electric barrier and is capable of penetrating and splitting the nuclei of even the heaviest elements.
Chadwick in this way prepared the way towards the fission of uranium and towards the creation of the atomic bomb. For this epoch-making discovery he was awarded the Hughes Medal of the Royal Society in , and subsequently the Nobel Prize for Physics in From to he worked in the United States as Head of the British Mission attached to the Manhattan Project for the development of the atomic bomb.
He returned to England and, in , retired from active physics and his position at Liverpool on his election as Master of Gonville and Caius College, Cambridge.
0コメント