the model of the atom began to evolve quite rapidly after the discovery of the electron in 1897 by JJ Thompson Thompson's Plum Pudding model lasted about a decade until eventually being replaced by Rutherford's model in 1911 which in turn was replaced by the bore model merely 2 years later in the latter two models though the nucleus of the atom was merely that a nucleus not much was known about the contents of the nucleus except for the fact that it is positively charged that all changed in 1919 when Rutherford discovered the proton and proposed that the
nucleus is composed of these positively charged particles as groundbreaking as these two decades of atomic research were there were still some obvious Atomic Mysteries that had yet to get answers one of these Atomic Mysteries stood out in particular among the rest at the time this mystery was the large dispar between the atomic number or amount of protons in the nucleus of an atom and the atomic weight of the atom to try and solve these two Mysteries Rutherford himself proposed the idea of a new type of particle in the atom one that consists of a proton
and an electron bound together having a neutral charge and existing in relatively the same quantity as the proton Rutherford though never proved this experimentally and the task to prove the existence of a neutral atomic particle fell into the hands of one of his students an English physicist by the name of James Chadwick James Chadwick grew up in a workingclass family but his school teachers noticed he had a talent for academics and this gave him much opportunity when the time came for secondary education he received his Masters in 1913 from the University of Manchester studying under
Ernest Rutherford and decided to traveled to Germany the following year to study under Hans Gyer Chadwick's timing though was very unfortunate for shortly after he arrived the first world war broke out and he was imprisoned in a camp for civilians of Allied Powers at Hulan although detained Chadwick was not restricted from pursuing his passion for science he and a group of fellow detainees formed a science club there where they lectured to one another and with permission from the guards set up a small lab he managed to build an electroscope in this lab with some wood
and tinf foil and experimented with radioactive toothpaste that was being sold in Germany at the time after the war James returned to England where he would complete his education studying under Rutherford and receiving his Doctorate from Cambridge in 1921 2 years later he was appointed assistant director of the Cavendish laboratory under Rutherford following in the footsteps of many greats who came before him Chadwick did not approach the proposed theory of neutral particles in the atomic nucleus for nearly a decade after completing his education for he was working on other experiments with both the atomic nucleus
and different forms of radiation his attention shifted though in 1932 an experiment had been done a couple years earlier in 1930 by a German scientist named volter B and his student Herbert Becker in which they bombarded three elements brillium Boron and lithium with Alpha Rays from the radioactive element polonium what they found was a new form of high penetrating radiation coming from the bombarded elements in 1932 husband and wife frederi and irin Julio kir replicated this experiment but put a layer of paraffin wax behind the burum to study the nature of this radiation what they
found from this was that hydrogen atoms in this paraffin wax sheet were ejected and then recoiled with high velocity from this frederi and irin came to the conclusion that this radiation was in the form of Gamay since it was so penetrating and had so much energy Chadwick though after seeing these results was not so convinced that the radiation was in the form of gamma rays and decided to perform his own experiments Chadwick's main opposition to the conclusion reached by frederi and irin Julio kirri regarded the con conservation of energy in the bombardment he referenced the
Klein nishina formula which is an equation that is used in this case to predict the scattering of gamma rays and noted that the frequency of scattering in the previous experiment was several thousand times higher than the kle nishina formula predicts for gamma rays he also is skeptical of gamma rays being the culprit due to the massive disparity of the calculated energy the buril radiation had compared to what it should have had had if it was in fact composed of gamma rays Chadwick experimented for two weeks with the same setup as frederi and urin but also
added new ways to test the new radiation on different elements Chadwick bombarded hydrogen helium nitrogen and lithium atoms with the radiation emitted from the burum to test its effect on atoms with different weights from this he used the resulting velocities and recoil energies from the ejected particles to Det determined the mass of the incoming radiation and found the mass to be very close to the mass of a proton but however slightly more massive to explain how such a massive particle could be so penetrating Chadwick proposed the idea that the particle was neutral in electric charge
he published his findings in February of 1932 first in a paper entitled the possible existence of a neutron and later in a more assertive paper in May of that same year entitled The existence of a neutron in his papers Chadwick Advanced retherford's proposal claiming that the neutron is a combined form of a proton and an electron explaining why it is slightly more massive than a proton and also why it has no electric charge by 1934 more accurate measurements of the Neutron's weight had been calculated showing that it was too heavy to be a combination of
a proton and an electron and was in fact an entirely new particle that existed in the nucleus James Chadwick won the Nobel Prize in physics in 1935 for the discovery of the neutron that same year he was appointed to a chair in physics at the University of Liverpool 5 years later he added to his influence in atomic science as he joined the modid committee a team of scientists in the United Kingdom designated to uncover the possibility of a nuclear weapon once they came to the conclusion in 1941 that it was in fact possible it gave
the United States massive incentive to undergo the now famed Manhattan Project of which Chadwick became head of the British delegation and he relocated to loamos during this time he was kned in 1945 and later won the copy medal in 1950 for his outstanding work in nuclear physics and in the development of atomic energy especially for his discovery of the neutron James Chadwick is an instrumental figure in in nuclear physics and still would be primarely even one of his many contributions the discovery of the neutron went down as Chadwick's greatest accomplishment and it completely redefined the
structure of the nucleus of the atom leading to a series of nuclear breakthroughs in the years to come if you enjoyed this video please consider liking and subscribing click here if you want to see more scientific progress made during this time period thank you for watching and I will see you in the next video
