1 00:00:00,240 --> 00:00:05,840 Speaker 1: Hi there, Welcome to this day in History class, where 2 00:00:05,840 --> 00:00:09,360 Speaker 1: we sift through the artifacts of history seven days a week. 3 00:00:10,320 --> 00:00:23,320 Speaker 1: Today is February. The day was February nine thirty two, 4 00:00:24,239 --> 00:00:27,880 Speaker 1: the journal Nature published a letter by the English physicist 5 00:00:28,000 --> 00:00:33,720 Speaker 1: James Chadwick. The letter was called possible existence of a neutron. 6 00:00:35,080 --> 00:00:38,559 Speaker 1: Up until this point, science hild that the atom contained 7 00:00:38,560 --> 00:00:43,160 Speaker 1: a positively charged nucleus or central core, that was surrounded 8 00:00:43,200 --> 00:00:48,199 Speaker 1: by negatively charged electrons, and scientists knew that most of 9 00:00:48,240 --> 00:00:51,800 Speaker 1: the mass of the atom was at its core. But 10 00:00:51,960 --> 00:00:56,440 Speaker 1: Chadwick's research confirmed the existence of a sub atomic particle 11 00:00:56,880 --> 00:00:59,800 Speaker 1: that had about the same mass as a proton, but 12 00:01:00,000 --> 00:01:04,760 Speaker 1: did not have an electric charge. Chadwick's findings marked a 13 00:01:04,840 --> 00:01:09,560 Speaker 1: major milestone in atomic theory and led to experimentation with 14 00:01:09,680 --> 00:01:14,960 Speaker 1: developing an atomic bomb. But many other scientists helped pave 15 00:01:15,120 --> 00:01:19,520 Speaker 1: the way for Chadwick to make his discovery. Chadwick got 16 00:01:19,560 --> 00:01:22,959 Speaker 1: his master's degree in physics at the University of Manchester, 17 00:01:23,480 --> 00:01:26,720 Speaker 1: where he worked with noted physicists and so called father 18 00:01:26,880 --> 00:01:32,520 Speaker 1: of nuclear physics, Ernest Rutherford. Then he went to Germany 19 00:01:32,560 --> 00:01:37,920 Speaker 1: to study under Hans Geiger of Geiger counter fame. After 20 00:01:38,000 --> 00:01:41,080 Speaker 1: spending years in a prison camp during the First World War. 21 00:01:41,720 --> 00:01:45,319 Speaker 1: Chadwick went back to England to study with Rutherford again, 22 00:01:46,080 --> 00:01:49,960 Speaker 1: this time earning his doctorate at the University of Cambridge, 23 00:01:51,200 --> 00:01:56,320 Speaker 1: and in nineteen Chadwick was appointed assistant director of Cambridge's 24 00:01:56,520 --> 00:02:02,600 Speaker 1: Cavendish Laboratory, where Rutherford was direct and there the two 25 00:02:02,640 --> 00:02:06,640 Speaker 1: of them worked on the transmutation of elements by bombarding 26 00:02:06,680 --> 00:02:10,720 Speaker 1: them with alpha particles and researched the structure of the 27 00:02:10,760 --> 00:02:16,960 Speaker 1: atomic nucleus. Rutherford postulated that there had to be something 28 00:02:17,000 --> 00:02:21,120 Speaker 1: else in the atomic nucleus besides protons. Why was the 29 00:02:21,160 --> 00:02:25,560 Speaker 1: atomic number or the number of protons and Adams nucleus 30 00:02:25,680 --> 00:02:31,160 Speaker 1: usually about half the mass number. Rutherford answered this question 31 00:02:31,240 --> 00:02:35,480 Speaker 1: in nineteen twenty by suggesting that a proton and electron 32 00:02:35,880 --> 00:02:39,800 Speaker 1: combined to form a neutral particle that was roughly the 33 00:02:39,840 --> 00:02:44,800 Speaker 1: same mass as a proton. But this neutral particle would 34 00:02:44,880 --> 00:02:48,040 Speaker 1: be hard to detect since most techniques at the time 35 00:02:48,400 --> 00:02:54,040 Speaker 1: measured charged particles. By About a decade later, other scientists 36 00:02:54,120 --> 00:02:58,360 Speaker 1: were working on the problem. German physicist Walter both and 37 00:02:58,440 --> 00:03:03,240 Speaker 1: his student Herbert Becker. We're doing experiments bombarding beryllium with 38 00:03:03,280 --> 00:03:07,680 Speaker 1: alpha particles emitted from polonium, and they found that the 39 00:03:07,760 --> 00:03:13,079 Speaker 1: beryllium emitted a highly penetrating radiation. As a result, they 40 00:03:13,120 --> 00:03:17,600 Speaker 1: interpreted that radiation to be high energy photons, which are 41 00:03:17,600 --> 00:03:23,320 Speaker 1: particles that represent a quantum of electromagnetic radiation. But Chadwick 42 00:03:23,440 --> 00:03:27,600 Speaker 1: thought that this radiation might instead consist of the neutral 43 00:03:27,639 --> 00:03:32,480 Speaker 1: particles his mentor Rutherford had proposed, and in nineteen thirty 44 00:03:32,480 --> 00:03:37,160 Speaker 1: two Chadwick's interest was piqued when Irene and Frederic Jolio 45 00:03:37,320 --> 00:03:42,720 Speaker 1: Curie decided to study the mysterious radiation. They studied the 46 00:03:42,800 --> 00:03:46,160 Speaker 1: radiation as it hit a block of paraffin wax, and 47 00:03:46,200 --> 00:03:50,520 Speaker 1: they found that the radiation ejected protons from the hydrogen 48 00:03:50,560 --> 00:03:54,240 Speaker 1: atoms in the paraffin wax, and the protons recoiled with 49 00:03:54,320 --> 00:03:59,600 Speaker 1: the high velocity. Irene and Frederic thought that the radiation 50 00:04:00,080 --> 00:04:04,480 Speaker 1: had to be high energy gamma photons, but Chadwick thought 51 00:04:04,800 --> 00:04:08,960 Speaker 1: that since photons have no rest mass, they couldn't possibly 52 00:04:09,040 --> 00:04:13,160 Speaker 1: knock heavy protons out of the paraffin wax. So that 53 00:04:13,320 --> 00:04:18,200 Speaker 1: same year Chadwick did similar experiments at the Cavendish Laboratory. 54 00:04:18,720 --> 00:04:22,359 Speaker 1: He used paraffin wax in the experiments, but he also 55 00:04:22,560 --> 00:04:28,760 Speaker 1: used other targets like helium, nitrogen, and lithium. After comparing 56 00:04:28,800 --> 00:04:32,400 Speaker 1: the energies of the protons that were knocked out, he 57 00:04:32,560 --> 00:04:35,760 Speaker 1: was able to determine that there was likely a neutral 58 00:04:35,800 --> 00:04:39,520 Speaker 1: particle with a mass that's slightly more than a protons. 59 00:04:40,880 --> 00:04:45,240 Speaker 1: After experimenting for only a couple of weeks, Chadwick published 60 00:04:45,720 --> 00:04:50,839 Speaker 1: possible existence of a neutron, and in June ninety two, 61 00:04:51,400 --> 00:04:55,520 Speaker 1: Chadwick's paper titled the Existence of a Neutron was published 62 00:04:55,560 --> 00:05:00,840 Speaker 1: in the journal Proceedings of the Royal Society A. Chadwick 63 00:05:00,920 --> 00:05:04,200 Speaker 1: received the Hughes Medal from the Royal Society of London 64 00:05:04,279 --> 00:05:08,000 Speaker 1: for his discovery in nineteen thirty two, and in nineteen 65 00:05:08,080 --> 00:05:11,240 Speaker 1: thirty five he got the Nobel Prize for Physics for 66 00:05:11,360 --> 00:05:15,600 Speaker 1: his discovery of the neutron. But even though his discovery 67 00:05:15,640 --> 00:05:18,919 Speaker 1: made waves in physics based on its importance to the 68 00:05:18,960 --> 00:05:23,800 Speaker 1: knowledge of atomic structure, it had implications far beyond that. 69 00:05:24,960 --> 00:05:28,320 Speaker 1: The discovery of the neutron led to the fission of 70 00:05:28,360 --> 00:05:32,839 Speaker 1: the uranium nucleus, which produced a ton of energy and 71 00:05:32,920 --> 00:05:38,200 Speaker 1: inspired the creation of nuclear weapons. During the Second World War, 72 00:05:38,920 --> 00:05:43,120 Speaker 1: Chadwick worked on the Manhattan Project, the US government research 73 00:05:43,200 --> 00:05:48,839 Speaker 1: and development endeavor that produced the first atomic bombs. I'm 74 00:05:48,839 --> 00:05:51,880 Speaker 1: Eve steff Coote and hopefully you know a little more 75 00:05:51,920 --> 00:05:56,919 Speaker 1: about history today than you did yesterday. We love it 76 00:05:56,960 --> 00:06:00,800 Speaker 1: if you left us a comment on Twitter, Instagram or Facebook. 77 00:06:01,240 --> 00:06:07,039 Speaker 1: At T d i h C Podcast, we'll be back 78 00:06:07,040 --> 00:06:10,880 Speaker 1: with more history tomorrow. M