If you look at some of his papers in the early days — I call McGill the early days — he was quite convinced that the alpha particles were atoms of helium, but he never said that in those words. He always said they were either atoms of helium or molecules of hydrogen or perhaps he may have said something else of that weight. It was quite characteristic of him that he would never say a thing was so unless he had experimental evidence for it that really satisfied him.
He worked out quickly and roughly that several quantitative relationships should be true if this basic theory were correct. Second, that number should be proportional to the square of the nuclear charge. These three ideas laid out the experimental program of Geiger and Marsden for the next year. He had done very little teaching in McGill. He was research professor. I suppose he gave some lectures but it would have been very few.
And his interest was quite naturally on the research side. He did give some lectures, but elementary lectures, the kind of thing you would expect a man to know before he came to the University. They were the lectures to the engineers. They were a rowdy lot and Rutherford could keep them under control. There was perhaps only one other man in the department who could have done it, and he Rutherford?
It's often been said to me that Rutherford was a bad lecturer. I never heard such nonsense. It is quite true that on occasion he would be a bit dull, a bit mixed up, but that was only on very rare occasions. There were other occasions when he was really most stimulating. There was a tremendous enthusiasm about him.
Rutherford entertained the possibility that the charged center is negative. That sounds odd today, so what made it reasonable? First, it wasn't very different from Thomson's model. He also considered a nearly forgotten model suggested by Japanese physicist Hantaro Nagaoka — — the Saturnian model. Nagaoka and Rutherford were in contact in and and Rutherford mentioned Nagaoka's model of "a central attracting mass surround by rings of rotating electrons" Birks, p.
The end result in this critical Rutherford paper, however, was Rutherford's announcement that whether the atom were a disk or a sphere, and indeed whether the central charge were positive or negative, would not affect the calculations. Rutherford was always careful not to claim more than his results could support. Rutherford did see possible tests of the nature of the central charge.
But these were only hints. Geiger and Marsden did indeed work systematically through the testable implications of Rutherford's central charge hypothesis. The first major publication of their results was in German in the Proceedings of the Vienna Academy of Sciences Sitzungberichte der Wiener Akademie der Wissenschaften in Slight differences between the two led one historian to suggest that Rutherford decided in favor of a positively charged center by August Trenn, Rutherford's other team members, especially Charles Galton Darwin — , H.
Moseley — , and Niels Bohr — figured prominently in the ultimate establishment of Rutherford's nuclear atom. Bohr returned to Denmark. Marsden accepted a professorship in New Zealand. Moseley died in the Battle of Gallipoli. James Chadwick — , who was working with Geiger at the Technical University of Berlin when war broke out, spent several years interned in the Ruhleben camp for prisoners of war. Other students went off to war, too, and Rutherford devoted considerable energy to mobilizing science for the war effort and specifically to anti-submarine techniques.
When the Great War ended, Ernest Marsden briefly helped with the tedious scintillation observations that provided clues to the nature of the nucleus. Rutherford reported the tentative results of these extensive experiments in Rutherford placed a source of radium C bismuth in a sealable brass container, fitted so that the position of the source could be changed and so that different gases could be introduced or a vacuum produced, as desired. Rutherford had several subtle questions in mind during these experiments, mostly concerned with the nature of the nucleus.
Rutherford rejected explanations of this variance based on different charges on the particles or other laws than inverse square laws. In alpha decay, a positively charged particle, identical to the nucleus of helium 4, is emitted spontaneously. This particle, also known as an alpha particle, consists of two protons and two neutrons. It was discovered and named by Sir Ernest Rutherford in The experiment involved firing alpha particles from a radioactive source at a thin gold foil.
Any scattered particles would hit a screen coated with zinc sulfide, which scintillates when hit with charged particles. Marsden was to sit in the darkened room, wait for his eyes to adjust to the darkness, and then patiently stare at the screen, expecting to see nothing at all.
Instead, Marsden saw lots of tiny, fleeting flashes of yellowish light, on average more than one blip per second. He could hardly believe what he saw. Rutherford too was astonished.
About one in every few thousand of the alpha particles fired at the gold target had scattered at an angle greater than 90 degrees. In this model electrons were believed to be stuck throughout a blob of positively charged matter, like raisins in a pudding.
But this sort of arrangement would only cause small angle scattering, nothing like what Marsden had observed. After thinking about the problem for over a year, Rutherford came up with an answer. The only explanation, Rutherford suggested in , was that the alpha particles were being scattered by a large amount of positive charge concentrated in a very small space at the center of the gold atom.
The electrons in the atom must be orbiting around this central core, like planets around the sun, Rutherford proposed. Ernest Rutherford is considered the father of nuclear physics. Indeed, it could be said that Rutherford invented the very language to describe the theoretical concepts of the atom and the phenomenon of radioactivity.
Particles named and characterized by him include the alpha particle, beta particle and proton.
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