History of Subatomic Physics

A brief history of subatomic physics from J. J. Thomson to Paul Dirac and Carl David Anderson

Transcript

1. History of Subatomic Physics Danial Papi Arash Badie Modiri Democritus; Hendrick ter Brugghen; Oil on canvas; 1628
2. Discovery of Electron What? Do we have to listen to this story again?
3. J.J. Thomson (1897) "Cathode Rays", The Electrician 39, 104 Retrieved via Google Books: https://books.google.com/books? id=vBZbAAAAYAAJ&pg=PA104&hl=en
4. Discovery of Corpuscles: J. J. Thomson and Cathode Rays A thousand times smaller than hydrogen atoms. It’s mass does not depend on source atom.
5. J. J. Thomson and Cathode Rays One can deflect cathode rays by a magnetic field. What about an electric field?
6. Corpuscle → Electron Thanks to George Johnstone Stoney
7. Where do these “Corpuscles” things come from? From the cathode or the tube? Are they from inside atoms? What does it even mean?
8. A Plum Pudding Photo retrieved from: http://deireland. com/2014/12/12/have-a-merry-olde-christmas-10- english-holiday-traditions/
9. Theory of Atomic Disintegration: Early Days of Nuclear physics Rutherford and Soddy: Thoron emitted from Thorium. Pierre and Marie Curie: Isolation of Radium and Polonium. William Crookes: Uranium transforms to Uranium-X
10. I accumulated alpha in a jar, but all I got was Helium and electric charge…
11. ” Geiger–Marsden Experiment It was quite the most incredible event that has ever happened to me in my life. It was almost as incredible as if you fired a 15-inch shell at a piece of tissue paper and it came back and hit you.
12. Geiger–Marsden Experiment A plum pudding should have deflected alpha particles by 10-4 radians. Some were deflected by > ½π
13. Transmuting Matter Nitrogen + Alpha → Oxygen + Hydrogen nuclei Hydrogen nuclei were a part of nitrogen nuclei (and probably other nuclei)
14. Dirac’s memorial stone. Photo retrieved from: https://en. wikipedia.org/wiki/File:Dirac% 27s_commemorative_marker.jpg
15. Q: How to link experiment to theory? A: Study one and marry the other. Sir Ralph Howard Fowler
16. Werner Heisenberg and his matrix mechanics. Erwin Schrödinger and his wave mechanics. I don’t like this at all.
17. I also don’t like how Schrödinger’s quantum mechanics are not quite compatible with Einstein's special relativity.
18. There you go. I fixed your equations in the most mathematically beautiful way possible. It’s so beautiful I want to engrave it on my grave. But I had to assume that there exists a particle, never seen before, with same general physical properties as electron only with a positive charge…
19. “Found your particle”, said Carl David Anderson a few years later in a paper titled “The Positive Electron” published in Physical Review for which he won a Nobel prize in physics. Photo retrieved from: https://commons.wikimedia. org/wiki/File:PositronDiscovery.jpg