1. To be charged : means the particle is capable of emitting and absorbing photons What’s the ground state or zero-point energy of a system? e  e  harmonic oscillator: ½h

2.  x  p ~ h  t  E ~ h The virtual photons in the sea that surround every charged particle, are wavepackets centered at the origin (source of charge) If these describe/map out the electrostatic potential and relate available momentum to be transferred to the distance from the field’s source consider the extremes:  x  0  x   other charges may be exposed to the full spectrum of possible momenta only vanishingly small momentum transfers are possible

3. Area within  1  68.26%  1.28  80.00%  1.64  90.00%  1.96  95.00%  2  95.44%  2.58  99.00%  3  99.46%  4  99.99% -2  -1  +1  +2   Let’s assume a wave packet tailored to be something like a Gaussian (or “Normal”) distribution

4. 1900-01 Using the procedure developed by J.J. Thomson in 1887 Becquerel determined the ratio of charge q to mass m for  : q/m = 1.76×10 11 coulombs/kilogram identical to the electron!  : q/m = 4.8×10 7 coulombs/kilogram 4000 times smaller!

5. Discharge Tube Thin-walled (0.01 mm) glass tube to vacuum pump & Mercury supply Radium or Radon gas Noting helium gas often found trapped in samples of radioactive minerals, Rutherford speculated that  particles might be doubly ionized Helium atoms (He ++ ) 1906-1909 Rutherford and T.D.Royds develop their “alpha mousetrap” to collect alpha particles and show this yields a gas with the spectral emission lines of helium!

6. Status of particle physics early 20th century Electron J.J.Thomson 1898 nucleus (  proton ) Ernest Rutherford 1908-09  Henri Becquerel 1896 Ernest Rutherford 1899   P. Villard 1900 X-rays Wilhelm Roentgen 1895

8. 1900 Charles T. R. Wilson’s ionization chamber Electroscopes eventually discharge even when all known causes are removed, i.e., even when electroscopes are sealed airtight flushed with dry, dust-free filtered air far removed from any radioactive samples shielded with 2 inches of lead! seemed to indicate an unknown radiation with greater penetrability than x-rays or radioactive  rays Speculating they might be extraterrestrial, Wilson ran underground tests at night in the Scottish railway, but observed no change in the discharging rate.

9. 1909 Jesuit priest, Father Thomas Wulf, improved the ionization chamber with a design planned specifically for high altitude balloon flights. A taut wire pair replaced the gold leaf. This basic design became the pocket dosimeter carried to record one’s total exposure to ionizing radiation. 0

10. 1909 Taking his ionization chamber first to the top of the Eiffel Tower (275 m) Wulf observed a 64% drop in the discharge rate. Familiar with the penetrability of radioactive  rays, Wulf expected any ionizing effects due to natural radiation from the ground, would have been heavily absorbed by the “shielding” layers of air.

11. light produces spots of submicroscopic silver grains a fast charged particle can leave a trail of Ag grains 1/1000 mm (1/25000 in) diameter grains small singly charged particles - thin discontinuous wiggles only single grains thick heavy, multiply-charged particles - thick, straight tracks 1930s plates coated with thick photographic emulsions (gelatins carrying silver bromide crystals) carried up mountains or in balloons clearly trace cosmic ray tracks through their depth when developed

12. November 1935 Eastman Kodak plates carried aboard Explorer II’s record altitude (72,395 ft) manned flight into the stratosphere

13. 50  m Cosmic ray strikes a nucleus within a layer of photographic emulsion 1937 Marietta Blau and Herta Wambacher report “stars” of tracks resulting from cosmic ray collisions with nuclei within the emulsion

14. Elastic collision

15. p p p p p p

16. 1894 After weeks in the Ben Nevis Observatory, British Isles, Charles T. R. Wilsonbegins study of cloud formation a test chamber forces trapped moist air to expand supersaturated with water vapor condenses into a fine mist upon the dust particles in the air  each cycle carried dust that settled to the bottom  purer air required larger, more sudden expansion  observed small wispy trails of droplets forming without dust to condense on!

18. Tracks from an alpha source

22. 1952 Donald A. Glaser invents the bubble chamber boiling begins at nucleation centers (impurities) in a volume of liquid along ion trails left by the passage of charged particles in a superheated liquid tiny bubbles form for ~10 msec before obscured by a rapid, agitated “rolling” boil hydrogen, deuterium, propane(C 3 H 6 ) or Freon(CF 3 Br) is stored as a liquid at its boiling point by external pressure (5-20 atm) super-heated by sudden expansion created by piston or diaphragm bright flash illumination and stereo cameras record 3 images through the depth of the chamber (~6  m resolution possible) a strong (2-3.5 tesla) magnetic field can identify the sign of a particle’s charge and its momentum (by the radius of its path) 1960 Glaser awarded the Nobel Prize for Physics

24. 3.7m diameter Big European Bubble Chamber CERN (Geneva, Switzerland) Side View Top View

27. 1936 Millikan’s group shows at earth’s surface cosmic ray showers are dominated by electrons, gammas, and X-particles capable of penetrating deep underground (to lake bottom and deep tunnel experiments) and yielding isolated single cloud chamber tracks