Discovery of the Proton

Introduction

• The lecture covers the discovery of the proton.
• Understanding the cathode ray tube is essential.

Cathode Ray Tube Components

1. Glass Tube
   • Contains gas, typically hydrogen, to facilitate electron flow.
2. Vacuum Pump
   • Used to decrease gas pressure to 10^-3 mm of Hg.
3. Metallic Strips
   • Cathode (negative) and anode (positive) are placed inside the tube.
4. High Voltage Source
   • Typically 10,000 volts to ionize the gas.
5. Ammeter
   • Detects the flow of current in the tube.

Discovery of Electron (JJ Thompson)

• Used a cathode ray tube with a hole in the anode, coated with zinc sulfide.
• Provided 10,000 volts, causing cathode rays to flow and hit the fluorescent screen.
• Cathode rays were proven to be negatively charged, known as electrons.

Discovery of Canal Rays (Goldstein)

• Conducted an experiment with a cathode ray tube, making a hole in the cathode.
• Observed rays traveling from anode to cathode, opposite to cathode rays.
• These rays were called canal rays (or anode rays) and were positively charged.
• Canal rays proved the existence of positive particles inside atoms.

Rutherford's Discovery of the Proton (1917)

• Rutherford used alpha particles and nitrogen atoms in his experiment.
• Alpha particles (helium nuclei) collided with nitrogen atoms.
• The collision produced fluorine-18, which decayed into oxygen-17 and a hydrogen nucleus.
• The hydrogen nucleus was identified as a proton.
• This was the first nuclear reaction to produce a proton, confirming it as a fundamental particle.

Significance of Rutherford's Discovery

• This experiment was the first artificial conversion of one atom into another (nitrogen to oxygen-17).
• It marked significant progress in nuclear physics, radioactivity, fission, and fusion.

Clarification on Discoveries

• Rutherford is credited with discovering the proton in 1917.
• Goldstein discovered canal rays, not protons.
• Important to distinguish between canal rays and protons in historical context.

Conclusion

• The lecture clarified the steps leading to the discovery of the proton and its significance in modern physics.