Melanie Carter and Jamie Hegarty

CLOUD CHAMBER OUTLINE Introduction: Cloud Chamber Principles All About Ionizing Radiation –Types of Radiation, why it’s “ionizing” –Where it comes from –How it interacts with vapor in the chamber Vapor, Condensation, and …Polarity? Introduction: Cloud Chamber Principles All About Ionizing Radiation –Types of Radiation, why it’s “ionizing” –Where it comes from –How it interacts with vapor in the chamber Vapor, Condensation, and …Polarity? The Wilson Chamber – A Brief History – Experimental Setup – Pictures and Video! – Discussion/Conclusions The Diffusion Chamber – Experimental Setup – Pictures Summary References The Wilson Chamber – A Brief History – Experimental Setup – Pictures and Video! – Discussion/Conclusions The Diffusion Chamber – Experimental Setup – Pictures Summary References

1.Liquid is placed into a chamber and allowed to reach an equilibrium state of evaporation and condensation. (saturation) 2.Chamber is adiabatically cooled or expanded, resulting in supersaturation of the air inside. (disruptions will cause quick & easy condensation) CLOUD CHAMBER PRINCIPLES PV = nRT

3.Ionizing radiation passing through the vapor ionize nearby atoms and molecules. 4.Condensation occurs around ionized molecules, revealing the path of the ionizing particles. CLOUD CHAMBER PRINCIPLES

IONIZING RADIATION Comes in 3 tasty flavors: alpha (  ), beta (  ), and gamma (  ). Must be at least 12.4 eV to be considered “ionizing”. Alphas (helium nuclei) are the most massive, slowest moving, and least dangerous of the three. Gammas (photons) are the least massive, fastest moving, and most dangerous. Betas (electrons) are in between. CAUTION: Ionizing Radiation is Harmful to Animals!

ALPHA DECAY Alpha Particles (2p + 2n) are primarily produced during the decay of heavy elements as part of a lengthy decay chain. Due to the Coulomb barrier, alpha particles must tunnel out of the nucleus! For this reason, half-lives of heavy elements are directly related to the decay energy of the alpha particle involved. Alpha decay energies typically range from 2-10MeV. In the cloud chamber, their tracks are thick due to the high ionization from the +2e charge. A 5.5MeV alpha will travel 4cm in air at STP. Alpha particles can be stopped by very thin physical barriers, such as skin, aluminum, or even thin plastic wrap.

BETA DECAY Beta Decay can occur in a number of ways, the most frequent being a neutron decay after an alpha decay: n ---> p + e + e The decay p ---> e + + n + e may occur for an excited atom. Beta particles travel faster than alpha particles, are less ionizing, and are not stopped as easily. Beta particles typically have energies around 175keV. In a cloud chamber, they produce very light streaks.

GAMMA DECAY Gamma Decay refers to any radioactive decay where photons are emitted. They can be either X-rays or Gamma rays. Gamma decay occurs either as a by-product of another decay process, or for excited atoms to release excess energy. Gamma decay may be observed through secondary pair- production interactions, via Compton scattering, or via the Photoelectric Effect. Auger electrons may also show up. Gamma energies may range from a few keV to several hundred MeV.

CLOUDS FORM ON IONS Water is a polar molecule, so it’s attracted to the ions. Many molecules begin to stick together, thus condensing into tiny droplets. Alcohols like Ethanol and Methanol are also polar, and behave similarly. Alcohols are less dense, and more readily form vapors, making them more suited to use in cloud chambers. Ethanol Stream Charged Rod

Invented by John Aitken, 1880 Couldn’t create clouds without dust particles Adapted by C.T.R. Wilson, between 1897 and Noticed droplets without dust at expansions over 125% Hypothesized clouds were forming on microscopic nuclei or ions Tested extensively with newly-discovered X-Rays WILSON CLOUD CHAMBER Images: Cambridge Physics

LIGHT IR FILTER 226 Ra SOURCE PISTON 500 V WILSON CLOUD CHAMBER 1 1

ADIABATIC EXPANSION 2 2

WILSON CLOUD CHAMBER  -PARTICLE TRACKS! ADIABATIC EXPANSION 3 3

WILSON CLOUD CHAMBER …in action!!

Operates on smooth temperature gradient Continuous Supersaturation in the sensitive region More sensitive than expansion chamber Tested beta, alpha, and x-ray sources Compton Effect, Photoelectric Effect Diffusion Cloud Chamber

First Run: 70% ethanol, 30% water … terrible results Conclusion: Requires 90% ethanol to prevent freezing Chamber must be filled before cooling in order for equilibrium to be established. Diffusion Cloud Chamber Freezing point for… 70/30 Ethanol: C 90/10 Ethanol: Below -80 C Dry Ice: C

Natural Thorium Rod Alpha Source Diffusion Cloud Chamber

C-14 Beta Source Diffusion Cloud Chamber

Fe-55 X-Ray Source Diffusion Cloud Chamber

CLOUD CHAMBER SUMMARY More interesting experiments could be done with a thermometer inside the Diffusion Chamber. Helmholtz Coils above and below the chamber could be used for quantitative measurement of particle charge/mass ratios. Tear them off the broken e/m device? Non-polar liquids should be tested. A career in video editing would suck. More interesting experiments could be done with a thermometer inside the Diffusion Chamber. Helmholtz Coils above and below the chamber could be used for quantitative measurement of particle charge/mass ratios. Tear them off the broken e/m device? Non-polar liquids should be tested. A career in video editing would suck.

REFERENCES Diffusion Cloud Chamber Owner’s Guide, v. 2.3 Tipler Modern Physics Whitten, Davis, Peck General Chemistry Cambridge Physics Wilson Chamber Photos: Ethanol Images: Diffusion Cloud Chamber Owner’s Guide, v. 2.3 Tipler Modern Physics Whitten, Davis, Peck General Chemistry Cambridge Physics Wilson Chamber Photos: Ethanol Images: A All other artwork and photos © 2004 Melanie and Jamie :)