Melanie Carter and Jamie Hegarty. CLOUD CHAMBER OUTLINE Introduction: Cloud Chamber Principles All About Ionizing Radiation –Types of Radiation, why it’s

Melanie Carter and Jamie HegartyMelanie Carter and Jamie Hegarty

CLOUD CHAMBER OUTLINECLOUD 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 PRINCIPLESCLOUD CHAMBER PRINCIPLES

PV = nRTPV = 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 PRINCIPLESCLOUD CHAMBER PRINCIPLES

IONIZING RADIATIONIONIZING 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 isHarmful to Animals!

ALPHA DECAY 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

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

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 IONSCLOUDS 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.

Eth

ano

l S

trea

m

Charged Rod

• Invented by John Aitken, 1880

• Couldn’t create clouds without dust particles

• Adapted by C.T.R. Wilson, between 1897 and 1912.

• 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 CHAMBERWILSON CLOUD CHAMBER

Images: Cambridge Physics

LIGHT

IR FILTER226Ra SOURCE

PISTON

500 V


11


ADIABATICEXPANSION

22

WILSON CLOUD CHAMBERWILSON CLOUD CHAMBER-PARTICLETRACKS!

ADIABATICEXPANSION

33

WILSON CLOUD CHAMBERWILSON CLOUD CHAMBER…in action!!…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 ChamberDiffusion 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.


Freezing point for…

70/30 Ethanol:-55.5 C

90/10 Ethanol:Below -80 C

Dry Ice: -78.5 C

Natural Thorium Rod Alpha SourceNatural Thorium Rod Alpha Source


C-14 Beta SourceC-14 Beta Source


Fe-55 X-Ray SourceFe-55 X-Ray Source


CLOUD CHAMBER SUMMARYCLOUD 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.

REFERENCESREFERENCES

Diffusion Cloud Chamber Owner’s Guide, v. 2.3

Tipler Modern Physics

Whitten, Davis, Peck General Chemistry

Cambridge Physics Wilson Chamber Photos: http://www.phy.cam.ac.uk/camphy/cloudchamber/cloudchamber1_1.htm

Ethanol Images:http://jchemed.chem.wisc.edu

Diffusion Cloud Chamber Owner’s Guide, v. 2.3

Tipler Modern Physics

Whitten, Davis, Peck General Chemistry

Cambridge Physics Wilson Chamber Photos: http://www.phy.cam.ac.uk/camphy/cloudchamber/cloudchamber1_1.htm

Ethanol Images:http://jchemed.chem.wisc.eduA

All other artwork and photos © 2004 Melanie and Jamie :)

http://www.phy.cam.ac.uk/camphy/cloudchamber/cloudchamber1_1.htm




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Melanie Carter and Jamie Hegarty. CLOUD CHAMBER OUTLINE Introduction: Cloud Chamber Principles All About Ionizing Radiation –Types of Radiation, why it’s