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Compton EffectCompton Effect
Arthur Holly ComptonNobel price 1927
Arthur Holly ComptonNobel price 1927
The Compton Effect
The Compton effect is one of the most fundamental effects: scattering of high energetic photons off a free or bound electron. It is important for the understanding of basic quantum mechanical effects.In this experiment the energy shift of the scattered gamma radiation and the scattering cross-section are examined in relation to the scattering angle. In the present set-up the probes are ring-shaped and one gets a much higher scattered yield than using the standard geometry.Using angles from 20 to 165 degrees the Compton relationship can be determined for the energy shift with an error of 3%. The validity of the Klein-Nishina formula for the effective cross-section can be proven with an error of approximately 10%.
PreAmpCanberra 2007B
HVTennelec
952A
AmpTennelec
TC241
Canberra Multiport II
Computer Dell PC
Bench with mm Scale
NaI Detector (inside lead shielding)
Shadow BarMetal Ring
Source and Holder
Voltage DividerCanberra 2007
Compton Effect
......
Compton Effect : Required Knowledge
Theory of the Compton effect
= Scattering of γ’s off electronsEnergy and momentum con-servation
Klein-Nishina formula
Interaction of γ’s with matter
Absorption of γ’s in matterCorrections required for the chosen set-up : Multiple scat-tering; absorption in the ring samples; variable solid angles
Principles of Gamma detectors,
especially NaI(Tl) detectors
Principles of γ-spectroscopyPhotomultipliers and basic
electronics
Advantage of collimated detec-
tor geometry (compare with
anti-Compton shield)
Advantage of ring samples
(compare with other methods
for the Compton effect measure-
ment)
Compton Effect : Tasks and GoalsCompton Effect : Tasks and Goals
Set-up of detector and electronics using a weak 137Cs source, put source above the end of the shadow bar. Never change the detectorCalibrate the detector with 662 keVline and Ba Kα-lineDetermine detector resolutionSet MCA to 512 channels Align source, sample, shadow bar and detector very precisely to the optical axisFirst think about an optimal setting for the scattering angles, work out a scheme
Measurement of 2 angular distributions using the strong 137Cs source for Cu or Al:
1. Energy of scattered γ’s in depen-dence of scattering angle
2. Angular distribution of the scattering
cross section (Klein-Nishina)
Always use differential measurement
with equal time for ring-sample-in and
–out spectra; use subtraction (stripping)
function
Determine uncertainties
Compare Compton effect for Cu and Al at
one convenient angle
WARNINGSBe careful with bad.Shut down spectroscopyNeverRemove source after measurement