Studying the effect of polarisation in Compton scattering in the undergraduate laboratory

Abstract

Abstract. An experiment for the advanced undergraduate laboratory allowing students to directly observe the effect of photon polarisation on Compton scattering is described. An initially unpolarised beam of photons is polarised via Compton scattering and analysed through a subsequent scattering. The experiment is designed to use equipment typically available at an undergraduate physics laboratory. The experimental results are compared with a Geant4 simulation and geometry effects are discussed.

An undergraduate laboratory study of the polarisation of annihilation photons using Compton scattering

“…The signals from Detector-0, Scatterer-1, and Scatterer-2 were fed to three timing single-channel analysers (TSCA). Energy windows for Detector-0, Scatterer-1 and Scatterer-2 were set to accept signals corresponding to energies between approximately 200 and 310keV, using a method similar to that employed in [20]. Subsequently, the TSCA signals were fed to a coincidence unit, with a resolving time of approximately 2 μs, while the gate signal for Detector-1 and Detector-2 had a width of approximately 3 μs.…”

“…This experiment complements a series of experiments on Compton scattering using γ-rays that has been an important part of the undergraduate laboratory for many decades. Various forms of such experiments have been proposed and implemented, from the measurement of absorption coefficients to probe the characteristics of the scattered photons [16], to experiments involving precision spectroscopy and timing components [17][18][19] and experiments investigating polarisation effects [20].…”

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“…It indicates that, in case of 511 keV annihilation photons, the correlation between the polarization direction ⃗ ε and the scattering plane is maximal at about θ = 82 • decreasing to negligible effect for forward (θ = 0 • ) and backward (θ = 180 • ) scattering. In general the analysing power (A p ) of the Compton polarimeter is expressed as [16,25,26]:…”

“…where E and E' denotes the energy of primary and scattered photon, respectively [26]. For 511 keV photons, maximum value of A p equal to 0.69 is reached at θ = 82 • .…”