Experiment of the Compton Scattering

 The popular Compton scattering focuses on the wave side of quantum phenomena rather than the particle aspect. It had been observed that the wavelength of X-rays is increased when they are scattered off matter. Arthur Compton (1892-1962) showed that this behavior could be explained by assuming that the X-rays were photons (light quantum). When photons are scattered off electrons, part of their energy is transferred to the electrons. The loss of energy is translated into a reduction of frequency, which in turn leads to a lengthening of the wavelength of the scattered photons. This happens because the relation E=hv=hc/λ holds. In these experiments, first carried out between 1919 and 1922, the scattering of X-rays is treated as a collision of photons and electrons.

EXPERIMENTAL SETUP:

Monochromatic X-rays with wavelength λ are incident on a sample of graphite (the “target”), where they interact with atoms inside the sample; they later emerge as scattered X-rays with wavelength λ'. A detector placed behind the target can measure the intensity of radiation scattered in any direction θ with respect to the direction of the incident X-ray beam. This scattering angle, θ, is the angle between the direction of the scattered beam and the direction of the incident beam. In this experiment, we know the intensity and the wavelength λ of the incoming (incident) beam; and for a given scattering angle, θ, we measure the intensity and the wavelength λ' of the outgoing (scattered) beam. Typical results of these measurements are shown in (Figure), where the x-axis is the wavelength of the scattered X-rays and the y-axis is the intensity of the scattered X-rays, measured for different scattering angles (indicated on the graphs). For all scattering angles (except for θ = 0), we measure two intensity peaks. One peak is located at the wavelength, λ, which is the wavelength of the incident beam. The other peak is located at some other wavelength, λ'. The two peaks are separated by λ, which depends on the scattering angle θ of the outgoing beam (in the direction of observation). The separation λ is called the Compton shift.

EXPERIMENTAL DATA:

Experimental data show the Compton effect for X-rays scattering off graphite at various angles: The intensity of the scattered beam has two peaks. One peak appears at the wavelength λ of the incident radiation and the second peak appears at wavelength λ'. The separation λ between the peaks depends on the scattering angle θ, which is the angular position of the detector in (Figure). The experimental data in this figure are plotted in arbitrary units so that the height of the profile reflects the intensity of the scattered beam above background noise.