Compton absorption

The most commonly used photons in radiation chemical studies are the gamma rays generated by the disintegration of Co nuclei. At the average energy of these photons, 1.2 MeV, Compton absorption predominates. In Compton absorption, photon absorption is followed by ejection of the most loosely bound electron and emission of a photon of lesser energy ... 

For 7-ray energies below 1 MeV (the range of interest) there are two principal modes of interaction with matter — Compton scattering and photoelectron absorption. Compton scattering is the elastic scattering of the 7 photon by an orbital electron in which part of the incident 7-energy is imparted to the recoiling electron. 

We are interested in the transmission of y-quanta through the absorber as a function of the Doppler velocity. The radiation is attenuated by resonant absorption, in as much as emission and absorption lines are overlapping, but also by mass absorption due to photo effect and Compton scattering. Therefore, the number Tt E2)AE of recoilless y-quanta with energies EXo E + AE traversing the absorber is given by... 

Scattered radiation. In a transmission experiment, the Mossbauer sample emits a substantial amount of scattered radiation, originating from XRF and Compton scattering, but also y-radiation emitted by the Mossbauer nuclei upon de-excitation of the excited state after resonant absorption. Since scattering occurs in 4ti solid angle, the y-detector should not be positioned too close to the absorber so as not to collect too much of this unwanted scattered radiation. The corresponding pulses may not only uimecessarily overload the detector and increase the counting dead time, but they may also affect the y-discrimination in the SCA and increase the nonresonant background noise. 

The thickness of a Mossbauer sample affects not only the strength of the Mossbauer signal but also the intensity of the radiation arriving at the detector because the y-rays are inherently attenuated by the sample because of nonresonant mass absorption caused by the photo effect and Compton scattering as mentioned earlier. The counting rate C in the detector decreases exponentially with the density of the absorber,... 

Absorption Coefficient—Fractional absorption of the energy of an unscattered beam of x- or gamma-radiation per unit thickness (linear absorption coefficient), per unit mass (mass absorption coefficient), or per atom (atomic absorption coefficient) of absorber, due to transfer of energy to the absorber. The total absorption coefficient is the sum of individual energy absorption processes (see Compton Effect, Photoelectric Effect, and Pair Production). 

Compton profile. Furthermore the contribution of the multiple scattered photons to the measured spectra has to be taken into account (for example by a Monte Carlo simulation [6]). Additionally one has to take heed of the fact that the efficiency of the spectrometer is energy dependent, so the data must be corrected for energy dependent effects which are the absorption in the sample and in the air along the beam path, the vertical acceptance of the spectrometer and the reflectivity of the analyzing crystal. 

Figure 5 X-ray mass attenuation coefficients for aluminum as a function of photon energy. At low energies, photoelectric absorption predominates. At higher energy, incoherent (Compton) scatter becomes almost the exclusive contributing mode. Eventually, pair production dominates at very high energies (above 10 MeV).

The absorption spectrum contains fine-structure details in the vicinity of this X-edge. The general subject has been reviewed by Compton and Allison (S), by Sandstrom (3), and by Tomboulian (4)- The review presented here will be brief. 

Photoeiectron, Auger-Electron (by Photoelectric Absorption) Compton Recoil Electron (by Compton Scattering)... 

K. T. Compton and 0. W. Richardson, with isotropic radiation, found a maximum for sodium at 225fifi and 360pp. and a maximum at 250pp for caesium. R. A. Millikan and W. H. Souder found that with new surfaces of lithium, sodium, and potassium there are definite maxima for the selective absorption about 250pp... 

Electromagnetic waves behave like particles in photoelectric effect, Compton effect and phenomena of absorption and emission. The quantum of energy, E=Av, is called a photon. Photons travel with the speed of light c, and possess a momentum hv/c. 

As the column depth of the supernova ejecta decreases as t 2, 7-rays and hard X-rays suffer from less Compton scattering and photoelectric absorption and eventually emerge from the surface. The timing of their emergences and light curves are sensitive to E, Menv, and the distribution of elements. In other words, X-ray and 7-ray observations provide another good diagnosis of the supernova interior. 

The experimental data were corrected for air scattering, polarization, absorption and Compton scattering applying well-known correction procedures (for example [15], [16]). Then the data were transformed into q-space using... 

Fig. 13. Measured scattering intensity of HDPE melt. Intensity corrections for air scattering, polarization, absorption, sample geometry and Compton scattering have beat performed...

---