Compton scattering of 0.279 MeV gamma rays fromK-shell electrons of lead

Differential cross-sections for Compton scatterig of 0.279 MeV gamma rays fromK-shell electrons of lead are measured at scattering angles ranging from 30 to 150° to study the effect of binding on the scattering process. Measurements are made employing two Nal(Tl) scintillation spectrometers and a slow-fast coincidence set-up of 30 nsec resolving time. The experimental results are compared with the available theoretical data. The totalK-shell Compton scattering cross-section is 34% of the free electron Compton cross-section.     

Compton scattering of gamma rays by electrons bound in heavy atoms

The energy spectra of 661.6 keV gamma rays scattered incoherently by lead have been measured for the scattering angles 62 °, 85 °, and 135 ° using a germanium detector. The differential cross sectionsdσdΩd E _y′ obtained from the experiment have been compared with formfactor calculations using relativistics-electron wave-functions for the initial state and relativistic Coulomb wave-functions for the unbound state. A good agreement has been obtained for large energiesE _y′ of the scattered quanta.     

Compton scattering from isotropic electrons

The exact Compton cross section for scattering of photons from isotropic monoenergetic electrons is given in analytical form. It is shown that the moments of the Legendre expansion of the scattering kernel can be obtained analytically, apart from an integration over the unknown electron distribution function.     

Incoherent scattering of 279 keV gamma rays by bound electrons

The differential cross section for 279 keV gamma rays scattered incoherently from K-shell electrons of thorium is determined experimentally at six angles from 30° to 150° and expressed in terms of the free electron scattering cross section. Two NaI(T1) scintillation spectrometers and a fast-slow coincidence circuit are employed. The scattered gamma rays are detected in coincidence with the fluorescent K X-rays. The bound-to-free electron cross section ratios are compared with those calculated from different non-relativistic theories. The bound electron cross sections are also directly compared with the Klein-Nishina values. At low scattering angles the experimental results agree well with those incoherent scattering function values based on the Thomas-Fermi model, while at large scattering angles there is no good agreement between the experimental values and any of the theories discussed in the text.     

Relativistic Compton scattering from moving electrons and angular moments

Using the invariant, four-dimensional representation of the photon-electron interaction derived from quantum electrodynamics, we obtain analytical expressions for the Legendre moments of the scattering kernel, given arbitrary distributions of initial electrons and specified energy ranges. Monoenergetic and Maxwellian electrons distributions are briefly discussed and the partial wave expansion of the static Klein-Nishina formula included.     

Relativistic Compton scattering from a relativistic maxwellian distribution of electrons

Using an earlier developed relativistic differential cross section formula for Compton scattering of photons from a given momentum distribution of electrons, an expression for the differential cross section is derived for the case of a relativistic Boltzmann distribution.     

Polarimetry of short-pulse gamma rays produced through inverse Compton scattering of circularly polarized laser beams

We have developed a polarimetry of ultrashort pulse gamma rays based on the fact that gamma rays penetrating in the forward direction through a magnetized iron carry information on the helicity of the original gamma rays. Polarized, short-pulse gamma rays of (1.1+/-0.2)x10(6)/bunch with a time duration of 31 ps and a maximum energy of 55.9 MeV were produced via Compton scattering of a circularly polarized laser beam of 532 nm off an electron beam of 1.28 GeV. The first demonstration of asymmetry measurements of short-pulse gamma rays was conducted using longitudinally magnetized iron of 15 cm length. It is found that the gamma-ray intensity is in good agreement with the simulated value of 1.0x10(6). Varying the degree of laser polarization, the asymmetry for 100% laser polarization was derived to be (1.29+/-0.12)%, which is also consistent with the expected value of 1.3%.     

Compton scattering of 59.5 keV gamma rays from p-Si sample in an external electric field

This study is related to Compton scattering of photons from a p-Si sample whose surface charge density distributions are changed by an external electric field. The external electric field intensity in the range 0-75 kV/m was used to change the surface charge density distributions of the sample. The sample surface perpendicular to the electric field was selected as the scattering surface. The p-Si sample was bombarded by 59.5 keV γ-photons emitting from an Am-241 point source. The Compton scattered photons at an angle of 90^o were detected by an Si(Li) detector. The Compton scattering intensity suddenly increased with the application of the electric field since the applied electric field distorts both the negatively charged scattering center (free electron, bound electron, ionized acceptor) and the positively charged scattering center (hole) and their momentum distribution in the sample. There is a good third-order polynominal relation between the Compton scattering intensity and the increasing (or decreasing) electric field intensity. The results show that the positively charged scattering centers behave like negatively charged scattering centers, but the latter are slightly more effective than the former in the Compton scattering of γ-rays from the sample in the electric field.     

Compton scattering of photon by atomic ion

The angular and energy dependences of the differential cross sections for the nonresonance Compton scattering of a linearly polarized X-ray photon by the Be atom and beryllium-like ions O⁴⁺ and Mg⁸⁺ are studied theoretically. The many-particle effects of radial relaxation of the electron shells in the field of vacancies and stabilization of the core shells were taken into account. The calculated results are predictive in character.     

Left-right asymmetry in Compton scattering on polarized electrons

In Compton scattering on polarized electrons a left-right asymmetry of the order 10⁻³ has been observed which must be attributed to higher-order corrections of the scattering amplitude. This effect might provide a test of quantum electrodynamics.     

Measurement of doubly differential collision cross-sections for double-photon Compton scattering of 0.662 MeV gamma rays

The doubly differential collision cross-sections of the double-photon Compton process have been measured experimentally for 0.662 MeV incident gamma photons. The measurements are carried out using a single gamma detector, a technique avoiding the use of the complicated slow–fast coincidence set-up used till now for observing this higher order QED process. The energy spectra of detected photons are observed as a long tail to the single-photon Compton line on the lower side of the full energy peak in the recorded scattered energy spectrum. The measured values of the cross-section for different independent energy levels of one of the two final photons are of the same magnitude but show deviation from the corresponding values obtained from the theory. However, the present measurements are first of its kind and in view of the nature and order of deviations, the agreement of measured values with theory is quite satisfactory.     

Experimental evaluation of multiple Compton backscattering of gamma rays in copper

The gamma ray photons continue to soften in energy as the number of scatterings increases in thick target, and results in the generation of singly and multiply scattered events. The number of these multiply scattered events increases with an increase in target thickness and saturates beyond a particular target thickness known as saturation depth. The present experiment is undertaken to study the saturation depth for 279 and 320 keV incident gamma ray photons multiply backscattered from copper targets of varying thickness. The backscattered photons are detected by a Nal(Tl) gamma detector whose pulse-height distribution is converted into a photon spectrum with the help of an inverse matrix approach. To extract the contribution of multiply backscattered photons only, the spectrum of singly scattered photon is reconstructed analytically. We observe that the numbers of multiply scattered events increases with an increase in target thickness and then saturate. The saturation depth is found to be decreasing with increase in incident gamma energy.     

The scattering of electrons by atomic hydrogen

A method is presented which reduces the problem to the scattering of a single electron in an equivalent potential. The complexities of the electron-electron interaction are embodied in this potential. An exact expression is given for the potential, and various approximation methods are discussed. The adiabatic approxmation is investigated and the imaginary part of the potential is examined.     

Incoherent scattering functions of 145 keV gamma rays by K-shell electrons in Y,Ag and Au

The values of incoherent scattering functions are determined experimentally for 145 keV gamma rays in elements Au, Ag and Y at scattering angles 40°, 70° and 100°, using a x-ray gamma coincidence technique. The corresponding theoretical values are obtained from the tabulations of Hubbellet al, and computed from the models of Jauch and Rohrlich and Shimizuet al. A comparison between the theoretical and experimental results showed that the non-relativistic approach adopted in the theory of Shimizuet al is inapplicable to the present cases. A gross agreement is noticed between the present experimental results and the other theoretical values.     

Magnetic neutrino scattering on atomic electrons revisited

We reexamine the role of electron binding effects in the inelastic neutrino–atom scattering induced by the neutrino magnetic moment. The differential cross section of the process is presented as a sum of the longitudinal and transverse components, according to whether the force that the neutrino magnetic moment exerts on electrons is parallel or perpendicular to momentum transfer. The atomic electrons are treated nonrelativistically. On this basis, the recent theoretical predictions concerning the magnetic neutrino-impact ionization of atoms are critically discussed. Numerical calculations are performed for ionization of a hydrogenlike Ge⁺³¹ ion by neutrino impact.     

Compton scattering of a spectrally narrow radiation flux by free electrons

A kinetic equation that includes spontaneous and induced Compton scattering is obtained for the propagation of electromagnetic radiation in a gas of free electrons. The derivation includes terms on the order on (v/c)² in the conservation laws. Numerical integration of the equation is performed for the case of plane-parallel propagation of the radiation flux in the electron gas.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 93–97, February, 1979.In conclusion, the author wishes to express his gratitude to S. Shikhovtsova for help in conducting the numerical calculations.     

An alternative gamma tracking method using the Compton scattering probability

A new gamma tracking method, called probabilistic method and based on the Compton scattering probability of photons in a highly segmented Ge spectrometer, has been evaluated with the GEANT simulation code. This method has been used to calculate the performances of a 4 array composed of planar detectors as their crystal shape allows to realize identical segments of quasi-cubic shape. The tracking algorithm selects the full-absorption events by taking into account only the centre of gravity of the segments hit and the partial energies released in each of them. The results obtained, in terms of photopeak detection efficiency and peak-to-total ratio, are comparable to the ones deduced from the usual tracking methods. The probabilistic algorithm seems also to apply efficiently for other types of detectors as simulation calculations performed on a single stack of planar detector and a single segmented CLOVER detector give nearly the same reconstruction efficiency.Received: 26 November 2002, Revised: 29 April 2003, Published online: 23 March 2004PACS: 29.30.Kv X- and -ray spectroscopyG. Duchêne: Spokesperson