The environment in which bremsstrahlung and pair creation occurs can strongly affect cross sections for these processes. Because ultrarelativistic electromagnetic interactions involve very small longitudinal momentum transfers, the reactions occur gradually, spread over long distances. During this time, even relatively weak factors can accumulate enough to disrupt the interaction. In the Landau-Pomeranchuk-Migdal effect, multiple scattering reduces the bremsstrahlung and pair production cross section. This review will discuss this and a variety of other factors that can suppress bremsstrahlung and pair production, as well as related effects involving beamstrahlung and QCD processes. After surveying different theoretical approaches, experimental measurements will be covered. Recent accurate measurements by the SLAC E-146 Collaboration will be highlighted, along with several recent theoretical works relating to the experiment.

/pdf/suppression-of-bremsstrahlung-and-pair-production-due-to-zpdpblmqea.pdf

Suppression of bremsstrahlung and pair production due to environmental factors

The coherent effects in the high energy particle interaction with crystals open up new opportunities for accelerating and detecting techniques. The effective electromagnetic fields that arise in this case can exceed a thousand times the fields that are now attainable at experimental installations. The first part of the thesis is devoted to the theoretical study of the multiple scattering effects on the dynamics and radiation of high energy charged particles in crystals. One of the goals of this study is to find optimal conditions to carry out the measurement of the anomalous magnetic moment of the charmed Lambda Baryon at the LHC. Due to the short lifetime of this particle the only way to provide such a measurement is to use a bent crystal, which can imitate the magnetic field of order of thousand Tesla. The optimization of the parameters for an experimental setup was carried out on the basis of computer simulation of the Lamda Baryon passage through a bent crystal using the binary collisions model, taking in to account incoherent scattering on thermal vibrations of atoms at lattice nodes, and scattering on an electronic subsystem of a crystal. The results of the research conducted in the thesis give an optimistic forecast for the possibility of carrying out such an experiment at the LHC and became the basis of the corresponding proposal. The multiple scattering effects of the thesis. This study is performed in the framework of classical electrodynamics approach for describing the relativistic particle radiation and the computer simulation of fast charged particles passing through a crystal using the above-mentioned model. It is shown, that the spectral-angular distribution and the polarization characteristics of radiation essentially differ from the results of the Bethe–Heitler theory. The conditions for the experimental observation of these effects are presented. The second part of the thesis is devoted to the study of transient processes in advanced fast reactor breeder working in a self-sustained nuclear burning wave (NBW) regime. It is a new concept of nuclear fission reactors with the so-called “intrinsic safety”, in which the development of uncontrolled chain nuclear reaction is impossible due to the physical principles of reactor operation. The promising concepts of NBW reactor in the case of its implementation allows to utilize the depleted Uranium and provides the treatment of long-lived radioactive waste. This study is based on numerical solving the non-stationary non-linear diffusion equation of neutron transport together with a set of the burn-up equations for fuel components and the equations of nuclear kinetics for precursor nuclei of delayed neutrons using effective multi-group approach. The model of cylindrical homogeneous reactor with metallic fuel of U–Pu, Th–U and mixed Th–U–Pufuel cycles is considered in the framework of the buckling concept. As a result of these studies the existence of the NBW mode in the case of mixed Th–U–Pu fuel and its essential advantages are demonstrated; the detailed analysis of a special kind of the negative reactivity feedback that is inherent to the NBW regime and underlies the “intrinsic safety” of such a reactor is performed; the scenarios of a smooth start-up, forced shutdown and subsequent restart of the NBW reactor are developed.

https://tel.archives-ouvertes.fr/tel-01777441/document

Multiple Scattering Effects on the Dynamics and Radiation of Fast Charged Particles in Crystals. Transients in the Nuclear Burning Wave Reactor

Radionuclide therapy in nuclear medicine : applying Monte Carlo simulation to investigate Bremsstrahlung imaging with a gamma camera

In this letter the high-energy expansion for scattering from extended targets, which the authors previously applied to beamstrahlung radiation and pair production, is applied to the problem of radiation in a medium with multiple scattering. The suppression of the emission of long wave-length photons, the Landau-Pomeranchuk-Migdal effect, is treated and explained in physical terms. This extends previous classical treatments of the problem to the quantum domain and corrects certain approximations made in these earlier works; for example, the effects of finite target thickness can be treated. A model of a random scattering medium is defined that allows a quantum treatment of multiple scattering and the resultant suppression of bremsstrahlung radiation. Submitted to Physical Review Letters ∗Work supported by Department of Energy contract DE–AC03–76SF00515. Perhaps the most ubiquitous process occurring in high-energy physics is the bremsstrahlung of photons by a charged particle in the field of an atom first described by Bethe and Heitler [1]. Following experimental confirmation in 1993 of the Landau–Pomeranchuk–Migdal (LPM) effect [2-6], there is renewed interest in extensions of this process, as well as in its strong interaction analogue, gluon radiation at very high energies in heavy nuclei. We describe here the application of eikonal techniques developed for the beamstrahlung process [7] that lead to a simpler, more straightforward, and physically transparent quantum mechanical derivation of the LPM suppression of soft photon radiation from high-energy electrons in dense matter. This effect was first described by Landau and Pomeranchuk [8] who treated the classical radiation of a high-energy particle in the fluctuating and ‘random’ field inside an infinitely thick medium. The longitudinal momentum transfer q|| of a high-energy electron of momentum p and mass m, radiating a photon of momentum k ≡ (1 − x)p, has a minimum value given by qmin || = m2(1 − x)/2xp. The uncertainty principle can be used to define the formation length lf = (1/q min || ) which at high energies (p >> m) and soft photon emission (1− x) << 1 can grow quite large relative to the interatomic spacing. In their classical derivation, which is appropriate to this kinematics limit, Landau and Pomeranchuk were the first to show that the familiar Bethe-Heitler radiated photon spectrum dN ∼ dk/k is modified by the multiple scattering of the electron as it traverses the rapidly varying electric fields of the medium. When the mean free path of the electron αL is comparable or less than the formation length lf , they found that the spectrum is suppressed, ultimately achieving the form dN ∼ dk/(p √ Lk) . (1)

/pdf/a-quantum-treatment-of-the-landau-pomeranchuk-migdal-effect-50vmi74a3s.pdf

A Quantum Treatment of the Landau-Pomeranchuk-Migdal Effect

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Calorimetry

We have developed a technique that allows SLAC to provide parasitic low-intensity secondary e/sup +/ and e/sup -/ beams up to 25 GeV to End Stations A and B and to the FFTB during SLC operation. This beam was successfully used for a one-month-long experimental run in End Station A by the SLAC E146 collaboration. The experiment used 400 MeV to 25 GeV electron beams at intensities averaging one electron per pulse and 120 pulses per second. The method for producing such a beam without the need for dedicated beam time was to operate parasitically from SLC: photons produced in the SLC beam scrapers in linac sectors 28, 29 and 30 were converted to positrons and electrons in a target downstream from the SLC splitter magnet. The secondary electrons or positrons were then transported to ESA with the A-line. >

/pdf/a-method-of-obtaining-parasitic-e-sup-or-e-sup-beams-during-1clvmohs6k.pdf

A method of obtaining parasitic e/sup +/ or e/sup -/ beams during SLAC linear collider operation

We have studied quantum-mechanical suppression of bremsstrahlung of low-energy 1-500 MeV photons from high-energy 25 GeV electrons. We measured the LPM effect, where multiple scattering of the radiating electron destroys coherence required for the emission of low-energy photons, and the dielectric effect, where the emitted photon traveling in the radiator medium interferes with itself. For the experiment, the collaboration developed a novel method of extracting a parasitic low-intensity high-energy electron beam into the fixed target area during normal SLC operation of the accelerator. The results agree quantitatively with Migdal`s calculation of the LPM effect. Surface effects, for which there is no satisfactory theoretical prediction, are visible at low photon energies. For very thin targets, the suppression disappears, as expected. Preliminary results on dielectric suppression of bremsstrahlung are in qualitative agreement with the expectation.

Quantum-mechanical suppression of bremsstrahlung

A study of LPM suppression of bremsstrahlung at 25 GeV

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A method of obtaining parasitic e/sup +/ or e/sup -/ beams during SLAC linear collider operation

Quantum-mechanical suppression of bremsstrahlung

A study of LPM suppression of bremsstrahlung at 25 GeV