Radiation from relativistic positrons channeled in single crystals

The characteristic of the radiation emitted from relativistic positrons channelled between the major planes in single crystal have been calculated. The sharp peaks of the emission spectrum in the keV region is predicted correctly and is compared with previous calculations.     

Emission of single gamma rays by electrons with energies of hundreds of GeV in oriented crystals

Cross sections are calculated for the emission of single hard photons by electrons with energies of 150–1000 GeV as they pass through oriented crystals at small angles to the crystallographic axes. The contribution of incoherent emission at isolated atoms of the crystal is taken into account in the calculations, along with the emission in the continuum potential. The calculations are compared with the customary Bethe-Heitler spectrum for a thick amorphous target with allowance for photon absorption due to electron-positron pair production. It is shown that, in this range of energies, an oriented crystal can be more efficient than a thick amorphous target for creating a larger number of hard gamma rays with energies comparable to the energies of the emitting electrons. Zh. Tekh. Fiz. 68, 37–41 (September 1998)     

Nonlinear Raman scattering of photons by a channeled particle

Channeled particles are characterized by the discrete spectrum of bound transverse motion. The interaction of photons with channeled particles in single crystals can be accompanied by energy transitions between the levels of transverse motion of the channeled particle. The Raman scattering of photons at a quasibound channeled particle leads to the appearance of a combination of frequencies: the incident radiation frequency ω₀ and the frequency Δω_{m, n}, i.e., ω = ω₀ ± Δω_m,n where Δω_m,n = 2Δε_m,nγ²; Δε_{m, n} is the energy of the transition between quantum states (m and n) of the transverse motion of the channeled particle; and γ = E/mc² is the Lorentz factor of the channeled particle. The appearance of a violet satellite (the anti-Stokes component) in the Raman scattering spectrum is analyzed. The three-photon Raman-type transition, which is the process of the simultaneous absorption of two photons with the frequency ω₀ with the emission of a photon with the frequency ωs = 2ω₀ ± 2Δε_m,nγ², is considered. The conditions for resonance observation during the formation of the second harmonic (ω = 2ω₀) are discussed.     

The number of photons emitted by a channeled electron

A discussion is presented of the influence of photon multiplicity in the emission from channeled electrons on the radiation spectrum measured by a total-absorption spectrometric device. It is shown that as the maximum in the spectrum shifts with increasing crystal thickness, in the absence of further information it is impossible to determine the multiplicity of the emission. A method is proposed for determining the presence of multiple emission from channeled electrons with a total-absorption spectrometer by using an absorber covering a specified portion of the -ray aperture. The presence of multiplicity is identified in emission from channeled electrons with energy E₀=900 MeV in a tungsten single crystal of 1.18 mm. Previously the presence of multiplicity in the radiation from channeled electrons had been detected for electron energies above 4.5 GeV.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 88–105, June, 1991.     

Angular correlation of annihilation photons in zinc single crystals

Linear slit angular correlation curves have been obtained at room temperature for the [0001], [10 0], and [11 0] directions in zinc single crystals. Small anisotropy of the curves was observed. Also larger angle parts of the curves showed anisotropy.     

Search for anomalous production of single photons at and 136 GeV

This letter reports the results of the measurement of single photon production in the reaction e⁺e⁻ → γ+ invisible particles at centre-of-mass energies and 136 GeV and an integrated luminosity of 5.83 pb⁻¹, collected with the DELPHI detector at LEP. The signal is compatible with the prediction of the Standard Model for the process , and the number of neutrino families has been determined to be N_ν = 3.1 ± 0.6. Limits have been derived on anomalous neutral gauge boson couplings and on compositeness in the framework of a specific model.     

Observation of light radiation induced by positrons in α-LiIO3 single crystals

Light radiation emitted by α-LiIO₃ single crystals under positron irradiation is detected. The radiation emergence model due to annihilation on two groups of electrons of the IO^-₃ quasimolecular complex is suggested to be in accordance with the annihilation data as well as with the electronic structure calculation results.     

Emission of matter waves by photons

A new hypothesis, based on the dualistic nature of matter and light, is proposed. The frequency shift of a photon creates an electron. The phenomenon is investigated according to the conservation laws of energy and momentum. The concept of particle velocity and wavelength of a photon, based on a relation between the energy and momentum conservation laws, is also introduced. The proposal is also supported by some experiments on matter–antimatter creation by the collision of photons.     

Neutron scattering by laser photons in crystals

It is shown that in crystals neutron-photon interaction increases drastically. Due to the fact that photon propagation in a crystal involves nuclear movement, the cross section of neutron scattering by photons appears to be proportional to the cross section of neutron scattering by nuclei.     

Modeling of the propagation of single photons in finite one-dimensional photonic crystals

A model of the propagation of a quantized electromagnetic field in a one-dimensional photonic crystal that contains two-level atoms that interact with the field is proposed. The model separately considers the interaction of the quantized radiation with the quantum system and with the photonic crystal. The use of the model is exemplified by its application to the study of the decay of excited states of one- and two-level atoms placed in the photonic crystal. The possibility of the transformation of the front of a single photon by a finite dielectric is demonstrated.     

Investigation of bismuth nuclei fission into three fragments with comparable masses by means of GeV energy photons

We present the results of experimental studies of the process of fission of ²⁰⁹Bi nuclei into three mass-comparable fragments by bremsstrahlung photons with maximum energies of 2 GeV and 4.5 GeV with use of nuclear photoemulsion implanted with bismuth nuclei. We compare the results with those obtained with proton beams.     

Momentum analysis of kaon and pion pairs produced from time-like photons at 1.6 GeV energy

We present results for the total cross section of e⁺e^? annihilation into two hadrons at 1.6 GeV: σ_ππ = σ_KK = (1.8 ± 1.1) × 10^-33 cm².From these values we obtain the time-like electromagnetic form factors these mesons: |F_π|² = 0.24 ± 0.14 and |F_K|² = 0.46 ± 0.26.     

Radiation of channeled 800 MeV electrons in diamond crystals

Measured data on γ-ray emission for the low-energy region of the bremsstrahlung spectra produced by 800 MeV electrons in diamond crystals are presented. The obtained spectral and orientational characteristics of the γ-ray yield indicate that the low-energy radiation is associated with the channeling of electrons.     

Monte-Carlo study of electromagnetic showers of high energy electrons and photons in aligned crystals

Abstract

A Monte–Carlo program to investigate electromagnetic shower formation in single crystals for particle energies up to 300 GeV is presented. It is based on the well known EGS4-code for amorphous materials and accounts for coherent radiation and pair production which arise in a crystal. Channeling radiation and crystal field assisted pair production are calculated within the uniform field approximation. The increase of energy loss of channeled electrons due to radiation cooling is also included. Good agreement with the available experimental data can be reported.     

Vacancy-type defect distributions near argon sputtered Al(100) surface studied by variable-energy positrons and molecular dynamics simulations

A beam of variable-energy positrons, whose back-diffusion probability is measured as a function of positron implantation energy, is applied to studies of depth distribution of sputtering damage in aluminum. The defects are produced by argon ion bombardment of an Al(110) surface in ultra-high vacuum. We have varied the Ar⁺ energy, incident angle and dose, as well as sputtering and annealing temperatures. The extracted defect profiles have typically a narrow peak at the surface with a width of 10–20 A and a broader tail extending down to 50–100 Å. The shape of the defect profile varies only slightly with the sputtering energy and angle. Defect production at less than 1 keV Ar⁺ energies is typically 1–5 vacancies per incident ion. The defect profiles become fluence-independent at about 2 × 10¹⁶ Ar⁺ cm⁻². The defect density at the outer atomic layers saturates at high argon fluences to a few at%, depending on sputtering conditions. The sputtering temperature (below or above the vacancy migration stage at 250 K) has little effect on vacancy profiles. Defects anneal out gradually between 100 °C and 400 °C. Sputtering damage was also evaluated with the molecular dynamics technique. The shape and depth scale of the simulated collision cascades are in agreement with the experimentally extracted quantities.     

Investigation of the emission of photons induced in the volume reflection of 10-GeV positrons in a bent silicon single crystal

The emission of photons in the motion of a 10-GeV positron beam in bent silicon crystals has been experimentally investigated. The experimental data are compared with the theoretical calculations.     

Thermalization of positrons and positronium atoms in ionic crystals

It is shown that total positron scattering on acoustic and optical lattice vibrations in atomic semiconductors and ionic crystals causes total positron thermalization before annihilation at both high and low (T≤10 K) temperatures.     

Observation of a four-pion vector-meson state of mass ≈ 1.5 GeV produced by linearly polarized 9.3 GeV photons

From a study of γp → 2π⁺2π⁻p using 9.3 GeV linearly polarized photons, evidence is found for a J^P = 1⁻, I^G = 1⁺ four pion enhancement of mass ∼ 1.5 GeV with a production cross section of 1.6 ± 0.4 μb.