PACS numbers: 41.60 (original) (raw)
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2001
We discuss the radiation generated by positrons channeling in a crystalline undulator. The undulator is produced by periodically bending a single crystal with an amplitude much larger than the interplanar spacing. Different approaches for bending the crystal are described and the restrictions on the parameters of the bending are discussed. We also present numeric calculations of the spontaneous emitted radiation and estimate the conditions for stimulated emission. Our investigations show that the proposed mechanism could be an interesting source for high energy photons and is worth to be studied experimentally.
Radiation from relativistic positrons channeled in single crystals
Radiation Effects and Defects in Solids, 1982
... Printed in Great Britain RADIATION FROM RELATIVISTIC POSITRONS CHANNELED IN SINGLE CRYSTALS BISWANATH RATH and ANAND P. PATHAKf School of Physics, University of Hyderabad, Central University PO Hyderabad 500134, India ...
Photon emission by ultra-relativistic positrons in crystalline undulators: the high-energy regime
This paper discusses the undulator radiation emitted by high-energy positrons during planar channeling in periodically bent crystals. We demonstrate that the construction of the undulator for positrons with energies of 10 GeV and above is only possible if one takes into account the radiative energy losses. The frequency of the undulator radiation depends on the energy of the particle. Thus the decrease of the particle's energy during the passage of the crystal should result in the destruction of the undulator radiation regime. However, we demonstrate that it is possible to avoid the destructive influence of the radiative losses on the frequency of the undulator radiation by the appropriate variation of the shape of the crystal channels. We also discuss a method by which, to our mind, it would be possible to prepare the crystal with the desired properties of its channels.
Channeling of ultra-relativistic positrons in bent diamond crystals
Results of numerical simulations of channeling of ultra-relativistic positrons are reported for straight and uniformly bent diamond crystals. The projectile trajectories in a crystal are computed using a newly developed module of the MBN Explorer package which simulates classical trajectories in a crystalline medium by integrating the relativistic equations of motion with account for the interaction between the projectile and the crystal atoms. The Monte Carlo method is employed to sample the incoming positrons and to account for thermal vibrations of the crystal atoms. The channeling parameters and emission spectra of incident positrons with a projectile energy of 855 MeV along C(110) crystallographic planes are calculated for different bending radii of the crystal. Two features of the emission spectrum associated with positron oscillations in a channel and synchrotron radiation are studied as a function of crystal curvature.
Annihilation of relativistic positrons in single crystal with production of one photon
International Journal of Modern Physics A, 2015
The energy and momentum conservation laws prohibit positron–electron single-photon annihilation in vacuum. It is shown that the situation is different in a single crystal with one of the leptons (e.g. positron) moving in the channeling (or in the quasi-channeling) mode. The transverse motion of an oriented or channeled particle may sharply increase the probability of the single-photon annihilation process.
We discuss radiation generated by positrons channeling in a crystalline undulator. The undulator is produced by periodically bending a single crystal with an amplitude much larger than the interplanar spacing. Different approaches for bending the crystal are described and the restrictions on the parameters of the bending are established. We present the results of numeric calculations of the spectral distributions of the spontaneous emitted radiation and estimate the conditions for stimulated emission. Our investigations show that the proposed mechanism provides an efficient source for high energy photons, which is worth to be studied experimentally.
Orientation dependence of relativistic-positron annihilation in single crystals
Physics of Atomic Nuclei, 2016
An effect of the orientation dependence of the cross section for the single-photon annihilation of relativistic positrons with atomic electrons in a crystal is predicted. It is shown that the probability for the single-photon annihilation of a channeled positron in a crystal may be either suppressed in a crystal in relation to a homogeneous medium or, on the contrary, enhanced. The reason is that, depending on their incidence angle, the positrons may be either in the vicinity of ion planes of the crystal, where the electron density is higher, or far away from them, where the electron density is lower.
Gamma radiation production using channeled positron annihilation in crystals
Laser Physics Letters, 2015
The possibility of channeling low-energy relativistic positrons in some ionic crystals with axial symmetry is shown. The annihilation processes of positrons with medium electrons are investigated in detail. The lifetime of a positron in the regime of channeling is estimated; the existence of a long relaxation lifetime has been shown.
Journal of Modern Optics, 2009
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pp.115-126 NEW EXPERIMENTS WITH BRIGHT POSITRON AND POSITRONIUM BEAMS
2015
Abstract: After half a century of work studying the interaction of positrons with ordinary matter, there remain several interesting fundamental questions that are uniquely suitable for investigation using antimatter, and several instances where interesting views of the world could be obtained using positrons. In this paper we examine the possibilities for imaging single molecules with positrons and for looking at a possible zero-temperature or quantum phase transition associated with the sticking of slow positronium at a cold surface. We also discuss prospects for future developments of LINAC positron beams using a rare gas moderator and for detecting positronium molecules. 1. OVERVIEW The field of positron physics includes several diagnostic techniques that have become useful, although not widely acclaimed, in certain niches under the skilful hands of some talented experimenters [1,2]. The positron is a strongly perturbing probe in many cases, but after much work we have good theor...
Radiation of fast positrons interacting with periodic microstructure on the surface of a crystal
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2016
Radiation of charged particles passing through a set of equidistant ridges on the surface of a single crystal is calculated. The ridges are rectangular in shape, each of thickness of half of the particle trajectory period at planar channeling in a thick crystal. Positively charged particle entering the first ridge with angle smaller than the critical channeling angle is captured into channeling and changes the direction of its transversal velocity to reversed. Between the halfwave ridges the particle moves along a straight line. Passing through such set of half-wave crystal plates the particle moves on quasi-undulator trajectories. Properties of the particle radiation emitted during their passage through such "multicrystal undulator" are calculated. The radiation spectrum in each direction is discrete, and the frequency of the first harmonic and the number of harmonics in the spectrum depends on the distance between the plates, on energy of the particles and on the averaged potential energy of atomic planes of the crystal. The radiation is bound to a narrow cone in the direction of the average particle velocity and polarized essentially in a plane orthogonal to the atomic planes of the crystal.
Optically excited states in positronium
1990
Optical excitation are reported of the 1 3S-2 3P transition in positronium, and a second excitation from n=2 to higher n states. The experiment used light from two pulsed dye lasers. Changes in the positronium annihilation rate during and after the laser pulse were used to deduce the excited state populations. The n=2 level was found to be saturable and
Optical spectroscopy of atomic and molecular positronium
Journal of Physics: Conference Series, 2014
Positronium (Ps) is a purely leptonic hydrogen-like atom formed from an electron and a positron. Since the interactions of electrons and positrons are thought to be almost entirely electromagnetic, precision measurements of the Ps energy levels should constitute a good test of QED theory. The ultimate precision is limited by the rapid annihilation of the various Ps states and the number of Ps atoms available. Much progress in making better Ps sources has been made since the 1950's when Ps was discovered and its principle characteristics measured in by the pioneering experiments of Martin Deutsch. The most notable milestones were the first reproducible schemes for making slow positrons and Ps in vacuum by Canter and his co-workers in the 1970's and the discovery of the enabling technology for accumulating slow positrons by Surko and co-workers in 1989. These techniques have made it possible to generate high density bursts of slow Ps atoms that has led to the production of dipositronium molecules, Ps 2 , and the observation of the Lyman-alpha-like transition in Ps 2 at a wavelength of 251 nm predicted by Varga and co-workers. The possibilities for 1S-2S spectroscopy of triplet and singlet Ps with precisions relevant to the proton charge radius problem and efficient production of slow Rydberg Ps atoms useful for measuring Ps free fall are discussed. ICPEAC-2013 INVOCATION We met at Lanzhou in a setting fit for kings To learn more about how the world works, Mindful of those who could not join us there.
2007
Theory of relativistic charged particle radiation was detailed developed in monographs [1–4]. Characteri stics of electron and positron radiation at planar chan neling, radiation at channeling (CR), along planes (100) and (110) of diamond, silicon and germanium crystals are more detailed studied in the work [1] by ap proximation of potential of a single crystal plane by a simple function of the type «inverse parabola». Howe ver, analytical treatment is complicated at channeling along so called double planes (111). It is connected to the following reasons: • potential of double plane system (111) is complica ted (Fig. 1, a); • analytical solution of equation ofmotion is impossi ble to be found in such potential. Trajectory of a particle in a crystal may be determi ned by a model of binary collisions [4] or by numerical solution of equation ofmotions. In the paper the second approach is used within which: • potential of double plane system (111) is calculated on the basis of the model...
Journal of Physics B: Atomic, Molecular and Optical Physics, 2019
We predict peculiar changes in spectral distributions of radiation emitted by ultra-relativistic positrons and electrons in periodically bent crystals with variation of the bending amplitude. It is shown that the changes, being sensitive to the projectile energy, manifest themselves differently for negatively and positively charged projectiles. We demonstrate that the features observed are due to the interplay of different radiation mechanisms occurring in periodically bent crystals. The observations are important for design, practical realization and channeling experiments with periodically bent crystals as the key element of the novel light sources. The analysis presented is based on the grounds of accurate numerical simulations of the channeling process.
Theoretical interpretation of radiation spectra from channeled positrons
Physics Letters A, 1985
The shape of the radiation spectra from planar channeled positrons is calculated by means of the quantum theory. The computed spectrum curves agree quantitatively with experimental data. The existence of the second peak of the radiation spectrum of the channeled positrons is theoretically predicted.
Physical Review A, 2009
The radiation emitted by 180-GeV/ c volume-reflected electrons and positrons impinging on a bent crystal has been measured by the H8RD22 Collaboration on the H8 beamline at the CERN SPS. A dedicated spectrometer has been developed to measure high-energy photon spectra ͑up to ϳ100 GeV͒ under volume reflection: photon and charged particle beams have been separated by a bending magnet and leptons were detected and tagged by microstrip silicon detectors and a Pb-scintillator sampling calorimeter. A comparison between the experimental and analytical data for the amorphous and volume-reflection cases is presented and the differences are discussed.