X-ray Transition Radiation Research Articles

On mean free path of X-ray transition radiation generation in radiator

An algorithm for the space distribution of X-ray transition radiation generated by a relativistic charged particle in regular radiators is discussed in the framework of the Geant4simulation toolkit. The model predictions are compared with experimental data.

On the Influence of the Parameters of a Layered Target and an Electron Beam on Diffracted Transition Radiation and Parametric X-Rays

On the Influence of the Parameters of a Layered Target and an Electron Beam on Diffracted Transition Radiation and Parametric X-Rays

The EXTRA-BL4S experiment for the measurement of the energy and angular distributions of transition radiation X-rays

We have designed and implemented an experiment to measure the angular distributions and the energy spectra of the transition radiation X-rays emitted by fast electrons and positrons crossing different radiators. Our experiment was selected among the proposals of the 2021 Beamline for Schools contest, a competition for high-school students organized every year by CERN, and was performed at the DESY II Test Beam facility area TB21, using a high-purity beam of electrons or positrons with momenta in the range from 1 to 6 GeV/c. The measurements were performed using a 100 μm thick silicon pixel detector, with a pitch of 55 μm. Our results are consistent with the expectations from the theoretical models describing the production of transition radiation in multilayer regular radiators.

Geant4 simulation of X-ray transition radiation at small angles

An algorithm for the angular distribution of X-ray transition radiation generated by a relativistic charged particle in regular radiators at small angles (less than 1 mrad) is discussed in the framework of the Geant4simulation toolkit. The model predictions are compared with experimental data recently obtained at the ATLAS TRT test beam.

Registration of the transition radiation with GaAs detector: Data/MC comparison

New developments of pixel detectors based on GaAs sensors offer effective registration of the transition radiation (TR) X-rays and perform simultaneous measurements of their energies and emission angles. This unique feature opens new possibilities for particle identification on the basis of maximum available information about generated TR photons. Results of studies of TR energy-angular distributions using a 500 |j.m thick GaAs sensor attached to a Timepix3 chip are presented. Measurements, analysis techniques and a comparison with Monte Carlo (MC) simulations are described and discussed.

Fine structure of angular distribution of x-ray transition radiation from multilayered radiator in Geant4

The present version of the Transition Radiation (TR) simulation module implemented in the Geant4 toolkit describes very well experimental data for the TR energy distribution; however, it does not allow reproducing the details of angular distribution at small angles. In order to solve this problem, corrections to the existing x-ray TR module in Geant4 are proposed. With these corrections, the results of the simulations are in a good agreement with the angular TR distributions predicted by theory and obtained in the test beam measurements using a 480 um Si pixel detector and Mylar radiator.

Formation region effects in x-ray transition radiation from 1 to 6 GeV electrons in multilayer targets

The formation region effects in x-ray transition radiation have been experimentally investigated. The radiation was generated using 1–6 GeV electrons impinging on two multilayer targets with considerably different periods. The absolute yield of transition radiation was measured and the wide spectral peak in the range from 10 to 30 keV was observed. In the most part of the electron energy range the emission from the short-period radiator was expectedly suppressed, compared to the case of the long-period one. But for the electron energy of 1 GeV an opposite effect, though rather small, of the emission enhancement in the short-period radiator was observed. The conditions, under which this effect is much stronger, are derived and its possible practical value is outlined. The theory accounting for an arbitrary transversal shape of the electron beam and the finite size of the detector is developed. This theory describes rather well the experimental results.

Studies of the spectral and angular distributions of transition radiation using a silicon pixel sensor on a Timepix3 chip

X-ray transition radiation detectors (TRDs) are used for particle identification in both high energy physics and astroparticle physics. In most of the detectors, emission of the X-ray transition radiation (TR) starts at Lorentz factors above γ∼500 and reaches saturation at γ∼2÷3⋅103. However, many experiments require particle identification up to γ∼105, which is very difficult to achieve with conventional detectors. Semiconductor pixel detectors offer a unique opportunity for precise simultaneous measurements of spectral and angular parameters of TR photons. Test beam studies of the energy and the angular distributions of TR photons emitted by electrons and muons of different momenta crossing several types of radiators were performed at the CERN SPS with a 480 μm thick silicon detector bonded to a Timepix3 chip. High resolution images of the energy−angle phase space of the TR produced by different radiators were obtained and compared with MC simulations. The characteristic interference patterns are in agreement with the theoretical models with an unprecedented level of details. The studies presented in this paper also show that simultaneous measurements of both the energy and the emission angles of the TR X-rays could be used to enhance the particle identification performances of TRDs.

Measurement of the energy spectra and of the angular distribution of the Transition Radiation with a silicon strip detector

We plan to develop an advanced Transition Radiation Detector (TRD) for hadron identification in the TeV momentum range, based on the simultaneous measurement of the energies and of the emission angles of the Transition Radiation (TR) X-rays with respect to the radiating particles. To study the feasibility of this project, we have carried out a beam test campaign at the CERN SPS facility with 20 GeV/c electrons and muons up to 300 GeV/c. To detect the TR X-rays and the radiating particles, we used a 300 μm thick double-sided silicon strip detector, with a strip readout pitch of 50 μm. A 2 m long helium pipe was placed between the radiators and the detector, in order to ensure adequate separation between the TR X-rays and the radiating particle on the detector plane and to limit the X-ray absorption before the detector. We measured the double-differential (in energy and angle) spectra of the TR emitted by several radiators. The results are in good agreement with the predictions obtained from the TR theory.

Transition radiation measurements with a Si and a GaAs pixel sensor on a Timepix3 chip

Growing energies of particles at modern or planned particle accelerator experiments as well as cosmic ray experiments require particle identification at gamma-factors (γ) of up to ∼105. At present there are no detectors capable of identifying charged particles with reliable efficiency in this range of γ. New developments in high granular pixel detectors allow one to perform simultaneous measurements of the energies and the emission angles of generated transition radiation (TR) X-rays and use the maximum available information to identify particles. First results of studies of TR energy-angular distributions using gallium arsenide (GaAs) sensors bonded to Timepix3 chips are presented. The results are compared with those obtained using a silicon (Si) sensor of the same thickness of 500 μm. The analysis techniques used for these experiments are discussed.

Identification of particles with Lorentz factor up to [formula omitted] with Transition Radiation Detectors based on micro-strip silicon detectors

This work is dedicated to the study of a technique for hadron identification in the TeV momentum range, based on the simultaneous measurement of the energies and of the emission angles of the Transition Radiation (TR) X-rays with respect to the radiating particles. A detector setup has been built and tested with particles in a wide range of Lorentz factors (from about 103 to about 4×104 crossing different types of radiators. The measured double-differential (in energy and angle) spectra of the TR photons are in a reasonably good agreement with TR simulation predictions.

Diffracted x-ray transition radiation by a “half-bare” electron

The process of diffracted x-ray transition radiation by a high-energy ``half-bare'' electron in a crystalline target is considered in Bragg geometry. The electron is supposed to appear in the mentioned state, in which the field around it is significantly suppressed comparing to the equilibrium Coulomb one, in the result of preliminary penetration through an upstream amorphous target situated on some distance from the crystal. It is shown that the process of the electron's field regeneration after its exit from the upstream target dramatically modifies both the diffracted transition radiation angular distribution and its total yield making them dependent on the distance between the targets. Analytical expressions for these quantities, as well as their simple approximations, are derived. Almost arbitrary crystal orientation is considered. Special attention is drawn to the case of backward radiation geometry when the emitted radiation has to penetrate through the upstream target on its way to the detector.

Small-angle x-ray transition radiation from multilayered structures

In this work, we construct for the first time the theory of small-angle transition radiation from multilayered structures. The theoretically obtained spectral and angular distributions of radiated photons are compared with those predicted by Geant4, a very popular package used today for numerical simulation of different physical processes. We demonstrate that, while spectral distributions ideally coincide, the angular ones differ. We argue that transition radiation from the multilayered structure must contain sharp spikes having the interference nature and caused by the effect of merging two maximum frequencies in dispersive media, and thus Geant4 needs improving in this respect. The transition radiation theory developed here for the small-angle case can play a vital part for the possible future Small Angle Spectrometer at the LHC, other experiments of this kind, and detectors for hadrons of the tera-electron-volt energy range.

X-Ray Transition Radiation from a Polypropylene Radiator: Experiment and Geant4

The propagation of relativistic electrons and muons within multilayer structures is considered. The Geant4 model of X-ray transition radiation (the yield of photons, their angular and spectral distributions, and the spectrum absorbed by a gas detector) is compared to experimental and RADIATOR data. It is demonstrated that the Geant4 spectral and, even more so, angular distributions differ from the experimental ones.

First measurements of the spectral and angular distribution of transition radiation using a silicon pixel sensor on a Timepix3 chip

Abstract X-ray Transition radiation detectors (TRDs) are used for particle identification in both high energy physics and astroparticle physics . Particle identification is often achieved based on a threshold effect of the X-ray transition radiation (TR). In most of the detectors, TR emission starts at γ factors above ∼ 500 and reaches saturation at γ ∼ 2 − 3 ⋅ 1 0 3 . However, many experiments require particle identification up to γ ∼ 1 0 5 , which is difficult to achieve with current detectors, based only on the measurement of the photon energy together with the particle ionization losses. Additional information on the Lorentz factor can be extracted from the angular distribution of TR photons. TRDs based on pixel detectors give a unique opportunity for precise measurements of spectral and angular distributions of TR at the same time. A 500 μ m thick silicon sensor bump bonded to a Timepix3 chip was used in a test beam measurement at the CERN SPS. A beam telescope was employed to separate clusters produced by the primary beam particles from the potential TR clusters. Spectral and angular distributions of TR were studied with high precision for the first time using beams of pions , electrons and muons at different momenta. In this paper, the measurement and analysis techniques are described, and first results are presented.

ATLAS Transition Radiation Tracker (TRT): Straw tubes for tracking and particle identification at the Large Hadron Collider

The ATLAS Transition Radiation Tracker (TRT) is the outermost of the three inner detector tracking subsystems and consists of ∼300,000 thin-walled drift tubes (“straw tubes”) that are 4mm in diameter. The TRT system provides ∼30 space points with ∼130micron resolution for charged tracks with |η|<2 and pT>0.5GeV/c. The TRT also provides electron identification capability by detecting transition radiation (TR) X-ray photons in an Xe-based working gas mixture.Compared to Run 1, the LHC beams now provide a higher centre of mass energy (13TeV), more bunches with a reduced spacing (25ns), and more particles in each bunch leading to very challenging, higher occupancies in the TRT. Significant modifications of the TRT detector have been made for LHC Run 2 mainly to improve response to the expected much higher rate of hits and to mitigate leaks of the Xe-based active gas mixture. The higher rates required changes to the data acquisition system and introduction of validity gate to reject out-of-time hits. Many gas leaks were repaired and the gas system was modified to use a cheaper Ar-based gas mixture in some channels. A likelihood method was introduced to optimise the TRT electron identification.

Interference effects in angular and spectral distributions of X-ray Transition Radiation from Relativistic Heavy Ions crossing a radiator: Influence of absorption and slowing-down

Theoretical analysis and representative calculations of angular and spectral distributions of X-ray Transition Radiation (XTR) by Relativistic Heavy Ions (RHI) crossing a radiator are presented taking into account both XTR absorption and RHI slowing-down. The calculations are performed for RHI energies of GSI, FAIR, CERN SPS and LHC and demonstrate the influence of XTR photon absorption as well as RHI slowing-down in a radiator on the appearance/disappearance of interference effects in both angular and spectral distributions of XTR.

Interference effects in radiation by the relativistic electron in the structure of “amorphous matter layers–single crystal”

In the present work a theory of coherent radiation of a relativistic electron moving at a constant speed in a combined target, consisting of several amorphous matter layers and a monocrystalline layer is built. The expressions describing the amplitudes of diffracted transition radiation (DTR) and parametric X-ray radiation (PXR) are derived within the framework of two-wave approach of the dynamic diffraction theory. The cases of one and two amorphous matter layers in the structure were considered. Also the extreme case, when vacuum is considered as the second amorphous layer in the structure, is investigated. The expressions obtained describe a spectral-angular distribution of DTR, PXR and their interference in such a structure. The X-ray wave generation and propagation processes in crystalline layer are considered in Laue scattering geometry for the general case of asymmetric reflection.

Gamma Cherenkov-transition radiation produced by charged particles at an interface and in a stack of plates

The spectral and angular distributions as well as the total number of photons of gamma-ray Cherenkov-transition radiation (GCTR) in the photon energy region (1÷10) MeV produced by charged particles passing through an interface between two media and a stack of plates are calculated using the formulae of X-ray transition radiation. The concept of formation length for GCTR is discussed.

X-ray transition radiation of electrons with energy of 300 to 900 MeV in periodic multifoil radiators

Results of experiments conducted at the Tomsk synchrotron to study resonant X-ray transition radiation generated by relativistic electrons in periodic multifoil radiators are reviewed. Both the internal synchrotron beam and the external secondary electron beam from the pair magnetic γ-spectrometer with energies ranging from 300 to 900 MeV were used in the experiments. The radiators consisted of many thin amorphous foils of various materials. The generation of X-ray radiation in a compound radiator consisting of a multifoil radiator and a crystal is also studied. In this case, the resonant X-ray transition radiation generated in the multifoil radiator is diffracted in the crystal and emitted at Bragg angles, together with the parametric X-ray radiation generated in the crystal. Spectral and angular properties of the resonant X-ray transition radiation and diffracted resonant X-ray transition radiation are investigated. The ratio between the contributions from the diffracted resonant X-ray transition radiation and other types of radiation to the total coherent X-ray radiation flux generated by electrons in periodic structures and crystals is estimated.