Quasi-monochromatic Beam Research Articles

Nondestructive determination of isotopic abundance using multi-energy nuclear resonance fluorescence driven by laser Compton scattering source

We report on the quantitative nondestructive analysis of the natural isotopic abundances of hafnium and tungsten elements using nuclear resonance fluorescence. Metallic samples of hafnium and tungsten were irradiated to six quasi-monochromatic γ-ray beams generated by laser Compton scattering in the energy range of 2.4–3.2 MeV. Multiple nuclei were simultaneously excited at each of the six γ-ray beam energies. A high-purity germanium detector array detected deexcitations of the nuclei. In total, 51 transitions were unprecedentedly employed to estimate the isotopic abundances of heavy elements nondestructively. The estimated abundances of three hafnium isotopes and three tungsten isotopes are consistent with standard known natural abundances within the experimental uncertainties. The deviation from the standard values ranges from 0.18% to 1.36%.

Polarimetric measurement of temporal coherence in electromagnetic light beams

We present a method to determine the degree of temporal coherence of a quasimonochromatic vectorial light beam by polarimetric measurements. More specifically, we employ Michelson’s interferometer in which the polarization Stokes parameters of the output (interference) beam are measured as a function of the time delay. Such a measurement enables us to deduce the magnitudes of the coherence (two-time) Stokes parameters, and hence the degree of coherence, of the input beam. Compared to existing methods the current technique has the benefits that neither optical elements in the arms of the interferometer nor visibility measurements are needed. The method is demonstrated with a laser diode and a filtered halogen source of various degrees of polarization.

Quasi-monochromatic gamma beam modulation at SLEGS

Basing on the slant Compton scattering of 10640 nm photons from a 100 W CO2 laser on 3.5 GeV electrons from the Shanghai Light Source, the Shanghai Laser Electron Gamma Source (SLEGS) produces gamma-ray in the energy range of 0.66 MeV–21.7 MeV and flux of 105–107 photons/s. A Gamma Modulation System (GMS) composed of the collimators, attenuator, beam spot imaging(MiniPIX) and flux monitor(LaBr3 detector) was developed to ensure producing bandwidth-variable quasi-monochromatic gamma-ray with a variable-flux at same time. Using the GMS, variable-flux quasi-monochromatic gamma-ray beams with a best bandwidth of 10% in the 90∘ slant-scattering and 4% in back-scattering were obtained respectively. We report on the performance of the GMS and results of gamma-ray beam modulating measurement with GMS at SLEGS.

Simulation of the dynamics of laser beams in an array of carbon nanotubes using the hydrodynamic approach

We simulated the propagation of a quasi-monochromatic laser beam in a medium with carbon nanotubes. Equations describing the dynamics of laser beams in an array of carbon nanotubes are obtained based on the hydrodynamic approach for the nonlinear Schrödinger equation. This equation is solved numerically using the smoothed particle method. The evolution of the beam is analyzed depending on the frequency of the electric field.

Relativistic transformations of quasi-monochromatic paraxial optical beams

A monochromatic plane wave recorded by an observer moving with respect to the source undergoes a Doppler shift and spatial aberration. We investigate here the transformation undergone by a generic, paraxial, spectrally coherent quasimonochromatic optical beam (of finite transverse width) when recorded by a moving detector. Because of the space-time coupling intrinsic to the Lorentz transformation, the monochromatic beam is converted into a propagation-invariant pulsed beam traveling at a group velocity equal to that of the relative motion and which belongs to the recently studied class of ``space-time wave packets.'' We show that the predicted transformation from a quasimonochromatic beam to a pulsed wave packet can be observed even at terrestrial speeds.

Monte Carlo simulations of synchrotron X-ray dose affecting root growth during in vivo tomographic imaging

Synchrotron X-ray computed tomography (XCT) has been increasingly applied to study the in vivo dynamics of root growth and rhizosphere processes. However, minimizing radiation-induced damage to root growth warrants further investigation. Our objective was to develop a robust approach for modeling and evaluating ways to reduce synchrotron X-ray dose effects on root growth during in vivo imaging. Wheat roots growing in soil were exposed to X-rays during XCT experiments resolved in space (3D) plus time (4D). The dose rate and cumulative absorbed dose in roots were modelled using the Monte Carlo code FLUKA for different experimental conditions of polychromatic and quasi-monochromatic X-ray beam configurations. The most impactful factors affecting damage to roots were incident X-ray energy spectrum, stored current in the accelerator machine, position of the root in the soil, and possibly the number of exposures during the 4D XCT experiments. Our results imply that radiation dose during in vivo imaging of plant roots can be diminished by using monochromatic radiation at the highest energy suitable for a given sample thickness and field of view, and by controlling the rotation axis of off-centered roots to increase attenuation of radiation by the soil matrix.

Transmission functions of transmissive multilayer inhomogeneous holographic photopolymer liquid crystal diffraction structures

A new analytical model of diffraction of quasimonochromatic light beams on spatially inhomogeneous multilayer diffraction structures formed in photopolymer material with nematic liquid crystals having smooth optical inhomogeneity in the thickness of layers is presented. It is shown that when an applied electric field isapplied to diffraction layers containing a photopolymer composition with a high proportion of liquid crystalline component, a transformation of the selective response with a significant shift in angular selectivity occurs

Prediction of prompt neutron spectra of the photon induced reactions on 238U and 232Th targets at incident energies from 4 to 22 MeV

The processing of experimental data for the photon induced reactions on 238U and 232Th investigated by quasi-monochromatic γ-ray beams (produced in Laser Compton scattering at the NewSUBARU facility) needs the prediction of prompt neutron spectra. They are obtained using reliable models and systematics, i.e. the most employed and well validated approach of the most probable fragmentation with input parameters provided by a recent systematic and fission chance probabilities based on nuclear reaction calculations performed with the EMPIRE code.

Density estimations and comparisons of a fragmented single fiber using X-ray computed tomography.

A commercial X-ray computed tomography (CT) apparatus using a quasi-monochromatic beam was utilized for density estimations and comparisons of a fragmented single fiber. The validation of quasi-monochromaticity of the X-ray source was investigated by radiograph measurements. For the case of a transmittance higher than 50%, the contribution of Cu Kα characteristic X-rays was dominant. To realize a sufficient statistical quality, an attempt to increase the number of averaged voxels was demonstrated using the neighboring slices of the 3D-CT image. A minimum value of the coefficient of variation (CV) was achieved using multiple images rather than using a single image. The observed values of the inverse of the transmitted X-ray intensity (CT value) of the polymers showed a fairly good relationship with their density. An analytical curve derived from measurements of reference samples of known densities could provide the relative density of an unknown fragmented fiber down to the size of 30μm in diameter and 35μm in length. The CV of the estimated density was from 1.5 to 2%, which was estimated from the CV of CT values. Moreover, the correlation of CT values was improved with the linear absorption coefficient than the density. A better performance of discrimination of polymers including fibers might be realized with the difference of linear absorption coefficients for X-rays.

Testing the equivalence principle with time-diffracted free-falling quantum particles

The equivalence principle of gravity is examined at the quantum level using the diffraction in time of matter waves in two ways. First, we consider a quasi-monochromatic beam of particles incident on a shutter which is removed at time \(t = 0\) and fall due to the gravitational field. The probability density exhibits a set of mass-dependent oscillations which are genuinely quantum in nature, thereby reflecting quantum violations to the weak equivalence principle, although the strong equivalence principle remains valid. We estimate the degree of violation in terms of the width of the diffraction-in-time effect. Second, motivated by the recent advances in the manipulation of ultracold atoms and neutrons as well as the experimental observation of quantum states of ultracold neutrons in the gravitational field above a flat mirror, we study the diffraction in time of a suddenly released beam of particles initially prepared in gravitational quantum bound states. In this case, we quantify the degree of violation by comparing the time of flight from the mean position of the initial wave packet versus the time of flight as measured from the mirror. We show that, in this case both the weak and strong versions of the equivalence principle are violated. We demonstrate that compatibility between equivalence principle and quantum mechanics is recovered in the macroscopic (large-mass) limit. Possible realizations with ultracold neutrons, cesium atoms and large molecules are discussed.

Isotope-selective radiography and material assay using high-brilliance, quasi-monochromatic, high-energy photons.

We demonstrate the possibility to directly detect microgram amounts of the isotope 7Li using a quasi-monochromatic high-energy photon beam. The isotope selective detection is based on a witness scatterer absorbing and re-emitting photons via nuclear resonance fluorescence. This enables the detection of isotopes with microgram accuracy at long distances from the actual sample. Further, we demonstrate that the technique can deliver quantitative information without specific knowledge of the photon flux and no spectral capabilities or knowledge of the resonance fluorescence cross section. Detection of low-atomic-weight isotopes screened by heavy shielding is also shown. The techniques described are applicable to all next-generation, ultrahigh brilliance, laser-Compton light sources currently under construction.

A Realistic Interpretation of Quantum Wavefunctions as Temperature Dependent Vacuum Polarization Waves

We discuss in this paper a novel interpretation of Born rule as an approximated thermodynamic law which emerges from the interaction of a quantum system with a non-stationary thermal bath associated to vacuum fluctuations induced by external environment radiation. In particular we assume that vacuum polarization is a real non relativistic phenomena caused by hidden vacuum charge oscillations which diffuses heat energy in a dispersive and dissipative dielectric medium with a temperature dependent speed of propagation. We propose a model which couples vacuum wavefunctions to vacuum charge fluctuations and we deduce a temperature dependent running fine structure constant function proportional, at first approximation, to the squared of the effective electron charge and compatible with known experimental data. We interpret the vacuum symmetry breaking energy fluctuations induced in scattering experiments of particle physics and in laser assisted nuclear reactions as thermal quasi-monochromatic beams produced by the decay of hidden non equilibrium massive photons propagating with a variable light speed. We suggest, exploiting an old analogy between plasmons and pseudo Goldstone bosons, to interpret heat diffusion of this non relativistic polarized vacuum as a real De Broglie electromagnetic scalar wave associated to the radiation emitted by the hidden massive photons with acceleration proportional to vacuum Unruh like temperature. We predict a temperature dependent deviation from Coulomb law and a generalized dispersive law of these hidden unstable photons that could be revealed as not stationary coloured noise in experiments on anomalous heat diffusions associated to the decay of unstable accelerated pairs produced in nuclear physics experiments. We discuss then how our proposal of a temperature dependent non relativistic vacuum polarization might be applied to deduce a dynamic generalization of Born rule based on a realistic interpretation of quantum wavefunctions as averaged electromagnetic waves of hidden massive photons. Finally we suggest to test our time asymmetric model looking for very fast oscillating polarization thermal waves emitted during the not instantaneous wavefunction collapse and revealed as not stationary bulk heating effects in experiments on accelerated conductors and nanoconductors.

Updated neutron-multiplicity sorting method for producing photoneutron average energies and resolving multiple firing events

Photoneutron measurements in the Giant Dipole Resonance region have been recently performed using quasimonochromatic Laser Compton Scattering γ-ray beams at NewSUBARU (Japan) for 59Co, 89Y, 103Rh, 139La, 159Tb, 165Ho, 169Tm, 181Ta, 197Au and 209Bi. Experimental (γ,xn) with x = 1–4 photoneutron cross sections have been obtained with a direct neutron-multiplicity sorting method associated to a flat-efficiency neutron detector, which operates under single firing conditions obtained by low reaction rates. In this paper, we discuss recent developments to the neutron-multiplicity sorting procedure dedicated to (i) resolving multiple firing events and to (ii) extracting the average energies of (γ,xn) photoneutrons. The method is tested on 159Tb experimental data.

Collimator system of SLEGS beamline at Shanghai Light Source

Shanghai laser electron gamma source (SLEGS) is an energy-variable gamma-ray source developed based on the inverse Compton scattering of 10640 nm photons from a 100 W CO2 laser on 3.5 GeV electrons from the Shanghai Light Source. It produces gamma-rays in the energy range of 0.4–21.7 MeV with a flux of 105–107 photons/s. A collimator system was designed to produce quasimonochromatic gamma-ray beams with a best possible bandwidth of 1.1%–4.4% and filter out the substandard gamma-rays. The collimator system composed of coarse and fine collimators, constitutes a critical component of the SLEGS. By Geant4 simulations, we show that the collimator system is effective in tuning beam bandwidths and regular dodecagonal beam spots at the target position.

Proposal for Anderson localization in transverse spatial degrees of freedom of photons

We propose an experimental setup for studying the Anderson localization of light in the continuous transverse spatial degrees of freedom of the photons. This physical phenomenon can be observed in the transverse profile of a paraxial and quasi-monochromatic beam of light using a spatial light modulator. The light modulator acts in the laser beam as a weak random potential. Here, differently from the standard models studied in the literature, our setup splits the dispersion and potential terms along the beam evolution. By numerical simulations we confirm the feasibility of our experimental proposal.

Development of a precise evaluation technique for the pre-sampled point spread function of X-ray imaging detectors with sub-micrometer resolution

This article presents a method for precisely measuring the charge spread inside a silicon sensor, before it is sampled by the pixels of an X-ray imaging detector. The shape of the charge spread or pre-sampled point spread function (PSF) of the silicon sensor was demonstrated with a sub-micrometer resolution. The measurement setup comprises quasi-monochromatic X-ray beams emitted by a synchrotron radiation source, 5-μm-diameter tungsten pinhole, sub-μm-resolution X-ray beam profiler, and photodiode array in automation mode for step-scanning measurements. We obtained a value of 16.5–17.1 μm (full width at half-maxima; sensor thickness: 650 μm; bias voltage: 750 V) based on preliminary experiments using 7.3 keV X-rays at BL19LXU of SPring-8. This value is consistent with the expected value obtained from the convolution of the beam profiles and pre-sampled PSFs corresponding to multiple photons for a dopant density of ∼1012cm−3 within a range of approximately 1 μm. We believe that our measurement method has sufficient potential for evaluating the pre-sampled PSF of a photodiode array with an accuracy of 1 μm or less. The single-photon capability of imaging detectors depends on the detector noise as well as the pre-sampled PSF. Our measurement method, with high spatial resolution, is beneficial in the sense that it optimizes the pixel design of X-ray image sensors using a sample piece with a limited number of pixels.

Bent Laue crystal anatomy: new insights into focusing and energy-dispersion properties

X-ray Laue-type monochromators are common and essential optical components at many high-power X-ray facilities, e.g. synchrotron facilities. The X-ray optics of bent Laue crystals is a well developed area. An incident X-ray beam penetrating a bent Laue crystal will result in a diffracted beam with different angles and energies. There is a need for a way of organizing the rays that allows one to sort out the energy and spatial properties of the diffracted beam. The present work introduces a new approach for describing the general behaviour of bent Laue crystals from a ray-tracing point of view. This quasi-monochromatic beam approach provides an intuitive view of bent-crystal diffraction and leads to deeper understanding. It explains the energy and spatial properties of common and special cases of bent Laue optics, predicts phenomena that can improve energy-dispersion-related X-ray imaging techniques and provides a theoretical framework that makes ray-tracing simulation easier to realize.

Diffraction of quasimonochromatic light beams on multilayer inhomogeneous photopolymer holographic diffraction structures

A theoretical model of quasimonochromatic light beams diffraction by spatially inhomogeneous transmitting multilayer diffraction structures formed in a photopolymer material by a holographic method is presented in this work. This model takes into account the heterogeneity of the amplitude profile of the first harmonic of the refractive index of each layer of the multilayer structure. The model is presented using method of transfer matrixes whose components are the solutions of the coupled waves equations of partial derivates.

Interaction between Light and Transmission Multi-Layered Heterogeneous Photopolymer Holographic Diffraction Structures

An analytical model of the diffraction of quasi-monochromatic light beams on spatially inhomogeneous multilayer diffraction structures formed in a photopolymer material by holographic means is presented. This model allows for inhomogeneities in the amplitude profile of the first harmonic of the refractive index of each layer of the multilayer structure.

Test Beams of the LPI Accelerating Complex Pakhra

In this paper, we report the characteristics of the generated beams, the extracted electron beam and the beam of secondary electrons/positrons, of the LPI accelerator complex Pakhra as of November 2019 for testing and calibrating detectors used in large accelerator and astrophysical experiments. At energies of 250–500 MeV of the electron beam ejected into Hall 1 from the S-25R synchrotron, its energy resolution is δ ~ 1% and the intensity can be changed by collimators in the range of 103–1010 s–1. The quasi-monochromatic beam of secondary electrons produced in Hall 2 typically has an energy in the range of 50–300 MeV, a corresponding energy resolution of δ = 14–2%, and an intensity of ~ 102 s–1. The performed simulation of the characteristics of the secondary positron beam allowed selecting the optimal geometry of the setup and showed good agreement with the experimental data obtained later.