Photons Of Different Energies Research Articles

Fluorescence Excitation Spectroscopy of Glucose Molecules

The measurement technique and the results obtained by optical spectroscopy during excitation of glucose molecules by photons are described. For the first time, the photoluminescence spectra of glucose were studied in the wavelength range 400-700 nm upon excitation by photons of different energies 3.26-4.51 eV. Peculiarities were found in the luminescence spectra (radiation intensity, positions of maxima), indicating the excitation of the OH hydroxyl radical and the COH carbonyl group as fragments of the glucose molecule by photon impact. X-ray diffraction spectra were measured, which confirmed the presence of glucose hydrate in the studied samples and certain structural changes after interaction with photons. It has been shown that photon irradiation results in modification of glucose molecular crystals both at the macro and micro levels.

Spectral information from photon statistics in x-ray radiography and computed tomography

Measuring spectral information requires distinguishing photons of different energies, typically achieved using filters or advanced detectors sensitive to individual photons. We prove that when the arrival of photons follows a Poisson distribution (i.e., is shot-noise dominated), the variance and mean of the total photon energy collected over a fixed interval provide independent information about the photon energy spectrum. This immediately leads to several striking corollaries. First, the variance data can be used in the same way as the mean data in both x-ray radiography and tomography. Second, the ratio of the variance data and mean data provides an indication of the average energy of the photon spectrum. Third, the variance data, when compared to the mean data, reveal information analogous to using a higher-energy spectrum. These corollaries show that spectral information can be recovered even from common x-ray detectors which only measure aggregate photon energy. As a demonstration, we performed beam-hardening correction in computed tomography using variance data for both simulations and experiments. We also achieved quantitative tomographic reconstruction in simulation and recover accurate attenuation coefficient values in addition to material density and atomic number.

Constraints on quantum gravity and the photon mass from gamma ray bursts

Lorentz invariance violation in quantum gravity (QG) models or a nonzero photon mass, $m_\gamma$, would lead to an energy-dependent propagation speed for photons, such that photons of different energies from a distant source would arrive at different times, even if they were emitted simultaneously. By developing source-by-source, Monte Carlo-based forward models for such time delays from gamma ray bursts, and marginalising over empirical noise models describing other contributions to the time delay, we derive constraints on $m_\gamma$ and the QG length scale, $\ell_{\rm QG}$, using spectral lag data from the BATSE satellite. We find $m_\gamma < 4.0 \times 10^{-5} \, h \, {\rm eV}/c^2$ and $\ell_{\rm QG} < 5.3 \times 10^{-18} \, h \, {\rm \, GeV^{-1}}$ at 95% confidence, and demonstrate that these constraints are robust to the choice of noise model. The QG constraint is among the tightest from studies which consider multiple gamma ray bursts and the constraint on $m_\gamma$, although weaker than from using radio data, provides an independent constraint which is less sensitive to the effects of dispersion by electrons.

On measuring the Hubble constant with X-ray reverberation mapping of active galactic nuclei

ABSTRACT We show that X-ray reverberation mapping can be used to measure the distance to type 1 active galactic nuclei (AGNs). This is because X-ray photons originally emitted from the ‘corona’ close to the black hole irradiate the accretion disc and are reemitted with a characteristic ‘reflection’ spectrum that includes a prominent ∼6.4 keV iron emission line. The shape of the reflection spectrum depends on the irradiating flux, and the light-crossing delay between continuum photons observed directly from the corona and the reflected photons constrain the size of the disc. Simultaneously modelling the X-ray spectrum and the time delays between photons of different energies therefore constrains the intrinsic reflected luminosity, and the distance follows from the observed reflected flux. Alternatively, the distance can be measured from the X-ray spectrum alone if the black hole mass is known. We develop a new model of our reltrans X-ray reverberation mapping package, called rtdist, that has distance as a model parameter. We simulate a synthetic observation that we fit with our new model, and find that this technique applied to a sample of ∼25 AGNs can be used to measure the Hubble constant with a 3σ statistical uncertainty of ${\sim} 6\,{\rm km}\,{\rm s}^{-1}\, {\rm Mpc}^{-1}$. Since the technique is completely independent of the traditional distance ladder and the cosmic microwave background radiation, it has the potential to address the current tension between them. We discuss sources of modelling uncertainty, and how they can be addressed in the near future.

Striking complexity of the photon field in medical devices with heterogeneous density distribution and challenges for industrial irradiators

Despite the emergence of electron beam sterilization, photons are, and most likely will remain the most commonly used agents for radiation sterilization of medical devices. While it is generally accepted that dose gradients have to be carefully addressed in electron beam dose mapping experiments, photon fields are regarded as permissively with respect to performance qualification and aroused little attention for systematic studies.In this paper a computational approach utilizing Monte Carlo simulation is taken to study dose characteristics from cobalt-60 and X-ray sources. The Compton effect as most important interaction mechanism and its impact on dose distribution are studied in detail. The core of the paper deals with attenuation effects by high density objects, particularly steel cylinders, where the dose along the circumference is computed for parallel photons of different energies, colbalt-60 and 7 MeV X-rays. Model results are validated by dedicated experiments in Co-60 and X-ray irradiators.The paper summarizes that dose distributions in photon field show a striking complexity for inhomogeneous materials, especially when photons are collimated in a parallel beam. In general, results suggest that more attention needs to be paid to dose gradients in performance qualification of medical devices with an inhomogeneous mass distribution and generic dosimeter grids inspired from operational qualification are not appropriate.

GrailQuest: hunting for atoms of space and time hidden in the wrinkle of Space-Time

GrailQuest (Gamma Ray Astronomy International Laboratory for QUantum Exploration of Space-Time) is a mission concept based on a constellation (hundreds/thousands) of nano/micro/small-satellites in low (or near) Earth orbits. Each satellite hosts a non-collimated array of scintillator crystals coupled with Silicon Drift Detectors with broad energy band coverage (keV-MeV range) and excellent temporal resolution (≤ 100 nanoseconds) each with effective area sim 100 text {cm}^{2}. This simple and robust design allows for mass-production of the satellites of the fleet. This revolutionary approach implies a huge reduction of costs, flexibility in the segmented launching strategy, and an incremental long-term plan to increase the number of detectors and their performance; this will result in a living observatory for next-generation, space-based astronomical facilities. GrailQuest is conceived as an all-sky monitor for fast localisation of high signal-to-noise ratio transients in the X-/gamma-ray band, e.g. the elusive electromagnetic counterparts of gravitational wave events. Robust temporal triangulation techniques will allow unprecedented localisation capabilities, in the keV-MeV band, of a few arcseconds or below, depending on the temporal structure of the transient event. The ambitious ultimate goal of this mission is to perform the first experiment, in quantum gravity, to directly probe space-time structure down to the minuscule Planck scale, by constraining or measuring a first-order dispersion relation for light in vacuo. This is obtained by detecting delays between photons of different energies in the prompt emission of Gamma-Ray Bursts.

Efficiency calibration and coincidence summing correction for a NaI(Tl) spherical detector

Spherical NaI(Tl) detectors are used in gamma-ray spectrometry, where the gamma emissions come from the nuclei with energies in the range from a few keV up to 10 MeV. A spherical detector is aimed to give a good response to photons, which depends on their direction of travel concerning the detector center. Some distortions in the response of a gamma-ray detector with a different geometry can occur because of the non-uniform position of the source from the detector surface. The present work describes the calibration of a NaI(Tl) spherical detector using both an experimental technique and a numerical simulation method (NSM). The NSM is based on an efficiency transfer method (ETM, calculating the effective solid angle, the total efficiency, and the full-energy peak efficiency). Besides, there is a high probability for a source-to-detector distance less than 15 cm to have pulse coincidence summing (CS), which may occur when two successive photons of different energies from the same source are detected within a very short response time. Therefore, γ-γ ray CS factors are calculated numerically for a152Eu radioactive cylindrical source. The CS factors obtained are applied to correct the measured efficiency values for the radioactive volumetric source at different energies. The results show a good agreement between the NSM and the experimental values (after correction with the CS factors).

Absolute Double Differential Cross Sections of Bremsstrahlung Produced from 4.0 keV Electrons Incident on Free Ar Atoms

New results are reported on the measurements of absolute double differential cross sections (DDCSs) of bremsstrahlung produced from 4.0 keV electrons incident on free Ar atoms in the angular detection range of 45°–120°. A significant reduction of the thick target bremsstrahlung (TTB) of the chamber wall and of the photon transmission windows has been achieved by modifying the experimental set-up used previously; a large reduction of TTB in the present experiments is supported by the results of our model calculations for the ratio of TTB background to the normal bremsstrahlung (NB) spectrum carried out for the employed geometry of the experimental set-up. The results of photon energy distribution measured at different angles and those of angular distributions of photons of a given energy are compared with theoretical predictions of Kissel–Quarles–Pratt (KQP) theory for ordinary bremsstrahlung and with predictions of total bremsstrahlung including polarization bremsstrahlung (PBS) of the stripping approximation (SA). A satisfactory agreement observed between experiment and predictions using SA theory for absolute DDCSs of bremsstrahlung provides evidence for an appreciable contribution of polarization bremsstrahlung at the considered impact energy of electrons on one hand, while on the other hand, it exhibits a large discrepancy (about a factor of 2) in DDCSs of bremsstrahlung photons obtained by experiment and by KQP theory for photon energy distributions at all detection angles measured in these experiments. In addition, present results of the angular dependence of photons of different energies show anisotropic distributions and they are found to be in reasonable agreement with both KQP and SA theories. The satisfactory agreement between experiment and theory for angular distributions is an indication of a significant reduction of the background produced from TTB photons.

Estimating relationship between the time over threshold and energy loss by photons in plastic scintillators used in the J-PET scanner

PurposeThe time-over-threshold (TOT) technique is being used widely due to itsimplications in developing the multi-channel readouts, mainly when fast signal processing is required. Using the TOT technique, as a measure of energy loss instead of charge integration methods, significantly reduces the signal readout costs by combining the time and energy information. Therefore, this approach can potentially be utilized in J-PET tomograph which is built from plastic scintillators characterized by fast light signals. The drawback in adopting this technique lies in the non-linear correlation between input energy loss and TOT of the signal. The main motivation behind this work is to develop the relationship between TOT and energy loss and validate it by the J-PET tomograph setup.MethodsThe experiment was performed using a 22Na beta emitter source placed in the center of the J-PET tomograph. This isotope produces photons of two different energies: 511 keV photons from the positron annihilation (direct annihilation or through the formation of a para-positronium atom or pick-off process of ortho-positronium atoms) and a 1275 keV prompt photon. This allows the study of the correlation between TOT values and energy loss for energy ranges up to 1000 keV. Since the photon interacts predominantly via Compton scattering inside the plastic scintillator, there is no direct information of the energy deposition. However, using the J-PET geometry, one can measure the scattering angle of the interacting photon. Since the 22Na source emits photons of two different energies, it is necessary to know unambiguously the energy of incident photons and their corresponding scattering angles in order to estimate energy deposition. In summary, this work presents a dedicated algorithm developed to tag photons of different energies and studying their scattering angles to calculate the energy deposition by the interacting photons.ResultsA new method was elaborated to measure the energy loss by photons interacting with plastic scintillators used in the J-PET tomograph. We find the relationship between the energy loss and TOT is non-linear and can be described by the functions TOT = A0 + A1 * ln(E dep + A2) + A3 * (ln(E dep + A2))2 and TOT = A0 - A1 * A2^{E_{dep}}phantom {dot {i}!}. In addition, we also introduced a theoretical model to calculate the TOT as a function of energy loss in plastic scintillators.ConclusionsA relationship between TOT and energy loss by photons interacting inside the plastic scintillators used in J-PET scanner is established for a deposited energy range of 100–1000 keV.

Decay Kinetics of CeF3 under VUV and X-ray Synchrotron Radiation

Characteristic dimensions and evolution times of regions of secondary electronic excitations created by the interaction of ionizing radiation with matter cannot be measured directly. At the same time these are essential parameters both for engineering of nanostructured composite materials defining optimal layer thickness and nanoparticles radii and for the development of optimized scintillators. The paper demonstrates how such spatial and temporal data can be extracted from luminescence decay kinetics excited by vacuum ultraviolet (VUV) and X-ray photons at modern sources of synchrotron radiation MAX IV and PETRA III. Specific features of energy-band structure of self-activated crystal CeF3 are discussed, and its potential for a super-fast detection of ionizing radiation evaluated. Diffusion-controlled dipole–dipole interaction of Frenkel excitons is demonstrated to account well for the luminescence non-exponential decay kinetics providing information on the scales of excited regions created by photons of different energy. For 20 eV photons the radius of excited regions is estimated to be 10 nm, and for 200 eV photons it increases to 18 nm. Effective radius of excited regions of complicated shape created by 19 keV is as large as 80 nm and the diffusion length of Frenkel excitons over radiative time is 14 nm.

Construction of Response Function of TES X-ray Microcalorimeter for STEM-EDS

A quantitative microanalysis of astromaterials (e.g., meteorite, returned samples from asteroids) is a key technology to understand the history of our solar system formation. To fulfill this, we developed an energy-dispersive X-ray spectroscopy (EDS) using a transition-edge sensor (TES) microcalorimeterarray on a scanning transmission electron microscope (STEM) for material analysis. To reduce the systematic errors of a spectral analysis, we investigated and constructed the response function of the STEM-EDS system, which consists of detection efficiency and a two-dimensional response matrix. The latter represents the pulse-height redistribution functions of the incident photons of different energies. Using the constructed response function, we demonstrated the quantitative determination of SiO $_2$ film and confirmed that the number–density ratio of oxygen to silicon (=2.29 $^{+0.32}_{-0.29}$ ) is consistent with the expected value of 2 within the statistical errors. We further study the systematic errors of the concentration determination with simulations. We analyze the simulated spectra of TES-EDS and SDD (silicon drift detector)-EDS without a priori knowledge about the continuum spectra and find that the systematic deviations of parameters from the model values are smaller than 1% for TES-EDS and larger than 10% for SDD-EDS.

Measurement of the relative non-degenerate two-photon absorption cross-section for fluorescence microscopy.

In non-degenerate two-photon microscopy (ND-TPM), the required energy for fluorescence excitation occurs via absorption of two photons of different energies derived from two synchronized pulsed laser beams. ND-TPM is a promising imaging technology offering flexibility in the choice of the photon energy for each beam. However, a formalism to quantify the efficiency of two-photon absorption (TPA) under non-degenerate excitation, relative to the resonant degenerate excitation, is missing. Here, we derive this formalism and experimentally validate our prediction for a common fluorophore, fluorescein. An accurate quantification of non-degenerate TPA is important to optimize the choice of photon energies for each fluorophore.

Tetrazolium salts-Pluronic F-127 gels for 3D radiotherapy dosimetry

This work is a follow-up study for a recently-proposed 3D radiochromic gel dosimeter that contains a tetrazolium salt and a physical gel matrix made of poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) (Pluronic F-127). Several tetrazolium salts were examined in this work, including tetrazolium violet, blue tetrazolium chloride, nitro blue tetrazolium chloride (NBT), tetranitro blue tetrazolium chloride (tNBT) and thiazolyl blue tetrazolium bromide (TBTB). The salt-containing gel dosimeters were compared with the first Pluronic gel composition that contained 2,3,5-triphenyltetrazolium chloride (TTC) as the radiation-sensitive component (dose sensitivity of 0.0023 (Gy cm)−1). The Pluronic gels with NBT and tNBT outperformed the other gels, including the TTC-containing gel, with respect to their dose sensitivity and low dose-response. The NBT gels were found to have better stability over time than tNBT gels. Sensitization of the gels to ionizing radiation was examined by addition of tert-butyl alcohol and sodium formate. The best composition was 0.0818% NBT (1 mM), 25% Pluronic F-127 and 0.136 × 10−2% sodium formate. This gel dosimeter was insensitive to changes in dose rate for photons of different energies. The mean dose sensitivity amounted to 0.0047 ± 0.1 × 10−4 (Gy cm)−1. A diversion in the dose-response was observed for the gel irradiated with electrons. Additional characteristics of the NBT gel were a linear-dose range and a dynamic-dose range between <1 and ⩾150 Gy and a dose threshold of <1 Gy. The dose distribution registered for the NBT-Pluronic gel was stable after irradiation for over 7 d with no visible diffusion of the irradiated part, which is analogous to the original TTC-Pluronic gel.

Systematic implementation of spectral CT with a photon counting detector for liquid security inspection

X-ray liquid security inspection system plays an important role in homeland security, while the conventional dual-energy CT (DECT) system may have a big deviation in extracting the atomic number and the electron density of materials in various conditions. Photon counting detectors (PCDs) have the capability of discriminating the incident photons of different energy. The technique becomes more and more mature in nowadays. In this work, we explore the performance of a multi-energy CT imaging system with a PCD for liquid security inspection in material discrimination. We used a maximum-likelihood (ML) decomposition method with scatter correction based on a cross-energy response model (CERM) for PCDs so that to improve the accuracy of atomic number and electronic density imaging. Experimental study was carried to examine the effectiveness and robustness of the proposed system. Our results show that the concentration of different solutions in physical phantoms can be reconstructed accurately, which could improve the material identification compared to current available dual-energy liquid security inspection systems. The CERM-base decomposition and reconstruction method can be easily used to different applications such as medical diagnosis.

Feasibility of beta-particle radioguided surgery for a variety of “nuclear medicine” radionuclides

PurposeBeta-particle radioguided tumor resection may potentially overcome the limitations of conventional gamma-ray guided surgery by eliminating, or at least minimizing, the confounding effect of counts contributed by activity in adjacent normal tissues. The current study evaluates the clinical feasibility of this approach for a variety of radionuclides. Nowadays, the only β- radioisotope suited to radioguided surgery is 90Y. Here, we study the β- probe prototype capability to different radionuclides chosen among those used in nuclear medicine. MethodsThe counting efficiency of our probe prototype was evaluated for sources of electrons and photons of different energies. Such measurements were used to benchmark the Monte Carlo (MC) simulation of the probe behavior, especially the parameters related to the simulation of the optical photon propagation in the scintillation crystal. Then, the MC simulation was used to derive the signal and the background we would measure from a small tumor embedded in the patient body if one of the selected radionuclides is used. ResultsBased on the criterion of detectability of a 0.1 ml tumor for a counting interval of 1 s and an administered activity of 3 MBq/kg, the current probe yields a detectable signal over a wide range of Standard Uptake Values (SUVs) and tumor-to-non-tumor activity-concentration ratios (TNRs) for 31Si, 32P, 97Zr, and 188Re. Although efficient counting of 83Br, 133I, and 153Sm proved somewhat more problematic, the foregoing criterion can be satisfied for these isotopes as well for sufficiently high SUVs and TNRs.

Curved spacetimes with local κ -Poincaré dispersion relation

We use our previously developed identification of dispersion relations with Hamilton functions on phase space to locally implement the $\kappa$-Poincar\'e dispersion relation in the momentum spaces at each point of a generic curved spacetime. We use this general construction to build the most general Hamiltonian compatible with spherical symmetry and the Plank-scale-deformed one such that in the local frame it reproduces the $\kappa$-Poincar\'e dispersion relation. Specializing to Planck-scale-deformed Schwarzschild geometry, we find that the photon sphere around a black hole becomes a thick shell since photons of different energy will orbit the black hole on circular orbits at different altitudes. We also compute the redshift of a photon between different observers at rest, finding that there is a Planck-scale correction to the usual redshift only if the observers detecting the photon have different masses.

Simulation of Single-Diode Equivalent Model of Polycrystalline Silicon Solar Cells

A solar module is composed of photons of different energies, and some are absorbed at the p-n junction. A single-diode equivalent model is used to describe the electronic properties of solar cells. The theory as well as the construction and working of photovoltaic cells using single-diode method are also presented. So, choosing a electrical equivalent model can is based on area in which we would like to realize for study of solar cell characteristics. Parameters solar cell (Short-Circuit Current, Open-Circuit Voltage) are changed due to changing the light intensity and temperature. In the current paper we present the effect of temperature, series resistance and shunt resistance on the (P-V) characteristics simulated in Matlab/Simulink.

Bayesian framework to constrain the photon mass with a catalog of fast radio bursts

A hypothetical photon mass, $m_\gamma$, gives an energy-dependent light speed in a Lorentz-invariant theory. Such a modification causes an additional time delay between photons of different energies when they travel through a fixed distance. Fast radio bursts (FRBs), with their short time duration and cosmological propagation distance, are excellent astrophysical objects to constrain $m_\gamma$. Here for the first time we develop a Bayesian framework to study this problem with a catalog of FRBs. Those FRBs with and without redshift measurement are both useful in this framework, and can be combined in a Bayesian way. A catalog of 21 FRBs (including 20 FRBs without redshift measurement, and one, FRB 121102, with a measured redshift $z=0.19273 \pm 0.00008$) give a combined limit $m_\gamma \leq 8.7 \times 10^{-51}\, {\rm kg}$, or equivalently $m_\gamma \leq 4.9 \times 10^{-15}\, {\rm eV}/c^2$ ($m_\gamma \leq 1.5\times10^{-50} \, {\rm kg}$, or equivalently $m_\gamma \leq 8.4 \times 10^{-15} \,{\rm eV}/c^2$) at 68% (95%) confidence level, which represents the best limit that comes purely from kinematics. The framework proposed here will be valuable when FRBs are observed daily in the future. Increment in the number of FRBs, and refinement in the knowledge about the electron distributions in the Milky Way, the host galaxies of FRBs, and the intergalactic median, will further tighten the constraint.

Light speed variation from gamma-ray bursts

The effect of quantum gravity can bring a tiny light speed variation which is detectable through energetic photons propagating from gamma ray bursts (GRBs) to an observer such as the space observatory. Through an analysis of the energetic photon data of the GRBs observed by the Fermi Gamma-ray Space Telescope (FGST), we reveal a surprising regularity of the observed time lags between photons of different energies with respect to the Lorentz violation factor due to the light speed energy dependence. Such regularity suggests a linear form correction of the light speed v(E)=c(1−E/ELV), where E is the photon energy and ELV=(3.60±0.26)×1017GeV is the Lorentz violation scale measured by the energetic photon data of GRBs. The results support an energy dependence of the light speed in cosmological space.

ON TESTING THE EQUIVALENCE PRINCIPLE WITH EXTRAGALACTIC BURSTS

ABSTRACT An interesting test of Einstein’s equivalence principle (EEP) relies on the observed lag in the arrival times of photons emitted from extragalactic transient sources. Attributing the lag between photons of different energies to the gravitational potential of the Milky Way (MW), several authors derive new constraints on deviations from EEP. It is shown here that potential fluctuations from the large-scale structure are at least two orders of magnitude larger than the gravitational potential of the MW. Combined with the larger distances, for sources at redshift z ≳ 0.5 the rms of the contribution from these fluctuations exceeds the MW by more than four orders of magnitude. We provide actual constraints for several objects based on a statistical calculation of the large-scale fluctuations in the standard ΛCDM cosmological model.