Compton Spectroscopy Research Articles

Compton spectroscopy analysis of Eu2O3 and applicability of first and second order GGA in deducing electron momentum densities

To validate the available experimental momentum densities (measured using 662 keV radiations) of a rare earth oxide Eu2O3, first and second order generalized gradient approximations (GGA and SOGGA) of density functional theory (DFT) have been employed to compute Compton profiles (CPs). The DFT computations have been performed within linear combination of atomic orbitals (LCAO) method. It is found that both the computed CPs reconcile with the experimental Compton line shape. Present comparison shows almost similar role of exchange and correlation potentials of GGA and SOGGA in predicting the electronic structures of the studied oxide, admittedly with a marginal better agreement with first order GGA approximation. Also, the anisotropies in CPs (J110-J100, J110-J100 and J111-J110) from GGA and SOGGA are found to be identical which strongly support the present investigations. The Fourier transform of CPs leading to real space B(z) functions concludes a metallic nature of Eu2O3.

Assessment of hybrid density functional in revealing electronic response and half-metallic character of TM2O3 (TM = Ti, V and Cr) and their Compton spectroscopy

Assessment of hybrid density functional in revealing electronic response and half-metallic character of TM2O3 (TM = Ti, V and Cr) and their Compton spectroscopy

On the mere exigency of exchange potential in ab initio calculations of nanocobalt ferrites: Compton spectroscopy and band structure calculations

On the mere exigency of exchange potential in ab initio calculations of nanocobalt ferrites: Compton spectroscopy and band structure calculations

Inelastic scattering and first principles study of tritium breeder materials Li2TiO3 and Li2ZrO3

First ever Compton spectroscopy of Li2TiO3 (LTO) and Li2ZrO3 (LZO) have been performed using 100 mCi 241Am Compton spectrometer. The experimental electron momentum densities (EMDs) of these compounds are compared with the theoretical EMDs computed using various generalized gradient approximations (GGA) under linear combination of atomic orbitals (LCAO) method namely Becke-Lee-Yang-Parr (BLYP), Perdew-Burke-Ernzerhof (PBE), revised Perdew-Burke-Ernzerhof for solids (PBEsol) and Perdew-Wang GGA (PWGGA). The BLYP based theoretical Compton profiles show best agreement with the experimental data for both the Li-ceramics. The electronic structure calculations predicted indirect band gap nature of both compounds with major contributions of Ti-3d, Zr-4d and O-2p states with some minor part due to Li-2sp states around Fermi energy. Further, experimental EVED profiles anticipated more covalent or less ionic character of LTO as compared to LZO. The elastic properties calculations verified mechanical stability of both compounds at ambient temperature and pressure. In addition, the optical properties of LTO and LZO are derived using full potential linearized augmented plane wave (FP-LAPW) method, which revealed high absorbent feature and photoconductive behavior of both compounds in UV region. Moreover, large values of electrical and thermal conductivities at high temperature make them suitable candidates for electrode materials in Li-ion batteries.

High-resolution Compton spectroscopy using x-ray microcalorimeters.

X-ray Compton spectroscopy is one of the few direct probes of the electron momentum distribution of bulk materials in ambient and operando environments. We report high-resolution inelastic x-ray scattering experiments with high momentum and energy transfer performed at a storage-ring-based high-energy x-ray light source facility using an x-ray transition-edge sensor (TES) microcalorimeter detector. The performance was compared with a silicon drift detector (SDD), an energy-resolving semiconductor detector, and Compton profiles were measured for lithium and cobalt oxide powders relevant to lithium-ion battery research. Spectroscopic analysis of the measured Compton profiles demonstrates the high-sensitivity to the low-Z elements and oxidation states. The line shape analysis of the measured Compton profiles in comparison with computed Hartree-Fock profiles is usually limited by the resolution of the semiconductor detector. We have characterized an x-ray TES microcalorimeter detector for high-resolution Compton scattering experiments using a bending magnet source at the Advanced Photon Source with a double crystal monochromator, providing monochromatic photon energies near 27.5keV. The momentum resolution below 0.16 atomic units (a.u.) was measured, yielding an improvement of more than a factor of 7 over a state-of-the-art SDD for the same scattering geometry. Furthermore, the lineshapes of narrow valence and broad core electron profiles of sealed lithium metal were clearly resolved using an x-ray TES compared to smeared and broadened lineshapes observed when using the SDD. High-resolution Compton scattering using the energy-resolving area detector shown here presents new opportunities for spatial imaging of electron momentum distributions for a wide class of materials with applications ranging from electrochemistry to condensed matter physics.

Extending the energy range of AstroSat-CZTI up to 380 keV with compton spectroscopy

ABSTRACT The CZTI (Cadmium Zinc Telluride Imager) onboard AstroSat is a high energy coded mask imager and spectrometer in the energy range of 20–100 keV. Above 100 keV, the dominance of Compton scattering cross-section in CZTI results in a significant number of 2-pixel Compton events and these have been successfully utilized for polarization analysis of Crab pulsar and nebula (and transients like Gamma-ray bursts) in 100–380 keV. These 2-pixel Compton events can also be used to extend the spectroscopic energy range of CZTI up to 380 keV for bright sources. However, unlike the spectroscopy in primary energy range, where simultaneous background measurement is available from masked pixels, Compton spectroscopy requires blank sky observation for background measurement. Background subtraction, in this case, is non-trivial because of the presence of both short-term and long-term temporal variations in the data, which depend on multiple factors like earth rotation and the effect of South Atlantic Anomaly (SAA) regions etc. We have developed a methodology of background selection and subtraction that takes into account for these effects. Here, we describe these background selection and subtraction techniques and validate them using spectroscopy of Crab in the extended energy range of 30–380 keV region, and compare the obtained spectral parameters with the INTEGRAL results. This new capability allows for the extension of the energy range of AstroSat spectroscopy and will also enable the simultaneous spectropolarimetric study of other bright sources like Cygnus X-1.

Electronic and optical responses, Compton spectroscopy and manifestation of trapping centres of LiF:Mg,Ti

Electronic structure to judge trapping centres and activation energies in Mg-doped (2–8%) and Mg,Ti co-doped (2–3% each) LiF phosphors are presented using full-potential linearized APW method. Compton measurement for LiF is performed for appropriate choice of exchange-correlation potentials used in electronic properties. It is seen that 2–6% of Mg activator leads to formation of electronic traps with activation energy between 0.79 and 0.49 eV. At high concentration (>6%) of Mg, the formation of trap centres vanishes. Co-doping of 2% Mg,Ti permits the formation of trap centres, which is in contrast to higher concentrations. Mg-3s states play key role in the building of electronic trap centres. Higher concentration of Ti and Mg activators in LiF leads to the widening of 3d and 3s states, respectively. Analysis of optical response (frequency-dependent dielectric constants, trapping centres, and absorption coefficients) of 2% Mg-doped and 2% Mg,Ti co-doped LiF suggest their dosimetric applications and in ultra-violet detection.

Validation of hybrid WC1LYP functional for ferroelectric LiNbO3 and LiTaO3 using Compton spectroscopy and first-principles computations

Electronic structure and theoretical momentum densities (EMDs) of LiNbO3 and LiTaO3 using linear combination of atomic orbitals (LCAO) scheme are deduced. Present energy bands and density of states using local density approximation, generalised gradient approximation and hybrid (HF + DFT) PBE0 and WC1LYP schemes show a direct band gap (varying between 3.13- 5.13 eV and 3.11–5.18 eV for LiNbO3 and LiTaO3, respectively) at Γ point of Brillouin zones. The WC1LYP hybrid functional based EMDs depict reasonable agreement with present experimental Compton lines (using 100 mCi Am-241 γ-ray Compton spectrometer) than other investigated exchange-correlation potentials, thereby suggesting the applicability of hybrid model like WC1LYP in such ferroelectrics. Accuracy of energy bands is also ensured via electronic and optical properties using modified Becke–Johnson potential as facilitated in the full-potential linearized augmented plane wave method. Presently reported UV–vis measurements for optical band gaps are in consonance with the hybrid potential (WC1LYP) for the both ferroelectrics, which further confirms usefulness of hybrid scheme. Moreover, equal–valence–electron–density scaled experimental data reveal more covalent character of LiNbO3 than that in LiTaO3, which is in agreement with the present LCAO based Mulliken's population analysis.

Hydrogen-bond network distortion of water in the soft confinement of Nafion membrane.

A Compton spectroscopy investigation is carried out in hydrated Nafion membranes, enabling identification of distortions in the hydrogen-bond distribution of the polymer hydrating water by means of the subtle changes reflected by the Compton profiles. Indeed, deformations of the Compton profiles are observed when varying hydration, and two different bonding kinds are associated with the water molecules: at low hydration, water surrounds the sulfonic groups, while on increasing hydration, water molecules occupy the interstitial cavities formed upon swelling of the membrane. The analysis is proposed in terms of averaged OH bond length variation. A sizable contraction of the OH distance is observed at low hydration (∼0.09 Å), while at higher hydration levels, the contraction is smaller (∼0.02 Å) and the OH bond length is closer to bulk water. An evaluation of the electron kinetic energy indicates that the spatial changes associated with the water distribution correspond to a consistent binding energy increase. Distinct temperature dependences of each water population are observed, which can be straightly related to water desorption into ice on cooling below the freezing point.

Influence of Te doping in titanium dichalcogenides: LCAO calculations and Compton spectroscopy

Role of Te doping in titanium disulfide using linear combination of atomic orbitals method and Compton spectroscopy is reported. The theoretical Compton profiles (CPs) of TiSTe derived using various exchange and correlation potentials like Perdew-Burke-Ernzerhof, Perdew-Wang generalized gradient approximation and von Barth-Hedin (VBH) are compared with corresponding experimental CP to check the applicability of considered potentials. From the total and partial density of states, we observe that doping of Te at S site vanishes the narrow band gap of TiS2 leading to metallic character of TiSTe. A good agreement between experimental and VBH potential based CP of TiSTe shows better performance of VBH approximation in this mixed metal-like dichalcogenide.

Electronic structure of tantalum dichalcogenide using Compton scattering technique and density functional theory

Compton spectroscopy measurements on tantalum dichalcogenide TaS0.5Se1.5 using a 100 mCi Am-241 γ-ray Compton spectrometer are presented. Experimental Compton profile (CP) is compared with those computed using linear combination of atomic orbitals (LCAO) method within the density functional theory (DFT) and hybrid functionals of Hartree-Fock and DFT. Hybrid functional namely WC1LYP based CP is found in better accordance with the experimental CP. The relative nature of bonding in TaS0.5Se1.5 and TaSSe is interpreted by scaling the experimental CP on equal-valence-electron-density and Mulliken's population analysis. Origin of metallic behaviour of TaS0.5Se1.5 is discussed in terms of energy bands and density of states. It is seen that the 5d states of Ta dominate around the Fermi level leading to metallic character of the compound. Fermi surface topology and optical response like dielectric constants, absorption coefficients, etc. of TaS0.5Se1.5 are also described using modified Becke-Johnson theory of full-potential linearized augmented plane wave approach.

High energy γ-ray Compton spectroscopy and electronic response of rare earth sesquioxides Er2O3 and Yb2O3

In this paper, we present Compton profiles (CPs) of sesquioxides Er2O3 and Yb2O3 using 662 keV gamma-rays emitted by 20 Ci 137Cs source. To validate experimental momentum densities, theoretical CPs, energy bands, density of states (DOS), Mulliken's population of the both sesquioxides have been computed using linear combination of atomic orbitals (LCAO) method with pure and hybrid density functional theory (DFT). Present CP measurements confirm the applicability of hybrid (HF+DFT) approximation, namely WC1LYP, for predicting electron momentum densities and thereby electronic properties of such rare earth oxides. Energy bands and DOS unambiguously show insulating nature of the both compounds and the band gap values are found to be in tune with the available data. Further, the nature of bonding in Er2O3 and Yb2O3 is explained interms of the Mulliken's population and equally normalized CPs. Sharpness in Compton lines is also discussed in terms of localization of valence 5d states.

Preface

The 1st National Conference on “Recent Advancements in Physical Sciences” (NCRAPS-2019) during December 19-20, 2019 at National Institute of Technology, Uttarakhand, Satellite Campus, MNIT Jaipur, India is jointly organized by Departments of Chemistry, Physics and Mathematics, NIT, Uttarakhand.NCRAPS-2019 has been deliberated to showcase research accomplishments and to enrich the educational experience in Basic Sciences with focus on emerging multidisciplinary research areas viz. Biophysics, Nanotechnology & Materials Science, Fluid Mechanics & Biomechanics, Applied Mathematics & Analysis, Optical Sensors/Devices, Modelling and Simulation of Molecules/Advanced Materials, etc. The details of the conference are available at www.nituk.ac.in/ncraps19/. The conference organizing committee has invited three keynote speakers and over dozen domain experts to deliver expert talks. The three keynote speakers covered the different areas of the conference i.e. 1. Prof. Rama Bhargava (Indian Institute of Technology, Roorkee) on “Exploring The Potential Of Mathematics”, 2. Prof. B. L. Ahuja (MLS University, Udaipur) will be talking on “Compton Spectroscopy and Electronic Response of Functional Materials”and 3. Prof. Rajeev Gupta (University of Delhi, Delhi) on “Designer Molecular Architectures: Applications In Catalysis, Solid-State Sensing And Energy Transfer”.The conference received in all 65 extended abstract submissions which were peer reviewed and 55 have been accepted for oral presentation. The abstracts have been split between two technical sessions in conference broad subject areas of Chemistry, Mathematics and Physics. The participants across the great country India made the conference of national scope. The two day conference with nearly 55 oral presentations created the heart of the conference and provided ample opportunity for discussion during the conference. The organizing committee will stringently examine the best research accomplishments out of 56 shortlisted abstracts and the work selected in second round will be processed to the full paper publication in Institute of Physics (IOP) as conference proceedings.As conferencechairs/secretaries, we have many people to thank and would like to put the appreciation of their contribution on record. In this regard, the largest burden fell upon the experienced shoulders of Keynote speakers, Invited speakers, Session chairs and our technical reviewers along with substantial assistance received from active student volunteers. Therefore, these are the foremost in the list of people to be thanked.We also thank to all the authors who submitted their papers. It was both a privilege and a great responsibility to oversee the reviewing of submitted papers. We sincerely thank to our Patron, Prof.Shyam Lal Soni, Director, NITUK and Sponsors State Bank of India and Paru Graphics Srinagar (Garhwal), Uttarakhand for generous financial support to the conference and helping us to make this event successful.Welcome you all to the pink City of Jaipur!Thank you!Conference Chair(s)/Secretaries

Study of magnetism in Fe doped CoCr2O4 using magnetic Compton scattering and first-principles computations

Temperature dependent spin momentum densities of polycrystalline CoCr2-xFexO4 (x = 0.4 and 1) with inverse spinel structure have been measured using magnetic Compton spectrometer. Estimated site specific and absolute spin moments are compared with the magnetization measurements to deduce the orbital magnetic moments. To supplement the present magnetic Compton scattering data, spin-polarized relativistic band structure calculations employing Korringa-Kohn-Rostoker Green’s-function formalism have also been performed. Ferri-magnetic nature of CoCr2-xFexO4 (x = 0.4 and 1) systems have been explained on the basis of distribution of Fe and Co atoms between tetrahedral and octahedral sites. The suggested mixed spinel structure arrangement is supported by experimentally observed spin magnetic moments and minimum ground state energies which shows the potential of magnetic Compton spectroscopy in resolving the structural-cum-magnetic issues of such oxides.

High energy X-ray Compton spectroscopy via iterative reconstruction

In this paper, we report on the design and implementation of a compact and robust Compton spectrometer capable of measuring x-rays in the energy range 1 to 20 MeV. An iterative reconstruction method was employed to reconstruct the x-ray spectrum without assuming an initial distribution function. Spectral resolution was further optimized by judicious choice of composition and thickness of the electron-convertor, as well as angular acceptance into the spectrometer. A particle transport code was used to account for all instrument-related factors. Performance of the spectrometer was demonstrated experimentally by characterizing x-rays generated by high-order multiphoton Thomson scattering.

Magnetic properties and spin momentum densities of Ni excess Ni-Mn-Sn Heusler alloys

Abstract The role of excess Ni in Ni2+xMn1−xSn (x = 0.05, 0.1) Heusler alloys has been reported using temperature dependent magnetic Compton spectroscopy. The experimental Compton profiles from magnetic electrons have been analyzed to quantify the contribution of Mn 3d electrons, Ni sites and sp-electrons in building-up the total spin moments. The experimentally deduced spin momentum densities, total and element-specific spin moments are examined using theoretical investigations within the spin polarized relativistic Korringa-Kohn-Rostoker method. The build-up of spin moments has been explored in terms of total and projected density of states. Site-dependent Ni magnetic moment is also discussed. Heisenberg exchange coupling parameters are also computed to study the change in Ruderman-Kittel-Kasuya-Yosida type exchange interaction on increasing Ni concentration in the Ni-Mn-Sn system.

Performance of hybrid exchange-correlation potential for photocatalytic silver chromate and molybdate: LCAO theory and Compton spectroscopy

Linear combination of atomic orbitals (LCAO) method has been employed to compute the Mulliken's population (MP), energy bands, density of states (DOS), band gaps and electron momentum densities (EMDs) of Ag2TMO4 (TM = Cr and Mo). The LCAO prescription has been considered within the framework of density functional theory (DFT) and a newly suggested Hartree-Fock incorporated DFT scheme namely PBESOL0. These approximations for exchange and correlation potentials have been validated by comparing the deduced EMDs with the experimental Compton profiles using 137Cs radio isotope. It is observed that PBESOL0 scheme based EMDs show better agreement with the experimental profiles than other approximations considered in the present work. The energy bands and DOS confirm the semiconducting nature of both the Ag-based oxides. In addition, the relative nature of bonding in both the iso-electronic compounds has also been compared on the basis of equal-valence-electron-density profiles and MP data, which depict that Ag2MoO4 has more ionic character than that of Ag2CrO4.

Compton spectroscopy and electronic structure study for tetragonal barium titanate

The Compton profile of tetragonal BaTiO3 is measured using 20Ci 137Cs Compton spectrometer. The experimental data have been analyzed using theoretical electron momentum densities computed using linear combination of atomic orbitals (LCAO) with density functional theory (DFT) and the hybridization of Hartree-Fock and DFT (WC1LYP scheme). It observed that hybrid scheme WC1LYP provides a better agreement with the experimental data than other approximations of exchange-correlation (with generalized gradient approximation like PBESol, SOGGA and local density approximation like LDAPZ) as considered in the present work. In addition, the energy bands and density of states have been reported using LCAO-WC1LYP scheme. The WC1LYP hybrid method confirms wide band gap semiconducting nature of tetragonal BaTiO3. Further, a relative nature of bonding among CaTiO3, SrTiO3 and BaTiO3 has also been discussed using equal-valence-electron-density profiles and Mulliken's population analysis which predict a trend of increasing iconicity in the order CaTiO3→BaTiO3→SrTiO3.

Unfolding X-ray spectrum in the diagnostic range using the Monte Carlo Code MCNP5

Introduction: Unfolding X-ray spectrum is a powerful tool for quality control of X-ray tubes. Generally, the acquisition of the X-ray spectrum in diagnostic radiology departments is complicated and difficult due to high photon flux. Measurement of x ray spectra using radiation detectors could not be performed accurately, because of the pulse pile up. Therefore, indirect methods, including Compton spectrometry, are usually used to determine the X-ray spectrum in diagnostic energy range. The x-ray spectrum could be unfolded using radiation absorbing materials, proper detectors. Materials and Methods: The Compton scattering procedure was simulated using MCNP5 Monte Carlo code. The pulse height distributions (PHD) recorded by HPGe detector were simulated for different primary beam spectra. Then the primary spectrum was reconstructed using Tikhonov unfolding technique. Results: The results of this study indicate that this study, the x-ray spectra for 40, 50, 80, and 100kVp were unfolded with good accuracy. Conclusion: Tikhonov method may be effectively used in unfolding x ray spectra using Compton spectroscopy.

Mass-selective neutron spectroscopy of glassy versus polycrystalline structures in binary mixtures of beryllium and zirconium

Exploiting the unique tandem of VESUVIO and TOSCA inverted geometry spectrometers at the ISIS pulsed neutron and muon source in the United Kingdom, specifically the capability of VESUVIO to measure concurrently neutron diffraction and Compton spectroscopy, we have performed a global study of the structural and dynamical origins of disorder in Zr —Be metallic glasses. To this end, a polycrystalline Zr30Be70 and an amorphous Zr40Be60 systems were investigated in a wide range of temperatures ranging from 10 to 300K. For the first time, neutron diffraction has provided clues as to the structural composition of the polycrystalline Zr30Be70. The Rietveld refinement of the diffraction data has revealed that the polycrystalline system is made up of three distinct structural phases; a hexagonal phase, Be2Zr, of the P6/mmm symmetry amounting to 87.11%, a second hexagonal phase, Be5Zr, of the P6/mmm point group symmetry, amounting to 12.89%, as well as trace amounts of a third orthorhombic phase of unspecified stoichiometry. The overall sample stoichiometry, inferred from the dissection of the diffraction data, was in excellent agreement with the Compton results, both confirming the Zr30Be70 formulation. The analysis of INS data agreed very well with the theoretical results from the recursion method. The INS data were cross-validated by the nuclear momentum distributions of both Zr and Be, obtained from the analysis of the NCS data. Systematic differences between the crystalline and amorphous Zr —Be systems were identified in the whole temperature range and attributed to low-frequency mode softening, when going from crystalline to the amorphous phase.