Compton Line 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.

Experimental and theoretical divulging of electronic structure and optical properties of Zn-doped SnSe thermoelectric materials

Electron momentum densities (EMDs) of undoped and Zn-doped SnSe are measured using a 100 mCi 241Am Compton spectrometer. Various density functional theories and hybrid exchange and correlation potentials (LDA, PBE, PBEsol, PBE0, and B3LYP) within the linear combinations of atomic orbitals (LCAO) calculations have been attempted to compute Compton profiles (CPs) and electronic structure of the doped and undoped SnSe. Among all the Compton line shapes predicted using first principles, B3LYP approximation-based EMDs are found to be in a better reconciliation with the CP measurements. Experimental data is also analyzed in terms of localization of Zn-d states. Going beyond the LCAO method, the density of state (DOS), energy bands, reflectance, dielectric constant, and absorption coefficient for Zn-doped (Sn0.97Zn0.03Se and Sn0.95Zn0.05Se) and undoped SnSe are computed using the FP-LAPW-mBJ method. It is seen that Sn-5s and Se-4p orbitals are responsible for the formation of the indirect band gap. Interestingly, Zn doping in SnSe (Sn0.97Zn0.03Se and Sn0.95Zn0.05Se) leads to interstitial bands in the low energy side of the conduction region leading to electron trapping centres and reduction of band gap (from 0.816 to 0.508eV in case of FP-LAPW-mBJ scheme and 1.152 to 0.510 eV in case of LCAO-B3LYP scheme). Our works evidently support the positive effect of Zn doping in enhancing the electronic and thermoelectric properties of the SnSe by forming interstitial bands. Apart from this, undoped and Zn-doped SnSe can also be used for solar cells as an absorber material and detection of ultraviolet (B and C) rays. Due to the formation of interstitial bands induced trapping centres, Zn-doped SnSe can also be uniquely employed in thermoluminescence devices (TLDs).

Electronic and optical properties of CaCl2 using Compton scattering and density functional theory

In this paper electron momentum density of CaCl2 using 241Am Compton spectrometer is reported. The experimental Compton profile is compared with the corresponding theoretical profiles, computed using different exchange and correlation potentials within linear combination of atomic orbitals (LCAO) scheme. The hybrid WC1LYP approximation within LCAO scheme shows a better agreement with experimental CP than other reported theoretical profiles. Going beyond Compton line shapes, the energy bands, density of states using LCAO scheme and modified Becke-Johnson (mBJ) potential within full potential linearized augmented plane wave (FP-LAPW) method are also reported. The optical properties like, dielectric tensors, absorption spectra, reflectivity and refraction are also discussed using FP-LAPW method. Energy band gaps computed using LCAO-WC1LYP and FP-LAPW-mBJ methods are found to be 6.89 and 6.76 eV, respectively which are in reasonable agreement with the available experimental data.

Magnetic Compton scattering study of Laves phase ZrFe2 and Sc doped ZrFe2: Experiment and Green function based relativistic calculations

Spin momentum densities of ferromagnetic ZrFe2 and Zr0.8Sc0.2Fe2 have been measured using magnetic Compton scattering with 182.65 keV circularly polarized synchrotron radiations. Site specific spin moments, which are responsible for the formation of total spin moment, have been deduced from Compton line shapes. At room temperature, the computed spin moment of ZrFe2 is found to be slightly higher than that of Sc doped ZrFe2 which is in consensus with the magnetization data. To compare the experimental data, we have also computed magnetic Compton profiles (MCPs), total and partial spin projected density of states (DOS) and the site specific spin moments using spin-polarized relativistic Korringa-Kohn-Rostoker method. It is observed that the spin moment at Fe site is aligned antiparallel to that of Zr site in both ZrFe2 and Zr0.8Sc0.2Fe2. The MCP results when compared with vibrating sample magnetometer based magnetization data, show a very small contribution of orbital moment in the formation of total magnetic moments in both the compounds. The DOS of ferromagnetic ground state of ZrFe2 and Zr0.8Sc0.2Fe2 are interpreted on the basis of a covalent magnetic model beyond the Stoner rigid band model. It appears that on alloying between a magnetic and a non-magnetic partner (with low valence), a polarization develops on the non-magnetic atom which is anti-parallel to that of the magnetic atom.

Feasibility Studies of a New Event Selection Method to Improve Spatial Resolution of Compton Imaging for Medical Applications.

A Compton imaging method for medical applications that includes new energy determination and data filtering techniques has been tested using several point sources with known emission lines. Using a prototype Compton camera, a distance-of-closest approach technique has been employed to determine the initial energy of the incoming γs and to ensure the reconstructed source position is within an acceptable distance from the known γ source location. Further analysis is done by implementing a Compton line filtering technique, keeping only those interactions whose deposited energy in the first interaction matches the theoretical energy deposition predicted by the Compton equation. Using this new event filtering method, we see improvements in the full width at half maximum in the lateral profiles of γ point sources of up to 70% over standard Compton imaging methods, as well as achievable spatial resolutions in the reconstructed images of better than 2 mm. In addition, this new Compton imaging method was able to reconstruct an extended source of γ rays emitted during irradiation of a water tank with a clinical proton radiotherapy beam.

Determination of main rock-forming elements, strontium and zirconium by X-ray fl uorescence analysis for the geochemical characterization of bottom sediments

Quantitative X-ray fluorescence determination of major rock-forming oxides (Na 2 O, MgO, Al 2 O 3 , SiO 2 , P 2 O 5 , K 2 O, CaO, TiO 2 , MnO and Fe 2 O 3 ) and some microelements (Sr and Zr) was performed in the samples of 143 cm-long sediment core of Lake Baunt (Buryat Republic) by the wavelength-dispersive X-ray fluorescence analysis on the S8 Tiger spectrometer. Calibration curves were obtained by measuring the certified reference materials of the sedimentary rocks. Both analyzed and reference samples were prepared as glass beads by fusion of 110 mg of sample with1.1 g of lithium metaborate. We have used 110 mg mass to ensure the formation of beads with appropriate 10 to 12 mm size across to be measured by the spectrometer with8 mm mask. Rh Kα Compton line was used as a background standard for Sr and Zr determination. The repeatability did not exceed the allowable standard deviation for a wide range of concentrations. Results of major rock-forming oxides determination were compared with the data of spectrophotometry and flame photometry techniques, results of Sr and Zr determination were compared with the data of synchrotron radiation excited X-ray fluorescence technique. All results of the X-ray fluorescence analysis were accepted as satisfactory. Quantitative analysis of each centimeter of Lake Baunt sediment core allowed building first reconstructions of the local environment during the last 7000 years with unique resolution of about 100 years. Keywords: wavelength-dispersive X-ray fluorescence analysis, synchrotron radiation induced X-ray fluorescence analysis, sediments, paleoclimate (Russian) DOI: http://dx.doi.org/10.15826/analitika.2017.21.1.003 A.A. Amosova, V.M. Chubarov,E.V. Kaneva, Iu.N. Markova Vinogradov Institute of Geochemistry, Siberian Branch of Russian Academy of Sciences, ul. Favorsky , 1A, Irkutsk , 664033, Russian Federation

SU‐F‐J‐189: A Method to Improve the Spatial Resolution of Prompt Gamma Based Compton Imaging for Proton Range Verification

Purpose:To test two new techniques, the distance‐of‐closest approach (DCA) and Compton line (CL) filters, developed as a means of improving the spatial resolution of Compton camera (CC) imaging.Methods:Gammas emitted from 22Na, 137Cs, and 60Co point sources were measured with a prototype 3‐stage CC. The energy deposited and position of each interaction in each stage were recorded and used to calculate a “cone‐of‐origin” for each gamma that scattered twice in the CC. A DCA filter was developed which finds the shortest distance from the gamma's cone‐of‐origin surface to the location of the gamma source. The DCA filter was applied to the data to determine the initial energy of the gamma and to remove “bad” interactions that only contribute noise to the image. Additionally, a CL filter, which removes gamma events that do not follow the theoretical predictions of the Compton scatter equation, was used to further remove “bad” interactions from the measured data. Then images were reconstructed with raw, unfiltered data, DCA filtered data, and DCA+CL filtered data and the achievable image resolution of each dataset was compared.Results:Spatial resolutions of ∼2 mm, and better than 2 mm, were achievable with the DCA and DCA+CL filtered data, respectively, compared to > 5 mm for the raw, unfiltered data.Conclusion:In many special cases in medical imaging where information about the source position may be known, such as proton radiotherapy range verification, the application of the DCA and CL filters can result in considerable improvements in the achievable spatial resolutions of Compton imaging.

Caustic structures in x-ray Compton scattering off electrons driven by a short intense laser pulse

We study the Compton scattering of x-rays off electrons that are driven by a relativistically intense short optical laser pulse. The frequency spectrum of the laser-assisted Compton radiation shows a broad plateau in the vicinity of the laser-free Compton line due to a nonlinear mixing between x-ray and laser photons. Special emphasis is placed on how the shape of the short assisting laser pulse affects the spectrum of the scattered x-rays. In particular, we observe sharp peak structures in the plateau region, whose number and locations are highly sensitive to the laser pulse shape. These structures are interpreted as spectral caustics by using a semiclassical analysis of the laser-assisted QED matrix element, relating the caustic peak locations to the laser-driven electron motion.

Ettore Majorana and the Theoretical Problem of Photon-Electron Scattering

Relevant contributions by Majorana regarding Compton scattering off free or bound electrons are considered in detail, where a (full quantum) generalization of the Kramers-Heisenberg dispersion formula is derived. The role of intermediate electronic states is appropriately pointed out in recovering the standard Klein-Nishina formula (for free electron scattering) by making recourse to a limpid physical scheme alternative to the (then unknown) Feynman diagram approach. For bound electron scattering, a quantitative description of the broadening of the Compton line was obtained for the first time by introducing a finite mean life for the excited state of the electron system. Finally, a generalization aimed to describe Compton scattering assisted by a non-vanishing applied magnetic field is as well considered, revealing its relevance for present day research.

X-ray Compton line scan tomography*

Abstract The potentials of incoherent X-ray scattering (Compton) computed tomography (CT) are investigated. The imaging of materials of very different atomic number or density at once is generally a perpetual challenge for X-ray tomography or radiography. In a basic laboratory set-up for simultaneous perpendicular Compton scattering and direct beam attenuation tomography are conducted by single channel photon counting line scans. This results in asymmetric distortions of the projection profiles of the scattering CT data set. In a first approach, corrections of Compton scattering data by taking advantage of rotational symmetry yield tomograms without major geometric artefacts. A cylindrical sample composed of PE, PA, PVC, glass and wood demonstrates similar Compton contrast for all the substances, while the conventional absorption tomogram only reveals the two high order materials. Comparison to neutron tomography reveals astonishing similarities except for the glass component (without hydrogen). Therefore, Compton CT offers the potential to replace neutron tomography, which requires much more efforts.

Electronic structure of lanthanum sesquioxide: A Compton scattering study

We present the first-ever experimental and theoretical momentum densities of La2O3. The Compton line shape is measured using a 20 Ci 137Cs Compton spectrometer at an intermediate resolution with full width at half maximum of 0.34a.u. The experimental Compton profile is compared with the theoretical electron momentum densities computed using linear combination of atomic orbitals (LCAO) method with density functional theory (DFT). It is seen that the generalized gradient approximation (GGA) within DFT reconciles better with the experiment than other DFT based approximations, validating the GGA approximation for rare-earth sesquioxides. The energy bands and density of states computed using LCAO calculations show its wide band gap nature which is in tune with the available reflectivity and photo-absorption data. In addition, Mulliken׳s population and charge density are also computed and discussed.

Magnetic properties of NiFe2−xRExO4 (RE=Dy, Gd) using magnetic Compton scattering

Temperature dependent spin momentum densities of NiFe2−xRExO4 (x=0, 0.05; RE=Dy, Gd) ferrites have been measured using a magnetic Compton spectrometer available at SPring-8, Japan. The experimental profiles of NiFe2O4 (NFO) with doping of Dy and Gd show almost similar spin moment as of undoped NFO. The contribution of different constituents in the formation of total spin moment is also deduced from the analysis of Compton line shape. It is seen that 5% doping of Dy3+ or Gd3+ ions at Fe3+ sites leads to a redistribution of spin moment at Fe3+ and RE3+ sites. The magnetic Compton data when compared with the magnetization data (using a vibrating sample magnetometer) show almost a constant orbital moment (0.21±0.03µB/f.u.) in the doped and undoped NFO.

Compton Profiles and Nature of Bonding in Tantalum Chalcogenides

Abstract. We report the Compton profiles of tantalum chalcogenides (TaS2 and TaSSe) using Hartree–Fock and hybridization of Hartree–Fock and density functional theories within linear combination of atomic (Gaussian) orbitals. To interpret the theoretical data on Compton line shapes, we have measured the Compton profiles using our in-house 100 mCi 241Am γ-ray Compton spectrometer. To understand the relative nature of bonding, we have obtained the equal-valence-electron-density (EVED) profiles. The EVED profiles shows that charge in TaSSe is more localized than TaS2 in the bonding direction which confirms that TaSSe is more covalent than TaS2, which is in agreement with the Mulliken’s population analysis.

Angular Distribution of Multiple Compton Scattered Gamma Rays in Carbon

This work studied the angular distribution of multiple Compton scattering of gamma energy 662 keV, obtained from 137Cs source. The gamma rays are incident on carbon scatterer of varying the scattering angles. The phenomenon of multiple Compton scattering has been successfully observed using NaI(Tl) scintillation detector. The energy spectra of the detected photons are observed as a long tail to the single-photon Compton line on the lower side of the full-energy peak in the recorded scattered energy spectrum. The full-energy peak corresponding to singly scattered events is reconstructed analytically and observe that the number of multiply scattered events, having same energy as in the singly scattered distribution.

AutoCal: a method for automatic energy calibration of β–γ systems based on a 137Cs spectrum

A method was developed and implemented that calculates energy versus channel calibrations. This method utilizes a 137Cs spectrum acquired in β–γ coincidence. Both the γ singles and the β–γ coincident spectrum are utilized. The γ singles spectrum is utilized to calculate the γ detector energy versus resolution function. The Compton line in the β–γ coincidence is then used to calculate the β detector energy versus resolution function. Currently a linear regression (y = mx + b) is utilized to fit the data. However, higher order polynomials may easily be implemented if desired.

Nature of bonding in CaTiO3 and SrTiO3: A Compton scattering study

Compton profile measurements for CaTiO3 and SrTiO3 perovskite compounds have been undertaken using 20 Ci 137Cs Compton spectrometer. To understand the nature of bonding in both the compounds, we have analyzed the Compton line shape in terms of equal-valence-electron-density profiles. Electron momentum densities, energy bands and density of states computed using linear combination of the atomic orbitals method (within the framework of density functional theory) are analyzed using the experimental Compton line shapes. It is seen that the recently developed second order generalized gradient approximation gives a better description of momentum densities than the local density approximation. Moreover, bonding in both the ceramic compounds has also been discussed in terms of Mulliken's population analysis.

A magnetic Compton scattering study of Ga rich Co–Ni–Ga ferromagnetic shape memory alloys

The temperature dependent spin momentum densities of Co1.8NiGa1.2 and Co2Ni0.76Ga1.24 alloys have been measured using the magnetic Compton scattering technique. The individual contributions of constituents in the formation of the total spin moment are also calculated using Compton line shape analysis. The magnetic Compton data when compared with the magnetization data obtained using a vibrating sample magnetometer show a negligible orbital contribution. The spin moments deduced from the experimental Compton data are compared with the theoretical results obtained from the full potential linearized augmented plane wave method and are found to be in good agreement. The origin of the magnetism in both alloys is also described in terms of the eg and t2g contributions of Ni and Co.

Compton scattering studies and electronic properties of cerium

Experimental electron momentum density of γ-Ce was measured at an intermediate resolution (0.38 a.u.) using 20 Ci 137Cs Compton spectrometer. The experiment was compared with the first ever theoretical Compton profiles computed using spin polarized relativistic Korringa-Kohn-Rostoker (SPR-KKR) method within atomic sphere approximation; and linear combination of atomic orbitals (LCAO) within generalised gradient approximation (GGA) and recently developed second order generalised gradient approximation (SOGGA). It was seen that the Compton profile derived from LCAO with GGA and SOGGA schemes gave a reasonable agreement with the experimental Compton line shape. Theoretical anisotropies in Compton profiles derived along [100], [110] and [111] directions were explained in terms of degenerate states in the energy bands.

Investigation of electronic properties of crystalline arsenic chalcogenides: Theory and experiment

The electronic structure of crystalline As 2S 3 and As 2Se 3 has been calculated in this paper. We present the energy bands, density of states (DOS) and the Compton profiles using the linear combination of atomic orbitals (LCAO) scheme based on the density functional theory (DFT). From the calculated total and partial density of states it is seen that the lone-pair p-states of sulphur/selenium contribute closest to the Fermi energy level. To interpret the theoretical data on the Compton line shape, we have measured the Compton profiles on a 100 mCi 241Am spectrometer. It is seen that the density functional theory within generalised gradient approximation gives a slightly better agreement with the experimental momentum densities. The nature of chemical bonding in arsenic chalcogenides is studied using Mulliken's population analysis and the experimentally measured equal-valence-electron-density profiles; As 2S 3 is found to be more ionic compared to As 2Se 3.

High energy Compton scattering study of TiC and TiN

We present the experimental Compton profiles of TiC and TiN using 661.65 keV γ-ray from 20 Ci (137)Cs source. To explain our experimental data on momentum densities, we have computed the theoretical profiles, energy bands and density of states using linear combination of atomic orbitals scheme within the framework of density functional theory. In addition the energy bands, density of states and Fermi surfaces using full potential linearised augmented plane wave method have also been computed. Energy bands and density of states obtained from both the theoretical models show metallic character of TiC and TiN. The anisotropies in Compton line shapes and the Fermi surface topology are discussed in term of energy bands.