Range Of Atomic Numbers Research Articles

Development of X-ray fluorescence methods by use of a Mo X-ray tube and their application in the case of biological samples

In the present work two different experimental arrangements, aiming in the X-ray fluorescence analysis of solid and liquid biological samples respectively, were developed and studied both theoretically and experimentally in combination with a Mo anode X-ray tube: The secondary target XRF (STXRF) and the Total Reflection XRF set-up (TXRF). The secondary target XRF irradiation chamber was designed and constructed in our laboratory. Careful choice of the materials combined with the tight geometry used, minimize the presence of interference peaks in the spectrum and offer high intensity of the exciting beam at the sample position. Optimum performance was ensured by means of an extended theoretical and experimental study of various parameters affecting the analytical capabilities of secondary target XRF systems, such as: The choice of secondary target material and the operational conditions of the X-ray tube. The secondary target XRF set-up was applied in the determination of the concentrations of trace elements in a pool blood serum sample. A simple preparation technique, like the freeze-drying process was employed, resulting in detection limits of 15 ng/ml for most metal trace elements and for a 6000 sec measuring time. The accuracy of the whole experimental procedure, examined by internal standardization and by analyzing the reference standard material A-13, was found to be about 4% over the whole atomic number range. For the determination of the mass absorption coefficients, necessary in the quantification step, a modified version of the emission transmission method was employed. Total Reflection X-Ray Fluorescence (TXRF) is a well-established method, mainly applied in the analysis of liquid samples, offering very low detection limits in most of the cases. Direct application of the TXRF method is not so efficient in blood serum analysis, since the high content of the organic matrix increases significantly the background due to Compton scattering. Chemical treatment of the blood serum samples and related preconcentration techniques have been suggested in literature, but they are time consuming and increase the possibility of adding contaminants in the sample. In this work, the applicability of direct TXRF analysis in blood serum samples was examined. The insertion of a Mo filter after the cut-off reflector has been found to improve significantly the peak to background ratio, especially for the elements of interest such as Cu, Zn, Se and Br. The influence of self-absorption phenomena in the quantification procedure was also investigated with respect to the internal standard used and the sample mass analyzed. Precision and accuracy in the analysis was found to be about 4% over the whole atomic number range. Detection limits were in the order of 25ng/ml for most metal trace elements and a measuring time of 3600 sec.

Lα X-ray satellites for 31 ≤ Z ≤ 38: Systematization

An examination of the problem of the energy values, their interpretation and the origin of the Lα x - ray satellites in the atomic number range Z = 31-38 reveals non existence and lack of sufficient data for the purpose. The energies of these satellites where not available are obtained using suitable semi-empirical method for the elements under investigation and the available systematization procedures namely Mosley plot and the self consistent doubly modified Mosley plot are considered. It is concluded that the self consistent method is not applicable in the present scenario. The energy values for the satellites Lα5, Lα6 and Lα7 are calculated using Mosley plot for the atomic number range Z= 31 to 35 and are reported for the first time.

Semi-empirical formula for alpha and cluster decay half-lives of superheavy nuclei

We have formulated a semi-empirical formula for alpha decay half-lives and cluster decay half-lives for superheavy nuclei of atomic number range [Formula: see text]. We have compared the logarithmic half-lives produced by the present formula with that of experiments and other formulae, such as universal decay law (UDL) [H. C. Manjunatha and K. N. Sridhar, Eur. Phys. J. A 53, 156 (2017)] and Horoi et al. [Horoi et al., J. Phys. G[Formula: see text] Nucl. Part. Phys. 30, 945 (2004)], Univ [D. Ni and Z. Ren, Phys. Rev. C 74, 014304 (2006)], Royer [G. Royer, J. Phys. G: Nucl. Part. Phys. 26, 1149 (2000)] and VSS [S. A. Gurvitz and G. Kalbermann, Phys. Rev. Lett. 59, 262 (1987)]. The constructed formula produces logarithmic half-lives for alpha and cluster decay (4He,9Be, [Formula: see text]B, [Formula: see text]C, [Formula: see text]N, [Formula: see text]O, [Formula: see text]F, [Formula: see text]Ne, [Formula: see text]Na, [Formula: see text]Mg, [Formula: see text]Al, [Formula: see text]Si, [Formula: see text]P, [Formula: see text]S, [Formula: see text]Cl, [Formula: see text]Ar, [Formula: see text]K and [Formula: see text]Ca) in superheavy nuclei of atomic number range [Formula: see text].

Mean atomic number analysis by the coherent to backscattering intensity ratios at 59.54 and 661.62 photon energies

In this work, the qualitative analysis has been performed by using ratio of coherent to backscattering intensity ratios. The samples in the mean atomic number range 4.268≤Z‾≤5.786 and 9.743≤Z‾≤83.00 were prepared by using dilution technique. 59.54 and 661.62 keV photon energies are obtained from the radioactive point sources of 241Am and 137Cs an activity of 0.43–0.20 MBq, respectively. The scattered gamma rays were counted by a HPGe detector with a resolution of 182 eV at 5.9 keV. The obtained intensity ratios are plotted as function of the mean atomic number and constituted a best-fit-curve. The correlation coefficients for the prepared samples in the mean atomic number range 4.268≤Z‾≤5.786 are 0.976 and 0.970 at 59.54 and 661.62 keV photons, respectively. The correlation coefficients for the prepared samples in the mean atomic number range 9.743≤Z‾≤83.00 are 0.964 and 0.967 at 59.54 and 661.62 keV photons, respectively. It is observed that there was a high correlation between coherent to backscattering intensity ratio and the mean atomic numbers. It was concluded that the recommended intensity ratio can be used for qualitative analysis.

Differential electron scattering cross-sections at low electron energies: The influence of screening parameter

For quantitative electron microscopy the comparison of measured and simulated data is essential. Monte Carlo (MC) simulations are well established to calculate the high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) intensities on a non-atomic scale. In this work we focus on the importance of the screening parameter in differential screened Rutherford cross-sections for MC simulations and on the contribution of the screening parameter to the atomic-number dependence of the HAADF-STEM intensity at electron energies ≤ 30 keV. Materials investigated were chosen to cover a wide range of atomic numbers Z to study the Z dependence of the screening parameter. Comparison of measured and simulated HAADF-STEM intensities with different screening parameters known from the literature were tested and failed to generally describe the experimental data. Hence, the screening parameter was adapted to obtain the best match between experimental and MC-simulated HAADF-STEM intensities. The Z dependence of the HAADF-STEM intensity was derived.

Dependence of albedo factors on mean atomic number for 662 keV gamma photons

The albedo factors (number, energy and dose) of the samples with various mean atomic number have been investigated at a scattering angle of 180°. Fourteen different samples in the mean atomic number range 9.743 ≤ Z‾ ≤ 83.00 were obtained with bismuth and cellulose powders by using dilution technique. Thus, albedo factors have been investigated in a wide atomic number range. The samples were irritated by 662 keV gamma rays emitted from a137Cs radioactive source. The scattered γ -rays were counted by an HPGe detector with active area of 200 mm2. It has been observed that albedo factors decrease with increasing mean atomic number. Also, there is a high correlation between albedo factors and mean atomic numbers.

K shell absorption jump ratios and jump factor measurements for some elements in the range of 40 ≤ Z ≤ 50

In this study, K shell absorption jump ratios (JK) and jump factors (rK) of specimens in the atomic number range of 40 ≤ Z ≤ 50 were measured using the energy dispersive X-ray fluorescence (EDXRF) technique. Related specimens were excited using 59.54 keV γ-photons that were radiated from a 241Am point source. Typical K X-rays emitting from specimens were detected from silicon drifted lithium (Si(Li)) semiconductor detector. Derived JK and rK values of related specimens were compared with calculated theoretical and other experimental values. The agreement of measured values was reasonable with theoretical calculations.

Atom-in-jellium equations of state in the high-energy-density regime.

Recent path-integral Monte Carlo and quantum molecular dynamics simulations have shown that computationally efficient average-atom models can predict thermodynamic states in warm dense matter to within a few percent. One such atom-in-jellium model has typically been used to predict the electron-thermal behavior only, although it was previously developed to predict the entire equation of state (EOS). We report completely atom-in-jellium EOS calculations for Be, Al, Si, Fe, and Mo, as elements representative of a range of atomic number and low-pressure electronic structure. Comparing the more recent method of pseudoatom molecular dynamics, atom-in-jellium results were similar: sometimes less accurate, sometimes more. All these techniques exhibited pronounced effects of electronic shell structure in the shock Hugoniot which are not captured by Thomas-Fermi based EOS. These results demonstrate the value of a hierarchical approach to EOS construction, using average-atom techniques with shell structure to populate a wide-range EOS surface efficiently, complemented by more rigorous three-dimensional multiatom calculations to validate and adjust the EOS.

Exploring the production of new superheavy nuclei with proton and α -particle evaporation channels

Existing experimental facilities limit the possibilities for discovery of new nuclides to those synthesized with cross sections above 100 fb, but the perspectives for future high current accelerators could lower this limit by two orders of magnitude. Therefore, in the present work excitation functions for fusion-$xn$ evaporation reaction channels induced not only by $^{48}Ca$ but also by heavier projectiles (usually leading to smaller cross sections) on actinide targets were calculated in the framework of the fusion-by-diffusion (FBD) model. For the first time, in this approach, channels in which a proton ($pxn$) or alpha particle ($\alpha$$xn$) is evaporated have been included in the first step of the deexcitation cascade. To calculate the synthesis cross sections entry data such as fission barriers, ground-state masses, deformations and shell effects of the superheavy nuclei calculated in a consistent way within the Warsaw macroscopic-microscopic model were used. The only adjustable parameter of the FBD model is the injection point distance $s_{inj}$ and the value determined in our previous analysis of experimental cross sections for the synthesis of superheavy nuclei of Z=114-118 has been used. Excitation functions for the synthesis of selected (cross section above a few fb) new superheavies in the range of atomic numbers 112-120 are presented. Observation of 21 new heaviest isotopes is predicted. A realistic discussion of the FBD model uncertainties is presented for the first time.

Semi-empirical formula for photon energy absorption buildup factors of elements and compounds

We have formulated a simple semi-empirical formulae for photon energy absorption buildup factors in the energy region 0.015-15 MeV, atomic number range 1≤Z≤92 and for mean free path up to 40 mfp. The results produced by the present formulae agree well with the data available in the literature. This semi-empirical formula may be extended to any compounds/mixtures/biological samples. This semi-empirical formula finds importance in the calculations of buildup factors of any materials which are required for radiation shielding, nuclear engineering, radiotherapy and nuclear medicine.

Semi-empirical formula for photon energy absorption buildup factors of elements and compounds

We have formulated a simple semi-empirical formulae for photon energy absorption buildup factors in the energy region 0.015-15 MeV, atomic number range 1≤Z≤92 and for mean free path up to 40 mfp. The results produced by the present formulae agree well with the data available in the literature. This semi-empirical formula may be extended to any compounds/mixtures/biological samples. This semi-empirical formula finds importance in the calculations of buildup factors of any materials which are required for radiation shielding, nuclear engineering, radiotherapy and nuclear medicine.

Synthesis of superheavy elements using 50,51V-induced fusion reactions

We have studied the synthesis of superheavy elements using 50, 51V-induced fusion reactions. We have also achieved the semi-empirical formula for fusion barrier heights (VB), positions (RB), curvature of the inverted parabola (ħω) of 50–51V-induced fusion reactions to synthesis super heavy nuclei with atomic number range 104≤Z≤123. It has been identified the most probable 50, 51V-induced fusion reactions for the synthesis of superheavy nuclei of atomic number range 104≤Z≤123 by studying the fusion cross section, evaporation residue cross section, compound nucleus formation probability (PCN) and survival probability (PSurv). The identified targets for 50V induced fusion reactions to synthesis superheavy elements of Z=104,105,106,107,108,112,113,114,115,116,117,118,119,120,121,122 and 123 are 205Tl, 210Pb, 210Bi, 210Po, 223Ra, 227Ac, 230Th, 232Pa, 237U, 236Np, 239Pu, 243Am, 246Cm, 246Bk, 249Cf, 252Es and 255Fm respectively. The suggested targets for 51V induced fusion reactions to synthesis superheavy elements of Z=104,105,106,107,108,112,113,114,115,116,117,118,119,120,121,122 and 123 are 205Tl, 208Pb, 210Bi, 210Po, 225Ra, 226Ac, 228Th, 231Pa, 234U, 238Np, 238Pu, 241Am, 244Cm, 247Bk, 250Cf, 254Es and 253Fm respectively. We hope that our predictions may be guide for the future experiments in the synthesis of more superheavy elements using 50,51V-induced fusion reactions.

Latest Geant4 developments for PIXE applications

We describe the recent inclusion in Geant4 of state-of-the-art proton and alpha particle shell ionisation cross sections based on the ECPSSR approach as calculated by Cohen et al., called here ANSTO ECPSSR. The new ionisation cross sections have been integrated into Geant4. We present a comparison of the fluorescence X-ray spectra generated by the ANSTO ECPSSR set of cross sections and, alternatively, the currently available sets of Geant4 PIXE cross sections. The comparisons are performed for a large set of sample materials spanning a broad range of atomic numbers. The two alternative PIXE cross sections approaches (Geant4 and ANSTO) have been compared to existing experimental measurements performed at ANSTO with gold, tantalum and cerium targets of interest for nanomedicine applications. The results show that, while the alternative approaches produce equivalent results for vacancies generated in the K and L shell, differences are evident in the case of M shell vacancies. This work represents the next step in the effort to improve the Geant4 modelling of the atomic relaxation and provide recommended approaches to the Geant4 user community. This new Geant4 development is of interest for applications spanning from life and space to environmental science.

Polycrystalline Crusts in Accreting Neutron Stars

Abstract The crust of accreting neutron stars plays a central role in many different observational phenomena. In these stars, heavy elements produced by H–He burning in the rapid proton capture (rp-) process continually freeze to form new crust. In this paper, we explore the expected composition of the solid phase. We first demonstrate using molecular dynamics that two distinct types of chemical separations occur, depending on the composition of the rp-process ashes. We then calculate phase diagrams for three-component mixtures and use them to determine the allowed crust compositions. We show that, for the large range of atomic numbers produced in the rp-process (Z ∼ 10–50), the solid that forms has only a small number of available compositions. We conclude that accreting neutron star crusts should be polycrystalline, with domains of distinct composition. Our results motivate further work on the size of the compositional domains and have implications for crust physics and accreting neutron star phenomenology.

Universal odd-even staggering in isotopic fragmentation and spallation cross sections of neutron-rich fragments

An evident odd-even staggering (OES) in fragment cross sections has been experimentally observed in many fragmentation and spallation reactions. However, quantitative comparisons of this OES effect in different reaction systems are still scarce for neutron-rich nuclei near the neutron drip line. By employing a third-order difference formula, the magnitudes of this OES in extensive experimental cross sections are systematically investigated for many neutron-rich nuclei with ($N\ensuremath{-}Z$) from 1 to 23 over a broad range of atomic numbers ($Z\ensuremath{\approx}3--50$). A comparison of these magnitude values extracted from fragment cross sections measured in different fragmentation and spallation reactions with a large variety of projectile-target combinations over a wide energy range reveals that the OES magnitude is almost independent of the projectile-target combinations and the projectile energy. The weighted average of these OES magnitudes derived from cross sections accurately measured in different reaction systems is adopted as the evaluation value of the OES magnitude. These evaluated OES magnitudes are recommended to be used in fragmentation and spallation models to improve their predictions for fragment cross sections.

Parametrisation of the experimental fusion–fission cross-sections

We have presented non-linear analytical formula for fusion–fission cross-sections. This is achieved by analysing many fusion–fission experiments of the compound nuclei of atomic number range $$23 \le Z \le 146$$ available in literature. Our parametrised formula can reproduce the fusion–fission cross-sections which agree well with the experiments. Our parametrisations depend on the charges and masses of the compound nuclei and fission fragments only. These results can be used as a guideline for estimating the fusion–fission cross-sections in those cases where measurements do not exist and also for studying new nuclei which are not yet explored.

13. Dual Energy Computed Tomography for Perfusion Imaging

The metastatic spreading ability of cancer heavily depends on microcirculation, requiring the formation of new blood vessels in the vascular network, or angiogenesis. Indirect measurement of angiogenesis can be performed by computed tomography (CT) perfusion imaging, where blood flow is observed using dynamic contrast-enhanced techniques. However, contrast-enhancement in tissues can be poor due to inadequate CT calibration, leading to an increase in radiation dose to the patient. It is hypothesized that the use of dual-energy CT will provide a more robust basis for calibration of contrast-enhanced imaging without increasing dose. The purpose of this study is to improve the sensitivity and accuracy of perfusion imaging by using atomic number extraction of Iodine contrast agent concentration from dual-energy datasets. A stoichiometric calibration for CT was done with the effective atomic number and relative electron density extracted in MATLAB, resulting in a wider dynamic range of effective atomic number per mgI/mL. Dual-energy CT as a tool for calibrating perfusion imaging shows promise of increasing the range and signal to noise ratio of contrast-enhanced CT imaging. Future work will extend the study from a static to dynamic quantification to explore dual-energy CT for perfusion imaging, with the goals of developing a robust stoichiometric calibration for quality assurance purposes, and further insights on tumour angiogenesis and cancer metastasis.

Fusion barrier characteristics of actinides

We have studied fusion barrier characteristics of actinide compound nuclei with atomic number range 89≤Z≤103 for all projectile target combinations. After the calculation of fusion barrier heights and positions, we have searched for their parameterization. We have achieved the empirical formula for fusion barrier heights (VB), positions (RB), curvature of the inverted parabola (ħω) of actinide compound nuclei with atomic number range 89≤Z≤103 for all projectile target combinations (6<A1<127, 101<A2<260, 3<Z1<51 and 45<Z2<100). This formula is obtained by studying the fusion barrier characteristics of 7205 projectile target combinations. The values produced by the present formula are also compared with experiments. The present pocket formula produces fusion barrier characteristics of actinides with the simple inputs of mass number (A) and atomic number (Z) of projectile-targets.

Effect of inserted metal at anode tip on formation of pulsed X-ray emitting zone of plasma focus device

The effect of the anode's insert material of a plasma focus device on the properties of X-ray emission zone was studied. Inserts were fabricated out of six different materials including aluminum, copper, zinc, tin, tungsten, and lead to cover a wide range of atomic numbers. For each anode's insert material at different gas pressures and different voltages, the shape of X-ray emission zone was recorded by three pinhole cameras, which were installed on sidewall and roof of the chamber of plasma focus device. The results indicated that by changing the gas pressure and the charge voltage of capacitor, the X-ray source of plasma focus emerges with different forms as a concentrated column or conical shape with sharp or cloudy edges. These structures are in the form of a combination of plasma emission and anode-tip emission with different intensities. These observations indicate that the material of the anode-tip especially affects the structure of X-ray emission zone.

Empirical formula for neutron scattering lengths and cross sections

The neutrons are important tool to study the condensed matter and they can also be used in nuclear physics. Hence in the present work, we have formulated an empirical formula for neutron absorption cross sections, coherent and incoherent neutron scattering cross sections and coherent neutron and incoherent scattering lengths for different mass number nuclei of wide atomic number range 1<Z<96. This formula successfully produces experimental values 412 nuclei available in the literature.