Determination of L3 subshell X-ray production cross-sections and fluorescence yields of Pb, Th and U

A study of L₃ subshell X-ray production cross-sections and fluorescence yields by using characteristic K X-rays as the exciting radiation is described. Only the L₃ subshells of Pb, Th and U were excited by the characteristic K X-rays of the elements used as secondary sources. The cross-sections for the production of L_l, L and L_β groups of L₃ subshell X-rays of Pb, Th and U have been measured using photoionization by Rb, Nb and Mo K X-rays. The measured L₃ X-ray production cross-section values for Pb, Th and U are in good agreement with the theoretical ones evaluated using L₃ subshell fluorescence yield ω₃, fractions of the radiative width F_3i and L₃ subshell photoionization cross-section σ₃. The L₃ subshell fluorescence yields (ω₃) have also been computed using the presently measured cross-section values and the theoretical L₃ subshell photoionization cross-section values. These results are compared with the theoretically predicted values.     

L-shell ionization of Cd, Sb, Te, Ba, La, Eu, Tb and Yb by O ions in the energy range from 0.19 to 0.75 MeV u

L_1,2, Lβ_1,3,4, Lβ_2,15, Lγ₁₍₅₎ and Lγ_2,3(4,4′) X-ray production cross-sections have been measured on selected medium-Z elements using ¹⁶O ions with energies from 0.19 to 0.75 MeV u⁻¹. Calculated L-subshell ionization cross-sections were compared with the predictions of the direct ionization theories: the ECPSSR theory, the semiclassical approximation (SCA) in the united atom limit (SCA-UA) and SCA coupled-channel calculations (SCA-CC) involving a few lowest lying states. For the ECPSSR theory, large discrepancies were found for all three subshells. Better overall agreement between the experiment and theory was found for the SCA-UA theory. SCA-CC calculations improved the agreement between experiment and theory for the L₂-subshell in the very adiabatic region. By measuring the L X-ray production cross-sections on W targets of different thickness, possible contribution of electron capture (EC) to the X-ray production cross-section was estimated to be less than 20%. The degree of multiple ionization of outer shells caused by heavy ion bombardment was estimated from the X-ray line energy shifts and by comparing the X-ray intensity ratios for heavy ions and protons.     

Applying elastic backscattering spectrometry when the nuclear excitation function has a fine structure

For some nuclei the (non-Rutherford) elastic scattering cross-section has a fine structure with a typical width of the resonances of 1–10 keV. It is shown that bulk sample backscattering spectra can be calculated correctly in these cases only if these are carefully taken into account. The proton elastic backscattering (EBS) spectrum from bulk aluminium was measured just above the interval 1.35–1.75 MeV where a strong resonance structure in the ²⁷Al(p,p₀)²⁷Al cross-section has a relatively high density. Different sets of the Al cross-section data were employed in the simulation: the high resolution proton resonance measurement results retrieved by R-matrix calculations and experimental data obtained later especially for use in IBA. These data sets were consistent, but the latter sets did not resolve the fine structure of the cross-section. The simulations reproduce the spectra well only for the high resolution data: that is, EBS spectra can be simulated provided that the scattering cross-section include all the detail of the fine structure.     

M-shell X-ray production cross sections for PIXE applications

M-shell X-ray production cross sections by protons of energies 0.1–4.0 MeV are reported for the most intense M_β(M_4,5N_6,7), M_γ(M₃N_4,5) and M₃O_4,5 M-X ray transitions appearing in PIXE spectra. The cross sections have been measured systematically for selected heavy elements between Ta and Th (Z₂=73–90). Measured M-X-ray production cross sections were found to be universal with respect of M-shell scaled velocity ξ_M. The data are compared with available theoretical calculations of M-shell ionization by charged particles based on the plane-wave Born approximation (PWBA) and the semiclassical approximation (SCA), as well as the ECPSSR theory and relativistic RPWBA-BC which are going beyond the first order treatment. Simple parameterization of experimental proton induced M-X-ray cross sections is proposed for PIXE applications. This parameterization, being accurate within ±5%, can be used for precise determination of heavy metal concentrations by PIXE technique.     

Observation of the evanescent wave excited by proton beam

An exit angle dependence of the intensity of carbon K line during proton bombardment was measured to observe the evanescent wave. A Soller type spectrometer was used to measure the intensity of X-ray lines. A mirror polished Si (1 1 1) wafer was used as a substrate and carbon was deposited onto this surface. As a result a curious exit angle dependence which is similar to the evanescent wave of X-rays was found . The calculated transmission coefficient of X-ray evanescent wave is compared with measured exit angle dependence of X-ray emission. The experimental and theoretical values are in good agreement. Utilization of this phenomenon permits to enhance the surface sensitivity of the PIXE analysis method.     

Cross-section for D(p,p)D elastic scattering from 1.8 to 3.2 MeV at the laboratory angles of 155° and 165°

The D(p,p)D cross-sections for elastic scattering of proton on deuterium over incident proton energy range from 1.8 to 3.2 MeV at both laboratory angles of 155° and 165° were measured. A thin solid state target Ni/TiD_x/Ta/Al used for cross-section measurement was fabricated by firstly depositing layers of Ta, Ti and Ni film on the Al foil substrate of about 7 μm in turn using magnetron sputtering and then deuterating under the deuterium atmosphere. The areal density of metal element in each layer of film was measured with RBS analysis by using a 4.0 MeV ⁴He ion beam, while the areal density of the deuterium absorbed in the Ti film was measured with ERD analysis by using a 6.0 MeV ¹⁶O ion beam. The results show that the cross-sections of p-D scattering under this experimental circumstance were much enhanced over the Rutherford cross-section value. It was found that the enhancement increases linearly as the energy of the incident beam increases. The total uncertainty in the measurements was less than 7.5%.     

Co γ-ray irradiation effects on dielectric characteristics of tin oxide films of different thicknesses on n-type Si(1 1 1) substrates

We have tried to determine the effects of ⁶⁰Co gamma irradiation on properties of Au/SnO₂/n-Si (MOS) structures such as dielectric constant (ε′), dielectric loss (ε″), tangent loss (tan δ) and ac conductivity (σ_ac). Three samples were fabricated with different deposition time. The samples were irradiated using a ⁶⁰Co γ-ray source irradiation with the total dose range of 0–500 kGy at room temperature. Capacitance and conductance (C–G–V) measurements were performed at a frequency of 500 kHz in the dark and at room temperature before and after irradiation. The experimental data were analyzed using complex permittivity and electric modulus. The values of ε′, ε″, tan δ and σ_ac showed a strong dependence on the applied voltage and irradiation dose. The dielectric properties of MOS structures have been found to be strongly influenced by the presence of dominant radiation-induced defects. Experimental results show that the interfacial polarization contributes to the improvement of dielectric properties of Au/SnO₂/n-Si (MOS) Schottky diodes.     

Analytical formulas for ionization cross sections and coster-kronig corrected fluorescence yields of the L1, L2, and L3 subshells

We present analytical formulas for three L-subshell ionization cross sections for proton impact based on the recent experimental data and for the Coster-Kronig corrected fluorescence yields based on the theoretical values due to Chen et al. and due to McGuire. Total L X-ray production cross sections were calculated using the analytical formulas and compared with experimental values. As a result, our semi-empirical values using the formulas fitted to the values of Chen et al. coincided with the experimental values very well. Furthermore our values for L_α, L_β, L_γ, L_η, and L_l X-ray production cross sections calculated using the analytical L1, L2, and L3 Subshell ionization cross sections, and the theoretical values of the fluorescent yields and of the Coster-Kronig transition probabilities due to Chen et al. also agreed with the experimental values.     

An efficient deterministic method for generating non-negative scattering cross-sections

In the conventional discrete ordinates approach, the scattering source is approximated as a truncated Legendre series. In case of highly anisotropic scattering problems (e.g., incident beam problems), the truncated Legendre scattering cross-sections give unphysical negative cross-sections in some values of μ (cosine of scattering angle). These unphysical artifacts cause negative scattering sources and negative angular fluxes. In addition to that, negative angular fluxes may cause wrong scalar flux as well. A new method to generate non-negative scattering cross-sections, which is very efficient and deterministic, is proposed in this paper. The main idea of this method is to make non-negative scattering cross-sections that produce equivalent scattering sources. This method does not have a practical limitation to generate non-negative scattering cross-sections because the calculations of the scattering sources are performed with the conventional truncated cross-section data provided from the standard processing codes. In the both neutron and the photon/electron coupled cases, an inadequate truncated Legendre order causes problems, e.g., inaccurate angular distribution of scattering for low order, oscillations of differential scattering cross-sections where cross-sections are small for high order expansions, and negative differential scattering cross-sections in some values of μ.

In the neutron case, if the anisotropy is very high compared to the truncated Legendre order, inaccurate angular distributions of scattering occur especially in within-group scattering. Even if the truncated Legendre order is quite high to represent angular distribution of scattering in the photon/electron coupled case, it still causes oscillations where the cross-sections are small.

The method in this paper achieves both an accurate angular distribution of scattering and non-negative scattering cross-sections for neutron and photon/electron coupled cases. The generated non-negative scattering cross-sections with the new method are compared to the conventional scattering cross-sections and tested in the transport calculations. The numerical results tested in the transport calculation give accurate results without unphysical negative angular fluxes.     

Stopping power of swift neon ions in dependence on the charge state in the non-equilibrium regime

We report on measurements of charge changing cross-sections and energy losses in dependence on the initial and final charge state of Ne ions at an incident energy of 2 MeV/u penetrating thin carbon foils. Different initial charge states could be separated in energy by applying a high voltage in front of the carbon foils; the final charges and their energy loss were measured with a high-resolution magnetic spectrometer. We derived a consistent evolution of the charge state distribution solving the corresponding rate equations for the measured cross-sections. Including the charge state dependent energy losses, ΔE(q_i,q_f), stopping power values for frozen charge states, S(q), could be extracted. The experimental data are compared with different theoretical predictions.     

Thermochemical study of vaporization of LiTiO by a mass spectrometric Knudsen effusion method

The vaporization of Li₄TiO₄ has been studied by a mass spectrometric Knudsen effusion method in the temperature range 1082–1582 K. Identified vapors are Li(g), LiO(g), Li₂O(g) and Li₃O(g). When the vaporization proceeds, the content of Li₂O in the Li₄TiO₄ sample decreases and the condensed phase of the sample changes to β-Li₄TiO₄ plus l-Li₂TiO₃ below 1323 K, to β-Li₄TiO₄ plus h-Li₂TiO₃ in the range 1323–1473 K and to h-Li₂TiO₃ plus liquid above 1473 K. On the basis of the partial pressure data, the enthalpies of formation for β-Li₄TiO₄ from elements and from constituent oxides have been determined to be ΔH_f,298^°(β-Li₄TiO₄,s) = −2247.8 ± 14.3 kJ mol⁻¹ and Δ_fox,298^°(β-Li₄TiO₄, s) = −107.3 ± 14.3 kJ mol⁻¹, respectively.     

Charge state dependence of L-shell X-ray production cross sections of 28Ni, 29Cu, 30Zn, 31Ga and 32Ge by 12 MeV O ions

L-shell X-ray production cross sections of elements from Z₂=28 to 32 were measured. A 12 MeV incident oxygen beam, with and without K-shell vacancies, was used to make a charge state dependence analysis. Simultaneous measurements were made of both scattered particles and X-rays from the ultra-clean foils that had been made sufficiently thin to reach the single-collision regime. Target L-shell to projectile K-shell electron capture for hydrogen-like (q=Z₁ − 1) and fully stripped (q=Z₁) oxygen ions were then extracted. The measurements are compared with the predictions of the ECPSSR theory using a single-hole fluorescence yield. In general and contrast to the first Born calculations, this theory gives reasonable agreement with the data for oxygen ions without K vacancies. However, the ECPSSR still significantly overpredicts the data for oxygen ions with K vacancies.     

Investigation of proton induced reactions on niobium at low and medium energies

Niobium is a metal with important technological applications: use as alloying element to increase strength of super alloys, as thin layer for tribological applications, as superconductive material, in high temperature engineering systems, etc. In the frame of a systematic study of activation cross-sections of charged particle induced reactions on structural materials proton induced excitation functions on Nb targets were determined with the aim of applications in accelerator and reactor technology and for thin layer activation (TLA). The charged particle activation cross-sections on this element are also important for yield calculation of medical isotope production (^88,89Zr, ^86,87,88Y) and for dose estimation in PET targetry. As niobium is a monoisotopic element it is an ideal target material to test nuclear reaction theories. We present here the experimental excitation functions of ⁹³Nb(p,x)^90,93mMo, ^92m,91m,90Nb, ^88,89Zr and ⁸⁸Y in the energy range 0-37 MeV.The results were compared with the theoretical cross-sections calculated by means of the code ALICE-IPPE, EMPIRE-3, TALYS and with the literature data. The theory reproduces the shape of the measured results well and magnitude is also acceptable.Thick target yields calculated from our fitted cross-section give reliable estimations for production of medically relevant radioisotopes and for dose estimation in accelerator technology.     

Study on production of Pd and characterisation of possible contaminants in the proton irradiation of Rh up to 28 Mev

Excitation functions for the proton-induced reactions on ¹⁰³Rh of importance in the production of the medically used ¹⁰³Pd were studied by the stacked foil technique. Several experiments at incident energies between 14.7 and 29.4 MeV allowed reliable determination of the cross-sections for ¹⁰¹Pd, ¹⁰³Pd, ^101m,101gRh and ^102m,102gRh. Measurements for ¹⁰³Pd were done in the X-line region as well as for γ-lines and show 25% difference. The new experimental values are compared to the available literature values and show mostly higher values. Thick target yields were calculated that are in good agreement with earlier published values. Practical upper limit of incident energy to be used in production runs is derived.     

Prediction of (n,3He) cross-sections around 14 MeV

A comprehensive review of the neutron-induced cross-sections for (n,³He) reactions has been made for the interval of 14⩽Z⩽84 around 14 MeV neutron energy. For practical purposes, an empirical expression has been found by using the experimental (n,³ He) cross section values as a function of (N-Z) and (E_n-E_th) where (N-Z) is the neutron excess of the target nucleus, E_n and E_th are the incident neutron energy and the (n,³He) threshold energy, respectively. The derived empirical relation gives a good fit with the experimental values     

Systematics for (n,p) excitation functions in the neutron energy between 13.3 and 15.0 MeV

Systematics of (n,p) excitation functions in the neutron energy between 13.3 and 15.0 MeV were studied on the basis of experimental data measured by the Nagoya and Fusion Neutronics Source groups. The empirical formulae of a cross section (σ₁₄) at 14.0 MeV and a relative slope (S) of excitation functions were deduced. These formulae covered the mass range between 19 and 188. The empirical formula of S was expressed as a function of (N—Z)/A and threshold energy, where N, Z and A are the mass, proton and neutron numbers numbers for the target nuclei, respectively. The empirical formula of σ₁₄ was expressed by a simple formula with two fitting parameters. By using the proposed empirical formulae, the partial excitation functions between 13 and 15 MeV were reproduced. Comparing the experimental data with the calculated excitation functions, we concluded that the accuracy of the proposed empirical formulae was ± 20%.     

Recommended values of the delayed neutron yield for: U-235; U-238 and Pu-239

Today there is no well-established theoretical model to predict the fission delayed neutron yield v_d with the required accuracy. In this field the recommended data result from the rare experimental data analysis or from purely phenomenological or semi-phenomenological models. There is another source of valuable information: the related integral data or β_eff- data. In this report we demonstrate, via a careful analysis of the experimental methods leading to revisited experimental β_eff values and associated uncertainties, that for the major nuclei the v_d evaluated data are of acceptable quality. For U-235 U-238 and Pu-239 we recommend v_d values for the thermal and the fast reactor ranges which have been obtained from a statistical consistent adjustment to the β_eff data. In the course of this study we show that the energy dependence of v_d, suspected from a physics point of view, probably exists with a different magnitude according to the nucleus. Concerning the major nuclei it is of negligible importance for the applications. The improvement of the higher Pu isotopes and minor actinides data is the main motivation for developing the theoretical investigations of the delayed neutron generation mechanism at the same level as the necessary experimental activity.     

Determination of sulphur and copper depth distribution in patina layers using nuclear reaction techniques

A method for Cu and S profiling in patina layers was developed by applying a combination of nuclear reaction analysis (NRA) and Rutherford backscattering spectroscopy (RBS). The copper profiling was performed by using the 1327 keV γ-ray deexciting the third excited state to the ground state of ⁶³Cu produced by the reaction ⁶³Cu(p,p^′γ)⁶³Cu. For the determination of sulphur the 2230 keV γ-ray was used deexciting the first excited state to the ground state of ³²S formed through the reaction ³²S(p,p^′γ)³²S, which exhibits three sharp resonances at projectile energies 3.094, 3.195 and 3.379 MeV. The relevant cross-sections were measured in the energy range between 3.0 and 3.7 MeV in steps of 20 keV at 125° to the incident proton beam direction. The technique was tested using artificially produced and natural copper patina layers. Supporting information on the depth distribution of the constituent elements of the patina samples was obtained by p-RBS (E_p: 1.5 MeV, θ: 160°).