Prompt gamma emission excitation functions for PIGE analysis

A proton energy scan from 2.2 to 3.8 MeV (Δ E = 20 keV) was performed to measure differential cross sections of prompt gamma reactions on Li, B, F, Mg, Al, Si and P at θ_lab = 90°. The purpose of the present work is to provide the basic data necessary to set up the PIGE (proton induced gamma ray emission) technique for the analysis of thin and intermediate samples.     

Electrically active defects in BF2+ implanted and germanium preamorphized silicon

Ultra-shallow p⁺-n junctions have been formed using 15 keV/10¹⁵ cm⁻² BF₂⁺ implantation into both Ge⁺-preamorphized and crystalline 〈1 0 0〉 silicon substrates. Rapid thermal annealing (RTA) for 15 s at 950°C was used for dopant electrical activation and implantation damage gettering. The electrically active defects present in these samples were characterized using Deep Level Transient Spectroscopy (DLTS) and isothermal transient capacitance (ΔC(t, T)). Two electron traps were detected in the upper half of the band gap at, respectively, E_c - 0.20 eV and E_c - 0.45 eV. They are shown to be related to Ge⁺ implantation-induced damage. On the other hand, BF₂⁺ implantation along with RTA give rise to a depth distributed energy continuum which lies within the forbidden gap between E_c - 0.13 eV and E_c - 0.36 eV. From isothermal transient capacitance (ΔC(t, T)), reliable damage concentration profiles were derived. They revealed that preamorphization induces not only defects in the regrown silicon layer but also a relatively high concentration of electrically active defects as deep as 3.5 μm into the bulk.     

Proton elastic scattering and proton induced γ-ray emission cross-sections on Na from 2 to 5 MeV

Differential cross-sections for proton elastic scattering on sodium and for γ-ray emission from the reactions ²³Na(p,p′γ)²³Na (E_γ = 440 keV and E_γ = 1636 keV) and ²³Na(p,α′γ)²⁰Ne (E_γ = 1634 keV) were measured for proton energies from 2.2 to 5.2 MeV using a 63 μg/cm² NaBr target evaporated on a self-supporting thin C film.The γ-rays were detected by a 38% relative efficiency Ge detector placed at an angle of 135° with respect to the beam direction, while the backscattered protons were collected by a Si surface barrier detector placed at a scattering angle of 150°. Absolute differential cross-sections were obtained with an overall uncertainty estimated to be better than ±6.0% for elastic scattering and ±12% for γ-ray emission, at all the beam energies.To provide a convincing test of the overall validity of the measured elastic scattering cross-section, thick target benchmark experiments at several proton energies are presented.     

Lifetime measurement of the 28Si compound state at 13.095 MeV by the blocking effect

The 〈110〉 axial and (111) planar blocking dips in an Al crystal are used to measure the lifetime of the state at 13.095 MeV in the compound nucleus ²⁸Si excited by the ²⁷Al(p, α)²⁴Mg reaction at E_p = 1565 keV. The blocking dips for 2.12 MeV α particles from this reaction at E_p = 1183.4 keV are also measured and the radiation damage in the crystal is investigated. Monte Carlo simulations and analytical methods in the axial blocking measurement and analytical methods in the planar blocking case are used. The measured lifetime at the E_p = 1565 keV resonance, τ = 15 ± 2 as, is in good agreement with the value derived from the reaction-yield measurement.     

Proton induced γ-ray emission yields for the analysis of light elements in aerosol samples in an external beam set-up

The PIXE technique is a reliable tool for the characterisation of thin aerosol samples, but it can underestimate the lightest measurable elements, like Na, Mg, Al, Si and P, owing to the absorption of their X-rays inside the sample. The PIGE technique is a valid help to determine corrections for such effect: in order to perform PIGE measurements relative to thin reference standards in an external beam set-up, we measured, at the external beam facility of the Tandetron accelerator of the LABEC laboratory in Florence, the γ-ray yields as a function of the proton beam energy for the reactions ¹⁹F(p,p′γ)¹⁹F (E_γ = 110 and 197 keV), ²³Na(p,p′γ)²³Na (E_γ = 440 keV) and ²⁷Al(p,p′γ)²⁷Al (E_γ = 843 and 1013 keV), in the proton energy range from 3 to 5 MeV. The measured yields are shown, and the determined most suitable energies for performing PIGE quantification of Na and Al are reported, together with the corresponding minimum detection limits (MDLs). The results of some test on PIGE accuracy and an evaluation of self-absorption effects in PIXE measurements on thin aerosol samples are also presented.     

Properties of Na implanted targets

Ten types of ²³Na implanted targets have been fabricated for the purposes of investigating the effects of proton beam bombardment on the implanted sodium distribution. Targets were implanted at energies of E_Na = 10-30 keV using copper, tantalum, and nickel as host materials. Thin layers (100-200 Å) of chromium and gold were also evaporated over some of the targets to provide a protective layer for the implanted sodium. The ²³Na(p, γ) resonance at a lab proton energy of E_p = 309 keV was used to determine the implanted distribution. Successive resonance profile measurements are presented for each implanted target, and the concurrent loss of ²³Na resulting from beam bombardment is reported. The calculated temperature rise of the targets indicates that beam heating has a negligible effect on the implanted sodium distribution, and that the principal mechanism for ²³Na loss during beam bombardment is sputtering.     

Oxygen detection by non-Rutherford proton backscattering below 2.5 MeV

Oxygen detection by proton backscattering has been investigated. The oxygen detection sensitivity of 2.5 MeV proton backscattering is shown to exceed that of ⁴He backscattering by even a factor of about 15 depending on the matrix. The needed proton elastic scattering cross sections of oxygen for θ_lab = 170° have been measured in the energy range E_lab = 770–2480 keV relative to Ti and Sn elastic scattering cross sections using thin TiO₂ and SnO₂ samples. The angular dependence of the cross section was measured at energies E_lab = 1790, 1990, 2191, and 2382 keV for backscattering angles. The experimental cross sections were found to be 1.1–5.7 times the pure Coulomb cross section. Theoretical calculations for the scattering cross sections were performed and their inapplicability to experimental purposes is demonstrated. Fits to experimental data are given.     

PIGE analysis and profiling of aluminium

In this work we present an alternative method for PIGE analysis of aluminium in thick samples. This method is based on the ERYA - emitted radiation yield analysis - code, which integrates the nuclear reaction excitation function along the depth of the sample. For this purpose, the excitations functions of the ²⁷Al(p,p′γ_1,2)²⁷Al reaction (with gamma-ray energies of 844 and 1014 keV) were employed. Calculated gamma-ray yields were compared, at several proton energy values, with experimental yields for thick samples made of inorganic compounds containing aluminium. The agreement is better than 5%.The 1684 keV resonance of the same reaction, with a natural width of 100 eV, was used to profile samples of Ti implanted with several doses of Al. We show that this resonance, stronger than the 992 keV resonance of the ²⁷Al(p,γ)²⁸Si usually employed for aluminium profiling, leads to similar depth resolution in shorter collection time.     

PIGE analysis of magnesium and beryllium

In this work, we present an alternative method for PIGE analysis of magnesium and beryllium in thick samples. This method is based on the ERYA – Emitted Radiation Yield Analysis – code, which integrates the nuclear reaction excitation function along the depth of the sample. For this purpose, the excitations functions of the ²⁵Mg(p,p′γ)²⁵Mg (E_γ = 585 keV) and ⁹Be(p,γ)¹⁰B (E_γ = 718 keV) reactions were employed. Calculated gamma-ray yields were compared, at several proton energy values, with experimental yields for thick samples made of inorganic compounds containing magnesium or beryllium. The agreement is better than 5%. Taking into consideration the experimental uncertainty of the measured yields and the errors related to the stopping power values, this agreement shows that effects as the beam energy straggling, ignored in the calculation, seem to play a minor role.     

Improved energy resolution of a cyclotron beam for RBS measurements

For RBS (Rutherford Back Scattering) analysis, the quality of the beam is of premium importance because the depth profile resolution of the method is strongly dependent on the energy resolution of the probing beam. A magnetic analyzer, consisting of two 90 left-right bending magnets forming an achromatic doublet has been adapted to the Liege 20 MeV (proton) AVF (Azimuthal Varying Field) cyclotron. The energy resolution of that system has been measured by recording the resonance width of a ³²S(p,p′γ)³²S (3.38 MeV. p⁺ lab. energy). We have obtained a value of ΔE = ± 2 keV, reducing by a factor of 20 the natural dispersion of our cyclotron.We describe our magnetic analyzer system and present the results of our RBS measurements at energies up to 14 MeV α.     

Combination of resonance integral and Maxwellian 30 keV data – A sensitive test of the resonance region

This paper presents the approach of a combined use of resonance integrals and average Maxwellian cross sections (MACS) at kT = 30 keV to test and validate the resolved resonance range or its reconstructed cross section curve. Based on these two integral measurements a sensitive and energy dependent test can be provided. These two integral quantities cover with their neutron spectra the energy region between E_n = 0.5 eV up to several hundred keV, respectively, with different weighting. Our principal motivation is to produce a validation tool, sensitive to the lower and upper parts of the resonance region through the difference in the applied 1/E and kT = 30 keV Maxwell–Boltzmann spectra of the resonance integral and MACS data.     

Effect of <200 keV proton radiation on electric properties of silicon solar cells at 77 K

The change in electric properties of back-field silicon solar cells was investigated under the irradiation of protons with the energies less than 200 keV at 77 K. Experimental results showed that the short circuit current, maximum output power and open circuit voltage decrease to different extent with increasing the fluence and energy of protons. Under the 120 keV proton irradiation for the fluence of 1 × 10¹⁶ cm⁻², a large amount of radiation-induced defects with the energy level H1 +0.47 eV were formed. In terms of analyzing the time dependence of electric properties, the performance lifetime of the silicon cells under the exposure of <200 keV protons was predicted.     

Determination of differential cross-sections for the natK(p, p0) and 39K(p, α0) reactions in the backscattering geometry

In the present work, new, differential cross-section values are presented for the ^natK(p, p₀) reaction in the energy range E_lab = 3000–5000 keV (with an energy step of 25 keV) and for detector angles between 140° and 170° (with an angular step of 10°). A qualitative discussion of the observed cross-section variations through the influence of strong, closely spaced resonances in the p + ³⁹K system is also presented. Information has also been extracted concerning the ³⁹K(p,α₀) reaction for E_lab = 4000–5000 keV in the same angular range. As a result, more than ～500 data points will soon be available to the scientific community through IBANDL (Ion Beam Analysis Nuclear Data Library – http://www-nds.iaea.org/ibandl/) and could thus be incorporated in widely used IBA algorithms (e.g. SIMNRA, WINDF, etc.) for potassium depth profiling at relatively high proton beam energies.     

Evaluation of Neutron Cross Sections of Plutonium-241

The neutron cross sections of ²⁴¹Pu were evaluated in the energy range between 10^?5 eV and 15MeV, and are stored in the Japanese Evaluated Nuclear Data Library Version-1 (JENDL-1). In the energy range below 100eV, the evaluated data contained in ENDE/B-IV and the resonance parameters recommended in BNL-325 were tentatively adopted. The unresolved resonance parameters were determined between 100 eV and 21.5 keV so as to reproduce the experimental data of the fission and capture cross sections. Above 21.5 keV, the fission cross section was evaluated on the basis of the experimental data, most of which were reported as the ratio to the fission cross section of ²³⁵U and then were normalized by the fission cross section of ²³⁵U adopted in JENDL-1. The capture cross section was obtained from the experimental data of a in the energy range up to 250 keV. The capture cross section above 250 keV and the elastic and inelastic scattering, (n, 2n) and (n, 3n) reaction cross sections above 21.5 keV were obtained on the basis of the theoretical calculations. The calculated cross sections are connected smoothly with those obtained from the unresolved resonance parameters at 21.5 keV. This suggests the self-consistency of the present evaluation.     

Recommended standards for gamma-ray energy calibration (1979)

A consistent set of γ-ray energies, all with uncertainties of at most 10 ppm, is recommended for use in the energy calibration of γ-ray spectra. Almost all γ rays listed are from commercially available sources. The half-lives of the isotopes selected are generally at least 30 days. The γ-ray energies, in the range E_γ = 60–6100 keV, are all based on the value of 411 804.4 ± 1.1 eV for the γ-ray from the decay of ¹⁹⁸Au. The energy of the 6129-keV line in ¹⁶O, which is the γ-ray with the highest energy of the present set, has also been measured relative to another standard; the two values are consistent.     

Contribution of (M+N+…) shells to total internal conversion coefficients for transition energies above 500 keV

The ratios of internal conversion coefficients, $\text{(M+N+…)}\text{L}$, are calculated for atomic numbers Z = 15, 20,…, 100. Nuclear transition energies from 500 to 4000 keV and multipolarities E1 … E4, M1 … M4 are treated. For energies above 1000 keV the internal conversion connected with s-electrons was found to play a dominant role, while conversion in the subshells d and f is negligible. The total conversion coefficients are presented in graphical form for the energy interval 200 to 4000 keV.     

A folding model for crystal defects in the shape analysis of blocking lifetime measurements

A new method of analysis is presented for experiments that measure nuclear reaction times exploiting the blocking effect in single-crystals. It is based upon a direct comparison between measured and calculated blocking patterns, obtained by folding the angular distribution for perfect crystals with a function describing the influence of the defects. Such a function is found by comparing measured and calculated “prompt” patterns. The resulting equations are solved using Tikhonov's regularization procedure. The whole method is applied to a reanalysis of an earlier series of results on the ²⁷Al (p, α₀) resonance at E_p=632.2 keV. The resulting lifetime of the ²⁸Si 12.195 MeV level, τ = (85.3 ± 5.3) as, agrees with that deduced from resonance reaction yields, and is somewhat different from an earlier analysis based on the filling-in parameter R.     

Profiling of titanium implanted into iron and nickel with the reaction 48Ti (p, γ)49V

A profiling technique for titanium is described which is based on an analog resonance in the cross section of the reaction ⁴⁸Ti(p, γ)⁴⁹V at E_P = 1.361 MeV. Primary γ radiation of the energy E_γ = 7.963 MeV is measured high detection efficiency is achieved. The properties of the technique are discussed and examples of its applications to Ti-implanted metals are given.     

气溶胶中F和Na分析的外束质子诱发γ射线激发曲线测量

在大气颗粒物离子束分析中,质子诱发γ射线分析（PIGE）作为质子诱发X荧光发射（PIXE）的补充方法,通常用于分析轻元素。为得到外束PIGE定量分析气溶胶样品中F和Na元素的最佳实验条件,本工作在北京师范大学串列加速器上测定了质子能量在1.8～2.9 MeV范围内,核反应¹⁹F(p,p’γ)¹⁹F（E_γ=110 keV和197 keV）和 ²³Na(p,p’γ)²³Na(E_γ=440 keV)的γ射线激发函数。     

First temperature stage evolution of irradiation-induced defects in tungsten studied by positron annihilation spectroscopy

The behaviour of vacancy like implantation-induced defects created in the track region of 800 keV ³He ions in polycrystalline tungsten was studied by Doppler broadening spectroscopy as a function of annealing temperature. A slow positron beam, coupled with a Doppler broadening spectrometer, was used to measure the low- and high-momentum annihilation fractions, S and W, respectively, as a function of positron energy in tungsten samples implanted at different fluences from 10¹⁴ to 5 × 10¹⁶ cm⁻². The behaviour of the S(E), W(E) and S(W) plots with the annealing temperature clearly indicates that the irradiation-induced vacancy like defects begin to evolve between 523 and 573 K, whatever the implantation fluence. This first temperature stage evolution corresponds to the migration of the monovacancies created during implantation to form larger vacancy like defects of which depth profile is different from the initial radiation-induced defects one.