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.     

Charge state distribution and its equilibration of 2 MeV/u sulfur ions passing through carbon foils

Charge state distributions of 2.0 MeV/u sulfur ions of various initial charge states (6, 10, 11, 13+) after passing through 0.9, 1.5, 2.0, 3.0, 4.7, 6.9 and 10 μg/cm² carbon foils have been studied. It is observed that the processes involving the L-shell electrons are equilibrated within the target thickness of 5 μg/cm² and the charge equilibration over this thickness is ruled by the K-shell processes. Measured charge state distributions do not flat off to establish equilibrium within the measured thicknesses, but the mean charge states almost saturate to 12.4 for all initial charge states examined. Calculation with ETACHA code, developed by Rozet et al. [Nucl. Instr. and Meth. B 107 (1996) 67], is employed, although the present impact energy is lower than the assumed region for the code.     

Energy loss calculations for fast light ions in celluloid including charge-exchange processes

A method is proposed to calculate the charge-exchange energy loss (−dE/dx)_ex and electronic energy loss (−dE/dx)_el on the basis of the electron capture and loss cross-sections, extracted from the experimental data. The experimental and calculated results are presented for energy loss of projectile ions Be, B, N and O with 0.35 MeV/nucleon, passing through celluloid films. The dependence of energy loss on the initial charge of projectile ions and target thickness in nonequilibrium conditions is examined.     

Neutralization rate for slow Ar ions in front of KCl(0 0 1)

Charge state distributions of reflected ions are measured when 5 keV Ar^q+(q = 0−2) ions are incident on a clean KCl(0 0 1) surface at grazing angle, θ_i. Although the charge state distribution does not depend on the incident charge state at larger θ_i, significant dependence of the charge state distribution on incident charge state is observed at smaller θ_i. The ionization of Ar⁰ is completely suppressed at θ_i < 20 mrad, while large neutralization probability is observed for Ar⁺ incidence. These features allow us to derive the position-dependent neutralization rate of Ar⁺ in front of KCl(0 0 1). The obtained neutralization rate decreases exponentially with distance from the surface as it is usually assumed.     

Fermi shuttle acceleration in atomic collisions: the case of ion induced electron emission

The “Fermi shuttle” acceleration of electrons in ion–atom collisions, i.e. multiple collision sequences of electrons bouncing off the projectile and target nuclei, can lead to the emission of very energetic electrons (i.e. with velocities higher than the binary encounter electrons). We performed measurements of the evolution of the Fermi shuttle electron yield with the induced perturbation and the target atomic number. The yield increases with the perturbation parameter (ratio of projectile charge and projectile velocity q/v_P), which was varied from q/v_P ≈ 0.2 (weak perturbation) to q/v_P ≈ 2 (strong perturbation). We also introduce a more realistic scaling parameter, which accounts for the re-bouncing of the electrons on target and projectile, and show that the yields increase as a function of this parameter. For a given projectile, the Fermi shuttle electron yield increases with the target atomic number. Furthermore, we show that the velocity distribution of the high-energy electrons is exponentially decreasing N(v)  exp(−nv) and exhibits the same evolution of the slope n with projectile velocity as in the case of Fermi accelerated deuterons.     

Convoy electrons measured in coincidence with exit charge states in ion-surface scattering

Convoy electrons produced at glancing-angle scattering of 1.4–3.5 MeV Li ions from a SnTe(001) surface are measured in coincidence with scattered ions of different charge state q_e. Acceleration of the convoy electron due to the surface wake induced by the projectile ion is observed. The observed acceleration is found to be almost independent of q_e. This indicates that the memory of the charge state of the ion at convoy-electron emission is erased by subsequent charge-exchange processes at the surface. Using Bohr and Bohr-Lindhard models, it is concluded that the observed convoy electrons are mainly produced in the immediate vicinity of the surface.     

Impact-parameter dependence of the electronic energy loss and angle-dependent energy loss for ions traversing thin foils

The impact-parameter dependence of the electronic energy loss has been investigated using the quantal harmonic oscillator model and the shell-wise model of atomic stopping for ions with velocity v > v₀ and v < v₀, respectively. The electronic energy losses obtained by the impact-parameter dependent formalism have been used in a Monte Carlo simulation code to give the angular dependence of the energy loss of protons, helium ions and heavy ions transmitted through thin foils. The model calculations are compared with available experimental data.     

Surface investigations using monolayer-resolvable high-resolution Rutherford backscattering spectroscopy

Energy spectra of scattered 0.5 MeV He ions from a clean (001) surface of SnTe are measured with a 90° sector magnetic spectrometer (ΔE/E 0.1%). The ions scattered from successive atomic layers can be resolved in the energy spectra. Inelastic energy losses and charge state distributions of 0.5 MeV He ions scattered from the topmost atomic layer of the SnTe(001) are measured. A position-dependent stopping power at the surface is proposed from the observed energy losses. The observed charge state distribution shows the importance of the charge-exchange processes with valence electrons in the tail of the electron distribution at the surface.     

Charge state distributions and resulting isotopic fractionation effects of carbon and chlorine in the 1–7 MeV energy range

Equilibrium charge state distributions have been measured for 2–7 MeV ³⁵Cl ions stripped in ca. 10 μg/cm² carbon foils and for 2–7 MeV ¹²C ions stripped in ca. 880 ng/cm² oxygen gas. In addition, for 4.95 MeV gas stripped ¹²C ions, the non-equilibrium distribution has been recorded for stripper thicknesses of 50–2500 ng/cm². The results are compared with previous measurements. Isotopic fractionation versus energy is shown for some charge states of carbon, chlorine and beryllium.     

Interactions of slow H, H2, and H3 with thin carbon foils

Interaction processes resulting from the transit of incident 2–30 keV H⁺, H⁺₂ and H⁺₃ through 1.2 to 2.5 μg cm⁻² carbon foils are investigated by examining the charge state and angular scatter distributions of atomic and molecular species that exit the foils. A comparison of the scatter distributions of exiting H⁺₂ and H⁰ from incident H⁺₂ and H⁺₃ show that the atomic components of transmitted molecules scatter independently from foil atoms. For a given foil thickness, the measured fractions of H⁺₂ from incident H⁺₂ and H⁺₃ are inversely proportional to the square of the angular scatter half-width.     

Energy straggling of 60 MeV 58Niq+ ions in thin carbon foils and gases

Energy straggling of 60 MeV ⁵⁸Ni^q+ ions in thin carbon foils and gas layers has been measured with a Q3D magnetic spectrograph in dependence of the incident and analysed charge state of the ions. The straggling increases with the number of electrons per gas molecule, thus showing strong correlation effects. In solid carbon, however, energy straggling is close to the data of deuterium gas. The small straggling in carbon is interpreted as an effect of the long range interaction of the heavy ions in dense solids. Furthermore, it is observed that energy straggling depends on the charge state of the projectiles unless the equilibrium charge state is reached.     

Beam-foil interaction of highly ionized chlorine ions in the high energy region

Distributions of charge states and multiple scattering widths of angular distributions have been simultaneously measured using a two dimensional-position sensitive detector for 150 MeV ³⁷Cl¹⁰⁺ ions emerging from carbon foils with thickness of 2.5–180 $\text{μg}\text{cm}{}^2$. For thinner foils, the scattering angle dependence of mean charge states verifies the evidence for the so-called single violent and/or plural collisions     

The stripper design and test at HIRFL-CSR

Charge stripping is employed to produce multi-charged ions for injecting the cooling storage ring.After penetrating through the carbon foil,the widened distribution of ion charge states poses a limit to the ion injection.Therefore,the carbon foil plays a key role in the charge stripping injection.In this paper,four strippers for Heavy Ion Research Facility at Lanzhou(HIRFL)and Cooling Storage Ring(CSR)are introduced.The charge state distribution of the stripped ions is measured and the stripping efficiency of the foils is investigated.The experimental results are consistent with the theoretical 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.     

Equilibrium charge state distributions for boron and carbon ions emerging from carbon and aluminum targets

Equilibrium charge state distributions of boron and carbon ions through carbon and aluminum targets were measured with an energy range of 3-6 MeV. Comparisons of the data with relevant semi-empirical models for the equilibrium mean charge states and for the charge state distribution widths could provide valuable insight on the underlying mechanisms for a fast ion to lose or capture electrons. In-depth examinations of the experimental results in combination with semi-empirical models suggest that equilibrium charge state distributions are well represented by Gaussian distributions.     

碳剥离膜的厚度对电荷态分布的影响

在SSC加速器的前束流输运线上探索碳剥离膜的厚度对被剥离后束流电荷态分布的影响,是本实验的目的。因为作为SSC的注入器,我们回旋加速器束流的引出能量较高,因此碳剥离膜的平衡厚度要求大大超过一般用在串列静电加速器头部所使用的碳膜厚度,有人曾用公式x(μg/cm~2)=5.9285+22.386w-1.1292w~2来估计碳膜的平衡厚度与能量之间的关系,误差范围为100％。式中,w以MeV/A为单位。为了研究碳剥离膜的厚度对束流电荷分布的影响我们进行了如下实验。     

An empirical formula for L line X-ray production cross-section of elements from Ag to U for protons below 3.5 MeV

When computing element concentration from proton induced X-ray emission analysis, an important parameter is the X-ray production cross-section. There have been numerous experimental and theoretical works in this field. Nonetheless, although there is a simple analytical formula to compute K X-ray cross-sections, there is no such ones for the L lines. We present here analytical formulas for the cross-section of the three main X-ray lines L, L_β and L_γ based on experimental data. So far, nearly 3000 values of cross-sections for elements from Ag to U and proton energy ranging from 0.5 to 3.5 MeV have been collected from various references. This experimental data set has been fitted for each X-ray line with an exponential function depending on the proton energy and on the element atomic number. These fitted values have then been compared to the experimental data and with theoretical values obtained by the ECPSSR theory and Coster–Kronig fluorescence yields.     

Design of the new superconducting microprobe system in Munich

At the Munich 15 MV tandem accelerator a new two-stage microprobe system is under construction. It will demagnify a beam spot by a factor 200 in both transversal directions for ions up to an energy of 200 MeV · q²/A. The second stage of the system is a superconducting quadrupole doublet lens, with overlayed 2n-poles, n = 4, 6 and 8. The multipole components of this lens have been determined by a ray tracing program with a special treatment of the fringing fields. As a result of these calculations, the overall geometrical aberrations at the focal point are 180 nm horizontally and 280 nm vertically at full angular acceptance (image coordinates ±9 and ±20 mrad, respectively). A main part of the superconducting lens is a central ceramic tube which defines the exact positions of the poles. Superconducting NbTi foils are used to shape the field to the desired one. Superconducting current loops automatically serve for a suppression of all odd harmonic field components.     

Measurement of recoil nuclei losses for proton-induced reactions in Al, Si, Mg and Fe at 200 and 500 MeV

The recoil losses of product nuclei in proton-induced reactions at 200 and 500 MeV in Al, Si, Mg and Fe targets were measured using carbon catcher foils or stacks of Mylar foils. In all cases, the recoil losses were less than 1% for the target thicknesses used and so in the ongoing systematic study to measure cross sections for proton- and neutron-induced reactions, these losses are not important. For Fe targets irradiated at 200 MeV, the recoil losses in the forward direction for several product nuclei measured in both a carbon catcher foil and a Mylar stack were in good agreement. From the recoil losses, the mean forward recoil ranges for several product nuclei were calculated.