Pure ionization cross section of helium and ionization mechanism

Pure target ionization was investigated for 0.4-6.4 MeV C^q+(q = 1-4) + He and O^q+(q = 1-4) + He collisions. The double-to-single target ionization ratios R₂₁ were measured using coincidence techniques. We compare our results with existing experimental results and find they are in good agreement. The ratio R₂₁ is nearly independent of projectile charge state. The relation of R₂₁ ∼ V is analyzed using the over barrier model (OBM) and ionization probability, which is described in our extended over barrier model. Our calculation agrees well with the experimental results.     

Cross sections for transfer ionization in ion-helium collisions

A simple model has been developed within the independent-particle model (IPM) based on the Bohr-Lindhard model and classical statistical model. Cross sections for transfer ionization of helium by ions A^q+ (q = 1-3) are calculated for impact energies between 10 and 6000 keV/u. The calculated cross sections are in good agreement with the experimental data of helium by He^(1-2)+ and Li^(1-3)+.     

Molybdenum L-shell X-ray production by 350-600 keV Xe (q = 25-30) ions

Molybdenum L-shell X-rays were produced by Xe^q+ (q = 25-30) bombardment at low energies from 2.65 to 4.55 keV/amu (350-600 keV). We observed a kinetic energy threshold of Mo L-shell ionization down to 2.65-3.03 keV/amu (350-400 keV). The charge state effect of the incident ions was not observed which shows that the ions were neutralized, reaching an equilibrium charge state and losing their initial charge state memory before production of L-shell vacancies resulted in X-ray production. The experimental ionization cross sections were compared with those from Binary Encounter Approximation theory. Taking into account projectile deflection in the target nuclear Coulomb field, the ionization cross section of Mo L-shell near the kinetic energy threshold was well described.     

Experimental L-shell x-ray production and ionization cross sections for proton impact

Cross sections for L-shell x-ray production and ionization by protons are tabulated according to target atomic number, target type, and incident proton energy. Cross sections for production of the individual L-shell component x-rays and for ionization of the three L subshells are presented separately. Ratios of Lα to Ll x-ray production cross sections are also listed. Literature is covered from 1975 to November 1982. Experimental details pertaining to the cross-section measurements and the theoretical models employed by the experimenters for comparison with their data are included. It is intended that this information will help the reader to ascertain the most reliable cross-section values without recourse to the literature.     

Polarization effects on the cross-section of ion-atom collisions

Coupled-channel cross-sections for electron capture, ionization and electron loss due to polarization effects are calculated. The maximum impact parameter for electron escape is analyzed within the classical framework. The probabilities of ionization and capture are analyzed simultaneously by a semi-empirical method. Differing from the n-body classical trajectory Monte Carlo method, the condition for electron escape is determined by Coulomb forces related to the two nuclei. This method can be used to calculate coupled-channel cross-sections rather than single-channel ones in other methods. Therefore the calculated results can be compared with experimental data directly. In the low energy range, neglecting the ionization effect, the single-capture cross-sections of hydrogen atoms induced by various partially-stripped ions were calculated. In the high energy range, neglecting the capture effect on ionization, the pure-ionization cross-sections of neon atoms induced by Ne^q+ (q = 4, 6, 8) and Ar^q+ (q = 4, 6, 8, 10) at an incident energy E = 1.05 MeV/u were calculated. Good agreement was found between our calculation and experimental data in the literature. This method had been partially applied for intermediate energy successfully.     

Au L-shell ionization by Si and S ions: Integral and differential cross sections and alignment

We present the following experimental results on Au L-shell ionization: (1) in the bombarding energy range 0.25—2.5 $\text{MeV}\text{u}$, absolute X-ray yields and the L₃-vacancy integral alignment for Si, and cross section ratios $\text{σ2}\text{σ3}$ for Si and S as projectiles; (2) MeV sulphur energy, subshell ionization probability ratios and the components A₂₀(b) and A₂₂(b) of the statistical tensor descr the L₃-vacancy for impact parameters b = 20–450 fm. A comparison of the data to SCA calculations reveals, except perhaps for the differential alignment, important discrepancies relative to the theoretical predictions. These discrepancies, increasing at lower projectile velocities, are most probable due to the mutual L-subshell coupling, as well as to the rotational coupling between the L₃ magnetic substates during the collision.     

“International” tables

Expressions used in the calculation of screened hydrogenic M-subshell and total M-shell cross sections for direct Coulomb ionization in the nonrelativistic plane-wave Born approximation have been numerically integrated and tabulated for a range of heavy charged-particle velocity and target-binding energy parameters. Explicit expressions are given for the calculation of x-ray production cross sections from ionization cross sections, Coster-Kronig transition rates, and fluorescence yields. The present results are in disagreement with those of Hansteen, Johnsen, and Kocbach.     

Monte Carlo simulation of Tabata’s electron backscattering experiments

Electron backscattering coefficients, η, obtained from several targets in the MeV range were calculated by using electron-photon Monte Carlo transport calculation codes, i.e., EGS5 and ITS 3.0. These calculated values were compared with those obtained from the electron backscattering experiment performed by Tabata using an ionization chamber [15]. We found that Tabata’s estimation of the multiplication factor of the ionization chamber, f, had a non-negligible error. Then, we calculated the ionization chamber output, I, which is a product of η and f. The ratios of I between the experimental and the calculated values were within 1.5 and 1.3 for the EGS5 code and the ITS 3.0 code, respectively. The ratios of η between the experimental and the calculated values were within 2.4 and 1.5 for the EGS5 code and the ITS 3.0 code, respectively. The differences between the experimental and the calculated values of I and η are large for low-Z targets (Be and C). Here, the ratios obtained by using the ITS 3.0 code are closer to unity than those obtained by using the EGS5 code. The reason of this is the fact that the calculated value obtained by using the ITS 3.0 code is underestimated for low-Z targets; this underestimation can, in turn, be attributed to the use of the default value of the number of steps in the electron transport algorithm in the ITS 3.0 code.     

Near-threshold positron impact ionization of hydrogen

The hyperspherical hidden crossing method (HHCM) is used to investigate positron impact ionization of hydrogen near threshold. An important feature of this method is that it can provide valuable insight into scattering processes. In the calculation of positron-hydrogen ionization, the adiabatic Hamiltonian is expanded about the Wannier saddle point; anharmonic corrections are treated perturbatively. The S-wave results are consistent with the Wannier threshold law and with the extended threshold law that was previously derived using the HHCM. We have extended the previous HHCM calculation to higher angular momenta L and have calculated the absolute ionization cross-section for L = 0, 1 and 2. The HHCM calculation confirms that the S-wave ionization cross-section is small and provides the reason why it is small. The HHCM ionization cross-section (summed over the lowest partial waves) is compared with a convergent close-coupling calculation, a 33-state close-coupling calculation and experimental data.     

Relativistic cross sections for atomic K- and L-shell ionization by protons,calculated from a Dirac-Hartree-Slater model

Relativistic direct ionization cross sections for proton impact have been computed for atomic K and L shells, with Dirac-Hartree-Slater wave functions. Corrections for binding, polarization, and Coulomb deflection are included. Results are tabulated for proton energies from about 0.1 to 3 MeV, for 27 elements with atomic numbers 22 ? Z ? 92.     

Ionization of He,Ne and Ar atoms by 1.05 MeVamuCq+(q = 2–6) and Arq+(q = 4–14) ion impact

Total “apparent” ionization cross sections and partial cross section of the production of highly ionized recoil ions of He, Ne and Ar in 1.05 MeV/amu highly charged C^q+(q = 2–6) and Ar^q+(q = 4,6,10–14) ion impact have been measured and compared with theoretical prediction and other experimental data. The total ionization cross sections have been found to scale as the square of the effective charge of projectile ions $\text{q}{}^1$, as predicted by theories.     

Boron suppression with a gas ionization chamber at very low energies (E < 1 MeV)

Efficient boron suppression for precise ¹⁰Be measurements with AMS is crucial. The performance of ΔE ? E_res gas ionization chambers is also very important for isobar suppression at low beam energies (<1 MeV). A boron suppression of 6–7 orders of magnitude is achievable with the ETH ΔE ? E_res gas ionization in the standard operational mode (readout of ΔE and E_res electrodes). Some physical effects such as pulse height defect or the energy focusing effect within a ΔE section will be discussed, emphasizing ¹⁰Be measurements below 1 MeV. Additionally the potential of silicon nitride membranes as passive energy degraders in front of the detector is demonstrated.     

Thermal ionization of Cs Rydberg states

Rates P_nl of photoionization from Rydberg ns-, np-, nd-states of a valence electron in Cs, induced by black-body radiation, were calculated on the basis of the modified Fues model potential method. The numerical data were approximated with a three-term expression which reproduces in a simple analytical form the dependence of P_nl on the ambient temperature T and on the principal quantum number n. The comparison between approximate and exactly calculated values of the thermal ionization rate demonstrates the applicability of the proposed approximation for highly excited states with n from 20 to 100 in a wide temperature range of T from 100 to 10,000 K. We present coefficients of this approximation for the s-, p- and d-series of Rydberg states.     

Influence of the projectile charge state on the ionization probability of sputtered particles

We present a computational study of the effect of the projectile charge state on secondary ion formation in sputtering. A molecular dynamics simulation of an atomic collision cascade is combined with a kinetic excitation model including electronic friction and electron promotion in close atomic collisions. The model is extended to account for potential excitation following the bombardment with a highly charged ion (HCI). The spatial spreading of the excitation generated in the cascade is treated in an diffusive approach. The excitation energy density profile obtained this way is parametrized via an effective electron temperature, which is then used to calculate the ionization probability of each sputtered atom in terms of a simple charge exchange model. The results obtained for the impact of a 5 keV Ag atom onto a solid silver surface show that the average ionization probability increases from 4.7×10^-4 for a neutral projectile to 5.4×10^-4 for a highly charged projectile ion with a total ionization energy of 576 eV.     

Measurement of specific energy losses of individual fission fragments with a back-to-back δE−E detector system

The specific ionization of fission fragments of specified charge and $\text{E}\text{M}$ values in thermal neutron induced fission of ²³⁵U have been measured employing a back-to-back gridded ionization chamber ΔE-semiconductor detector E setup. The measurements were carried out for the case of a mixture of argon (95%) and methane (5%) gases at two gas pressures, 44 Torr and 270 Torr. The experimental data for the lower gas pressure were used to determine the effective charge parameter γ for the fragments at various velocities. These γ-values have been used to compute the fragment energy losses at the higher gas pressure and are compared with the measured energy loss values.     

He+ (np) cross sections for 2, 3, 4 and 5 MeV C4+ ions colliding with He atoms

The cross sections of ionization plus excitation of He are measured by the C⁴⁺ + He prototype reaction with energies ranging from 2 to 5 MeV. Theoretically the independent electron approximation is used to calculate the HeII (np) ionization plus excitation cross sections. The results of the calculations are compared with our experimental data.     

Predictions of multiple K- and L-shell ionization by alpha-particle impact on atoms with Z = 10 to 100

The peaked binary-encounter approximation is used to compute cross sections for removing one or more electrons from K- and L-shells of atomic targets with Z = 10, 15, 20, 25, 30, 40, 60, 80 and 100 by bombardment with alpha particles. The cross sections, σ_{1K, nL} and σ_{2K, nL}, are plotted over a range of alpha energies in the MeV region near the peaks of these cross sections. The relative magnitudes of the σ_{1K, nL} and σ_{2K, nL} cross sections are similar. Estimates of multiple-ionization cross sections for other projectiles may be determined in some instances by means of the z² scaling law for the ionization probability.     

Lower and upper bounds on M-shell X-ray production cross sections by heavy ions

In inner-shell ionization by heavy ions, a significant shift of X-ray lines to the higher energy side and broadening of the peaks indicate that simultaneous multiple ionization of the M and higher shells can dramatically change the values of the atomic parameters. ₁₄Si^3,4+ and ₁₆S^3,4+ ions in the energy range of 5-10 MeV were used to bombard gold (200 μg/cm²) and bismuth (80 μg/cm²) targets. Eight main M X-ray lines have been detected with a Si(Li) detector. Without a possibility for a realistic way to modify the atomic parameters and an accurate extraction of M-subshell ionization cross sections, theoretical cross sections for M-shell ionization are converted to X-ray production cross sections with two extreme choices that presume (i) no multiple ionization and (ii) the certainty that all shells outer to the M-shell are completely ionized in the full multiple ionization. These choices impose the lower and upper limits on theoretical predictions. The X-ray production data should be bracketed by the bounds calculated with any theory. We test this proposition by comparison of the measured cross sections for production of the main X-ray lines and their sum for the total M-shell X-ray production with the predictions of the First Born and ECUSAR [G. Lapicki, Nucl. Instrum. Meth. B 189 (2002) 8] theories in those two extreme limits. With the extreme assumption of no multiple ionization, the First Born approximation shows overall satisfactory agreement with the data while the ECUSAR theory drastically underpredicts our measurements. With the opposite extreme assumption of the full multiple ionization, the ECUSAR exhibits better agreement with the data than the First Born approximation. While neither agreement suggests sure preference for either of these theories, such extreme conversions - as they would have for of any ionization theories - set the lower and upper bounds on their predictions.     

Cross sections for K-shell ionization by 1H, 2H, 3He,and 4He ion impact

Cross section for K-shell ionization derived from experimental measurements with the light ions ¹H, ²H, ³He, and ⁴He are tabulated according to projectile energy and target atomic number.