Description: This article discusses M-shell x-ray production cross sections for 0.5-2.5-MeV Be+ ions incident upon selected elements from praseodymium to bismuth. M-shell x-ray production cross sections are reported for ₄⁹Be+ ions incident upon thin ₅₉Pr, ₆₀Nd, ₆₃Eu, ₆₆Dy, ₆₇Ho, ₇₂Hf, ₇₄W, ₇₉Au, ₈₂Pb, and ₈₃Bi targets. Incident-beam energies range from 0.5 to 2.5 MeV (55.6-267 keV/u). The results are compared to the predictions of the first-Born-approximation theory and the perturbed-stationary-state theory with energy-loss, Coulomb-deflection, and relativistic corrections (ECPSSR). The first-Born-approximation theory overpredicts the measured cross sections everywhere, especially at high energies, while the ECPSSR theory tends to underpredict them, especially at low energy. This discrepancy between the measurements and the ECPSSR theory may be due in part to multiple-ionization effects which could change the fluorescence yields from the single-hole values used to convert total ionization to x-ray production cross sections in the theoretical calculations.

Description: This article discusses nuclear lifetime of states in ⁹⁴TC and ⁹⁶TC via the pulsed-beam, direct-timing technique. The mean lifetimes of the 333 keV level in ⁹⁴TC and the 119 and 315 keV levels in ⁹⁶TC were measured by the pulsed-beam, direct-timing technique. The values obtained for the mean lifetimes are: τ(333 keV)=2.2(-0.3)(+0.5) nsec, τ(119 keV)=37.0(-0.3)(+0.6) nsec, and τ(315 keV)=2.9(-0.2)(+0.5) nsec. The transition strengths are in agreement with those for other transitions in this mass region.

Description: This article discusses fabrication of silicon-based optical components for an ultraclean accelerator mass spectronomy negative ion source. Abstract: An ultraclean accelerator mass spectronomy negative ion source for semiconductor material mass analysis has been built and is in operation at the University of North Texas' Ion Beam Modification and Analysis Laboratory (IBMAL). The source is unique in that the active surfaces and apertures of the optical components in the ion source have been fabricated from high-purity single crystal silicon. This prevents both the 133Cs+ beam incident on the semiconductor samples and the negative ions from the sample surfaces from "seeing" and sputtering any metal surfaces (mostly stainless steel) in the beamline. The Cs+ beam can be rastered across the sample surface and the impact energy is adjustable to control depth-profiling rates. An ultraclean ion source of this type is necessary to prevent the injection of Fe and other beamline elements onto the sample or into the tandem accelerator, which is equivalent to putting an impurity signal into the mass analysis of the semiconductor sample. Suppression of these elements increases the sensitivity of the analysis to one part in 10¹² for many masses. The fabrication and alignment of the optical components-einzel lenses, ...

Description: This article discusses high sensitivity measurement of implanted As in the presence of Ge in Ge(x)Si(1-x)/Si layered alloys using trace element accelerator mass spectrometry. Abstract: Various devices can be realized on strained GeSi/Si substrates by doping the substrate with different impurities such as As. As is an n-type dopant in both Ge and Si. As cross contamination can also arise during germanium preamorphization implantation due to inadequate mass resolution in the implanter. Thus, it is important to be able to accurately measure low-level As concentrations in the presence of Ge. Secondary ion mass spectrometry (SIMS) is the standard technique for these types of measurements but is constrained by mass interferences from molecular ions (⁷⁴GeH, ²⁹Si³⁰Si¹⁶O). The trace element accelerator mass accelerator technique allows the breakup of interfering molecules. As is measured in a GeSi matrix with sensitivity significantly better than SIMS.

Description: This article discusses K-shell ionization of elements ₁₅P to ₂₈Ni for 0.4 to 3.8 MeV/amu ₅¹⁰B-ion bombardment. Abstract: K-shell x-ray production cross sections, Kβ/Kα x-ray intensity ratios and Kα and Kβ x-ray energy shifts have been determined for thin solid targets of ₁₅P, ₁₉K, ₂₀Ca, ₂₁Sc, ₂₂Ti, ₂₃V, ₂₅Mn, ₂₆Fe, ₂₇Co, and ₂₈Ni for 4-38-MeV ₅¹⁰B ion bombardment. Comparisons of the cross sections were made to direct Coulomb ionization and electron-capture theories by means of fluorescence yields corrected for multiple-ionization effects. The dominant contribution to K-vacancy production for these projectile-target combinations is believed to be direct ionization. Electron capture is expected to be important only for the lighter target elements and then primarily at the higher velocities. The direct-ionization theories employed were the binary-encounter approximation and the plane-wave Born approximation (PWBA) both of which overestimated the experimental data especially at the lower incident ion velocities. The PWBA was modified for increased target-electron binding, Coulomb deflection of the incident ion, polarization of the target-electron wave functions due to the passage of the incident ion, and relativistic target-electron velocities. The experimental data were found to agree quite well with the sum of the theoretical predictions of the modified PWBA and electron capture.