Surface Structure of √3x√3R 30 Cl/Ni(111) Determined Using Low-temperature Angle-Resolved-Photoemission Extended Fine Structure

A surface structural study of the √3 × √3 R30° Cl/Ni(111) adsorbate system was made using low-temperature angle-resolved photoemission extended fine structure. The experiments were performed along two emission directions, [111] and [110], and at two temperatures, 120 and 300 K. The multiple-scattering spherical-wave analysis determined that the Cl atom adsorbs in the fcc threefold hollow site, 1.837(8) Å above the first nickel layer, with a Cl-Ni bond length of 2.332(6) Å, and an approximate 5% contraction between the first and the second nickel layers (the errors in parentheses are statistical standard deviations only)

Source description and sampling techniques in PEREGRINE Monte Carlo calculations of dose distributions for radiation oncology

We outline the techniques used within PEREGRINE, a 3D Monte Carlo code calculation system, to model the photon output from medical accelerators. We discuss the methods used to reduce the phase-space data to a form that is accurately and efficiently sampled

Treatment of patient-dependent beam modifiers in photon treatments by the Monte Carlo dose calculation code PEREGRINE

The goal of the PEREGRINE Monte Carlo Dose Calculation Project is to deliver a Monte Carlo package that is both accurate and sufficiently fast for routine clinical use. One of the operational requirements for photon-treatment plans is a fast, accurate method of describing the photon phase-space distribution at the surface of the patient. The open-field case is computationally the most tractable; we know, a priori, for a given machine and energy, the locations and compositions of the relevant accelerator components (i.e., target, primary collimator, flattening filter, and monitor chamber). Therefore, we can precalculate and store the expected photon distributions. For any open-field treatment plan, we then evaluate these existing photon phase-space distributions at the patient`s surface, and pass the obtained photons to the dose calculation routines within PEREGRINE. We neglect any effect of the intervening air column, including attenuation of the photons and production of contaminant electrons. In principle, for treatment plans requiring jaws, blocks, and wedges, we could precalculate and store photon phase-space distributions for various combinations of field sizes and wedges. This has the disadvantage that we would have to anticipate those combinations and that subsequently PEREGRINE would not be able to treat other plans. Therefore, PEREGRINE tracks photons through the patient-dependent beam modifiers. The geometric and physics methods used to do this are described here. 4 refs., 8 figs

Threshold Photoelectron Spectrum of the Argon 3s Satellites

Lately a variety of techniques have studied the electron correlation satellites with binding energies between the Ar 3s ionization potential (29.24 eV) and the lowest 2p−2 ionization potential (43.38 eV). One of these techniques, threshold photoelectron spectroscopy, with ≈90 meV electron resolution, revealed at least 25 Individual electronic states. All of these could contribute to any other satellite spectrum, and this observation helped explain some discrepancies between previous measurements. This technique has been applied here to the same region (30 eV ⩽ Hv ⩽ 45 eV) with higher resolution (3s−1 peak). In this higher resolution spectrum at least 29 Individual electronic states are present. In some cases multiplet splitting Is observed