Studies on highly oxidized cyclohexanes. Structure and absolute configuration assignments.

The absolute configurations of pipoxide, ferrudiol and zeylenol, pictured below, are found to parallel those of crotepoxide and senepoxide, suggesting a unified biogenesis.     

Thed(7Li,p)8Li cross section nearE cm=0.61 MeV

The absolute cross sectionσ of thed(⁷Li,p)⁸Li reaction near theE _cm=0.61 MeV resonance has been measured using a⁷Li ion beam and a windowless gas target system filled with D₂ gas. The proton yield of the reaction and theβ-delayedα-activity of the residual nuclides⁸Li were observed both concurrently with the elastic scattering yield, relatingσ to the Rutherford scattering cross sectionσ _R. The resulting values,σ (fromp)=143.6±8.9 mb andσ (from⁸Li)=151±20 mb, lead to a weighted mean value ofσ=153±6 mb (x ²=2.26) including all available values andσ=146±5 mb (x ²=0.05) removing some values from the data set. The consequences for the expected flux of high-energy solar neutrinos are discussed.     

Temperature effects on positron annihilation in metallic single crystals

A Ge(Li) spectrometer was used to measure the temperature-dependence of the intensity of gamma rays resulting from positron annihilation in single crystals of Pb, Sn, Ge and Cu. In contrast to recent angular distribution results, no significant temperature effects were observed.     

Multiplicities of secondary hadrons produced in vp and vp charged current interactions

In an experiment with the hydrogen bubble chamber BEBC at CERN multiplicities of hadrons produced in νp and $\text{v}\text{p}$ interactions have been investigated. Results are presented on the multiplicities of charged hadrons and neutral pions, forward and backward multiplicities of charged hadrons and correlations between forward and backward multiplicities. Comparisons are made with hadronic reactions and e⁺e^? annihilation. In the framework of the quark-parton model the data imply similar charged multiplicities for the fragments of a u- and a d-quark, and a larger multiplicities for the fragments of a uu- than for a ud-diquark. The correlation data suggest independent fragmentation of the quark and diquark for hadronic masses above ～ 7 GeV and local charge compensation within an event.     

A new equilibrium effect in positron trapping in metals

The equilibrium lineshape for positrons annihilating in Cd shows an anomalous temperature dependence which complicates analysis for vacancy formation energies. The phenomenon, tentatively identified as trapping by transient dilatations, probably occurs in all metals.     

Fluctuations in 88Sr(p,p0) and 90Zr(p,p′) in the energy region from 12 MeV TO 13 MeV

The low cross sections in the diffraction minima of elastic proton scattering at 12.5 MeV incident energy and far backward scattering angles for target nuclei with mass numbers A of about 90 were used to investigate compound nucleus effects in the framework of the statistical model. In the case of ⁹⁰Zr(p, p′) energy averaged T^< fluctuations are observed, while in the case of ⁸⁸Sr(p, p₀) resolved structures with a coherence width of Γ = 22 keV are found, which is assumed to be the coherence width Γ^> of overlapping T^> states.     

A theory of thin metal films: electron density,potentials and work function

Electron densities, potentials, and work functions of thin metal films are calculated self-consistently. The planar uniform-background model and the density-functional formalism are used similarly as in the theory of metal surfaces by Lang and Kohn. Electron densities and potentials are discussed for r_s = 4 both as function of the position in the film and of film thickness. Numerical results for the dependence of the work function on film thickness are given for r_s = 2, 3, 4, 5, 6. As functions of film thickness electron densities, potentials and work functions show oscillations with a period of one-half the Fermi wavelength. The amplitude of the oscillations in potentials and work functions is about 1 eV for one monolayer and 0.1 eV for films of 20 Å thickness. A comparison with non-self-consistent calculations reveals the necessity of self-consistent computations. The relevance of the results to work function measurements and to investigations of thermodynamic and transport properties are discussed. The influence of the film geometry on calculations designed for surfaces per se is examined.     

On the theory of the work function

Starting from a definition of the work function in terms of total energies of the electron system it is shown that this work function can be obtained from the single-particle Schrödinger equations in the density-functional formalism in the way suggested by the Sommerfeld model. It is also shown that the change of the equilibrium ion positions accompanying the ionization of the crystal has no influence on the work function. A comparison is made with Koopmans' theorem. The use of several potentials for computations of the work function is critically investigated.     

Stability problems in annihilation photon energy spectroscopy: A case study

Errors caused by instrumental instabilities in annihilation photon energy spectrometers can be much larger than statistical errors. The performance of a typical spectrometer is investigated in detail and both empirical and theoretical approaches to correcting data for residual fluctuations are examined.