Recent High-precision Measurements Research Articles

High precision calculation of fine structure splittings in helium and He-like ions.

Fine structure splittings for the 1{ital s}2{ital p} {sup 3}{ital P} state of helium are calculated to a computational accuracy of 3 parts in 10{sup 9}, including all terms up to {ital O}({alpha}{sup 6}{ital mc}{sup 2}). The results differ notably from recent high precision measurements in He and Be{sup 2+}, but there is good agreement for Li{sup +}, B{sup 3+}, and F{sup 7+}. A comparison with relativistic configuration interaction calculations [M. H. Chen {ital et} {ital al}., Phys. Rev. A {bold 47}, 3692 (1993)] indicates close agreement for {ital Z}{ge}10, and lends strong support to both calculations.

Comprehensive calculations of 4p and 4d lifetimes for the Cu sequence.

Computed lifetimes for the 4p $^{2}P_{1/2}$, 4${p}^{2}$${P}_{3/2}$, 4d $^{2}D_{3/2}$, and 4${d}^{2}$${D}_{5/2}$ levels in the copper isoelectronic sequence are presented for atomic numbers Z=29--92. These calculations agree well with recent high-precision lifetime measurements, conflict with the isoelectronic trend of single-configuration Dirac-Fock calculations, and agree at lower Z with the multiplet values of multiconfiguration Hartree-Fock calculations using experimental transition energies. Our calculations involve the inclusion of experimental energy-level data and the use of a Hartree-Slater potential to represent the ionic core. It is found that the core-polarization effects are significant and must be included to obtain agreement with experiment, at least for the lower members of the isoelectronic sequence. As part of the study, we have combined semiempirical parametrizations of the existing database with Dirac-Fock calculations to produce a set of values for the ionization potentials and the 4p and 4d excitation energies for all stable ions in this sequence.

Accurate calculations of 3pand 3dlifetimes in the Na sequence

Computed lifetimes for the 3p $^{2}P_{1/2}$, P3${p}^{2}$${P}_{3/2}$, 3d $^{2}D_{3/2}$, and 3${d}^{2}$${D}_{5/2}$ levels in the sodium isoelectronic sequence are presented for Z=11--54, 74, 79, 90, and 92. These calculations agree well with recent high-precision lifetime measurements, and conflict with some ab initio estimates which indicated lifetimes shorter than those experimentally observed. Our calculations involve the inclusion of experimental energy-level data and the use of a realistic model potential, which utilizes comprehensive spectroscopic measurements that have recently become available. We also demonstrate that the core-polarization effects are significant and must be included to obtain agreement with experiment. As part of the study, we used the existing data base and Dirac-Fock methods to determine new values for ionization potentials in this sequence.

An empirical determination of the dipole moment function of OH(X 2Π)

An electric dipole moment function (EDMF) for OH has been derived by combining airglow and laboratory intensity measurements with recent high precision measurements of the dipole moments for v=0,1, and 2. This empirical EDMF shows remarkable agreement with the a priori MCSCF(7)-SCEP EDMF. However, it differs sufficiently to produce transition probabilities which are in much better agreement with observations than previously available sets.

The role of high-precision gravimetry in detecting and monitoring recent crustal movements in view of the African situation

High precision relative gravimetry can play a dual role in the study of vertical recent crustal movemen: exploring and monitoring. A number of G-meters of LCR type have been calibrated over the full measurement range so that they can be used in almost any part of African. Recent high precision measurements in desert, tropical and subtropical zones reveal clearly that even under unfavorable climatical and transportation conditions precise gravity is available within ± 10 to 20 microgal accuracy.

Detailed analysis of refractive index effects produced by ion implantation

A major effect of ion implantation in insulators is the modification of the refractive index. This has been used in LiNbO3 and quartz to define optical waveguides and as a first model the decreases in refractive index were assumed to arise from amorphisation of the crystals. However, recent high precision measurements and a detailed reflectivity theory have revealed considerable complexity in the refractive index profiles of these materials. For example there are major differences in the refractive index profiles of the ordinary and extraordinary indices for LiNbO3 and LiTaO3 and more subtle effects dependent on the wavelength and polarisation of the measuring light. This paper will discuss the possible origin of some of these features and their relationship to damage mechanisms and damage stability in these materials.

Energy levels for S, P, and D states in He through precision variational calculations.

Nonrelativistic variational calculations with the relativistic correction to order ${\ensuremath{\alpha}}^{2}$ have been carried out to obtain the energy levels for the n $^{1}$,3S, n $^{1}$,3P, and ${n}^{1}$,3D series in He up to n=8. The calculated term values have converged generally to within an uncertainty of \ensuremath{\sim}${10}^{\mathrm{\ensuremath{-}}4}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$, a value matching the accuracy of recent high-precision wavelength measurements. The results are combined with theoretical Lamb shifts and systematically compared with currently available high-precision experimental data. The consistency between theory and experiment is good, although for some low-lying (n=3--6) S and P states there exist small discrepancies, presumably caused by the estimated Lamb shifts. The calculated term values for high-lying excited states have better accuracies than existing experimental data. Addition of the theoretical term values to the corresponding experimental excitation energies suggests a value of 198 310.7725(5) ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ for the ground-state ionization energy on the energy scale fixed by the ${2}^{1}$P value of 171 135.0000 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$.

The magnetocrystalline anisotropy of cobalt

Recent high precision measurements of the uniaxial anisotropy constants K 1 and K 2 are reported taken from three samples grown by different techniques. The results vindicate the early work of Succksmith and Thompson and agree well with the recent measurements of Ono. While some variation was observed between results from the three samples we conclude that these are insufficient to account for the spread of results in the literature and suggest inaccurate shearing corrections as the most probable cause of discrepancy. A very good fit to the K 1 data was obtained using a single ion model and the c/a ratio as an adjustable parameter. These c/a values gave a satisfactory fit to K 2 and also lay within the scatter of the experimentally measured c/a values. However, a definitive test of the single ion theory was not possible due to these experimental uncertainties in c/a. Data for the temperature variation of the basal plane anisotropy constant K 4 are reported for the first time. The single ion model predictions are not in very good agreement with the K 4 data.

Precision measurement and a theoretical calculation of lifetimes in the 4p^5 5p configuration of singly ionized rubidium (Rb ii)

A theoretical investigation is made of the 4p55p–4p65s transition array in Rb ii. When the calculation is carried to the first order only, the resulting lifetimes are bound to be systematically shorter than the available set of experimental data by some 30%. By taking account of second-order corrections (including configuration interaction with the continuum), the overall agreement with experiment is improved but a large discrepancy still remains between the calculation and a recent high-precision lifetime measurement on the p10 level. The quality of that measurement is confirmed by a new precision experiment using a coaxial ion-laser beam geometry. This remeasurement rules out any unaccounted experimental systematic error at the 1% level. As a result we conclude that caution must still be taken in the extrapolation along isoelectronic sequences of data obtained by semiempirical methods that have been previously found to be successful for the calculation of rare-gas transition probabilities. Further precision lifetime measurements in singly charged alkali ions are needed in order to better define the range of validity of such calculations.

Analyzing Power inppScattering at Low Energies: The Paris-Potential Predictions

Predictions of the Paris potential for the analyzing power in $\mathrm{pp}$ scattering at low energies are compared with recent high-precision measurements at 6.141 MeV and earlier measurements at 10 and 16 MeV. Phase-shift values are also presented and discussed in view of previous analyses.

Energies and intensities of thermal neutron capture γ rays from Cl, Al and Fe relative to N

A precise comparison has been made of the spectra of γ rays from chlorine and nitrogen. Chlorine has a 33 b thermal capture cross section and produces many intense γ rays between 1.5 and 8.6 MeV. These properties make it a convenient standard for energy and intensity calibrations. These results were used to calibrate the spectra from Fe and Al. With the improved chlorine energies derived from the present results, consistency is obtained with recent high precision measurements of the iron doublet.

Primary cosmic-ray nucleon spectrum from the atmospheric gamma-ray and muon data

The available experimental inclusive cross-sections for single-pion and kaon production in proton-proton collisions between 0.01 and 2 TeV incident-proton laboratory energy have been used to determine a phenomenological form for the inclusive cross-sections. This has been used together with the recent high-precision measurements of atmospheric gamma-ray and single-muon spectra between 0.002 to 50 TeV to derive the primary nucleon spectrum in the formI(E)=I0E-γ up to the primary energy ≥100 TeV. The parametersI0 and γ, vary in the range 1.75┌2.7 and 2.63┌2.78, respectively.

Elastic scattering of 0.1-1-MeV photons

Theoretical values of Rayleigh scattering amplitudes for the $K$ shell and for higher atomic shells are calculated from the second-order $S$ matrix of quantum electrodynamics. The calculations are combined with nuclear Thomson scattering to predict elastic scattering differential cross sections for photon energies between 100 keV and 1 MeV, and for elements with $Z$ ranging from 30 to 82. The resulting cross sections are compared with recent high-precision measurements.

Positron Decay ofCo58

The allowed positron transition from the Co/sup 58/ ground state (2+) to the Fe/sup 56/ first excited state (2+, 810 kev) was studied using a 4 pi positron-scintillation spectrometer. The experimental shape factor exhibits a small systematic deviation from that theoretically predicted for an allowed transition and corresponds to an excess of low-energy positrons. The experimental shape factor can be fit by a curve proportional to (1 + b/W) with b = 0.3. The FermiKurie plot is linearized by this correction factor and yields an end-point energy of 474 plus or minus 5 kev. Similar discrepancies between the experimental and theoretically predicted shapes of Gamow-Te-ller beta transitions for negatrons (In/sup 114/, P/sup 32/, and Y/sup 90/) and positrons (Na/sup 22/) have been reported. In these cases it was found that this same shape factor with 0.2 < b < 0.4 would linearize the theoretically-corrected Fermi-Kurie plots. No satisfactory explanation for this effect has been offered. As previously suggested by other investigators, the shape factor (1 + b/W) must, for the present, be regarded as a purely empirical correction. The end-point energy from the present investigation combined with the recent high-precision measurement of the gamma-ray transition energy from the first excitedmore » state to the ground state of Fe/sup 58/ yields a Co/sup 58/-Fe/sup 58/ mass difference of 2306 plus or minus 5 kev. (auth)« less