Quantum Electrodynamic Corrections to the g Factor of Helium P States

The Lande g factor describes the response of an atomic energy level to an external perturbation by a uniform and constant magnetic field. In the case of many-electron systems, the leading term is given by the interaction mu_B*(L+2S.B), where L and S are the orbital and spin angular momentum operators, respectively, summed over all electrons. For helium, a long-standing experimental-theoretical discrepancy for P states motivates a reevaluation of the higher-order terms which follow from relativistic quantum theory and quantum electrodynamics (QED). The tensor structure of relativistic corrections involves scalar, vector, and symmetric and anti-symmetric tensor components. We perform a tensorial reduction of these operators in a Cartesian basis, using an approach which allows us to separate the internal atomic from the external degrees of freedom (magnetic field) right from the start of the calculation. The evaluation proceeds in a Cartesian basis of helium eigenstates, using a weighted sum over the magnetic projections. For the relativistic corrections, this leads to a verification of previous results obtained using the Wigner-Eckhart theorem. The same method, applied to the radiative correction (Bethe logarithm term) leads to a spin-dependent correction which is different for singlet versus triplet P states. Theoretical predictions are given for singlet and triplet 2P and triplet 3P states and compared to experimental results where available.Comment: 11 pages; RevTe

Electron-correlation effects in the gg-factor of light Li-like ions

We investigate electron-correlation effects in the $g$-factor of the ground state of Li-like ions. Our calculations are performed within the nonrelativistic quantum electrodynamics (NRQED) expansion up to two leading orders in the fine-structure constant $\alpha$, $\alpha^2$ and $\alpha^3$. The dependence of the NRQED results on the nuclear charge number $Z$ is studied and the individual $1/Z$-expansion contributions are identified. Combining the obtained data with the results of the all-order (in $Z\alpha$) calculations performed within the $1/Z$ expansion, we derive the unified theoretical predictions for the $g$-factor of light Li-like ions.Comment: 9 pages, 4 table

Black-Body Radiation Correction to the Polarizability of Helium

The correction to the polarizability of helium due to black-body radiation is calculated near room temperature. A precise theoretical determination of the black-body radiation correction to the polarizability of helium is essential for dielectric gas thermometry and for the determination of the Boltzmann constant. We find that the correction, for not too high temperature, is roughly proportional to a modified hyperpolarizability (two-color hyperpolarizability), which is different from the ordinary hyperpolarizability of helium. Our explicit calculations provide a definite numerical result for the effect and indicate that the effect of black-body radiation can be excluded as a limiting factor for dielectric gas thermometry using helium or argon.Comment: 8 pages; RevTe

Isotope shift of the 3 2S1/2−2 2S1/2 transition in lithium and the nuclear polarizability

High precision calculation of the isotope shift of the 3 2S1/2−2 2S1/2 transition in lithium is presented. The wave function and matrix elements of relativistic operators are obtained by using recursion relations. Apart from the relativistic contribution, we obtain the nuclear polarizability correction for 11Li. The resulting difference of the squared charge radii 11Li−7Li based on the measurements of Sánchez et al. [Phys. Rev. Lett. 96, 033002 (2006)] is δr2ch=0.157(81)  fm2, which significantly differs from the previous evaluation

Fertilisation with ash from wood and with sewage sludge versus contents of macro- and microelements in the soil following cultivation of Helianthus tuberosus L.

The present study investigated the effects produced in the soil by municipal sewage sludge and wood ash applied during the cultivation of Jerusalem artichoke. The impact of the presence of applied the fertilizer materials on changes in soil and a macro- and microelements contents were investigated. The comparative analyses took into account 3 factors; the first factor - 4 levels of wood ash – 0; I–4.28; II–8.57; III–12.85 t ha-1, the second factor – 2 levels of sewage sludge – 0; 1 – 30.3 t ha-1, the third factor – 2 varieties of Jerusalem artichoke (Helianthus tuberosus L.) – Gigant, Albik. Application of the fertilisers did not resulted in significant change in the total contents of phosphorus, potassium and magnesium in soil examined after Jerusalem artichoke was harvested. Application of ash from coniferous trees, with high levels of calcium, resulted in increased total contents of calcium in the soil. Fertilisation of the soil with ash from coniferous trees or with sewage sludge, as well as cultivation of two varieties of Jerusalem artichoke, resulted in a significant increase in the concentrations of cadmium and lead, and produced no effects in the levels of nickel, zinc and copper identified in soil. The above findings, and in particular the fact that the limit values were not exceeded, indicate the possibility of using both sludge and biomass ash for fertilizing Jerusalem artichoke

Ultracold mixtures of metastable He and Rb: scattering lengths from ab initio calculations and thermalization measurements

We have investigated the ultracold interspecies scattering properties of metastable triplet He and Rb. We performed state-of-the-art ab initio calculations of the relevant interaction potential, and measured the interspecies elastic cross section for an ultracold mixture of metastable triplet $^4$He and $^{87}$Rb in a quadrupole magnetic trap at a temperature of 0.5 mK. Our combined theoretical and experimental study gives an interspecies scattering length $a_{4+87}=+17^{+1}_{-4}$ $a_0$, which prior to this work was unknown. More general, our work shows the possibility of obtaining accurate scattering lengths using ab initio calculations for a system containing a heavy, many-electron atom, such as Rb.Comment: 11 pages, 11 figures, accepted for publication in Phys. Rev.