No Arabic abstract
We report new experimental Fe I oscillator strengths obtained by combining measurements of branching fractions measured with a Fourier Transform spectrometer and time-resolved laser-induced fluorescence lifetimes. The study covers the spectral region ranging from 213 to 1033 nm. A total of 120 experimental log(gf)-values coming from 15 odd-parity energy levels are provided, 22 of which have not been reported previously and 63 values with lower uncertainty than the existing data. Radiative lifetimes for 60 upper energy levels are presented, 39 of which have no previous measurements.
The multi-configuration Dirac-Hartree-Fock method was employed to calculate the total and excitation energies, oscillator strengths and hyperfine structure constants for low-lying levels of Sm I. In the first-order perturbation approximation, we systematically analyzed correlation effects from each electrons and electron pairs. It was found that the core correlations are of importance for physical quantities concerned. Based on the analysis, the important configuration state wave functions were selected to constitute atomic state wave functions. By using this computational model, our excitation energies, oscillator strengths, and hyperfine structure constants are in better agreement with experimental values than earlier theoretical works.
We present lifetime measurements using beam-foil techniques for radiative transitions from the 3$p^4$($^1S$)4$s$ $^2S_{1/2}$, 3$p^4$($^3P$)5$s$ $^2P_{1/2,3/2}$, and 3$p^4$($^3P$)3$d$ $^2F_{5/2}$ levels in Cl I and the corresponding results of the oscillator strengths for transitions at 1004.68, 1079.88, 1090.73, and 1094.77 AA, respectively. We compare our experimental results with available theoretical calculations and astronomical observations in an effort to resolve discrepancies among them.
We report lifetimes, branching fractions, and the resulting oscillator strengths for transitions within the P II multiplet (3s23p2 3P - 3s3p3 3Po) at 1308 {AA}. These comprehensive beam-foil measurements, which are the most precise set currently available experimentally, resolve discrepancies involving earlier experimental and theoretical results. Interstellar phosphorus abundances derived from {lambda}1308 can now be interpreted with greater confidence. In the course of our measurements, we also obtained an experimental lifetime for the 3p4s 3P0o level of P IV. This lifetime agrees well with the available theoretical calculation.
Electron Capture (EC) decay of $^{146}$Gd($it{t_{1/2}}$ = 48d) to the low lying states of $^{146}$Eu has been studied using high-resolution $gamma$ ray spectroscopy. The $^{146}$Gd activity was produced by ($alpha$, 2n) reaction at E$_{alpha}$ = 32 MeV using 93.8% enriched $^{144}$Sm target. The level structure has been considerably modified from the measurement of $gamma$ ray singles, $gammagamma$ coincidences and decay half lives. Lifetime measurement has been performed for the 3$^-$ (114.06 keV) and 2$^-$ (229.4 keV) levels of $^{146}$Eu using Mirror Symmetric Centroid Difference (MSCD) method with LaBr$_3$ (Ce) detectors. The lifetimes for these two states have been found to be 5.38 $pm$ 2.36 ps and 8.38 $pm$ 2.19 ps respectively. Shell model calculation has been performed using OXBASH code in order to interpret the results.
Bipolar spherical harmonics (BiPoSHs) provide a general formalism for quantifying departures in the cosmic microwave background (CMB) from statistical isotropy (SI) and from Gaussianity. However, prior work has focused only on BiPoSHs with even parity. Here we show that there is another set of BiPoSHs with odd parity, and we explore their cosmological applications. We describe systematic artifacts in a CMB map that could be sought by measurement of these odd-parity BiPoSH modes. These BiPoSH modes may also be produced cosmologically through lensing by gravitational waves (GWs), among other sources. We derive expressions for the BiPoSH modes induced by the weak lensing of both scalar and tensor perturbations. We then investigate the possibility of detecting parity-breaking physics, such as chiral GWs, by cross-correlating opposite parity BiPoSH modes with multipole moments of the CMB polarization. We find that the expected signal-to-noise of such a detection is modest.