19 research outputs found
Ab initio oscillator strengths for transitions between J=1 odd and J=1,2 even excited states of Ne I
Ab initio theory is developed for radiative transitions between excited
states of neon. Calculations of energies for even excited states J=1, J=2
supplement our previous calculations for J=1 odd excited states. Line strengths
for transitions between J=1 odd and J=1,2 even states of Ne I are evaluated. A
comparison with experiments and semiempirical calculations is given.Comment: 5 page
Detection of NMR signals with a radio-frequency atomic magnetometer
We demonstrate detection of proton NMR signals with a radio frequency atomic
magnetometer tuned to the NMR frequency of 62 kHz. High-frequency operation of
the atomic magnetometer makes it relatively insensitive to ambient magnetic
field noise. We obtain magnetic field sensitivity of 7 fT/Hz using only
a thin aluminum shield. We also derive an expression for the fundamental
sensitivity limit of a surface inductive pick-up coil as a function of
frequency and find that an atomic rf magnetometer is intrinsically more
sensitive than a coil of comparable size for frequencies below about 50 MHz.Comment: 7 page
Calculations of liquid helium and neon VUV emission spectra, self-absorption and scattering for a neutrino detector
To evaluate the feasibility of the recently proposed detection scheme of low
energy neutrinos released from the Sun and supernovae called CLEAN, Cryogenic
Low Energy Astrophysics with Noble Gases, which relies on the transparency of
noble-gas cryogenic liquids to VUV radiation produced by neutrinos, we analyze
theoretically VUV emission, self-absorption, and scattering of liquid helium
and neon, primary candidates for CLEAN. Owing to strong repulsion of noble-gas
atoms in the ground states at the equilibrium distance of the relevant excited
state, the emission spectrum is substantially shifted from the absorption
spectrum, and in principle the absorption is expected very small, allowing
building large detectors. Our analysis, however, shows that the self-absorption
and Rayleigh scattering are comparable to the size of the proposed detector.
Our theoretical emission spectra are found in agreement with experimental
observations although some deviation exists due to binary-interaction
approximation, and our ab initio Rayleigh scattering lengths are found in
agreement with other calculations based on the extrapolation of experimental
refraction indices. The absorption process can result in either re-emission,
which conserves the number of photons but delays their escape from the liquid,
or in non-radiative quenching
Laser gas-discharge absorption measurements of the ratio of two transition rates in argon
The ratio of two line strengths at 922.7 nm and 978.7 nm of argon is measured
in an argon pulsed discharge with the use of a single-mode Ti:Sapphire laser.
The result 3.29(0.13) is in agreement with our theoretical prediction 3.23 and
with a less accurate ratio 2.89(0.43) from the NIST database.Comment: 5 pages, 2 figures, 1 tabl
SQUID-based microtesla MRI for in vivo relaxometry of the human brain
SQUID-based MRI (magnetic resonance imaging) at microtesla fields has
developed significantly over the past few years. Here we describe application
of this method for magnetic relaxation measurements in the living human brain.
We report values of the longitudinal relaxation time T1 for brain tissues,
measured in vivo for the first time at microtesla fields. The experiments were
performed at 46 microtesla field using a seven-channel SQUID system designed
for microtesla MRI and MEG. Values of T1, measured for different tissues at
this field, are found to be close (within 5%) to the corresponding values of
the transverse relaxation time T2 at the same field. Implications of this
result for imaging contrast in microtesla MRI are discussed.Comment: To appear in Proceedings of 2008 Applied Superconductivity Conferenc
Energy levels and lifetimes of Nd IV, Pm IV, Sm IV, and Eu IV
To address the shortage of experimental data for electron spectra of
triply-ionized rare earth elements we have calculated energy levels and
lifetimes of 4f{n+1} and 4f{n}5d configurations of Nd IV (n=2), Pm IV (n=3), Sm
IV (n=4), and Eu IV (n=5) using Hartree-Fock and configuration interaction
methods. To control the accuracy of our calculations we also performed similar
calculations for Pr III, Nd III and Sm III, for which experimental data are
available. The results are important, in particular, for physics of magnetic
garnets.Comment: 4 pages 1 tabl
Multipole (E1, M1, E2, M2) transition wavelengths and rates between states with n<= 6 in heliumlike carbon, nitrogen, oxygen, neon, silicon, and argon
Transition wavelengths and rates are given for E1, E2, M1, and M2 transitions
between singlet and triplet S, P, D, and F states in heliumlike ions of
astrophysical interest: carbon, nitrogen, oxygen, neon, silicon, and argon. All
possible transitions between states with n <= 6 are considered. Wave functions
and energies are calculated using the relativistic configuration-interaction
(CI) method including both Coulomb and Breit interactions. For transitions to
the ground state, the present theoretical wavelengths agree to five digits with
precise measurements.Comment: 8 pages of text 97 pages of tables submitted to Atomic & Data Nuclear
Datable
Mixed configuration-interaction and many-body perturbation theory calculations of energies and oscillator strengths of J=1 odd states of neon
Ab-initio theory is developed for energies of J=1 particle-hole states of
neutral neon and for oscillator strengths of transitions from such states to
the J=0 ground state. Hole energies of low-Z neonlike ions are evaluated.Comment: 5 pages, 1 figure, 4 table
Third-order relativistic many-body calculations of energies and lifetimes of levels along the silver isoelectronic sequence
Energies of 5l_j (l= s, p, d, f, g) and 4f_j states in neutral Ag and Ag-like
ions with nuclear charges Z = 48 - 100 are calculated using relativistic
many-body perturbation theory. Reduced matrix elements, oscillator strengths,
transition rates and lifetimes are calculated for the 17 possible 5l_j-5l'_{j'}
and 4f_j-5l_{j'} electric-dipole transitions. Third-order corrections to
energies and dipole matrix elements are included for neutral Ag and for ions
with Z60. Comparisons are made
with available experimental data for transition energies and lifetimes.
Correlation energies and transition rates are shown graphically as functions of
nuclear charge Z for selected cases. These calculations provide a theoretical
benchmark for comparison with experiment and theory.Comment: 8 page
Combined CI+MBPT calculations of energy levels and transition amplitudes in Be, Mg, Ca, and Sr
Configuration interaction (CI) calculations in atoms with two valence
electrons, carried out in the V(N-2) Hartree-Fock potential of the core, are
corrected for core-valence interactions using many-body perturbation theory
(MBPT). Two variants of the mixed CI+MBPT theory are described and applied to
obtain energy levels and transition amplitudes for Be, Mg, Ca, and Sr