T-band phenomena in 183Re

Abstact: High-spin states in ¹⁸³Re have been studied using the ¹⁷⁶Yb(¹¹B,4n) reaction at 52 and 57 MeV. Two high-K bands have been observed directly by a time-correlated γ-γ coincidence measurement. One of the bands is built on an isomeric K ^π=(25/2)⁺ state at E _x= 1908 keV with a half-life of 0.82(2) ms. The other band, assigned as K ^π=(29/2)⁻ at E _x= 2739 keV, decays to the (25/2)⁺ band. These bands are interpreted as three-quasiparticle structures, π(5/2)⁺[402] &⊗ν(9/2)⁺[624] ⊗ν(11/2)⁺[615] for the (25/2)⁺ band and π(9/2)⁻[514] ⊗ν(9/2)⁺[624] ⊗ν(11/2)⁺[615] for the (29/2)⁻ band. The K ^π= (29/2)⁻ band becomes strongly Coriolis mixed with increasing spin and is gradually changing into a low-K s-band structure. Received: 20 April 1998     

NMR study of the magnetic properties of the polymerized phase of Cs1C60

\chem{Cs_{1}C_{60}} . The NMR spectrum allows, when the Magic Angle Spinning (MAS) technique is used, to get information about the electronic structure of this phase, which points out that the spin density is not uniformly distributed on the ball. An estimation of the strength of the quadrupolar effects on is then given, which shows that it is possible to analyse the spin-lattice relaxation time in terms of magnetic effects. A comparison with the of is then justified and allows us to point out the importance of low dimensional antiferromagnetic fluctuations in this compound. We also investigate the nature of the magnetic ground state in : the broadening of the spectra states unambiguously its magnetic nature and a detailed analysis of their shape gives further indications on the antiferromagnetic nature of the magnetic order, which seems characterized by a large amount of disorder. Received: 19 November 1996/Accepted: 19 December 1996     

Laser-induced fluorescence study of a xenon Hall thruster

2 ⁰→6p[3/2]₂(³P₂-¹D₂) transition at 823.2 nm and the xenon-ion 5d[3]_7/2→6p[2]_5/2 ⁰(⁴D_7/2-⁴P_5/2) transition is used to measure plasma parameters in the plume of a laboratory-model xenon Hall thruster. The Hall discharge operates nominally at 62 V, 4.2 A, and 3.2 mg s^-1 xenon flow, with an overall thruster power of 320 W. A tunable semiconductor diode laser and an Ar⁺-pumped dye laser are used to probe the respective excited-state transitions. Axial velocity measurements are made at a number of axial and radial locations up to 4.5 cm downstream of the thruster-exit plane and under a variety of thruster operating conditions. Neutral velocities from 100 m s^-1 to 400 m s^-1 and ion velocities as high as 12 km s^-1 are calculated from measured Doppler shifts. The charge-exchange phenomenon evidently does not significantly affect the xenon neutrals. The spectral-line shapes of the ion indicate a spread in ion energies through a non-Maxwellian distribution of axial velocities. Neutral kinetic temperatures of 500 (±200) K are observed under standard operating conditions. Zeeman and Stark effects on the spectral-line shapes, from the thruster’s magnetic and electric fields, are not substantial. The measured line center of the ion transition is 16521.23 (±0.02) cm^-1. Received: 20 January 1997/Revised version: 12 May 1997     

Ultimate quantum limits for resolution of beam displacements

We compare two high sensitivity techniques which are used to measure very small displacements of physical objects by optical techniques: the interferometric devices, measuring longitudinal phase shifts, and the devices used to monitor transverse displacement of light beams. We detail the differences and the similarities for the quantum limits on the resolution of both systems. In both cases squeezed light can be used to resolve beyond the standard quantum limit and number correlated states allow us to reach the “Heisenberg” limit. Received 12 September 2002 Published online 21 January 2003     

Effect of the initial phase of the field in ionization by ultrashort laser pulses

We report on observable new features related to ionization of atoms by laser pulses of only few cycles and some intensity. We show that for particular photo-electron energies, the angular distribution becomes asymmetric and that this asymmetry is related to the initial phase of the field. Received: 4 November 1997/Revised: 21 January 1998/Accepted: 23 February 1998     

Anharmonic dynamical behaviour in bcc zirconium

We present inelastic neutron scattering measurements of the low energy and strongly damped phonons in the high temperature bcc phase of zirconium. These phonons were investigated at different scattering vectors but equivalent phonon wave vectors in different Brillouin zones or along different but equivalent paths in the same Brillouin zone. Neither the observed differences in intensity nor in line shapes can be explained by the coherent one-phonon scattering law . This leads to an apparent violation of the fundamental symmetry of lattice dynamics. Taking into account the strong anharmonicity of these phonons, interferences between one- and multi-phonon scattering are held responsible for these effects. Measurements in different scattering planes reveal that due to the symmetry of the bcc lattice, these effects can only be observed in certain directions. Received: 24 December 1997 / Received in final form: 9 March 1998 / Accepted: 19 March 1998     

Efficient J=0-1 soft-X-ray lasing in neon-like ions at pump powers below 250 GW

2 . By using a 0.7% prepulse that precedes the main pulse by 5 ns and applying a total pump energy of 100 J or less, the J=0-1 lasing is at least one order of magnitude higher than the non-lasing background. For the 32.6-nm line of Ti, the 25.5-nm line of Fe, and the 23.1-nm line of Ni, gain coefficients of (±) 4.20.4cm^-1, (±) 3.90.3cm^-1, and (±) 3.60.6cm^-1, respectively, were measured for 2.4-cm-long curved targets, resulting in gain–length products of ∼10. Angle-resolved spectra indicate a beam divergence of 3 mrad (FWHM), typically. The space-resolved spectra show that the J=0-1 lasing lines are emitted from an approximately 60-μm-wide (FWHM) plasma region, whereas the nearby continuum emission is produced in a considerably broader plasma region of ∼250 μm. Lasing at 25.5 nm in neon-like iron was observed at a pump power as low as 180 GW (∼9 TW/cm²), with, however, considerable shot-to-shot scatter in the absolute laser output. Received: 5 September 1997/Revised version: 10 November 1997     

Transient gain enhancement for picosecond pulses by suppressing intra-cavity ASE in a large-aperture KrF laser amplifier

Received: 30 March 1998/Revised version: 4 August 1998     

Cavitation in superfluid helium-4 at low temperature

We have studied the nucleation of bubbles in pure superfluid helium-4 at temperatures down to 65 mK. We have found that the nucleation is a stochastic process, and that at temperatures below 600 mK the nucleation rate is independent of temperature. These results are consistent with the assumption that the nucleation takes place via quantum tunneling. Received: 15 November 1997 / Received in final form: 19 December 1997 / Accepted: 22 January 1998