Local structure and magnetism of Fe, Co and Ni doped Cr3Si

The lattice site occupation of 3d-type impurities in Cr₃Si doped with Fe, Co and Ni were studied using the Extended X-ray Absorption Fine Structure (EXAFS) technique, X-rays and magnetic susceptibility measurements. The EXAFS measurements were performed particularly carefully on the K-edge of chromium and cobalt. EXAFS data strengthened by simulations of the spectra show unambiguously that the impurities are occupying mostly Cr-sites. The magnetic state of the alloys has been studied theoretically using the Wien2k code. It is observed that if calculations are not carried out on an appropriately fine mesh of points in k-space, one can get the result indicating ferromagnetism although the overall magnetic moment per formula unit is weak.     

Lifetime measurements in166Er

The lifetimes of five states in the ground band, from spin 6⁺ up to spin 14⁺, and of all even states in the gamma band up to spin 12⁺, have been measured in¹⁶⁶Er using the recoil distance method. The reduced electric quadrupole transition probabilities have been determined from the measured lifetimes using previously measured branching ratios, and the mixing between the ground band and theγ-band has been studied. The transitional electric quadrupole moments for the ground band and theγ-band have been deduced and are discussed.     

Preparation and optical properties of soda-lime silicate glasses partially substituted by copper

The ion-exchange process was used to introduce copper ions into soda lime silicate glasses (SLS), the composition of which corresponds to the miscibility gape in the Na 2 O-SiO 2 system. The samples have been immersed either in a molten Cu 2 Cl 2 or CuCl 2 at various temperatures from the range 720-940 v K for different time. The observed green colour of glass is related with the 790-nm absorption band related to the cupric ions. The annealing either in air or in the hydrogen atmosphere was used for the reduction of copper. The effectiveness of these procedures was analysed on a basis of the penetration profiles monitored by roentgenographic methods (diffraction and EDAX). Transmission electron microscopy (TEM) observations of the replicated surface and common optical absorption measurements have been used to study the morphology of the dopant ions.     

Ultra-intense femtosecond super-heavy ion beams driven by a multi-PW laser

The paper reports the results of numerical studies on the laser-driven acceleration of super-heavy ions by a multi-PW laser pulse of ultra-relativistic intensity attainable with the Extreme Light Infrastructure lasers currently being built in Europe. Using a multi-dimensional (2D3V) particle-in-cell code, it is shown that multi-GeV super-heavy (thorium) ion beams with an intensity of $～{10}^{21}\text{–}{10}^{22}\text{W}/{\text{cm}}^2$, fluence $～{10}^{17}\text{–}{10}^{18}{\text{cm}}^{?2}$ and time duration $～20\text{–}100\text{fs}$ can be produced from a sub-μm thorium target irradiated by a 150-J, 20-fs laser pulse with an intensity of ${10}^{23}\text{W}/{\text{cm}}^2$. Such ion beams are impossible to obtain presently with the use of conventional RF-driven accelerators, so they can open the door to new areas of research in both nuclear and high energy-density physics.     

Calculations of Three-Nucleon Reactions

Faddeev calculations using the chiral three-nucleon force in next-to-next-to-next-to-leading-order show that this force is too weak to provide an explanation for the low-energy A _y puzzle. The large discrepancy between data and theory for the neutron–neutron quasi-free-scattering cross section in low energy neutron–deuteron breakup requires a modification of the ${^{1}S_0}$ neutron–neutron force. We discuss the consequences that a bound ${^{1}S_0}$ state of two neutrons has on neutron–deuteron scattering observables. At higher energies we compare the solutions of the non-relativistic three-nucleon Faddeev equations with three-nucleon force included to the solutions of its Poincaré invariant version.     

Self-organisation of di(perfluorohexyl)hexane in Langmuir and LB films

Symmetrical triblock semifluorinated n-alkane, di(perfluorohexyl)hexane of the formula F(CF₂)₆(CH₂)₆(CF₂)₆F (abbreviated F₆H₆F₆), has been synthesised and investigated at the air/water interface. Our results show for the first time that this unusual film-forming material, completely hydrophobic in nature and possessing no polar group, is capable of stable film formation at the free water surface. The surface pressure–area isotherm of the studied compound exhibited two regions: corresponding to monotonous pressure rise, followed by a pseudo-plateau region. Visualisation of film structure with Brewster angle microscope (BAM) proved the formation of domains within the pseudo-plateau region. A closer insight into the structure of these domains with atomic force microscope (AFM) proved their ordered, circular shape. The average area of F₆H₆F₆ domain was found to depend on surface pressure value, as it is 4.98 ± 1.75 μm² at π = 1.2 mN/m to 16.54 ± 0.31 μm² at π = 1.7 mN/m. Following performed quantum-chemical calculations, it can be concluded that the observed surface aggregates from F₆H₆F₆ are formed by linear conformers with shifted CF and CH parts. The calculated domain thickness is between 20 and 21 Å, which perfectly agrees with the experimental value estimated from AFM measurements (20.3 ± 1.4 Å).     

Growth and comparison of physicochemical properties of pure,Ca and Sr doped NH4Sb3F10 single crystals for electro optic applications

Single crystals of pure, Ca²⁺ and Sr²⁺ doped NH₄Sb₃F₁₀ are grown by slow evaporation technique. The effect of dopants on the growth and physicochemical properties also have been investigated and reported for the first time. The grown crystals are characterized with the aid of single crystal X-ray diffractometry to confirm the crystal structure. EDAX studies are done to confirm the presence of dopants in the crystal lattice. The vibrational frequencies of various group ligands in the crystals have been derived from the Fourier transform infrared (FT-IR) spectrum. From the optical absorption spectrum the band gap energy was calculated and it was found to be 5.76, 6.29 and 6.35 eV for pure, Ca²⁺ and Sr²⁺ doped NH₄Sb₃F₁₀ crystals respectively. Thermal stability of the sample has been analysed using TG-DTA analysis. The activation energy of pure, Ca²⁺ and Sr²⁺ doped NH₄Sb₃F₁₀ crystals were calculated from the dc conductivity measurements and it is found to be 0.2728, 0.2816 and 0.3622 eV Experimental results shows improved physicochemical properties when the dopant is added to the pure material.     

High-spin states in 44Ca

High-spin states of the ⁴⁴Ca nucleus populated in the 68 MeV ¹⁸O + ³⁰Si reaction have been studied in a γ-γ-recoil coincidence experiment. The level scheme of ⁴⁴Ca has been extended up to 12.2 MeV. In particular, the negative-parity band has been identified with the highest I = 13^- level at 10.6 MeV. This state is interpreted as the band-terminating state for the ( d _3/2 ^-1 f _7/2 ⁵) configuration. Received: 7 November 2001 / Accepted: 3 December 2001