New high-spin states of 147Nd and 145Ce: Octupole correlation in the N = 87 isotones

High-spin states of the N = 87 nuclei, ¹⁴⁷Nd and ¹⁴⁵Ce, have been populated in the ¹²C + ²³⁸U and ¹⁸O + ²⁰⁸Pb fusion-fission reactions at 90 MeV and 85 MeV bombarding energy, respectively. The emitted γ-radiation was detected using the Euroball III and IV arrays. High-spin states of the ¹⁴⁷Nd isotope have been identified for the first time. The high-spin yrast and near-to-yrast structures of the ¹⁴⁵Ce nucleus have been considerably extended. The newly observed structures, discussed by analogy with the neighbouring isotones, show the coupling of an h_9/2 neutron to the quadrupole and octupole excitations of the core.     

Polyhedral units and network connectivity in calcium aluminosilicate glasses from high-energy X-Ray diffraction

Structure factors for Ca (x/2)Al xSi 1-xO (2) glasses (x = 0,0.25,0. 5,0.67) extended to a wave vector of magnitude Q = 40 A (-1) have been obtained by high-energy x-ray diffraction. For the first time, it is possible to resolve the contributions of Si-O, Al-O, and Ca-O coordination polyhedra to the experimental atomic pair distribution functions. It has been found that the connectivity of Si/Al-O tetrahedral network decreases with increasing x due to the emerging of nonbridging oxygens located on Si-O tetrahedra. Calcium maintains a rather uniform coordination sphere for all values of x and so it plays a certain role in determining the glass structure.     

EMMA—a new underground cosmic-ray experiment

An experiment observing underground muons originating from cosmic-ray air showers is under preparation in the Pyhäsalmi mine, Finland. The aim is to cover an area of about 200–300 m², and the detector setup is capable of measuring the muon multiplicity and their lateral distribution. The detector is placed at a depth of about 85 m (corresponding about 240 m w.e.), which gives a threshold energy of muons of about 45 GeV. The detection of the multimuon events is motivated by partly unknown composition of the primary cosmic rays in the energy region of 10¹⁵–10¹⁶ eV, i.e., the knee region. In addition, by measuring only the higher energy muons of the air shower, the lowest energy muons being filtered out by the rock overburden, the data is sensitive also to the studies of the upper parts of the air shower. The experiment will be constructed mainly using drift chambers used previously in LEP detectors at CERN, but it can also be expanded using plastic scintillator detectors. The prototype detector is expected to be running in the beginning of 2006, and the full-size detector by the end of 2007.     

Short-range order in RE4Al3 metallic glasses (RE = Pr, Gd, Tb, Dy)

A suitable model structure of RE₄Al₃ metallic glasses (RE = Pr, Gd, Tb, Dy) has been selected by comparing experimental pair correlation functions with model pair correlation functions for disordered crystal structures. A non-linear least-squares profile analysis of the experimental pair correlation functions has been performed with the use of the characteristic structural parameters of the model structure as variable parameters. The partial atomic distances and the partial coordination numbers have been estimated on the basis of the best fitting parameters. It is established that the local atomic arrangement in RE₄Al₃ metallic glasses resembles that in tetrahedrally close-packed Zr₄Al₃-type crystalline compounds.     

Density functional study of hydrogen bond formation between methanol and organic molecules containing Cl, F, NH2, OH, and COOH functional groups

Various hydrogen-bonded complexes of methanol with different proton accepting and proton donating molecules containing Cl, F, NH(2), OH, OR, and COOH functional groups have been modeled using DFT with hybrid B3LYP and M05-2X functionals. The latter functional was found to provide more accurate estimates of the structural and thermodynamic parameters of the complexes of halides, amines, and alcohols. The characteristics of these complexes are influenced not only by the principle hydrogen bond of the methanol OH with the proton acceptor heteroatom, but also by additional hydrogen bonds of a C-H moiety with methanol oxygen as a proton acceptor. The contribution of the former hydrogen bond in the total binding enthalpy increases in the order chlorides < fluorides < alcohols < amines, while the contribution of the second type of hydrogen bond increases in the reverse order. A general correlation was found between the binding enthalpy of the complex and the electrostatic potential at the hydrogen center participating in the formation of the hydrogen bond. The calculated binding enthalpies of different complexes were used to clarify which functional groups can potentially form a hydrogen bond to the 2'-OH hydroxyl group in ribose, which is strong enough to block it from participation in the intramolecular catalytic activation of the peptide bond synthesis. Such blocking could result in inhibition of the protein biosynthesis in the living cell if the corresponding group is delivered as a part of a drug molecule in the vicinity of the active site in the ribosome. According to our results, such activity can be accomplished by secondary or tertiary amines, alkoxy groups, deprotonated carboxyl groups, and aliphatic fluorides, but not by the other modeled functional groups.     

Li insertion in ball-milled graphitic carbon studied by total x-ray diffraction

Ball-milled graphitic carbon, both not and electrochemically lithiated, has been studied by total x-ray diffraction involving high-energy synchrotron radiation scattering and atomic pair distribution function analysis. The experimental data has been used to guide reverse Monte Carlo simulations of the three-dimensional structure of the not-lithiated samples. Experimental and modeling results show that ball milling for short times breaks the graphitic layers into smaller pieces as well as generates extended atomic vacancies. Those increase the overall ability of the material to accommodate lithium. Ball milling for longer times keeps generating even more atomic vacancies in the graphitic layers. Carbon atoms displaced from the layers, however, move in between the layers, turning heavily ball-milled graphitic carbon into an assembly of almost-fused-together, heavily buckled layers that have an impaired ability to accommodate Li atoms. This helps explain well the initial substantial increase and then decrease in the Li storage capacity of ball-milled graphitic carbon. The study demonstrates the great ability of total x-ray diffraction to provide precise structural information for complex materials that are being increasingly explored for energy applications.     

INFLUENCE OF pH AND PRESENCE OF Cu2+ IONS ON THE PROPERTIES OF POLYACRYLOYLACETONE (PAA)MONOLAYERS

The influence of pH on the properties of polyacryloylacetone (PAA) monolayers at air/water interface was examined by using surface pressure-area isotherm measurement,a new rheological approach and AFM imaging. The isotherms and AFM-imaging detect phase transitions in PAA monolayers and growth of microdomains during compression in the case of pH 6.6 and missing of such kind of structures at pH 9. The rheological study below and above the phase transition shows an existence of a large relaxation time related to the process of formation of microdomains.

The influence of divalent ions on the properties of a PAA monolayer was studied. The presence of Cu²⁺ ions leads to polymer - ion interaction which results in the formation of microdomains.     

Half-life measurements of 137, 139Cs excited nuclear states

A fast-timing setup has been developed to measure the nuclear-state half-lives of neutron-rich nuclei. The first on-line measurements were performed on ^{137, 139}Cs obtained from the β decay of ^{137, 139}Xe. These neutron-rich Xe nuclei were produced by the ²³⁸U photofission induced by the 50MeV electron beam delivered by the ALTO facility. The half-lives of the first excited state in ¹³⁷Cs and of six excited states in ¹³⁹Cs were measured for the first time. Taking into account new information given by the deduced transition probabilities, we discuss the structure of the first excited states in ^{137, 139}Cs : it is shown that, in both nuclei, the first excited $\tfrac{5} {2}^ +$ level corresponds mainly to the one-proton state issued from the π2d _5/2 orbital and that the most probable spin values for the states located at 289.8, 393.5, and 393.8keV in ¹³⁹Cs are $\tfrac{5} {2}^ +$ , $\tfrac{3} {2}^ +$ , and $\tfrac{1} {2}^ +$ , respectively.     

Formation of linear momentum in a rod during a laser pulse–matter interaction

Recently, we developed an optodynamic experimental technique that makes it possible to measure the linear momentum obtained by a metal target sample in the shape of a rod during a nanosecond laser pulse interaction in the ablative regime. The height of the rod’s rear end axial step-like displacement, caused by the first reflection of the laser-generated ultrasonic wave, is proportional to the linear momentum acquired by the rod. In comparison with commonly used ballistic methods, we can determine the acquired momentum on a much shorter time scale corresponding to the wave transition time, from the front to the rear end of the rod. Using this method we investigated the ambient air pressure dependence on the formation of linear momentum over a laser intensity range, from the ablation threshold to values about ten times higher. Steel rods of various diameters were used to demonstrate the effect of an expanding blast wave which delivers additional momentum to the target, when the laser beam on the target surface is smaller than the target itself. The typical value of the acquired target momentum is on the order of μN s and 10 μN s/J for the momentum coupling coefficient.