Oblate high spin isomer

Energies of high spin states are calculated with the use of an oblate deformed oscillator potential with the purpose of finding possible yrast traps or isomers. Pairing forces are included and different methods of solving the pairing Hamiltonian (including the exact solution) are compared. The stability of the oblate regime against gamma vibrations is investigated with use of the random phase approximation. Pairing forces are included also here.     

Binary fission in Tb and Ag by 600 MeV protons

The binary fission process in ¹⁵⁹Tb and ^natAg induced by 600 MeV protons has been investigated yielding fission cross sections (1.9 and 1.0 mb, respectively) and mean values of the total kinetic energies (100 and 62 MeV, respectively).     

Structure of CO adsorbed on Ni (100)

The c(2 × 2) configuration of CO chemisorbed on Ni(100) has been examined by the dynamical LEED method of surface structure analysis. Experimental LEED intensity spectra of the (00), ($\text{1}\text{2}\text{1}\text{2}$) (10) and (11) LEED beams measured at 175 K are compared with the corresponding calculated spectra for two different CO potential constructions and a number of trial structures. The best agreement was found for a structure where the CO molecules sit directly above the Ni atoms with vertical spacings between the Ni and C and the C and O layers of 1.80 ± 0.10 A and 0.95 ± 0.10 Å respectively. It is proposed that the CO molecule is tipped over at an angle of 34° ± 10° with respect to the surface normal so that the actual carbon-oxygen bond length is close to the figure 1.15 Å found in Ni(CO)₄.     

Mass yields in the binary fission of Ag,La and Tb

The mass distributions from the binary fission of Ag, La and Tb induced by 600 MeV protons are presented. The experimental results are compared with the predictions of macroscopic theories, in particular the version of the liquid drop model including dynamical and statistical effects.     

A quark parton model for hadronic fragmentation distributions

The one-particle inclusive distributions in the fragmentation regions in hadronic interactions are described in a parameter free way by a simple additative quark parton model by means of the quark fragmentation functions measured in leptoproduction. We interpret the result so that while the main interaction in hadronic collisions is due to the wee partons almost all the momenta is carried by one of the valence quarks yielding fragmentation region distributions similar to the ones in leptoproduction.     

The (twin) composition plane as an extended defect and structure-building entity in crystals

The burden of this paper is the recognition of the composition plane as an extended (planar) “defect” in twinned crystals, together with the notion that new structure types may be generated from simple prototype structures by regular and frequent repetition of a twinning operation, usually on a very fine scale. Less regular application of the operation leads to disorder and variation in stoichiometry, without point defects being necessary.

The range of compounds whose structures may be described in these terms is very wide, from metal alloys through metal carbides and borides etc. and inorganic materials, such as metal oxides and sulphides, to minerals, including silicates and the “sulphosalts” of the heavy metals (Pb, Bi etc.). Isostructural compounds frequently span this whole gamut of substances.

The main reasons for the twinning appear to be () the generation of new types of interstices (not present in the prototype) of appropriate size for some of the constituent atoms, and/or (b) a variation in the concentration of appropriate interstices, i.e. in the stoichiometric ratio anion/cation.

After a general introduction to the relevant aspects of twinning, attention is successively concentrated on reflection-twinned h.c.p., then c.c.p. and finally mixed c.p. arrays: first with “interstitial” atoms only in the composition planes; and then with other interstices also occupied. In each case lamellar twinning is first considered, and then cyclic twinning. Glide-reflection-twinning of similar arrays is then considered.

Attention is also drawn to small topological distortions that, for example, convert the octahedra in a c.c.p. array (twinned or even un-twinned) to arrays of capped trigonal prisms (or to cubes). In this way the apparently complex structures of a number of compounds are derived from those of much simpler twinned c.c.p. arrays.

Finally, the not-very-large amount of available, relevant, experimental evidence is reviewed. As far as it goes, this confirms that the notion of the composition plane as an extended defect is well founded. But more experimental data are needed.

[In most cases specific literature references are provided for each structure. For a few, rather common, structures they are not. In such cases reference may be made to standard texts, e.g. for alloys, to Schubert⁹⁹ or Pearson¹³³ and, for more ionic structures, to Wyckoff¹³⁴ or Povarennykh¹³⁵. Diagrams are to scale: 1 cm = 4.0 Å.]