The19F(n, γ)20F reaction

The gamma-ray spectrum emitted following thermal neutron capture in¹⁹F has been studied with curved crystal and Ge(Li) spectrometers. From the 109 transitions assigned to²⁰F, 85 have been placed in a level scheme containing 26 levels. An average gammaray multiplicity of 2.8 gammas per neutron capture was observed. The neutron binding energy was found to be 6601.33(14) keV. The experimental level scheme is compared to rotational model predictions. In addition it is shown that the decay of the capture state is non-statistical and that there is a strong correlation between the strengths of excitation of levels by the (n, γ) and (d, p) reactions. Calculations of the partial cross-sections using the direct capture theory of Lane and Lynn give order of magnitude agreement with experiment.     

Nitric oxide reduction by CO ON Rh(111): Temperature programmed reaction

The reaction of NO with CO on Rh(111) has been studied with temperature programmed reaction (TPR). Comparisons are made with the reaction of O₂ with CO and the reaction of NO with H₂. The rate-determining step for both CO oxidation reactions is CO(a) + O(a) → CO₂(g). Repulsive interactions between adsorbed CO and adsorbed nitrogen atoms lead to desorption of CO in a peak at 415 K which is in the temperature range where the reaction between CO(a) and O(a) produces CO₂(g). Thus the extent of reaction of CO(a) with NO(a) is less than that between CO(a) and O(a) due to the lower coverage of CO caused by adsorbed N atoms and NO. A similar repulsive interaction between NO(a) and H(a) suppresses the NO + H₂ reaction. CO + NO reaction behavior on Rh(111) is compared to that observed on Pt(111).     

On the evolution of the mass asymmetry in damped heavy-ion collisions

TotaT kinetic energy vs. fragment mass distributions have been measured in the reactions of⁶⁴Zn projectiles with¹¹⁴Sn,^natAg and¹³⁹La nuclei at incidence energies of 20–50% above the Coulomb barrier. Conclusions are drawn on the possible influence of nuclear structure effects on the energy dissipation and the mass drift behaviour of the present collision systems.     

Picosecond dynamics of the photoinduced spin polarization in epitaxial (Ga,Mn)as films

Static and time-resolved magneto-optical spectra of the ferromagnetic semiconductor (Ga,Mn)As show that a pulsed photoexcitation with a fluence of 10 microJ/cm(2) is equivalent to the application of an external magnetic field of about 1 mT, which relaxes with a decay time of 30 ps. This relaxation is attributed to the spin relaxation of electrons in the conduction band and is found to be not affected by interactions with Mn ions.     

Control of single emitter radiation by polarization- and position-dependent activation of dark antenna modes

We study the modification of the decay rates of a single dipolar emitter positioned in the vicinity of metallic linear nanoantennas when higher-order plasmonic excitations are induced. We show that it is possible to effectively tune the enhancement or suppression of both the radiative and nonradiative decay processes by controlling the position and orientation of the dipole with respect to the antenna. Transverse polarization of a single emitter, with respect to the antenna axis, located at the center of the antenna activates dark antenna modes that modify dramatically both the intensity and the spectral features of the decay rates.     

Magneto-photoluminescence study of type-II charge confinement in epitaxially grown GaInP2

We have studied the photoluminescence from GaInP₂ grown by molecular beam epitaxy as a function of laser power, magnetic field and temperature. We show that the single luminescence peak observed in such samples arises from weakly bound (type-II) excitons in which the electrons are localised and the holes are free, and that it is the same as the additional low-energy peak typically observed in strongly CuPt-ordered GaInP₂ grown by chemical vapour deposition techniques. We propose that the electron is confined in In-rich regions of the sample and the hole is delocalised by coupling between heavy- and light-hole bands.     

Ground States of the 2D Sticky Disc Model: Fine Properties and N 3/4 Law for the Deviation from the Asymptotic Wulff Shape

We investigate ground state configurations for a general finite number N of particles of the Heitmann-Radin sticky disc pair potential model in two dimensions. Exact energy minimizers are shown to exhibit large microscopic fluctuations about the asymptotic Wulff shape which is a regular hexagon: There are arbitrarily large N with ground state configurations deviating from the nearest regular hexagon by a number of ～N ^3/4 particles. We also prove that for any N and any ground state configuration this deviation is bounded above by ～N ^3/4. As a consequence we obtain an exact scaling law for the fluctuations about the asymptotic Wulff shape. In particular, our results give a sharp rate of convergence to the limiting Wulff shape.