H. Leeb

Neutron capture cross section of unstable 63Ni: implications for stellar nucleosynthesis.

The 63Ni(n,γ) cross section has been measured for the first time at the neutron time-of-flight facility n_TOF at CERN from thermal neutron energies up to 200 keV. In total, capture kernels of 12 (new) resonances were determined. Maxwellian averaged cross sections were calculated for thermal energies from   kT=5-100  keV with uncertainties around 20%. Stellar model calculations for a 25M⊙ star show that the new data have a significant effect on the s-process production of 63Cu, 64Ni, and 64Zn in massive stars, allowing stronger constraints on the Cu yields from explosive nucleosynthesis in the subsequent supernova.

DETERMINATION OF THE PHASE IN NEUTRON REFLECTOMETRY BY POLARIZATION MEASUREMENTS

Abstract New specular reflection experiments to determine the phase of the reflection coefficients, even in the regime of total reflection, are proposed. The method exploits the interference of the spin-components of a polarized neutron beam in the presence of a magnetic field and requires the measurement of the polarizations.

Quark core contribution to the electric polarizability of hadrons

Abstract The quark core contributions to the electric polarizability of the nucleon, the δ-particle and several mesons are calculated in the framework of a non-relativistic potential model. For the nucleon the electric polarizability due to the valence quarks amounts to к = 3.1 × 10 −4 fm 3 , which is in good agreement with recent estimates in the chiral quark model. The quark core polarizability of light mesons turns out to be two orders of magnitude smaller.

A proposal for the determination of the phases in specular neutron reflection

Abstract A method is proposed for solving the phase problem in specular neutron reflection. A differential equation for the reflection phase is derived and solved in terms of the reflectivity and the dwell time. This opens the possibility of determining surface profiles from measured quantities by inversion. A schematic example is presented.

Complete determination of the reflection coefficient in neutron specular reflection by absorptive nonmagnetic media

An experimental method is proposed which allows the complete determination of the complex reflection coefficient for absorptive media for positive and negative values of the momenta. It makes use of magnetic reference layers and is a modification of a recently proposed technique for phase determination based on polarization measurements. The complex reflection coefficient resulting from a simulated application of the method is used for a reconstruction of the scattering density profiles of absorptive non-magnetic media by inversion.

GEANT4 simulation of the neutron background of the C6D6 set-up for capture studies at n_TOF

The neutron sensitivity of the C6D6 detector setup used at n TOF for capture measurements has been studied by means of detailed GEANT4 simulations. A realistic software replica of the entire n TOF experimental hall, including the neutron beam line, sample, detector supports and the walls of the experimental area has been implemented in the simulations. The simulations have been analyzed in the same manner as experimental data, in particular by applying the Pulse Height Weighting Technique. The simulations have been validated against a measurement of the neutron background performed with a nat C sample, showing an excellent agreement above 1 keV. At lower energies, an additional component in the measured nat C yield has been discovered, which prevents the use of nat C data for neutron background estimates at neutron energies below a few hundred eV. The origin and time structure of the neutron background have been derived from the simulations. Examples of the neutron background for two di erent samples are demonstrating the important role of accurate simulations of the neutron background in capture cross section measurements.

An optical potential from inversion of the 350 MeV 16O-16O scattering data

Abstract A quantal inversion of the 16O-16O scattering data at 350 MeV yields an optical potential which gives an excellent fit ( χ 2 F =1.65 ) to the measured cross-section. The real part of this potential is shallower than any potential used by others for distances between 2 and 6 fm. The imaginary potential is also relatively weak. This potential does not favour a rainbow interpretation of the structure in data observed at large scattering angles.

Surface profiles from polarization measurements in neutron reflectometry

A method is proposed for the determination of the phase of the reflection coefficient, which can be applied even in the regime of total reflection. It exploits the interference of the spin components of a polarized neutron beam in the presence of a magnetic field and requires the measurement of polarizations. The results of a simulated determination of the complex reflection coefficient are used as input for the calculation of the surface profile by inversion.

Interferometric phase contrast tomography

Abstract The recently proposed implementation of the tensorial magnetic tomography concept into perfect crystal neutron interferometry is considered. The mathematical relations between the observables of neutron interference and standard depolarization experiments are given.

Violation of pseudospin symmetry in nucleon-nucleus scattering: Exact relations

An exact determination of the size of the pseudospin symmetry violating part of the nucleon-nucleus scattering amplitude from scattering observables is presented. The approximation recently used by Ginocchio turns out to underestimate the violation of pseudospin symmetry. Nevertheless the conclusion of a modestly broken pseudospin symmetry in proton-208Pb scattering at EL=800MeV remains valid.