R. Lipperheide

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.

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.

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.

Aspects of the inverse scattering problem in neutron specular reflection

Abstract A two-step Marchenko inversion method is presented for samples mounted on a thick substrate, representing the substrate by a background potential. The inversion for complex potentials is discussed in regard to the elimination of negative wave numbers and the phase problem. The effect of a wave number cut-off in reflectivity measurements is illustrated.

Potential inversion for p- and α-scattering at fixed energy

Abstract The previous rational and nonrational Bargmann-type schemes for solving the inverse scattering problem are combined and generalized to include the long-range Coulomb force. The method is applied to p-58Ni, α-α and α-12C scattering with excellent results. Comparisons are made with the Newton-Sabatier inversion method as modified by Munchow and Scheid, and with the WKB-inversion method of Kujawski.

Heavy-ion reaction cross sections from elastic scattering data

Abstract The generalized optical theorem for charged particles is rederived. Its use for the determination of the reaction cross section and forward nuclear elastic scattering amplitude is discussed. Nonforward angles are considered. An error analysis is applied to theoretical as well as experimental data.

Determination of the potential for back-angle enhanced elastic heavy-ion scattering: Application to the scattering of 16O on 28Si

Abstract The potential describing the recently measured complete angular distribution for the elastic scattering of 16 O on 28 Si at 55 and 50 MeV is determined by inversion of the corresponding scattering function, which is parametrized in terms of a background term and a Regge pole.

Thick samples in neutron specular reflection

Abstract Taking account of the finite thickness of thick samples (instead of treating them as bulk) can have appreciable effects on the average reflectivity, and may thus influence the interpretation of the measured data in neutron specular reflection.