Fast neutron inelastic scattering from 7Li

The inelastic scattering of fast neutrons from 7Li nuclei was investigated at the nELBE neutron-time-of-flight facility. The photon production cross section of 478 keV γ-rays from the first excited state of 7Li was determined by irradiating a disc of LiF with neutrons of energies ranging from 100 keV to about 10 MeV. The target position was surounded by a setup of 7 LaBr3 scintillation detectors and 7 high-purity germanium detectors to detect the de-excitation γ-rays. A 235U fission chamber was used to determine the incoming neutron flux. The number of detected photons was corrected for the detection efficiency, multiple scattering and the time-of-flight dependent data acquisition dead time. The preliminary results show reasonable agreement with some previous measurments but are about 15 % below the recent data taken at the GELINA facility.

Collective Reactions in the Continuum

We show that pre-equlibrium inelastic scattering reactions to the continuum contain substantial collective components in addition to the multistep direct and multistep compound reactions. These collective reactions are investigated for the vibrational nuclei 56Fe, 58Ni, 90Zr, 93Nb, 208Pb and 209Bi , and the strongly-deformed, rotational W nucleus. The collective cross-sections are calculated using the experimental data for low-lying collective excitations supplemented where necessary by the giant multipole resonances evaluated using the energy-weight ed sum rule. The MSC and MSD cross-sections are evaluated by the Feshbach-Kerman-Koonin theory using a consistent set of parameters determined by analyses of (p, xn) reactions, that have practically no collective components. The results are compared with high-resolution neutron inelastic scattering data and prove able to account for the absolute magnitude of the cross-sections and also their detailed structure.

Glassy carbon, NIST Standard Reference Material (SRM 3600): hydrogen content, neutron vibrational density of states and heat capacity

Commercial glassy carbon plates being used as absolute intensity calibration standards in small-angle X-ray scattering applications (NIST SRM 3600) have been characterized in several recent publications. This contribution adds to the characterization by measuring the hydrogen content of a plate to be (4.8 ± 0.2) × 10−4 (mol H)/(mol C), and by measuring the vibrational spectrum by neutron inelastic scattering. The spectrum bears a strong resemblance to published measurements on graphite, allowing the identification of several spectral features. The measured spectrum is used to calculate the heat capacity of low-hydrogen-content glassy carbon for comparison with measurements reported here from 20 to 295 K.