THE MEASUREMENT OF ACCURATE TOTAL CROSS-SECTIONS FOR LEAD AND CARBON IN THE ENERGY RANGE 50 eV TO 100 keV
Institute of Nuclear Physics, Technical University, Vienna, Austria
Harwell Laboratory, Didcot, Oxon. UK
The transmission of Pb and C has been accurately measured in the neutron energy range 50 eV to 100 keV using a 150 m flight path on the fast neutron target cell of HELIOS. The measurements were made with a 10B loaded liquid scintillator using a new fast electronics system capable of recording simultaneously, with a dead time of 10 ns, both time-of-flight and pulse amplitude. The neutron time-of-flight resolution and backgrounds in the experiment were determined from measurements on W, Co, Mn, and 238U by using the REFIT resonance analysis code. The 10B loaded scintillator gave better signal to background ratios than other normally used systems and recording both time-of-flight and pulse height information enabled accurate cross-section values to be obtained from the data. The zero energy free atom scattering cross-sections for Pb and C are determined to be 11.258±0.005 and 4.7438+0.0020 barns respectively. After correcting for neutron-electron, Schwinger and resonance scattering effects the electric polarizability of the neutron (αn) is determined from the energy dependence of the Pb total cross-section to be (1.2±1.0)×10-3 fm3. The experimental measurements and the analysis of the results are discussed.
KEYWORDS: time-of-flight system, detectors, Pb, C, total cross-section, resonance parameters, 50 eV - 100 keV, electric polarisability of the neutron