Measurements Of Neutron Emission Cross Sections Research Articles

Double-Differential Neutron Emission Cross-Section Measurements of 6Li and 7Li at Incident Neutron Energies of 8.17 and 10.27 MeV

Energy angular neutron emission double-differential cross sections (DDXs) of 6Li and 7Li were measured at incident neutron energies of 8.17 and 10.27 MeV, respectively, using normal and normal + abnormal fast neutron time-of-flight (TOF) spectrometers. The effects of breakup neutrons from a D(d,n) source and the influence of an aluminum container of Li samples, as well as 7Li in the 6Li sample and 6Li in the 7Li sample, on the secondary neutron spectra were eliminated. The data were derived by comparing the net TOF spectra with the calculated spectra using a realistic Monte Carlo simulation. The differential cross sections were determined by comparing the measured and simulated TOF spectra with respect to specific scattering fractions, i.e., with respect to the elastic lines and the resolved inelastic lines related to single levels or level groups, and normalized to n-p scattering. The angular distributions for the 6Li and 7Li elastic and inelastic neutron scattering were obtained also. The angle-integrated cross sections were derived for elastic scattering from 6Li and for the sum of elastic and 0.478-MeV state inelastic scattering from 7Li. Inelastic scattering cross sections were obtained for the 2.186-MeV state in 6Li and the 4.652-MeV state in 7Li. Meanwhile, based on the unified Hauser-Feshbach and exciton model, the calculated results of the DDXs for n + 6,7Li were compared with measurements.

Developments of a long liquid scintillation detector for fast neutron time-of-flight experiments

We have developed a long NE213 liquid scintillation detector (LLSD, 80 cm × 6.5 cm × 10 cm) which is useful as a position sensitive detector and a high-efficiency neutron detector for measurements of neutron emission cross sections. LLSD is a long rectangular shaped NE213 scintillator coupled with two photomultipliers at both ends of the scintillator cell. Position information along the long cell axis is obtained by the time difference method. The time compensated signal needed for time-of-flight (TOF) experiments is provided by a mean timer. Data are acquired for TOF, position and pulse-height signals gated by n-γ discriminator signals using a three-parameter data acquisition system. The updated data acquisition system and a position-dependent biasing analysis could achieve a remarkably lower bias level down to ∼1 MeV neutrons with good n-γ discrimination compared to the similar type NE213 detectors and remove position dependence of detection efficiency. LLSD with the sophisticated data taking and processing techniques proved to be very effective for neutron emission cross section measurements for 10–18 MeV incident neutrons as a wide-angle scattering detector and a high-efficiency single detector.

A compact post-acceleration beam chopper for a 4.5 MV Dynamitron pulsed neutron generator

A post-acceleration beam chopper (PACS) has been installed for a 4.5 MV Dynamitron accelerator to improve the energy resolution of neutron time-of-flight (TOF) experiments by shortening the duration of the ion beam pulses. The PACS sweeps the accelerated ion pulses across a chopping slit and eliminates the tails of the beam pulses. It operates sinusoidally at a frequency of 8 MHz with a maximum voltage of 10 kV peak to peak in synchronization with the accelerated ion pulses. The high voltage generator of the PACS was constructed of commercially available amplifiers and components, which realized easy maintenance and low cost. The PACS proved to be very effective to improve the pulse shape and has been applied for double-differential neutron emission cross section measurements.

A spectrometer for double-differential neutron-emission cross section measurements in the energy range 1.6 to 16 MeV

A neutron spectrometer for the measurement of double-differential neutron-emission cross sections has been set up. An electron linac (GELINA) is used as a pulsed white neutron source. The energy of the incident neutrons is determined by the time-of-flight method. The secondary neutron spectra are determined by unfolding the pulse-height distributions observed in eight NE213-scintillators surrounding the sample. The measured spectra are normalised to the shape of the incident neutron flux measured with a 235U-fission chamber, and afterwards converted to absolute cross sections using as standard the carbon differential elastic scattering cross section below 2 MeV.

Neutron emission cross section measurements with a 14 MeV neutron generator

The PINSTECH 14 MeV Neutron Generator Facility has been used for the measurements of double differential neutron emission cross sections of Al, Cu and Pb in the emitted neutron energy range of 3–14 MeV and in the 30°–130° range. Integrated neutron emission cross sections are given and compared with previously reported values.

Scattering of 14.6 MeV neutrons from Fe: Neutron emission cross section measurements.

Measurements have been carried out for 14.6 MeV neutrons incident on natural iron using the associated particle time-of-flight technique. The elastic differential and neutron emission cross sections have been measured in the energy range 4.5--13.5 MeV and laboratory angular range 30\ifmmode^\circ\else\textdegree\fi{}--130\ifmmode^\circ\else\textdegree\fi{}. Monte Carlo simulation has been used for multiple scattering and flux attenuation corrections. A value of 477\ifmmode\pm\else\textpm\fi{}48 mb has been obtained for the neutron emission cross section in the energy range 4.5--13.5 MeV. The present measurements have been compared with previous measurements and model calculations.