Neutron-neutron quasifree scattering in neutron-deuteron breakup at 10 MeV

Abstract

New measurements of the neutron-neutron quasifree scattering cross section in neutron-deuteron breakup at an incident neutron energy of 10.0 MeV are reported. The experiment setup was optimized to evaluate the technique for determining the integrated beam-target luminosity in neutronneutron coincidence cross-section measurements in neutron-deuteron breakup. The measurements were carried out with a systematic uncertainty of ±5.6%. Our data are in agreement with theoretical calculations performed using the CD-Bonn nucleon-nucleon potential in the Faddeev formalism. The measured integrated cross section over the quasifree peak is 20.5 ± 0.5 (stat) ± 1.1 (sys) mb/sr 2 in comparison with the theory prediction of 20.1 mb/sr 2 . These results validate our technique for determining the beam-target luminosity in neutron-deuteron breakup measurements. *

Measurement of the $^1S_0$ neutron-neutron effective range in neutron-deuteron breakup

“…This removes several sources of systematic uncertainty because the nd elastic scattering yields are measured simultaneously with the breakup yields and the absolute neutron flux and number of deuterium nuclei in the target do not need to be known independently. This technique has been successfully implemented in a previous measurement [36]. The present experiment was conducted at a different energy with more configurations sensitive to nn QFS than previous work [33,34].…”

“…For each detector pair, the raw and accidental coincidence spectra were projected onto the ideal kinematic locus of allowed neutron energies, referred to as the S curve. The variable S measures the arc length along the curve in a counterclockwise direction beginning at the point where the energy of the second neutron reaches a minimum [35,36]. The projection was carried out in the k 1 −k 2 plane, where the momenta of the two breakup neutrons (k 1 and k 2 ) in each breakup event define a point in that plane.…”

“…We used the technique of Ref. [37], which produces equivalent results to the method used in a previous experiment [36,38]. The projected accidental coincidence spectrum was subtracted from the projected raw spectrum for each detector pair.…”

“…The TOF spectra measured with the empty target holder were normalized to the spectra measured with the CD 2 and graphite samples using the integrated beam current (BCI), the gas pressure in the neutron production cell, and the DAQ live time fraction.The TOF spectra measured with the graphite sample were normalized to the spectra measured with the CD 2 sample in a similar way. The normalization factor also included the ratio of carbon nuclei in the two samples determined using data from a previous experiment [36]. The normalized graphite TOF spectra were subtracted from the CD 2 TOF spectra to obtain the raw yields from nd elastic scattering.…”

“…The uncertainty in the overall normalization and shape of the efficiency curve were determined from those measurements as in Ref. [36]. The effect of small changes in the detector gain on the simulated detector efficiency was estimated using variations of the efficiency curve due to changes in the detector threshold setting.…”