C. Lebo

Large volume neutron detectors with subnanosecond time dispersions

Abstract Design criteria and performance characteristics are described for large-volume (13.1 1 to 118 1) mean-timed plastic-scintillator detectors for neutrons from ≈2 MeV to 2 GeV. Detectors were constructed in six sizes (all 0.102 m thick) from 0.126 m × 1.016 m × 0.102 m to 0.762 m × 1.524 m × 0.102 m. Overall energy resolutions of 230 keV for 80 MeV neutrons, 320 keV for 133 MeV neutrons, and 440 keV for 157 MeV neutrons were achieved in time-of-flight experiments with flight paths of 76, 68, and 91 m, respectively. The detectors have pulse-height responses uniform to ±5% except close to the ends, position resolutions less than 5 cm, and intrinsic time dispersions less than 400 ps. Typical neutron detection efficiencies are 20% for 20 MeV neutrons at a pulse-height threshold of 2 MeV equivalent-electron energy (MeV ee) and 3.5% for 200 MeV neutrons at a pulse-height threshold of 50 MeV ee.

A comparison of methods for determining neutron detector efficiencies at medium energies

Abstract We compare the “Lithium Activation” (LiA) method and the “Isospin Clebsch-Gordan Ratio” (ICGR) method for determining detection efficiencies of neutrons between 100 and 160 MeV. Each method was used to determine the efficiency by relating a measured neutron yield to a cross section measured in another way: γ-ray activation cross sections for LiA; (p, p′) cross sections from experiments at the Indiana University Cyclotron Facility for ICGR. Efficiencies determined by the two methods disagree substantially. Efficiencies calculated with the Monte Carlo code of Cecil et al. agree with the ICGR results. We conclude that the Lithium Activation method is inconsistent at these energies.

High-Spin States in the (p,n) Reaction

In 1974, Moffa and Walker1 stressed that certain “exotic states” of relatively high spin should dominate medium-energy (p,p’) and (p,n) reactions at large momentum transfers. They predicted that the study of the excitation of these states would be important to determine the high-momentum transfer components of the nucleon-nucleon (N-N) effective interaction at medium energies. Since the discussion of Moffa and Walker, experimental studies of high-spin states have been performed with both the (p,p’) and (p,n) reactions. These studies are providing not only information regarding the high-momentum transfer components of the N-N effective interaction, but are also beginning to provide nuclear structure information.