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Time-of-flight neutron spectrometry and the reaction Be⁹ (d,n [gamma]) B¹⁰ Hardy, James Edward

Abstract

The sensitivity, resolution, and efficiency of a time-of-flight neutron spectrometer developed in this laboratory (Neilson and James, 1955) have been improved by the use of a liquid scintillator neutron detector and improved electronic techniques. By observation of the D(d,n)He³ reaction, the neutron detection efficiency of the liquid scintillator for neutrons in the energy range 2 to 3.5 mev has been shown to follow the curve ε = 0.146 + 0.45 / E[subscript n] + 0.82 where E[subscript n] is the neutron energy in mev. Investigation of the Be⁹(d,n γ)B¹⁰ reaction has shown that the γ-radiation from the 0.72, 2.15, and 3.58 mev levels in B¹⁰ is isotropic to within 5% in the reaction plane while that from the 1.74 mev level is isotropic to within 15%. Further, the radiation from the 0.72, 1.74, and 3.58 mev levels is isotropic to within the same precision about the respective recoil axes, while the angular distribution from the 2.15 mev level is 1 + (0.07 ± 0.05) sin²θ , where θ is measured from the normal to the reaction plane. Since energy selection of the γ radiation was not performed, it is not known which of the three transitions listed by Ajzenberg and Lauritsen (1955) is responsible for this anisotropy. The angular distributions of the four neutron groups associated with the B¹⁰ levels listed above, at E[subscript d] = 500 kev, indicates that at this energy stripping is unimportant for the 0.72, 1.74 and 2.15 mev levels, in agreement with the work of Pruitt et al. (1953) at E[subscript d] = 945 kev. The neutron group associated with the 3.58 mev level undoubtedly proceeds via ℓ = 1 stripping, but to obtain the observed position of the peak at this energy from Butler theory, it is necessary to assign a radius of 13.4 10⁻¹³ cm to Be⁹. The observed peak is twice as broad as that predicted by the theory, (undoubtedly a coulomb effect) and there is an isotropic background roughly one third the peak height, presumed due to compound nucleus formation.

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