N.S.P. King

Improved predictions of neutron detection efficiency resulting from new measurements of 12C(n,p) and 12C(n,d) reactions at 56 MeV☆

Abstract We have obtained new data for the 12 C(n, p) and 12 C(n, d) reactions at 56 MeV and used these to obtain improved predictions of neutron detection efficiency for a plastic scintillator. Previously reported discrepancies between efficiency data and the predictions of Stantons and Kurzs codes in the energy region 6 to 41 MeV are now largely resolved. The prime culprit, applying equally to Stantons, Kurzs and the O5S codes, is the treatment of the 12 C(n, p) reactions. Alterations have also been made to the cross sections and to the scintillation light output function assumed by Stanton and Kurz. Following these changes, agreement between data and predictions for a 4.2 MeV threshold improved from the order of 10% to the order of 3%.

Measurements of 7Li(p,n) and 9Be(p,n) cross sections at 15, 20 and 30 MeV

Abstract Cross sections have been measured at 0° for the (p,n) reaction on 7Li and 9Be for 15, 20, and 30 MeV protons incident on thin targets. Results are presented as a function of neutron energy for neutrons above about 3 MeV.

A 50 MeV polarized neutron facility incorporating a high pressure tritium gas target

A collimated beam of 50 MeV neutrons with a polarization of 0.46±0.02 and a flux of ∼104n/cm2s at 3 m is produced via the T(d,n)4He reaction. Beams up to 20 μA of 38 MeV deuterons are directed through a liquid nitrogen cooled, pressurized (5.5 atm) tritium target. Details of the design, construction, and operation of the neutron facility are presented. The procedures for transferring the tritium to and from the target are also discussed as well as several safety features.

Polarization in proton-deuteron scattering at 50 MeV☆

Abstract The analyzing power for 50 MeV polarized proton scattering from deuterons has been measured for center-of-mass angles 10 to 160 degrees. Relative uncertainties are generally less than 0.01.

Proton pickup from 27Al via the (n, d) reaction at 56.3 MeV☆

Abstract Energy spectra of deuterons from the 27 Al(n, d) 26 Mg reaction due to 56.3 MeV neutrons incident have been measured for 10° ≦ θ c.m. ≦ 55°. The angular distributions for the excitations observed at 0.0, 1.81, and 4.33 MeV are quite well described by DWBA calculations and yield spectroscopic factors in agreement with shell model calculations; but with calculations based on the rotational model, the agreement is less satisfactory particularly for the 4.33 MeV level. For the states at 7.86 and 9.16 MeV the fits, assuming p-shell pick-up, are only fair. Comparison with 27 Al(d, 3 He) 26 Mg measurements shows that the deduced spectroscopic factors for the two reactions agree quite well.

3H+d⇌n+4He measurements and absolute neutron-polarization determination at 50 MeV

Abstract The reaction 3 H(d, n ) 4 He is used to produce 50 MeV polarized neutrons, which at Θ n = 29.7° lab are analyzed in the inverse reaction 4 He( n , d) 3 H. At Θ d )(deut) = 25° lab the two reactions are time reversed (or more specifically, reciprocal), corresponding to the same center-of-mass angles and energies, so that the neutron polarization, P , and the (inverse reaction) neutron- 4 He analyzing power, A , are equal. Thus the measured asymmetry e = P 2 and the absolute neutron polarization at 50 MeV is determined as P = 0.480±0.016. A ( Θ d ) and σ d ( Θ d ) are also measured.

4He(p,d)3He analyzing powers and differential cross sections at 32, 40, 50 and 52.5 MeV

Abstract Measurements of the analyzing powers and differential cross sections for the 4 He( p , d) 3 He reaction at 32, 40, 50 and 52.5 MeV have been carried out using a polarized proton beam from the 88 inch cyclotron at LBL. Legendre polynomial fits of the cross section and differential analyzing power (σA) as a function of energy have smoothly varying coefficients.

A study of the 12N 2.43 MeV level

Abstract We have measured the differential cross sections for the reactions 12 C( τ , τ ′) 12 C(17.77 MeV 0 + T =1) and 12 C( τ , t) 12 N(2.43 MeV) at E τ =44 MeV. The similar shapes of the angular distributions and the relative magnitudes of the cross sections suggest that the 12 N 2.43 MeV level is the 0 + T =1 analog to the q12 C 17.77 MeV level. We have also studied the reaction 14 N(p,t) 12 N(2.43 MeV) at E p =52 MeV. The strength with which this level is excited in this reaction is consistent with reasonable two-step calculations assuming the 2.43 MeV level to have J π =0 + .

Neutron-deutron differential cross section at 26.5 MeV☆

Abstract The angular distributions of 26.5 MeV neutrons scattered elastically by deuterons between 90° and 166° (C.M.) were measured by using charged particle telescopes. The absolute n-d cross section ( of ≈ 5% precision ) was obtained by normalizing to the precision n-p cross section. Within the errors, the magnitude of the minimum cross section was found to be in agreement with that of the proton-deuteron differential cross section at the same energy and in disagreement with some recent results.