J.W. McClure

Energy levels in Si27, Co56 and Zn63

Abstract The neutron spectra from the (p,n) reaction on Al, Fe 56 and Cu 63 have been measured at a laboratory angle of 23° to determine the energy levels of the residual nuclei. The protons were obtained from the Livermore variable energy cyclotron. The neutron energies were measured using time-of-flight techniques and a long (9 to 15 meter) flight path. In Si 27 eighteen levels were resolved. The agreement with the nine levels up to an excitation of 4.13 MeV previously reported from charged particle work is excellent. The additional levels are 4.29, 4.45, 4.70, 5.00, 5.08, 5.21, 5.30, 5.38 and 5.51 MeV with an error of ±0.04 MeV. Neutron groups were observed corresponding to the following excitations in Co 56 : 0.165, 0.560, 0.825, 0.980 and 1.105 MeV with an error of ±0.015 MeV. In Zn 63 the following levels were excited: 0.214, 0.640, 1.047, 1.246, 1.386, 1.640, and 1.697 MeV with an error of ±0.025 MeV.

Neutron spectrum from the T+T reaction

Abstract The neutron spectrum from the T+T reaction has been measured by time-of-flight techniques using the swept and bunched 0.5 MeV tritium beam from the Cockcroft-Walton accelerator. The 90° neutron spectrum shows evidence for the following reaction modes: (a) direct breakup into 2 neutrons plus alpha particle (T+T → n+n+He 4 , Q = 11.33 MeV) the three-body breakup shape being modified by the presence of the neutron-neutron interaction; (b) sequential decay proceeding via the He 5 ground state; and (c) sequential decay proceeding via a broad He 5 excited state. The branching ratios for the T+T reaction at 90° are approximately 70% for (a), 20% for (b) and 10% for (c). The neutron group leading to the He 5 ground state, estimated width 0.74±0.18 MeV, is isotropic to within an accuracy of ±10%.

The (α, n) cross sections on 17O and 18O between 5 and 12.5 MeV

Abstract The excitation functions for the (α, n) reaction on 17 O and 18 O have been measured from 5 to 12 MeV using long counters. Also, the neutron differential cross sections were measured at 9.8, 11.6 and 12.2 MeV, using the Livermore neutron time-of-flight facility. Neutron spectra were obtained every 15° between 3° and 135° with gas targets of enriched 17 O and 18 O. The angular distributions are roughly symmetric about 90°. Small forward peaking is observed at the higher bombarding energies for some of the states, mainly for the ground and first excited states.

Elastic and inelastic scattering of 14 MeV neutrons from the lithium isotopes

The angular distributions of elastically scattered 14-Mev neutrons have been measured for Li/sup 6/, Li/sup 7/, and natural Li from 20 deg to 130 deg . Inelastic scattering to the 2.18 Mev level in Li/sup 6/ and the 4.6 Mev level in Li/sup 7/ has been measured over a more restricted angular range. In Li/sup 6/ the 3.57 Mev level is not excited appreciably. The inelastic neutrons from the 2.18 Mev level in Li/sup 6/ and the 4.6 Mev level in Li/sup 7/ are peaked in the forward direction, which is indicative of a direct reaction. (auth)

Energy levels of 31S and 19Ne

Recently Colli et al., using the 32S(n, d)31P reaction, reported the existence of a 450 keV level in 31P. However, the investigation of other reactions has shown no evidence for such a level. Using the Livermore neutron time-of-flight facility and the (p, n) reaction on 31P, we have searched for the analogue of this proposed level in the mirror nucleus 31S. Neutron spectra were obtained for angles between 30° and 120° and for proton energies from 7.5 to 13.0 MeV. Although the correspondence between the observed levels in 31S and those reported for 31P was excellent up to the maximum excitation energy studied, viz., 3.7 MeV, no evidence for a level at 450 keV excitation was obtained. The reaction 19F(p, n)19Ne also was studied up to an excitation energy of 3.0 MeV in 19Ne. Besides confirming the results obtained by Freeman and West, a previously unreported level at 2.8 MeV was observed.

ELASTIC SCATTERING OF 7- TO 14-MeV NEUTRONS FROM NITROGEN.

Abstract The differential cross sections for the scattering of neutrons with incident energies of 6.78, 7.41, 7.93, 8.35, 8.57, 9.38, 10.10, 10.93, 11.55, 12.25, 13.50 and 13.96 MeV from nitrogen have been measured for lab angles between 15° and 135° in 15° steps. The measurements were made with a liquid target in cylindrical geometry with a thickness of approximately one half of the total mean free path. The neutrons were produced by the D(d, n) 3 He reaction in the Livermore variable-energy cyclotron; the average neutron energy spread was ±200 keV. A multiple detector time-of-flight system was used for simultaneous recording of the data. The experimental differential cross sections are analysed in terms of the optical model, with only the real and imaginary potentials varied.

Quasi-elastic (p,n) angular distributions: Instrumentation

Abstract The modifications of the Livermore 90-in. cyclotron time-of-flight facility necessary for the measurement of quasi-elastic (p,n) angular distributions are discussed. These modifications include: 1) the construction of shielded 10-m flight paths at 3, 30, 60, 90, 120 and 135°; 2) the installation of an additional bending magnet and auxiliary equipment to bend the proton beam such that it strikes the target at an angle of 18° to the normal beam line, thus effectively doubling the number of angles for which measurements can be made; 3) modification of the electronic system such that all detectors can record data simultaneously. Future expansion to include 10-m flight paths in 15° intervals, which will make possible measurements from 0 to 157.5° in 7.5° steps and the electronics necessary for this more complex system are discussed.

Neutron spectra from the (p, n) reaction in medium-mass nuclei using 7–13 MeV protons

Abstract The 23° neutron spectra from the (p, n) reaction on V51, Fe56, Co59, Cu65, Nb93 and Rb103 have been measured using 9–13 MeV protons. Using a shorter flight path, 90° neutron spectra have also been measured using 7–10 MeV protons. The neutron spectra have been analysed to yield level density information using the Fermi gas level density expression [ 1 (U-δ) 2 ] exp {2[a(U-δ)] 1 2 } , where U is the excitation energy in the residual nucleus and δ is Camerons pairing energy. The a values are given by a = 1 8 A , where A is the mass number of the residual or target nucleus. These a values agree well with those determined from inelastic neutron scattering experiments, from charge particle experiments and from level densities observed at the neutron binding energy.

An accurately positionable thin window XRF sample cell for radioactive solution samples

Described in this paper is a liquid sample holder for XRF measurement of radioactive solutions. Using tensioned polyimide windows assures accurate positioning and thickness of the sample.