E. R. Flynn

Evidence for near-stable octupole deformation in 225Ra

The low lying level structure of 225Ra, studied with the 226Ra(d, t) reaction and 225Fr β-decay, has approximately degenerate K = 12± and K = 32± bands. Hybrid absolute values of the decoupling parameters of the K = 12± bands, intermediate between the theoretical values expected for the pure Nilsson configurations, are deduced and presented as evidence for near-stable octupole deformation in the 225Ra ground state.

The rotational structure of 227Ra

Abstract The level structure of 227Ra has been studied using the (n, γ), (d, p) and ( t , d) reactions and the β− decay of 227Fr. A model-independent level scheme was established including 28 levels below 1500 keV. Cross sections and excitation energies have been measured for 72 levels below 2.5 MeV and analysing powers have been measured for 25 levels below 1.4 MeV. The level structure is interpreted in terms of the Nilsson model. The ground-state configuration is 3 2 + [631↑] and the first excited band [633↓] starts at 1.7 keV. Several octupole vibrations coupled to single-particle configurations are tentatively assigned above 280 keV. The neutron binding energy was determined to be 4561.41 ± 0.27 keV. The half-life of 227Fr was measured to be 148 ± 2 s.

One- and two-neutron transfer reactions with 14C

Abstract The one- and two-neutron transfer reactions ( 14 C, 13 C) and ( 14 C, 12 C) have been measured on a series of targets. The angular distributions of the differential cross sections were analyzed in the DWBA approach. An excellent description of the one-neutron transfer angular distributions is obtained. The two-neutron transfer cross sections are shown to be underpredicted in DWBA by typically a factor of ten. A calculation which includes the two-step transfer process yields absolute magnitudes consistent with the observed differential transfer cross sections.

Elastic and inelastic scattering of 14C from medium heavy nuclei

Abstract The elastic and inelastic scattering of 14 C at 51 MeV from targets of 40 Ca, 56 Fe, 60 Ni, 66 Zn and 88 Sr has been measured using a Q3D spectrometer. The 14 C-nucleus potentials have been derived by optical-model analysis of the observed elastic scattering; the inelastic scattering differential cross sections were interpreted in the distorted-wave Born approximation and also in the coupled-channels approach. The analysis yields 14 C-nucleus potentials that closely resemble 12, 13 C and 16 O potentials.

Single-proton states in 151Pm

Abstract The 152 Sm ( t , α) 151 Pm reaction was studied using 17 MeV polarized tritons from the tandem Van de Graaff accelerator at the Los Alamos Scientific Laboratory. The α-particles were analyzed using a Q3D magnetic spectrometer and detected with a helical-cathode position-sensitive counter. The overall resolution was ∼ 18 keV FWHM. Measurements of the 150 Nd( 3 He, d) 151 Pm reaction were made using 24 MeV 3 He beams from the McMaster University tandem accelerator. The deuteron spectra were analyzed with a magnetic spectrograph using photographic emulsions for detectors, yielding a resolution of ∼ 13 keV FWHM. By comparing the measured angular distributions of ( t , α ) and ( 3 He, d) cross sections and ( t , α ) analyzing powers with DWBA predictions it was possible to assign spins and parities to many levels. The present results confirm earlier assignments of rotational bands based on the low-lying 5 2 + [413], 5 2 − [532], 3 2 + [411] and 1 2 + [420] orbitals. In addition, states at higher excitation have now been assigned to the 1 2 + [411] and 7 2 + [404] orbitals, and members of the 3 2 + [422], 5 2 + [402], 3 2 − [541] and 7 2 − [523] bands are tentatively proposed. The spectroscopic strengths can be explained reasonably well by the Nilsson model when pairing and Coriolis mixing effects are included.

Two-particle transfer in O (6) nuclei

Abstract We present the first comparison between empirical two-neutron transfer strengths in Pt and Os nuclei and the predictions of the O (6) limiting symmetry of the interacting boson approximation model.

The nuclear structure of 225Ra

Abstract The level structure of 225 Ra has been studied using the (d, t) reaction with both unpolarised and polarised deuterons and the β − decay of 225 Fr. Cross sections and excitation energies have been measured for 41 levels below 1800 keV in the (d, t) reaction, and levels up to 724 keV have been established from the β − decay measurements. The level structure is interpreted in terms of the Nilsson model.

(t,p) reactions onHe4,Li6,Li7,Be9,B10,B11, andC12

A study of the (t,p) reactions on /sup 4/He, /sup 6/Li, /sup 7/Li, /sup 9/Be, /sup 1/0B, /sup 1/1B, and /sup 1/2C has been carried out using 23 MeV tritons and an Elbek-type spectrograph using photographic emulsions as detectors. A total of 71 states of /sup 6/He, /sup 8/Li, /sup 9/Li, /sup 1/1Be, /sup 1/2B, /sup 1/3B, and /sup 1/4C have been studied. Some of the states had not been previously reported. In other cases new values of excitation energies and widths are proposed. Attempts have been made to fit the 62 angular distributions we obtained with the distorted-wave Born approximation: no systematic analysis was possible except in the case of L = 0 distributions.

136,138Ba(t, p) and the systematics of neutron pairing vibrations at N = 82

Abstract The 136,138 Ba(t, p) reaction has been studied at E t = 17 MeV. The neutron monopole and quadrupole pairing vibration states were located in 138 Ba at 3.612 MeV and 4.043 MeV, respectively. These results, when combined with previous observations in the Ce and Nd isotopes at the N = 82 closed shell, lead to a linear relationship between the two-neutron binding energies and the proton number. Predictions of locations of other pairing vibration states at the N = 82 shell are possible from these relations.

The nuclear structure of 161,163Ho studied with the (t,α) reaction

Abstract The 162,164Er( t , α)161,163Ho reactions have been studied using a beam of 17 MeV polarized tritons from the tandem Van de Graaff accelerator at the Los Alamos Scientific Laboratory. The reaction products were analyzed with a Q3D magnetic spectrometer using a helical-cathode position-sensitive detector in the focal plane. Comparisons of the measured angular distributions of cross sections and analyzing powers with DWBA predictions made it possible to assign spins and parities to a number of previously unknown levels in each residual nucleus. The results are interpreted in the framework of the Nilsson model with pairing and Coriolis mixing effects included. The 7 2 − [523], 1 2 + [411], 3 2 + [411], 7 2 + [404], 5 2 + [413], 5 2 − [532] and 1 2 + [420] bands were observed in both 161Ho and 163Ho. In previous stripping reaction studies anomalously large strengths were reported for the 3 2 3 2 + [411] and 5 2 1 2 + [411] states, apparently because of unusually strong mixing with the 3 2 1 2 + [411] and 5 2 3 2 + [411] states, respectively. In the present work the pickup strengths to these states are also found to be larger than expected. A new Coriolis mixing calculation with revised parameters is capable of explaining part, but not all, of the mixing effects. In particular the very large strength of the 3 2 3 2 + [411] state in 163Ho remains unexplained.