C. R. Bingham

Heavy-ion inelastic scattering from deformed nuclei

Abstract Theoretical and experimental methods for studying heavy-ion inelastic scattering from deformed nuclei are described. The theoretical methods involve classical-limit approximations, while particle- γ-spectroseopy techniques are employed experimentally. With these approaches, heavy-ion excitation in the Coulomb-nuclear interference region acquires a transparent interpretation, despite the apparent complexity of the multistep excitation processes involved. The examples discussed provide a good illustration of the relationship between classical and quantum physics. The sensitivity of the inelastic scattering to details of the surface ion-ion potential due to radial and angular localization is exploited to provide a method of determining the equipotential contours in a direct manner which bypasses particular model-dependent parametrizations. The method is used to construct ion-ion potentials from inelastic scattering data for the systems 40Ar + 160Gd, 156Gd, 162Dy, 164Dy, and180Hf. The contribution of adiabatic giant resonance polarization to this potential is discussed. The relation between the deformed ion-ion potential and nuclear shapes is illustrated by comparing the experimental potentials to deformed double-folding and deformed proximity-potential calculations.

Rotation-aligned coupling and axial asymmetry in 189−195Au

Abstract Levels in 189, 191, 193Au have been studied by radioactive decay of isotopically separated 189, 191, 193Hg. The systematics of the levels are followed from 195Au to 189Au and show a remarkable insensitivity to neutron number. The h 1 1 2 bands are identified and provide a critical test of the model of a single-j nucleon subject to rotation-aligned coupling to an asymmetric core. Within the framework of the model the triaxial degree of freedom appears to be very stable.

Alignment processes and shape variations in 184Pt

Abstract High-spin states in the transitional nucleus 184Pt were populated via the reactions 154Sm(34S, 4n)184Pt and 172Yb(16O, 4n)184Pt. The yrast band was extended up to I = 28 ħ and six new side bands built on both neutron and proton quasiparticle configurations were observed. Shell correction-type calculations indicate variations of the nuclear shape in different bands, especially as a result of band crossings due to the process of angular momentum alignment. Comparison of the band characteristics are made between 184Pt and eight adjacent nuclei. The pattern of band crossings in these nine nuclei is considered from the viewpoint of blocking comparisons and of theoretical calculations. The competition between low-frequency vi 13 2 and πh 9 2 band crossings is discussed.

High-spin states in 183Pt

Abstract High-spin states in 183 Pt have been studied for the first time using the reactions 154 Sm( 34 S, 5n) and 170 Yb( 16 O,3n). Rotational bands built on the Nilsson configurations 1 2 − [521], 7 2 − [514] and 9 2 + [624] were observed up to spin values of 39 2 − 49 2 h . Quasiparticle alignments and band crossing frequencies were investigated in these bands. A large signature splitting was observed in the νi 13 2 - band structure . The experimental results were compared with total routhian surface calculations, in which the shape of the nucleus could be followed as a function of rotational frequency for different quasiparticle configurations.

Isomerism in 96Ag and non-yrast levels in 96Pd and 95Rh, studied in β decay

The β decay of 96Ag (Z=47,N=49) was investigated by measuring positrons, X rays as well as β-delayed protons and γ rays. The γ radiation was studied by means of germanium detectors and a NaI total-absorption spectrometer. Two β-decaying isomers in 96Ag were established with half-lives of 4.40(6) and 6.9(6) s and tentative spin–parity assignments of (8+) and (2+), respectively. For both isomers, the intensities of β transitions to low-lying levels of 96Pd (Z=46,N=50) and β-delayed proton decays to levels in 95Rh (Z=45,N=50) were measured. Several new 96Pd levels were firmly established. The level energies, their γ decays and the Gamow–Teller decay of 96Ag are compared to shell-model predictions. A new low-lying level in 95Rh was found at 680 keV excitation energy. Through a comparison with low-lying states of N=50 isotones, this level is interpreted as the first excited 7/2+ state built on the proton 9/2+ ground state. The assignments of further excited states in 95Rh are discussed.

g-factor measurements of μs isomeric states in neutron-rich nuclei around 68Ni produced in projectile-fragmentation reactions

We report the first g factor measurement on microsecond isomers of neutronrich nuclei produced in projectile-fragmentation reactions at intermediate energies. The nuclides in the vicinity of 68 Ni were produced and spin oriented following the fragmentation of a 76 Ge, 61.4 MeV u −1 beam at GANIL. The LISE spectrometer was used to select the nuclei of interest. The time-dependent perturbed angular distribution (TDPAD) method was applied in combination with th eh eavy-ion–gamma correlation technique to measure the g factors of 69m Cu (J π = 13/2 + , T1/2 = 350 ns) and 67m Ni (J π = 9/2 + , T1/2 = 13.3 µs). Specific details of the experimental technique and the comparison of the results (|g( 69m Cu) |= 0.225(25) and |g( 67m Ni) |= 0.125(6)) with theoretical calculations are discussed. These results provide another indication of the importance of proton excitations across the Z = 28 shell gap.

-decay characteristics of neutron-deficient 190, 192Po nuclei and alpha branching ratios of 186, 188Pb isotopes

By using complete fusion reactions and , leading to and compound nuclei, improved -decay characteristics for neutron-deficient isotopes have been obtained. The experiments have been performed at the fragment mass analyzer (Argonne) and at the RITU gas-filled separator (Jyvaskyla). In the l = 0 decay to the excited state in is two times faster than the decay to the ground state. For more precise values of the alpha-decay energy keV and half-life ms were measured. By using correlated -decay chains -branching ratios of 38(9)% and 9.3(8)% were experimentally deduced for the first time for and , respectively. The reduced -width systematics is extended for even Po isotopes, confirming a persistence of the saturation towards the lighter isotopes. Absence of any anomalies in the reduced -widths for the neutron-deficient Pb isotopes is confirmed.

Very slow M4 transitions and shell-model intruder states in 199, 201Bi

Abstract The isomeric decays of the 1 2 + shell-model intruder states in 199,201Bi have been investigated. In the case of 201Bi we show that the s 1 2 → h 9 2 isomeric transition is pure M4 within experimental error and is 2200 times slower than any other M4 transition observed in odd-mass nuclei. Its l-forbiddenness and the possibility of an E5 admixture and penetration effects are discussed.

Microscopic and macroscopic DWBA analysis of the reactions 28Si(α, d)30P, 32S(d, α)30P and 32S(α, d)34Cl studied at Eα = 50MeV and Ed = 40MeV

Abstract The reactions 28 Si(α, d) 30 P, 32 S(d, α) 30 P and 32 S(α, d) 34 Cl have been studied at E α = 50 MeVand E d = 40 MeV. The angular distributions have been analysed in terms of the single-step, zero-range DWBA with microscopic as well as macroscopic form factors. By requiring an almost identical shape in the microscopic and macroscopic radial form factors for all L -values with L ⩽ 6 the size parameters of the Woods-Saxon well in which the transferred cluster is bound to the nucleus were determined as r 0 = 1.15 fm and a = 0.76 fm . Despite the differences between the two approaches with these parameters the shape of the microscopic angular distribution is well reproduced and the corresponding strengths agree to within 25%. The method has been applied to the three reactions and relative two-nucleon spectroscopic factors have been deduced. A comparison is made with the results of two shell-model calculations.

Competing shapes in light Tl nuclei

In-beam γ-ray spectroscopic experiments have been performed on 191Tl, 189Tl, and 187Tl, and multiple band structures are established. These enable a study of the shape competition in the transitional region below the Z = 82 gap. Among the structures observed for the first time in odd-A Tl are bands built on the low-K prolate πh9/2, low-K oblate πh11/2, and perhaps high-K oblate πi13/2 excitations.