Phase-shift analysis of 16O + 16O elastic scattering

A phase-shift analysis has been carried out for ¹⁶O + ¹⁶O elastic scattering, resulting in unambiguous values for the reflection coefficients in the energy range of the first gross structure of the 90° excitation function, and answering some of the questions still open regarding the calculations existing so far.     

Phase-shift analysis of 16O + 16O elastic scattering data

A phase-shift analysis of precisely measured elastic ¹⁶O + ¹⁶O data has been carried out in order to establish the existence of molecular resonances between E_c.m = 15.5 and 18 MeV and to investigate the possible structure of these resonances.     

A re-investigation of 19O(β−)19F

Gamma rays observed in¹⁹O(β^?)¹⁹F have been studied with Ge(Li) spectroscopy utilizing activity created via the ¹⁸O(d, p) ¹⁹O reaction. Precision measurements of γ-ray energies and intensities, in conjunction with previous work, define the following excitation energies (in keV) and β-branching ratios (in %) for states of ¹⁹F: 109.894(5), 0.055(13/38); 197.143(4), 45.4(1.5); 1345.67(13), 0.017(2); 1554.038(9), 54.4(1.2); 2779.849(34), < 0.002; 3908.17(20), 0.0081(5); 4377.700(42), 0.0984(30). The corresponding values of logft are 8.34(30/10); 5.384(14); 8.25(5); 4.625(10); > 8.17; 6.133(27); and 3.859(17), respectively. The β-branches to the 1346 and 3908 keV states had not been observed previously. The β-branch for the 4378 keV state is in significantly better accord with theoretical expectations than the previous value of 0.160(12) %.     

Beta-delayed proton emission from 97Cd and 99Cd

Two new β-delayed proton precursors, ^97,99Cd, have been identified at the ISOLDE on-line isotope separator. The proton branching ratio for ⁹⁹Cd is (1.7^+1.1_?0.5) × 10^?3. The ⁹⁹Cd proton spectrum is discussed in terms of the statistical model with Porter-Thomas fluctuations. The half-life of ⁹⁹Cd was determined to be 16±3 sec. A search for ⁹⁸Cd was also performed and it was found to be a pure β-emitter with a probable half-life of ≈ 8 sec.     

Beta-delayed proton and alpha emission from 36K

Protons and α-particles emitted from levels in ³⁶Ar following the β-decay of ³⁶K have been measured. Proton transitions were found from levels at 9217, 9493 and 9870 keV in ³⁶Ar and α-transitions from levels at 8860, 8890, 9680 and 10548 keV. Seven previously unreported β-transitions to highly excited states in ³⁶Ar have been identified. The assignments of spins and parities to the particle emitting levels are discussed.     

The 6.05 MeV 0+ state in 16O: A shape isomer

A variational calculation predicts the existence of a quadrupole deformed isomeric state in ¹⁶O, which may be associated with the observed rotational band starting at 6.05 MeV. Calculated B(E2) value and strength in the ¹⁸O(p, t) reaction support this interpretation.     

Generator-coordinate study of elastic 16O + 40Ca scattering

Elastic ¹⁶O + ⁴⁰Ca phase shifts are calculated using a generator-coordinate method. A rotational band of molecular resonances is found with a rotational constant of about 30 keV. The width of these resonances should make them observable in the energy range 30 to 50 MeV. These features can be approximately reproduced by a shallow local potential. Properties of the imaginary part of the optical potential are discussed qualitatively. The optical potential should be transparent in a window of J-values comprised between about 16 and 25. Odd-even effects are shown to be negligible in the real part of the potential but might be important in its imaginary part. A possible confirmation of these predictions is found in an experimental excitation function.     

Microscopic study of elastic 16O28Si scattering

Elastic ¹⁶O²⁸Si scattering is studied microscopically within the Generator Coordinate Method. A resonance analysis supplies a series of three rotational bands; the two excited bands agree very well with rotator-like structures found in experiment. The phase shifts do not show any parity dependence.     

Microscopic study of elastic 12C+16O scattering

The L=0 to 17 phase shifts are calculated microscopically for elastic ¹²C+¹⁶O scattering with a generator coordinate method. The experimental resonances are shown to belong to four different bands. Interpretations and spin assignments are suggested for several recently observed anomalies. A spin J=15 seems likely for the 22.8 MeV resonance. A missing J=13 resonance should be searched for between 17 and 18 MeV.     

Quasi-elastic pion scattering on 16O: A comparison between the Δ-hole approach and a standard first-order calculation

We present calculations of quasi-elastic pion scattering on ¹⁶O in both the Δ- hole model and a standard first-order theory. The basic approach is a modified “DWIA”, where the same in-medium πN t-operator is used for the transition and the optical potential generating the distorted pion wave functions. In order to allow a meaningful comparison with the recent SIN data, all technical complications such as background interactions, non-static vertex-corrections, 1/A effects, are taken into account, and the DWIA amplitude is evaluated without further numerical simplification like, e.g., factorization. In contrast to the closure approximation, the Δ-hole model predicts correctly the doubly differential cross sections for (π, π') on ¹⁶O over a wide range of angles and energy-losses.     

Optical model parameter searches for 16O + 11B elastic scattering

The direct search with pattern search technique of Hooke and Jeeves has been programmed to search for heavy-ion optical model parameters and the results of unconstrained searches using this method for ¹⁶O + ¹¹B elastic scattering are presented.     

Nuclear sizes of 40,48Ca and 32,34S isotopes determined from 1 GeV proton elastic scattering

Differential cross sections for 1 GeV proton elastic scattering from ^40,48Ca and ^32,34S have been measured. The parameters of the nucleon distributions were obtained from an analysis of the experimental data. The difference between the neutron distributions in ⁴⁰Ca and ⁴⁸Ca is discussed in particular.     

Regge poles and backward elastic α-particle scattering from 16O

The experimental angular distributions of α-particles scattered from ¹⁶O energies around 20 and 29 MeV are analysed using a two-Regge-pole representation. The spins of the observed resonances are extracted.     

Statistical fluctuations and compound elastic scattering for 12C(12C, 12C)12C and 16O(16O, 16O)16O

The difference between the observed fluctuations in the elastic excitation functions for carbon-carbon and oxygen-oxygen scattering, just above the Coulomb barrier, is interpreted in terms of the compound nucleus model.     

Microscopic and macroscopic aspects of 135 MeV proton scattering from 16O

Differential cross sections have been measured for the scattering of 135 MeV protons from ¹⁶O and data from the transitions to 13 states (up to 19.5 MeV excitation) have been analysed using microscopic and macroscopic nuclear reaction models. Extensive collective model calculations have been made of the transitions to all natural-parity states. The deformation parameters for the 4p4h rotational band are in good agreement with theoretical models. The inelastic scattering data from the excitation of the negative-parity states have also been analysed in the distorted-wave approximation using microscopic (shell and RPA) models of nuclear structure and with density-dependent two-nucleon t-matrices. For positive-parity states, we report the first shell-model calculation using the complete 2?ω basis space and find that the triplet of 2p2h states (4⁺, 2⁺, 0⁺) around 11 MeV excitation is quite well described by this model, as may be a 1⁺ state which is observed for the first time by proton scattering from ¹⁶O.     

An optical potential description of 16O + 28Si elastic scattering

The differential cross sections for ¹⁶O + ²⁸Si elastic scattering at seven energies between 21 and 35 MeV in the centre of mass are described well over the whole angular range from 20° to 180° by an optical potential whose real part consists of a double-folded potential supplemented by a phenomenological model-independent correction term. This surface correction is predominantly attractive and has structure which depends only weakly on the energy. The associated imaginary potentials imply surface transparency and have detailed structure which varies rapidly with energy. However there is a systematic trend for the absorptive region to extend to larger radii as the energy increases. A simple parameterization of this trend allows the main features of the excitation function for 180° scattering to be reproduced.     

Microscopic study of elastic scattering of almost identical nuclei: The 16O18O system

Elastic ¹⁶O¹⁸O scattering has been studied microscopically using the Generator Coordinate Method. The calculation supports the predictions by LeMere et al. concerning the influence of the core-exchange term.     

Nuclear structure studies of 97Ru from the decay of 97g,mRh

The energy levels of ⁹⁷Ru have been studied through the decay of 31.1 min ^97gRh and 44.3 min ^97mRh using Ge(Li), Si(Li), Nal, plastic and anthracene detectors in singles and in coincidence experiments. A total of 139 γ-rays were observed. Ninety-eight γ-rays have been placed into the decay schemes involving 38 excited levels in ⁹⁷Ru. The level energy of ^97mRh was determined to be 258.6 keV. The spin and parity of ^97gRh and ^97mRh are assigned as $\text{9}\text{2}{}^{\mathrm{+}}\text{and}\text{1}\text{2}{}^{\mathrm{?}}$, respectively. The fraction of decay of the isomer by the isomeric transition was measured with the Si(Li) detector, and α_k values were determined for strong transitions. The half-life of the 188.6 keV, $\text{3}\text{2}{}^{\mathrm{+}}$ state in ⁹⁷Ru was determined as 0.23 ± 0.02 ns by delayed e-γ coincidence measurements. The nuclear structure of low-lying levels is compared with similar levels in other odd-mass nuclei (N = 53) isotones and Ru isotopes).     

Nuclear orientation of 160Tb in Tb metal

The decay of ¹⁶⁰Tb oriented at low temperatures in Tb metal has been investigated, and angular distributions of 19 γ-rays have been determined. The reduction in anisotropy in polycrystalline metal samples is discussed. Multipole mixing ratios have been determined for many of the γ-rays. A critical discussion is given of the previously reported $\text{M2}\text{E1}$ mixing ratios, and previous nuclear orientation studies are re-analyzed in a consistent manner so that their results can be compared. It is shown that the nuclear orientation and angular correlation results for the 1178 keV transition are consistent only if E3/E1 mixing is present. The El branching ratios and $\text{M2}\text{E1}$ mixing ratios are analyzed on the basis of Coriolis-mixed K = 0, 1 and 2 character for the negative-parity levels of ¹⁶⁰Dy.