Isobaric Analog Resonances Research Articles

Analogue–antianalogue transition for the 11.14-MeV level in 49V

The g9/2 isobaric analogue resonance (IAR) is located at the excitation energy Ex = 11.139 MeV in 49V through the 48Ti(p, γ)49V reaction, (p, p1γ) angular distributions and the presence of the transition from the resonance to the 2.178-MeV (Jπ = 9/2+) level in 49V arc used to identify this resonance. The analogue–antianalogue M1 transition strength is found to be Γγ(M1) = 0.050 ± 0.009 eV or 0.2% of the single-particle estimate. This reduction in transition strength can be attributed partly to the fragmentation of the analogue and partly to the nonsingle-particle character of the antianalogue state.

Sm144(p,p′) scattering through isobaric analog resonances and the structure ofSm145

Angular distributions of the cross section for the elastic and inelastic scattering of protons have been measured at four isobaric analog resonances of the /sup 144/Sm+p system and at two off-resonance energies. Spectroscopic information about the (7/2)/sub 1//sup -/, (3/2)/sub 1//sup -/, (1/2)/sub 1//sup -/, and (5/2)/sub 1//sup -/ states of the parent nucleus /sup 145/Sm is extracted, with the core /sup 144/Sm in the states 0/sub 1//sup +/, 2/sub 1//sup +/, 3/sub 1//sup -/, 4/sub 1//sup +/, and 2/sub 2//sup +/. The analysis includes direct and fluctuating nonresonant processes. The direct scattering amplitude is obtained from a coupled channel treatment. Different methods for the calculations of the single-particle widths have been employed. The experimental spectroscopic amplitudes were compared with nuclear structure calculations based on the particle-vibrator model. Both the liquid drop model and the quasi-particle random phase approximation were used to describe the vibrator. The calculations based on the latter model show good agreement with the experimental results.

Compound elastic cross sections in the isobaric analog resonances 88Sr(p,p 0) at 5.06 MeV and 86Sr(p,p 0) at 6.02 MeV

We have measured the K-shell ionization probability P K across the isobaric analog resonances in the elastic channel of the reactions 88Sr(p,p 0) 88Sr at 5.06 MeV and 86Sr(p,p 0) 86Sr at 6.02 MeV. The dependence of P K on the beam energy for two scattering angles 90° and 155° is analysed in the framework of the theory developed by Anholt et al. taking into account the effect of compound-nucleus scattering. A compound elastic cross section ( dσ dω ) CE = 40 ± 10 mb/sr at the peak of the resonance is deduced in the reaction 88Sr + p at 5.06 MeV, while the experimental results agree with a negligible value of ( dσ dω ) CE for the resonance in 86Sr + p at 6.02 MeV.

Elastic and inelastic scattering of polarized protons fromPb206near isobaric analog resonances

Excitation functions have been measured for the elastic and inelastic scattering of polarized protons from $^{206}\mathrm{Pb}$ at ${\ensuremath{\theta}}_{\mathrm{lab}}=120\ifmmode^\circ\else\textdegree\fi{}, 135\ifmmode^\circ\else\textdegree\fi{}, 150\ifmmode^\circ\else\textdegree\fi{}, \mathrm{and} 165\ifmmode^\circ\else\textdegree\fi{}$ in the energy range ${E}_{\mathrm{p}}=14.25\ensuremath{-}18.00$ MeV. Excellent fits to the elastic scattering data were obtained using a parametrized background and the isobaric analog resonances of 35 states in $^{207}\mathrm{Pb}$ (the states) with ${E}_{x}=2.3\ensuremath{-}5.7$ MeV; spinparity assignments and resonance parameters were determined for all of these isobaric analog resonances. The data for inelastic scattering to the first excited state (${2}^{+}$, 0.803 MeV) were described using a distorted-wave Born approximation background and the same isobaric analog resonances; good fits to the data were obtained by varying only the inelastic partial width amplitudes. A set of spectroscopic amplitudes was then found, for both the single-particle and the particle-core components of the parent states, by comparing the best-fit resonance parameters with those given by model calculations. The internal consistency of this set was verified by using sum rules. The spectroscopic amplitudes are compared with those given by simple weak-coupling model predictions; there is considerable disagreement, probably because too few configurations were used in the theoretical calculations.

Energy levels in 93Mo populated by the 93Nb(p, nγ) reaction

Energy levels of 93Mo have been investigated by means of the 93Nb(p, nγ) 93Mo reaction. The excitation functions of the level de-excitation γ-rays were measured with a Ge(Li) detector under proton bombardment in the energy range 3.0 to 5.0 Me V. A detailed γ-ray decay scheme which includes 69 levels and 123 γ-ray lines was constructed from the threshold energies for 64 γ-rays and the γ-ray excitation functions around five isobaric analogue resonances in the 93Nb(p, nγ) reaction. Spin-parity values for 59 levels and favourable values for 8 levels were assigned from the analysis of relative neutron yields via the isobaric analogue resonances of the parent odd-odd nucleus 94Nb. The results of the present experiment are compared with shell-model calculations.

Isobaric analogue resonances in the 41K and 65Cu(p, n) reactions

The total (p, n) reaction cross sections for 41K and 65Cu have been measured as a function of proton energy in the energy ranges 1.46–4.10 and 2.25–4.20 Me V, respectively. Several prominent isobaric analogue resonances have been identified. A detailed shape analysis of these isobaric analogue resonances has been performed to determine the proton width Γ p, the spreading width W and the spectroscopic factor S n for the various resonances.

Effective Coupling Constants for Spin-Flip and Non Spin-Flip E1 Transitions in A∼90 Nuclei

Radiative proton capture reactions through two isobaric analogue resonances (IAR) in 89 Y were studied, one was the 12.07 MeV 2d 5/2 state lying just above the neutron threshold energy B n and another was the 14.48 MeV 2d 3/2 state lying well above B n . E1 transitions from these IAR's were studied for favoured cases with no spin-flip and no change of radial nodes, and for unfavoured cases spin-flip and/or change of radial nodes. At the 2d 3/2 IAR lying well above B n , the favoured transitions show the resonance feature, but the unfavoured ones not. At the 2d 5/2 IAR near B n , however, both the favoured and unfavoured transitions show the resonance feature. Anormalous resonant feature of the unfavoured transitions is interpreted mainly due to the compound process. Favoured transitions are all found to be reduced by factors ∼0.3 over the shell model values.

Γ radiation from50Cr(p,p'γ)50Cr at E=5.46-6.15 MeV

The gamma radiation due to the de-excitation of the 21+ and 41+ levels in 50Cr was studied as a function of the energy, which was varied in 10 keV steps. In particular, strong peaks in the cross sections were observed for scattering to the 41+ level. Using experimental data on spin-flip probability the contribution of the statistical mechanism to the excitation of the 21+ level has been estimated. The estimated ratio Gamma 0/D0=0.24 was obtained for 11 MeV excitation of the compound nucleus. The contribution of direct reaction and isobaric analogue resonances to the cross section is discussed.

Investigation of isobaric analog resonances in 53Mn

The isobaric analog resonances in 53Mn with different spins and parities are investigated by means of the 52Cr(p, p), (p, p′), (p, p′γ), and (p, γ) reactions. Spectroscopic factors are derived and the experimental (p, γ) strengths are compared with theoretical single-particle estimations.

K-shell ionization across isobaric analog resonances

K-shell ionization probabilities P K near isobaric analog resonances are calculated including contributions from compound-nucleus scattering. For projectile scattering angles less than 90°, compound-nucleus scattering has a negligible effect on P K, but at large angles P K is affected considerably if compound-nucleus scattering is included.

Reaction48Ca (p, n)48Sc fromE p =1.885 to 5.1 MeV

The total (p, n) reaction cross section for48Ca has been measured as a function of proton energy in the energy range 1.885 to 5.100 MeV with an overall resolution of ∼ 2 keV and in ∼ 5 keV energy steps. The fluctutions in fine resolution data have been analysed to determine the average coherence width 〈Γ〉. The excitation function averaged over large energy intervals has been analyzed in terms of the optical model. The isobaric analogue resonances atE p ∼ 1.95 and 4 MeV have been shape-analyzed to extract the proton partial width and the spectroscopic factorS n . A comparison of the gross structures observed in ∼ 55 keV averaged excitation function with the predictions of Izumo’s partial equilibrium model has also been made.

Isospin and the proton-absorptive-potential anomaly near mass 100

An isospin coupled-channels analysis of sub-Coulomb-proton-absorption cross sections has been performed for $^{92,94,96}\mathrm{Zr}$ and $^{94,96,98,100}\mathrm{Mo}$. Introduction of coupling to the channel consisting of a neutron plus the isobaric analog of the target is shown to shift and damp the single-particle resonances, in addition to giving rise to isobaric-analog resonances. In spite of these effects due to the coupling, large variations in the absorptive potentials were still required to fit measured ($p, n$) cross sections. $^{96}\mathrm{Zr}(p, n)$ and $^{100}\mathrm{Mo}(p, n)$ cross sections were measured and analyzed with a standard optical model for this work. Other $\mathrm{Zr}(p, n)$ and $\mathrm{Mo}(p, n)$ cross sections were taken from previous results.

On resonance phenomena in nuclear reaction cross sections

The conclusions obtained using the continuum shell model for resonance phenomena are compared with experimental data from the 52Cr+p reaction obtained at energies with and without isobaric analogue resonances. The influence of channel coupling on the result of an autocorrelation analysis is investigated for the 15N+n nuclear reaction cross section calculated theoretically. Some conclusions are drawn on resonances in heavy-ion reactions.

Gamma decay of d5/2 isobaric analogue resonances in the 64Zn(p,γ) reaction

The resonances at Ep = 3.249 and 3.253 MeV in 64Zn(p,γ) are identified as fragments of the d5/2 isobaric analogue resonance from (p,p′γ) angular distributions. Gamma decay schemes and angular distributions are measured. In 65Ga, the level at 2.21 MeV is assigned a spin of Jπ = 5/2−. From angular distributions and symmetry potential considerations, the level at 2.82 MeV is considered to be the antianalogue state. The analogue–antianalogue transition strength is found to be compatible with single nucleon transfer data, thus showing that the interference effects from core polarized components arc negligible in this case.

Pion charge-exchange reaction and transition densities to isobaric analog states

Distorted wave impulse approximation calculations were performed for the (${\ensuremath{\pi}}^{+}$,${\ensuremath{\pi}}^{0}$) reaction to isobaric analog resonances in a series of nuclei employing two types of transition densities. The calculations are sensitive to the types of transition densities used, giving substantially different cross sections in the two cases.NUCLEAR STRUCTURE Pion charge exchange to isobaric analog states.

Purity of analog spin in isobaric analog resonances

It is shown that the position of the pole of the inverse averageS-matrix of an isolated isobaric analog resonance (IAR) is a very useful parameter, which allows one to distinguish between the weak and the strong coupling case of the finestructure distribution of the resonance. It gives also a direct measure of the purity of analog spin of the resonance. As an example the lowest IAR in208Bi is discussed.

Neutron particle-hole electric dipole states in 206, 207, 208Pb

Inelastic proton scattering on 206Pb, 207Pb and 208Pb through isobaric analog resonances has been used to study neutron particle-hole excitations with large ground-state γ-branches in these Pb isotopes. Relative (p, p′) cross sections at 90° are extracted for structures selectively excited on the d 5 2 , s 1 2 and d 3 2 − g 7 2 resonances. Interpretation of excitations is 206Pb and 207 Pb in terms of coupling to states in 208Pb is discussed. Branching ratios for 1 −states in 208Pb at 4.84, 5.29, 5.94 and 6.31 MeV and the 1 2 + state in 207Pb at 4.63 MeV are deduced.

Nuclear-Structure Effects Connected with Charge-Exchange Resonances

The excitation energies and the ($p$,$n$) cross sections of the giant Gamow-Teller resonance as well as the isobaric analog state in $^{208}\mathrm{Pb}$ are calculated. Similar to the results in electron scattering, the theoretical spin-flip strength overestimates the experimental one appreciably. The excitation energies of the spin-dependent excitations and the isobaric analog resonance can only be explained simultaneously if the effects of the dynamical theory of collective states and of the one-pion- and one-$\ensuremath{\rho}$---exchange potential are taken into account.

Cross Section Measurements for the Reactions 53Cr(p,g)54Mn, 53Cr(p,n)53Mn and 53Cr(p, p')53Cr

Cross sections have been measured for the reactions 53Cr(p, y)5 4Mn, 53Cr(p, n)53Mn and 53Cr(p, p/)53Cr over the proton energy range O'88-2'40 MeV. The results are compared with the predictions of statistical model, calculations with global optical model parameters, with particular reference to the role of isobaric analogue resonances. Satisfactory agreement between theory and experiment is achieved for all three reactions.

ISobaric analog state excitation in proton radiative capture

The direct-semidirect model for proton radiative capture so far formulated is unable to describe the observed (p, γ) excitation functions in the energy region where the isobaric analog resonances are located. To remove this difficulty, an extension of the model to include capture proceeding via isobaric analog state (IAS) excitation is here proposed. The calculated results are compared with the measured 90° excitation curve of the 208Pb(p, γ 1) 209Bi reaction and satisfactory agreement is achieved. A detailed analysis of the three mechanisms involved in the El dominant capture process is presented. In the case considered the model seems to provide a useful tool for study of the striking effects arising from IAS excitation.