Analog Resonances Research Articles

G9/2 isobaric analogue resonances in 64,66Zn(p,γ) reactions

Gamma decay schemes and angular distributions have been measured for g9/2 isobaric analogue resonances (IAR) in the 64,66Zn(p,γ) reactions. In 65Ga, the IAR is seen to be fragmented into four components at resonance energies ER = 6.810, 6.819, 6.830, and 6.835 MeV, and two fragments are observed in 67Ga at ER = 8.554 and 8.569 MeV. The total analogue–antianalogue M1 strengths are, respectively, 7 and 4% of the single particle estimates in 65Ga and 67Ga. These results are examined in the light of a model proposed by Aleshin. In 65Ga, the level at 1.286 MeV is determined to have a spin of 9/2 from angular distributions. This level is most likely a member of [Formula: see text] multiplet.

Multipolarities of γ-rays from 92, 94Nb and 94,95,96,97,98Tc

92, 94Nb and 94, 96, 98Tc have been produced by the (p, n) reaction at proton energies on and near the d 5 2 isobaric analog resonance. 95,97Tc have been produced by the (p, γ) reaction below the (p, n) threshold. Internal conversion electrons due to the decay of their excited states were detected on-line with a mini-orange spectrometer which is optimized for the energy range 50 to 500 keV. Gamma rays from these nuclei were detected with a thin Ge(Li) detector. Isomeric-delayed internal conversion electrons and γ-rays were observed, using a nanosecond-pulsed beam. The internal conversion coefficients for 55 transitions in these nuclei have been determined and their multipolarities deduced. The multipolarity of the transitions in these nuclei is predominantly M1. Negative parities have been assigned through use of the d 5 2 isobaric analog resonance enhancements of the population of negative-parity final states. The systematic behavior of the 2 −, 3 − doublet and of the g 9 2 ⊗ d 5 2 multiplet in these nuclei is discussed.

Application of the crystal blocking technique to the study of the highly excited nuclear continuum

The crystal-blocking lifetime technique (BLT) was used to examine several effects in the in-elastic scattering through 90° of ≈ 5 MeV protons from ≈ 1.5 μm thick germanium crystals to various excited states, using the elastic scattering observed simultaneously as a “promptness” monitor: (a) the enhancement effect an isobaric analog resonance has on the underlying fine-structure states in its vicinity; (b) the effect of different level densities and hence level widths at different excitation energies in different Ge isotopes; (c) the effect on the mean lifetime of the final-state spin in the same isotope; and (d) a slight difference in the mean lifetimes for two different proton groups in the same isotope leading to states of the same spin, a result revealing a possible nuclear (intermediate) structure effect, i.e. one that cannot be explained on the basis of the statistical model. The excitation energies reached in the compound nuclei of arsenic range between 10 and 12 MeV. All results were obtained below the respective lowest neutron thresholds; the resulting lifetimes lie in the range 10 −16–10 −17 sec, corresponding to mean level widths around 20 eV; this is still considerably less than the estimated mean level spacing, even when the fine structure is enhanced within the analog resonance; i.e. Γ/ D ⪡ 1. The actual contact between experiment and calculations based on computer simulations of charged-particle penetration through crystal lattices is made at the level of comparisons of the depths of characteristic blocking dips.

Isobaric analogue resonances in the 80Se(p, n)80Br reaction

Abstract The toral (p, n) reaction cross section for 80 Se has been measured as a function of proton energy in the energy range from ≈ 2.7 to 5.375 MeV with fine resolution (≈ 5 keV). Several prominent isobaric analogue resonances have been measured. A detailed shape analysis of the isobaric analogue resonances has been performed to determine the proton width Γ p , the spreading width W and the spectroscopic factor S for the various resonances.

Vibrational spectra and carbon–hydrogen stretching mode assignments for a series of n-alkyl carboxylic acids

The Raman and infrared spectra for the C4, C8, C12, and C16 carboxylic acid series were obtained at liquid nitrogen temperatures, in the 2900 cm−1 spectral region and were compared to spectra for selected branched and straight chain alkane systems. For hexadecanoic acid-d3 the Fermi resonance interaction between the CD3 symmetric stretching mode and the overtone level of the CD3 asymmetric deformation vibration was examined as a function of physical state. In this example of a negative Fermi resonance perturbation, in which the lower frequency overtone component is more intense than the higher frequency fundamental, the coupling increases as the system passes from either the matrix isolated species or solution phase to the polycrystalline state. The spectra of the carboxylic acid series, as well as the spectra of 2,2,4-trimethyl pentane and n-octane, suggest that in the 2900 cm−1 region an analogous Fermi resonance coupling exists between the CH3 symmetric stretching vibration at ∼2938 cm−1 and the 2871 cm−1 overtone transition of the CH3 asymmetric deformation. Unfortunately, the 2930–2940 cm−1 region for the solid systems is further complicated by transitions attributed to crystal interactions. Although the Fermi interaction for the methyl group has been recognized in the simpler halomethane system, for example, it has not been previously discussed in the more general context of significantly larger branched and straight chain molecules. Comparisons of the carboxylic acid spectra in the 2900 cm−1 region have also led to assignments for the α-CH2 (adjacent to the carbonyl group) and the ω-CH2 (adjacent to the methyl group) C–H stretching modes.

A comment on the absolute determination of the spectroscopic factor in (d, p) sub-Coulombian reactions

A comparison is made between the spectroscopic factorS extracted from the40Ar(d, p)41Ar 1.354 MeV (3/2−) sub-Coulombian-stripping reaction and the one deduced from the analysis of the corresponding isobaric analog resonance. The dependence ofS on the neutron well geometrical parameters is investigated in detail. An effect due to the Nolen-Schiffer anomaly has been found in the investigation of the Coulomb displacement energy.

Properties of the Intermediate Structure inAs71

The spins and parties of the five reported $l=0$, ${J}^{\ensuremath{\pi}}={\frac{1}{2}}^{+}$ substructures nested within the br\'oad $l=0$ analog resonance in $^{71}\mathrm{As}$ at ${E}_{p}=5.05$ MeV have been measured. Three of the five substructures were determined as having ${J}^{\ensuremath{\pi}}$ different from ${\mathrm{\textonehalf{}}}^{+}$, casting doubt on the interpretation of this resonance as an example of intermediate structure.

Calculation of the time-development function for proton-nucleus inelastic scattering at isobaric analogue resonances

The time-development functions of the inelastic scattering of protons from 92Mo, which can be measured by crystal blocking experiments, are calculated at the energies of isobaric analogue resonances. The decay curves of compound nuclear levels show nearly exponential behaviour. Contributions from level-level correlations are also estimated.

ReactionMn55(p, n)Fe55fromEp=1.35 to 5.42MeV

The total ($p, n$) reaction cross section for $^{55}\mathrm{Mn}$ has been measured as a function of proton energy in the energy range 1.35 to 5.42 MeV with fine resolution (\ensuremath{\sim}5 keV). Several strong isobaric analog resonances have been located in the excitation function. The excitation function, averaged over a 200 keV energy interval has been compared with the optical model, Hauser-Feshbach, and Hauser-Feshbach-Moldauer calculations. The strong isobaric analog resonance at ${E}_{p}\ensuremath{\sim}1.54$ MeV has been shape analyzed to extract the proton width ${\ensuremath{\Gamma}}_{p}$, the spreading width $W$, the spectroscopic factor, and the reduced normalization.NUCLEAR REACTIONS $^{55}\mathrm{Mn}(p, n)$, ${E}_{p}=1.35\ensuremath{-}5.42$ MeV; measured $\ensuremath{\sigma}(E)$; optical model and Hauser-Feshbach analysis, isobaric analog resonance analysis.

Isobaric analogue resonances in56Fe corresponding to 335.5 and 340.9 keV states in56Mn

Excitation functions for the reaction 55Mn(p, gamma )56Fe in the proton energy range 1660-1710 keV have been measured. Three relatively strong resonances at Ep=1678, 1687 and 1695 keV have been observed. It is found that the decay characteristics of the first two resonances are nearly identical, while those of the third are distinctly different. Angular distributions of gamma rays have been measured. Analysis of the angular distribution data leads to an assignment of Jpi =(2+, 3+) for the 1695 keV resonance and the most probable assignment of Jpi =4+ for the 1678 and 1687 keV resonances. The 1695 keV resonance in 56Fe is identified as the isobaric analogue resonance (IAR) of the 340.9 keV state of 56Mn. The 1678 and 1687 keV resonances are the fine-structure components of the IAR of the 335.5 keV state in 56Mn.

Study of isobaric analogue states in52Cr

A detailed investigation of the gamma decay of four analogue resonances in the reaction 51V(p, gamma )52Cr has been performed in the proton energy range Ep=0.7-2.0 MeV. From (p, gamma ) angular distributions, mixing ratios of primary gamma transitions depopulating the analogue resonances and Jpi values of some states populated in the gamma decay have been obtained. Decay schemes, branching ratios, partial gamma widths and resonance strengths have been determined for these IARs. Upper limits of M1 transition rates from analogue states to low-lying states are found to be of the order of few mWu. The analogue states are seen to decay significantly to a group of states in the region of excitation 3.4 to 6.0 MeV.

G9/2isobaric analogue resonances in the56Fe(p,γ)57Co reaction

Resonances consistent with fragmented g9/2 analogue resonance have been found in 57Co corresponding to the Ex=2.454 MeV level in the 57Fe parent nucleus. The resonance was located through the 56Fe(p, gamma )57Co reaction. Total gamma -ray spectra were measured with a Ge(Li) detector in 2 keV steps in the expected proton energy range. Excitation functions for the different primary gamma transitions were constructed. The g9/2 IAR were found in two components at Ep=3728 and 3735 keV. The angular distributions of gamma rays were measured at these two bombarding proton energies. The two resonances were suggested to have spin and parity Jpi =9/2+ based on the gamma -ray excitation functions and angular distribution measurements. The gamma -branchings and absolute transition probabilities were also determined. The Ml gamma transitions from the g9/2 IAR components going to the possible anti-analogue level at Ex=4.585 MeV excitation energy have absolute transition strengths of 1.8*10-2 Wu and 1.2*10-2 Wu.

Study of isobaric analogue resonances in f-p shell nuclei: A unified-model description

Spectroscopic factors as well as parentage coefficients for collective J i π = 2 1 +, 3 1 − and 4 1 + states have been obtained for N = 29 nuclei and 59Ni via (τ, d p ) reactions through isobaric analogue resonances (IAR). In the framework of a unified-model calculation, treating the one-neutron core-coupling ( N = 29) and three-neutron core-coupling as well as pure three-neutron shell-model calculations ( 59Ni), a description can be given for most of the observed phenomena (energies, spectroscopic factors, parentage coefficients on the J i π = 2 1 +, 3 1 −, 4 1 + levels). Some discrepancies remain, especially with respect to the description of the splitting of the 2 p 1 2 neutron single-particle state. A comparison with earlier calculations for the N = 29 nuclei is carried out. With respect to 59Ni, the three-particle-cluster effects are pointed out and an extensive comparison between both types of calculation and with experiment is made.

Reduced normalizations from (d, p) reactions and from elastic proton scattering on isobaric analog resonances

The determination of reduced normalizations by measuring ($d, p$) reactions in the energy region of sub-Coulomb and quasi-Coulomb stripping with an experimental accuracy which has not been attained in former investigations allows reasonable comparisons with corresponding reduced normalizations of analog states obtained by elastic proton scattering via isobaric analog resonances. This comparison includes 38 states with known spins and parities formed by adding a further nucleon to the nuclei $^{124}\mathrm{Sn}$, $^{130}\mathrm{Te}$, $^{138}\mathrm{Ba}$, $^{140}\mathrm{Ce}$, $^{142}\mathrm{Nd}$, and $^{208}\mathrm{Pb}$. The reduced normalizations of the proton analog states are based on the experimental partial widths given by other authors and on own calculations according to two different shell model theories of isobaric analog resonances. The uncertainties still remaining in the theoretical description of some effects inherent in the direct reaction mechanism of transfer reactions as well as in the shell model reaction theoreis do not permit a unique decision concerning the validity of the different theoretical approaches in determining the decay widths of single particle states.

Study of isobaric analogue resonances in65Cu by proton scattering from64Ni

Excitation functions of the elastic proton scattering by64Ni were measured in the energy rangeEp=5.0–6.2 MeV at 90°, 125° and 141° and in the energy intervals 5.00–5.25 MeV and 5.85–6.20 MeV at 110° and 160°. At 90° the excitation function of the inelastic proton scattering leading to the 2+(1.34 MeV) state in64Ni was measured too. Out of the ten resonances found in the whole energy range, the resonances at 5.105, 5.985, 6.042 and 5.35 MeV were studied in more detail. The analysis of the elastic scattering provided the energy, orbital momentum, total and partial widths of the first three resonances. The inelastic scattering cross section for the last three resonances was sufficient to permit the spin determination by (p, p′ γ) angular correlations in the Goldfarb-Seyler geometry. The spectroscopic factorsSpp are in good agreement with those obtained from (d, p) experiments. The resonance at 5.35 MeV exhibits an important 2p ⊗21+ amplitude in its wave function. Its inelastic partial widths and the corresponding spectroscopic factorsSpp′, were determined. The nonresonant background in the elastic channel is well described by shape and compound elastic scattering calculations with Perey's optical model parameters.

On an intermediate structure of giant analog resonances in medium and heavy nuclei

The effect of coupling of the usual particle-hole states to particle-hole states built above a collective state on the decay characteristics and structure of a giant resonance with higher isospin (T>) has been estimated. Numerical calculations are carried out for60Ni,90Zr and208Pb.

Analysis ofXe136(p,p1)on analog resonances and the structure ofXe137

Analysis of proton inelastic scattering through analog resonances in /sup 1/37Cs is carried out by the addition of a resonant scattering matrix to a coupled-channel scattering matrix. Neutron coupling to the 2/sup +//sub 1/ excited state of /sup 1/36Xe in wave functions of the parent states in /sup 1/37Xe is thus determined. For low lying levels, the parentage coefficients extracted from experimental data are in general agreement with calculations performed using the particle-vibrator coupling model.

Isobaric analog resonances in theZn68(p,γ)Ga69reaction

Isobaric analog resonances in /sup 6/9Ga corresponding to the ground (1/2/sup -/) and first excited (9/2/sup +/) parent states of /sup 6/9Zn have been studied by the /sup 6/9Zn(p,..gamma..) reaction. The ..gamma.. decay of the gound state of /sup 6/9Zn is compared with the ..beta.. decay of the parent isobaric analog state. The latter is a pure Gamow-Teller transition to the ground (3/2/sup -/) and third (3/2/sup -/) excited states, while both Gamow-Teller and Fermi matrix elements can contribute in the decay to the second excited (1/2/sup -/) state of /sup 6/9Ga. The M1 decay widths obtained from the ..gamma.. decay of the J/sup ..pi../ = 1/2/sup -/ isobaric analog state are in good agreement with the widths extracted from the logft values in the first two of the three ..beta..-decay branches. However, the M1 decay width to the third excited state disagrees with the value deduced from the logft value of the ..beta.. decay of the /sup 6/9Zn g.s. to this state. In addition, the M1 transition strength of the 9/2/sup +/ (T/sub greater-than/) state to the 9/2/sup +/ (T/sub less-than/) state in /sup 6/9Ga has been measured and is compared with the recently published systematic trends for themore » analog to antianalog transition in other f-p shell nuclei.« less

Strength Functions for Isobaric Analog Resonances

A new strength function continuous in energy and a smoothing parameter is constructed which arbitrarily closely approximates the discontinuous strength function for line broadening defined by Lane. The functional form of the Lane strength function is then derived for a fragmented isobaric analog resonance. Its non-Lorentzian form is explicitly and qualitatively different from that assumed in a recent analysis of isobaric analog resonances.

Angular Distribution Measurements of Gamma-rays from Unbound T = 1 States in 22Na

Angular distributions have been measured at six 21Ne(p, γ)22Na analogue resonances, with Ep = 0.70, 0.77, 1.09, 1.21, 1.56 and 1.84 MeV, and at a candidate for analogue resonance with Ep = 1.11 MeV. Gamma-ray mixing ratios have been obtained for the first time for the decays of these levels with determination of spin-parity assignments. The spins and parities for the bound states at 1.98 and 4.36 MeV have been deduced. Transition strengths provide information on the isoscalar and isovector strengths in the self-conjugated nucleus 22Na.