Elastic and inelastic scattering of 178 MeV protons from 58Ni and 60Ni

The elastic and inelastic scattering of 178 MeV protons from ⁵⁸Ni and ⁶⁰Ni has been studied. Angular distributions were measured for the differential cross sections for elastic scattering as well as inelastic scattering from excited states below about 5 MeV, all with natural parity. For the elastic and for the inelastic scattering from the first excited state (2⁺ in both nuclei, the angular distributions for the polarization were also measured. The measurements extend out to c.m. angles of about 60°, corresponding to a momentum transfer of about 600 MeV/c.The elastic and inelastic scattering data were compared to the results of coupled-channel calculations in the vibrational model using a deformed spin-orbit interaction of the full Thomas form. Good agreement was found in general showing that the main features of the experimental results are well described in this model.     

Experimental and shell-model studies of the reactions 91Zr(d,p)92Zr and 90Zr(t,p)92Zr

The results of high-resolution studies of the ⁹¹Zr(d, p) reaction at E_d = 12 MeV and the ⁹⁰Zr(t, p) reaction at E_t = 11.85 MeV are presented. Absolute cross sections have been measured for both reactions and (d, p) spectroscopic factors determined. A comparison of these results with earlier data has been made, and although many of the previous assignments have been confirmed, many new features concerning the structure of ⁹²Zr have been discovered. Shell-model calculations have been performed for ⁹¹Zr and ⁹²Zr using a neutron space which includes the $\text{2}\text{d}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}$, $\text{3}\text{s}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$, $\text{2}\text{d}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$, $\text{1}\text{g}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}$ and $\text{1}\text{h}{}_{\mathrm{<mtext>11</mtext><mtext>2</mtext>}}$ orbits and a proton space comprising the $\text{1}\text{g}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}$ and $\text{2}\text{p}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ orbits. Realistic proton-neutron and neutron-neutron interactions based on the Sussex matrix elements were used in the calculations. Spectroscopic factors have been calculated for the ⁹⁰Zr(d, p) and ⁹¹Zr(d, p) reactions and cross sections calculated for the ⁹⁰Zr(t, p) reaction. In general, good agreement between the theoretical and the experimental results has been obtained.     

Excitation of low-lying levels and giant resonances in 90Zr via 57.5 MeV polarized proton inelastic scattering

Differential cross section and analyzing power angular distributions have been measured for transitions to low-lying bound states with J^π = 2⁺, 3^?, 4⁺ and 5^?, and the giant resonance region from 6 to 27 MeV excitation energy. Collective model calculations using a full Thomas form factor reproduce the data fairly well. The so-called LEOR turns out not to be seen as pure E3 in (p, p′). In the giant resonance region the data do not reveal the presence of a sizeable monopole strength, 10–20% of the energy-weighted sum rule at most. There is strong indication for a mixture of E2 (18% of the EWSR) and E4 (16% of the EWSR). Calculations were also carried out using RPA (1p1h) wave functions. They reproduce the experimental data rather poorly, except for the general behaviour of the cross-section angular distributions.     

Elastic scattering of 56 MeV polarized deuterons on 4He

The differential cross section and the vector and tensor analyzing powers A_y, A_xx, A_yy and A_xz were measured for the d-⁴He elastic scattering at 56 MeV. The measurement of A_xz was performed using a deuteron beam polarized in the horizontal plane. An optical-model analysis of the experimental data was carried out. The magnitude of the tensor analyzing powers could not be reproduced without the tensor potential. By including the T_R type tensor potential, the optical-model calculations give a reasonable reproduction of the experimental data at θ_c.m. < 120°. The obtained T_R tensor potential was much stronger than that predicted by the folding model. The strength of the real T_R potential was roughly in accordance with that obtained from the optical-model analysis of d-⁴He elastic scattering at 20.2 MeV.     

Yrast cascade in 60Ni

Yrast levels of ⁶⁰Ni were investigated via the study of in-beam γ-rays induced by 15–25 MeV α-partictes on ⁵⁸Ni, 26–48 MeV ¹²C ions on ⁵⁰Cr and 30–60 MeV ¹⁶O ions on ⁴⁶Ti. The compound nucleus formed by these target-projectile combinations is ⁶²Zn, and its decay by two-proton emission populates yrast levels of ⁶⁰Ni. The ordering and decay modes of the yrast levels were determined from the analyses of in-beam γ-ray angular distribution and γ-γ coincidence measurements. The new levels established are at 4.262, 5.345 and 6.807 MeV. These together with the known 2₁⁺ (1.332 MeV) and 4₁⁺(2.505 MeV) levels constitute the yrast cascade. The spin assignments based on the present study are 6, 7, 9 for the 4.262, 5.345 and 6.807 MeV levels, respectively. The excitation functions for the yrast γ-rays from the ⁵⁰Cr(¹²C, 2p)⁶⁰Ni reaction show peaks near 33 MeV incident energy.     

A study of the 90Zr(6Li, 6He)90Nb reaction at E6Li = 93 MeV

The energy spectra of ⁶He nuclei from the ⁹⁰Zr(⁶Li, ⁶He) reaction at E_{⁶Li = 93 MeV} have been measured over the angular range of 7 ° ? θ_lab ? 20 °. The theoretical DWBA analysis of these spectra and angular distributions was performed employing transition densities of bound and resonance states obtained on the basis of the theory of finite Fermi systems. It is shown that up to excitation energies of E_x ≈ 10 MeV in ⁹⁰Nb a direct charge-exchange mechanism dominates in this reaction, while at higher E_x the contribution made by multistep processes increases significantly. It is also shown that the quasi-elastic cross section is determined by a sum of partial contributions of spin-isospin-flip transitions with multipolarities L=0 through L=6.     

Isobaric spin mixing in the analog states of 90Zr

A 90° photoproton energy spectrum has been obtained from the reaction ⁹⁰Zr(γ, p)⁸⁹Y using an isotopically enriched target foil. Previously unreported proton groups are observed at E_p = 6.95, 9.55, 10.68 and 11.03 MeV. A total photoneutron cross section and a low-energy neutron energy spectrum are also presented, and isospin mixing is demonstrated by comparison with the photoproton data. The possibility of T_> strength in the region 23–24 MeV excitation is noted.     

Lifetimes and decays of energy levels in 60Ni

The Doppler shift attenuation technique was used to investigate the lifetimes of 33 states of ⁶⁰Ni up to 5.6 MeV of excitation; 18 were measured for the first time. Gamma rays from the ⁶⁰Ni(p,p′ψ) reaction were observed in coincidence with protons by two Ge(Li) detectors at 40° and 130° lab. We find a new doublet (3.381–3.393 MeV) and give several previously unknown ψ-ray branching ratios; the lifetimes allow one to attribute some spins or parities or to reject other assignments. In order to complement the existing information on ⁶⁰Ni, we have studied the proton configuration by the ⁵⁹Co(³He,dψ) reaction. The results are different from those expected from simple 1p-1h states of the proton core; many of the levels observed are multiplets decaying by cascades.     

A study of the γ-ray decays from single particle states in 91Zr and 93Mo

Lifetimes have been measured in ⁹¹Zr and ⁹³Mo by the Doppler shift attenuation method through the ⁹⁰Zr(¹³C, ¹²C)⁹¹Zr and the ⁹²Mo(¹³C, ¹²C)⁹³Mo reactions. Gamma rays were observed in coincidence with the back scattered particles and the reactions took place at sub-Coulomb energies. The lifetimes measured in ⁹¹Zr are τ(1205) = 250⁺⁹⁰_?70 fs, τ(1467) = 280⁺¹⁶⁰_?110 fs, τ(2042) < 30 fs, τ(2558) = 180⁺⁹⁰_?60 fs. The lifetimes measured in ⁹³Mo are τ(1361) = 170⁺⁸⁰_?40 fs, τ(1494) = 60 ± 40 fs, τ(1697) = 440⁺²³⁰_?130 fs, τ(2705)=160⁺⁸⁰_?60fs These results are compared with the expectations of the shell model and the $\text{3}\text{s}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{→ 2}\text{d}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}\text{E}\text{2}$ transition is shown to be very enhanced.     

The B(E2↑) and Rtr of 21+ states in90Zr and60Ni

The ground state transition probabilities for the 2₁⁺ states in⁹⁰Zr and⁶⁰Ni as determined by resonance fluorescence and reorientation effect methods are used as constraints to deduce transition densities from inelastic electron scattering data. The (e, e') cross sections for the ⁹⁰Zr, 2₁⁺ state at 2.186 MeV were measured at the Kelvin Laboratory, while for the 2₁⁺ state at 1.333 MeV in⁶⁰Ni, the existing (e, e') data of Yale and Sendai were used. The discrepancy between the model independent (e, e') result of Yale for⁹⁰Zr and the (γ, γ') measurement is explained. The importance of an accurate knowledge of the ground state charge distribution for analysis of (e, e') data is emphasized. For⁹⁰Zr, the B(E2↑) is 674 ± 60 e²· fm⁴ and ^R_tr is 5.74 ± 0.11 fm. For the 1.333 MeV state in⁶⁰Ni, these values are 918 ± 26 e²· fm⁴ and 5.33 ± 0.03 fm respectively.     

The elastic and inelastic scattering of 33 MeV polarized 3He from oxygen and iron isotopes

Angular distributions of differential cross sections and analysing powers have been measured for elastic and inelastic scattering of polarized 33 MeV ³He from ¹⁷O, ¹⁸O, ⁵⁴Fe and ⁵⁶Fe targets. The elastic data have been analysed to deduce the optical model parameters. The inelastic scattering together with the elastic scattering have been interpreted in terms of a macroscopic model within a coupled-channels framework. From this analysis the deformation parameters, β, were deduced.     

A study of the 58Ni(p, γ)59Cu reaction

Eleven resonances in the reaction ⁵⁸Ni(p, γ)⁵⁹Cu have been investigated in the proton energy region 0.9 ≦ E_p < 2.3 MeV. Gamma-ray angular distribution measurements on six resonances yield the following resonance spins $\text{(E}{}_{\mathrm{<mtext>p</mtext>}}\text{(}\text{keV}\text{); J): (1376;}\text{3}\text{2}\text{), (1424;}\text{3}\text{2}\text{), (1833;}\text{5}\text{2}\text{,}\text{9}\text{2}\text{), (1883;}\text{3}\text{2}\text{), (2238;}\text{7}\text{2}\text{), (2275;}\text{5}\text{2}\text{)}$. In addition spins of several low-lying levels were determined (or limited). They are $\text{E}{}_{\mathrm{<mtext>x</mtext>}}\text{(}\text{keV}\text{); J): (1398;}\text{7}\text{2}\text{), (1865;}\text{7}\text{2}\text{), (1987;}\text{5}\text{2}\text{), (2265;}\text{3}\text{2}\text{), (2318; (}\text{1}\text{2}\text{)), (2324;}\text{3}\text{2}\text{), (2663;}\text{5}\text{2}\text{,}\text{9}\text{2}\text{), (2707;}\text{5}\text{2}\text{), (2714;}\text{7}\text{2}\text{), (2927;}\text{5}\text{2}\text{), (3022;}\text{5}\text{2}\text{,}\text{7}\text{2}\text{), (3025; (}\text{3}\text{2}\text{)), (3114; (}\text{5}\text{2}\text{)), (3130; (}\text{3}\text{2}\text{)), (3434; (}\text{5}\text{2}\text{)), (3438; (}\text{1}\text{2}\text{)), (3615;}\text{3}\text{2}\text{), (3663;}\text{1}\text{2}\text{,}\text{3}\text{2}\text{),}\text{and}\text{(4181;}\text{5}\text{2}\text{,}\text{9}\text{2}\text{)}$. Previously unreported states have been observed at E_x = 2663, 2707, 3022, 3025, 3114, 3438, 3742 and 4181 keV. Branching ratios and multipole mixing ratios have been measured for the decay of several bound levels and these results are compared with recent theoretical calculations. Four of the resonance studied have been identified as isobaric analogues of low-lying ⁵⁹Ni levels. As well, the γ-decay of the (presumed) ⁵⁹Ni g.s analogue at 3905 keV has been observed. The log ?:t values for the β⁺ decay of ⁵⁹Cu to various ⁵⁹Ni states are calculated from measured γ-widths in analogue state decay and are compared to values measured in β⁺ decay.     

Low-lying levels of 92Nb from the 92Zr(3He,t) and 92Zr(3He,p2nγ) reactions

The structure of ⁹²Nb has been investigated using the 33.8 MeV ⁹²Zr(³He, t) and (³He, p2nγ) reactions. Several previously unobserved levels, including several belonging to the $\text{π(}\text{g}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}\text{)ν(}\text{g}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}\text{)}{}^{\mathrm{?1}}$ multiplet, are reported. The results are discussed in terms of the shell model.     

Large-angle elastic scattering of α-particles from 20Ne and 22Ne

Resonances observed in the 177° (lab) excitation function of α-particles scattered elastically from ²⁰Ne are investigated in terms of a single Regge pole. The position of the pole in the complex angular momentum plane is determined from angular distributions measured at incident α-particle energies of 25.8 and 27.0 MeV, at which energy values prominent maxima were observed in the excitation function and the pole contribution to these angular distributions is therefore expected to be a maximum. The complete trajectory of the pole over the energy region investigated (24.6 to 31.7 MeV) is obtained by means of extrapolation. The pole trajectory across the surface absorption region of the target nucleus clearly shows the reason for the occurrence of only three large resonances in this energy region, the remaining resonances being attenuated considerably. An angular distribution obtained for ²²Ne(α, α)²²Ne at an incident energy of 27.0 MeV also indicates the presence of the Regge pole found for ²⁰Ne at the same energy, even though its strength is severely reduced due to the isotopic dependence effect.     

Study of (d, α) reactions on 94Zr and 96Zr

The nuclear structure of ⁹²Y and ⁹⁴Y has been investigated by the (d, α) reaction on ⁹⁴Zr and ⁹⁶Zr with 11.5 MeV deuterons. Some new levels have been seen in ⁹²Y and ⁹⁴Y. The angular distributions for these levels have been measured. A zero-range DWBA analysis has been carried out for these distributions and spin-parity assignments have been made for the new levels.     

(p, γ) reaction studies on 60Ni

The γ-ray spectra from the ⁶⁰Ni(p, γ)⁶¹Cu reaction were measured for 27 isolated resonances. From these studies the J^π assignment of the compound states in ⁶¹Cu were made. Moreover, a value for the El photon strength function k(El) = 1.03 × 10^?9 MeV^?3 was obtained from seven l = 0 resonances to the 16 low-lying states. This value was then compared with the theoretical estimates of El strengths as predicted from the s.p. and giant dipole resonance models. The distribution of partial radiative widths about their mean value was determined from a Monte Carlo technique and was found to be consistent with the Porter-Thomas distribution when the Γ_{γ, ij} were divided by the E_γ⁵ energy dependence.Values for the coefficients of the correlation R between Γ_{λ, p} and Γ_{λ, γj} and T between Γ_{λ, yj} and $\text{Γ}{}_{\mathrm{\lambda ,\; \gamma ?}}$ where f ≠ j, were computed with the values R = 0.14 and T = 0.39, respectively. Also the correlation coefficients C(〈 Γ_{λ, yj}〉, I₃He, d, j) and $\text{C(〈Γ}{}_{\mathrm{\lambda ,\; y?}}\text{〉 I}{}_{\mathrm{<mtext>d,\; n</mtext><mtext>,\; ?</mtext>}}\text{)}$ yielded the values ρ = 0.87 and ρ = 0.80 respectively. All these correlations which are found to be statistically significant, imply that the (p, γ) reaction in ⁶⁰Ni is partly due to direct capture such as given by valence and doorway state contributions.