High-spin states in 59Ni

High-spin states in ⁵⁹Ni have been investigated via the study of in-beam γ-rays following the reactions ⁵⁰Cr(¹²C, 2pn)⁵⁹Ni (26–58 MeV) and ⁵⁶Fe(α, n)⁵⁹Ni (10, 15, 22.5 MeV). The spins of previously known levels have been confirmed or determined for the first time, in particular for those at $\text{3376.8}\text{keV}\text{(J =}\text{11}\text{2}\text{)}\text{and}\text{4141.3}\text{keV}\text{(J =}\text{13}\text{2}\text{or}\text{15}\text{2}\text{)}$. New states have been established and their spin determined, at $\text{1739.2}\text{keV}\text{(J =}\text{9}\text{2}\text{), 2349.2}\text{keV}\text{(J =}\text{11}\text{2}\text{), 2535.5}\text{keV}\text{(J =}\text{13}\text{2}\text{), 4455.4}\text{keV}\text{(J =}\text{13}\text{2}\text{), 4947.5}\text{keV}\text{(J =}\text{15}\text{2}\text{)}\text{and}\text{5251.7}\text{keV}\text{(J =}\text{13}\text{2}\text{or}\text{15}\text{2}\text{)}$. The resulting ⁵⁹Ni decay scheme is discussed in the framework of nuclear models.     

54Cr, 54, 58Fe, 58Ni(d,p)55Cr, 55, 59Fe, 59Ni Vector analyzing power measurements

(d, p) cross sections and vector analyzing powers have been measured at 10 MeV bombarding energy for targets ⁵⁴Cr, ⁵⁴Fe, ⁵⁸Fe and ⁵⁸Ni. The systematic behaviour of the analyzing powers with Q for states of a given J^π has been observed. Spins of a number of states in ⁵⁵Cr and ⁵⁹Fe have been deduced.     

Lifetime measurements in 56Co

Lifetimes of six excited states in ⁵⁶Co below 1.75 MeV have been measured by the Doppler-shift attenuation method. The levels were excited via the ⁵⁴Fe(³He, pγ) reaction with 10.4 MeV ³He particles. Gamma rays were measured in a 45 cm³ Ge(Li) detector in coincidence with protons backscattered near 180°. Reduced transition probabilities extracted from measured lifetimes compare favourably with shell model predictions of McGrory.     

Lifetime measurements in 29 Al

The lifetimes of the first six excited states of ²⁹Al have been measured by the DSA method with two different reactions,²⁶Mg(α, p)²⁹Al and²⁷Al(t, p)²⁹Al. The recoil distance method was also used to remeasure the mean lifetime of the first excited state, leading to a value τ_m = 6.5 ± 0.5 ps. Experimental results are compared with shell model calculations.     

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.     

Study of 59Cu by means of 58Ni(d,n)

The reaction ⁵⁸Ni(d, n)⁵⁹Cu has been studied at 7.0 MeV bombarding energy. Angular distributions of transitions to 16 states in ⁵⁹Cu have been extracted and analysed with DWBA to yield absolute spectroscopic strengths. The results are compared to those of other measurements.     

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.     

High-spin states in 58Ni

High-spin states of ⁵⁸Ni were investigated via the study of in-beam γ-ray induced by the compound reaction ⁴⁸Ti(¹²C, 2n)⁵⁸Ni between 26 and 48 MeV. The energies and decay modes of these levels were determined from the analysis of γ-γ coincidence measurements at 35 MeV. The most intense lines in the ⁵⁸Ni γ-ray spectrum correspond to a cascade to the ground state, through levels at 1.454, 2.459, 3.619 and 4.381 MeV, also fed in other reactions, and by two previously unknown levels at 5.125 and 5.662 MeV; the spin assignments based on the present study are (apart from the ground state) 2, 4, 4, 5, 6 and 7 respectively for these levels. The first three were already known and the last three are new. The mixing ratios for the transitions between these levels are also determined. We observe also the same cascade in the reaction ⁵⁶Fe(α, 2n)⁵⁸Ni at an incident energy 18–24 MeV. Comparisons with other reactions, previous studies and recent shell-model calculations are presented.     

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.     

Lifetimes of some excited states in 64Ni, 66Zn and 68Zn

Mean lives and excitation energies of the lowest levels in⁶⁴Ni,⁶⁶Zn and⁶⁸Zn were measured with the aid of the (α, α′γ) and (α, pγ) reactions. The γ-rays were detected in coincidence with the outgoing particles. The following mean lives were determined from DSA measurements: 400 ± 150 fs for the level at E_x = 1.35 MeV in ⁶⁴Ni; 270 ± 100, 210 ± 110, 330 ± 200, 80 ± 70 fs for the levels at E_x = 1.87, 2.45, 2.83, 2.94 MeV in ⁶⁶Zn, and 1300 ± 300, > 160, 600 ± 200 fs for the levels at E_x = 1.08, 1.89 and 2.76 MeV in ⁶⁸Zn, respectively.     

The 64Ni(6Li,d)68Zn reaction

The ⁶⁴Ni(⁶Li, d)⁶⁸Zn reaction has been studied at 28 MeV bombarding energy. For several low-lying states in ⁶⁸Zn, S-values extracted via DWBA analysis are compared with shell model and collective model (IBA) predictions.     

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.     

Spectroscopy of 62Ni with the 61Ni(d, p) reaction

Differential cross sections, vector and tensor analysing powers have been measured for the ⁶¹Ni(d, p) reaction at a deuteron energy of 12.3 MeV. Most of the 30 transitions observed below 8.5 MeV excitation are dominated by a single j-value, which was determined from behaviour of the analysing power data. For a number of transitions it was possible to make unambiguous j-assignment relying on the established j-dependence of the T₂₂ tensor analysing power. The deduced spectroscopic factors indicate that the full strength of neutron transfer to the ($\text{2p, 1f}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}$) and $\text{1}\text{g}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}$ orbits was found and seven $\text{5}\text{2}{}^{\mathrm{+}}$ transitions were located above 5.3 MeV. The separated strengths of the $\text{3}\text{2}{}^{\mathrm{?}}\text{,}\text{1}\text{2}{}^{\mathrm{?}}\text{and}\text{5}\text{2}{}^{\mathrm{?}}$ transitions are compared with shell-model calculations for the low-lying states of ⁶²Ni.     

Energy dependence of the optical model parameters for 3He ions scattered from 40Ca and 58Ni

The differential cross sections for the elastic scattering of ³He ions on targets of ⁴⁰Ca and ⁵⁸Ni have been measured at incident energies of 27.7, 51.4, 73.2 and 83.5 MeV. The results of optical model analyses showed that only one unique potential (J_R ≈ 330 MeV · fm³) with a surface absorptive term can provide acceptable fits to the large angle elastic scattering cross sections at 83.5 MeV. The particular geometrical set found at 83.5 MeV could not, however, give an adequate fit to the data with energy less than 40 MeV. Subsequent analyses indicated that a break in the energy dependence of the real potential is observed for the low energy data. Explicit energy dependent terms were obtained by fitting all the data simultaneously. These phenomenological potentials were also compared with the folded nucleon-nucleus potential. The influence of the α-particle channels on the elastic scattering of ³He ions at 83.5 MeV was also examined.     

Deep inelastic collisions in the interaction of 280 MeV 40Ar with 58Ni

Masses and charges of all the nuclei with 5 ≦ Z ≦ 20 produced in the reaction ⁴⁰Ar + ⁵⁸Ni have been identified using combined ΔE · E and time-of-flight techniques. Energy spectra, angular distributions and cross sections have been measured. The formation of an intermediate composite system, in which charge equilibrium is achieved, is discussed. Also, the transition between the quasi-elastic and the deep inelastic process is studied. The angular distribution behaviour is shown to be related to the interaction time. The total cross section of the deep inelastic process has been found to be 700 mb and is compared to the evaporation residue cross section.     

Lifetime measurements in 22Ne, 28Si and 31P relevant to the interpretation of the Z2 variation in low velocity DSAM results

Accurate lifetimes have been measured for low-lying levels in ²²Ne, ²⁸Si and ³¹P by bombarding ⁴He implanted targets with beams of ¹⁹F and ²⁸Si ions. Mean lifetimes determined by fitting Doppler-broadened γ-ray lineshapes were $\text{(E}{}_{\mathrm{<mtext>x</mtext>}}\text{in MeV}\text{, τ}\text{in ps}\text{):}{}^{22}\text{Ne}\text{(1.275, 5.15 ± 0.31; 3.357, 0.324 ± 0.009),}{}^{28}\text{Si}\text{(1.779, 0.667 ± 0.035),}{}^{31}\text{P}\text{(1.266, 0.70 ± 0.07; 2.234, 0.363 ± 0.024}$). The lifetime values for the 3.357 MeV level in ²²Ne and the 2.234 MeV level in ³¹P are used to calibrate low velocity DSAM lifetime data for these two levels and to obtain scaling factors to theoretical electronic stopping powers for Ne and P ions.     

Reorientation effect measurements in 124Te, 126Te and 128Te

Coulomb excitation probabilities of the first 2⁺ states of ¹²⁴Te, ¹²⁶Te and ¹²⁸Te have been determined. The measurement was performed by resolving the inelastically and elastically backward scattered ⁴He and ¹⁶O projectiles using an annular surface barrier detector. Quadrupole moments (Q₂₊) as well as the B(E2, 0⁺ → 2⁺) values were extracted by analyzing the excitation probabilities with the Winther-de Boer multiple Coulomb excitation program. The Q₂ deduced for the positive sign of the 2⁺ interference term are ?0.41 ± 0.08 e · b, ?0.144 ± 0.11 e · b and ?0.12 ± 0.09 e · b for ¹²⁴Te, ¹²⁶Te and ¹²⁸Te, respectively.     

A study of the elastic scattering of polarized deuterons from 60Ni and 90Zr nuclei

Five quantities, σ₀, iT₁₁, T₂₀, T₂₁ and T₂₂, have been measured for the elastic ($\text{d}$, d) scattering from ⁶⁰Ni at 9 and 12 MeV and from ⁹⁰Zr at 10, 11 and 12 MeV over a wide angular range. Excitation functions for σ₀ and T₂₀ have been also measured at an angle of 175°(lab) in the approximate energy range of 6–13 MeV for both target isotopes. The experimental results, together with similar data published earlier for 15 MeV have now been analysed using the optical model with the complex central, spin-orbit and tensor T_R potentials. Excellent fits are obtained for the angular distributions for all five measured quantities. The main features of the excitation functions are also well reproduced. Five of the optical-model parameters can be fixed. Three other parameters can be constrained by simple mass dependence functions. Further evidence for the presence of an imaginary component of the spin-orbit potential is supplied by the analysis of the present data.