J.A. Kuehner

Studies of superdeformation in the gadolinium nuclei

Abstract We have used the 8π γ-ray spectrometer at the Chalk River TASCC facility to study superdeformed rotational bands in the chain of isotopes 145–149 Gd. The five bands already known have been extended to higher spin, while four new excited bands have been discovered. The use of very similar reactions, data-acquisition parameters and data-analysis techniques, combined with the enlarged set of data, has allowed us for the first time to approach the topic of superdeformation in the A = 150 mass region from a comprehensive point of view. Transition energies of neighbouring nuclei were compared to extract effective aligned spins of the added particle. Such a comparison requires knowledge of relative nuclear spins, which we have to assume. Nevertheless, we find that a very illustrative picture emerges making it possible to understand all nine bands in the Gd isotopes within a very simple scheme of orbital assignments.

A study of the reaction

Cross-section and vector analyzing-power angular distributions for the S30i(d→,α)28Al reaction at Ed = 18.0 MeV are used to obtain spectroscopic information. The angular distributions of strongly populated levels can be adequately described by DWBA calculations assuming deuteron-cluster pickup. The analyzing powers at forward angles allow distinction between J = l + 1 and J = l− 1 and provide unambiguous spin assignments for strongly fed levels. The spin of the 2581 keV level in 28Al is determined to be 5+. This assignment combined with information on the γ-decay and parity implies that the spins of the levels at 2275, 3475 and 4035 keV are 4+, 4− and (5, 3)−, respectively. The spins of the levels at 4517 and 4597 keV are each determined to be 3+.

Dynamic moment of inertia of the 192Hg superdeformed band at high rotational frequencies

Abstract The superdeformed band in 192Hg has been extended to higher transition energies from a new analysis of a large set of double and triple coincidence data. Contrary to the results of cranked shell model calculations including monopole pairing, the dynamic moment of inertia I (2) is found to continue to increase with rotational frequency.

The l-forbidden m1 decay of the 2522 keV level in 39K

Abstract The mean lifetime of the first excited 1 2 + level in 39 K has been measured to be τ = 93 ± 13 fs by high recoil velocity DSAM. The level was excited by bombarding a 4 He-implanted Ta target with a 100 MeV 39 K beam. The lifetime was determined by fitting the Doppler-broadened lineshape of the 2522 keV gamma-ray transition to the 3 2 + ground state. Together with the measured B (E2), the B (M 1; d 3 2 → S 1 2 ) for this l -forbidden M1 transition was determined to be 0.0100 ±0.0027 μ 2 N . A theoretical calculation, taking into account core polarization, delta excitation and mesonexchange current contributions, underestimates the B ( M )1) by more than a factor of six. The experiment also measured the lifetimes of the 3019 keV and 3883 keV levels to be 20 ±4 fs and 11 ± 6 fs, respectively.

Nuclear spectroscopy of the (fcase72)2, f72p32xand f72p12 multiplets from the 41Ca(d, p)42Ca reaction

Angular distributions of the cross section and the vector analyzing power have been measured for the 41Ca(d, p)42Ca reaction using 11 MeV deuterons. The vector analyzing power data have been used to determine the total angular momentum j of the captured neutron for 42 positive parity levels. Spectroscopic strengths were extracted separately for each of the allowed j-values which contributed to the cross section and identification of the major components of the f72, p32and p12 strength distributions have been obtained. An almost total absence of mixing of the p32and p12 strength was observed. Of 32 states populated by pure l = 1 transfer, only two consist of a mixture of p32and p12. The effective (f72)2, (f72p32) and (f72p12) two-particle matrix elements are compared with the modified Kuo-Brown matrix elements of McGrory. They agree to within a few hundred keV. The monopole energy centroid of the (f72p32) and (f72p32) multiplets are measured to be slightly repulsive, whereas Kuo-Brown predict a small attractive monopole contribution.

Proton orbit sizes in 208Pb

Abstract The sub-Coulomb (t,α) reaction has been employed in the determination of the rms radii of the 3s 1 2 , 2 d 3 2 , 1 h 11 2 , and 2 d 5 2 proton orbits in 208Pb. The experimental values are compared to the results of Hartree-Fock calculations.

The 1h92 proton orbit size in 209Bi

Abstract Angular distributions of α-particles from the reaction 209Bi(t, α)208Pb (ground state) have been measured at bombarding energies Et = 8.5 MeV and Et = 9.0 MeV. Zero-range (ZR) DWBA analyses of the data are used to determine the radial extent of the wave function of the lh 9 2 orbit in which the transferred proton is bound in 209Bi. The applicability of the sub-Coulomb ZR DWBA treatment is investigated by comparison of ZR and exact finite-range DWBA calculations. A value of the (t, α) normalization constant of (20.8 ± 3.1) × 104 MeV2 · fm3, based on forward dispersion relations, has been obtained from this comparison. The asymptotic amplitude of the wave function is measured directly and the rms radius is extracted via a Woods-Saxon model. A value of √〈r2〉 = 6.10−0.08+0.12 fm, corresponding to a point proton and to a local Woods-Saxon potential, is obtained. The rms radius and radial wave function of the 1 h 9 2 proton are compared with the results of electron scattering and muonic atom data on targets of 209Bi and 208Pb and with the results of Hartree-Fock calculations.

The effective T = 1 two-particle matrix elements in the fp shell

Abstract The 41 Ca( d , p) 42 Ca reaction has been used to locate the strength distributions for p 3 2 and p 1 2 transfer in 42 Ca. Effective ( f 7 2 ) 2 , f 7 2 p 3 2 and 7 2 1 2 two-body matrix elements are derived from the data and compared to theoretical predictions.

Spin-parity determinations to 40K levels via the 42Ca(d, α) reaction

Abstract The 42 Ca( d , α ) 40 K reaction has been studied at extreme forward angles ( θ α , = 4°). Tensor analyzing powers ( T 20 ) to the 40 K excited states were measured. Over 70 excited states of 40 K were populated, six of them not previously reported. T 20 data of sufficient precision to allow the determination of natural or unnatural parity were obtained for 37 levels. More tentative assignments were made for 14 other states. Seventeen new unambiguous J π assignments, four spin limits, and seven suggested spin and parity values were deduced. Notable results were an unambiguous J π = 0 − assignment to the 2.63 MeV level and 15 J π = 2 − assignments to states between 3.4 and 5.2 MeV excitation. The anti-analogue 0 + level at 1.64 MeV was not observed, in agreement with a recently noted selection rule.

Spin-parity assignments for 66Cu levels via the 68Zn(d, α)66Cu reaction

Abstract The 68 Zn( d , α) 66 Cu reaction populating low-lying states in 66 Cu has been studied at θ lab = 4° using deuteron beams in the energy range 9.0 to 10.5 MeV. Tensor analyzing powers were calculated and natural- or unnatural-parity assignments were made for thirteen states in 66 Cu. By combining these results with existing limits unambiguous J π assignments of 2 + , 2 + , 2 + and 1 + have been made for the levels at 186, 465, 822 and 1344 keV respectively. The previous tentative assignments to seven other levels have been confirmed while that for the 1247 keV level has been shown to be incorrect. The identification of the quartet of levels based on the π( P 3 2 )v( f 5 2 ) configuration has been confirmed.