P.O. Tjøm

Collective vibrational states in even Gd nuclei

Abstract The energy levels of the even nuclei of gadolinium have been investigated by inelastic scattering of 12 MeV deuterons. The deuteron spectra were recorded in a magnetic spectograph with an overall energy resolution of ≈ 8 keV. On the basis of semi-empirical rules governing the intensities and angular distributions of the inelastics groups, collective octuple and quadrupole pole vibrations were localized. As a rule, two or three octupole state wereidentified in each nucleus below an excitation energy of approximately 2.5 MeV. In the same region, the collective γ-vibrations and, in some cases, β-vibrations have been identified. Only few other groups were present.

Collective vibrational states in even erbium nuclei

Abstract The cross sections for inelastic scattering of 12 MeV deuterons from all the even Er isotopes have been measured at 90° and 125° by means of a magnetic spectrograph. The 2 +′ and 4 +′ states in the gamma vibrational bands were observed in all nuclei, but only in a few cases the K = 0 β-vibrations were observed. Several octupole vibrational states were identified in each nucleus below an excitation energy of approximately 2.3 MeV. The reduced transition probabilities B (E2) and B (E3) were determined from the observed inelastic cross sections.

Study of high angular momentum states in 155Gd and 157Gd by means of the (3He,α) reaction

Abstract Levels in 155 Gd and 157 Gd have been studied by means of the ( 3 He, α) reaction with 20.3 MeV 3 He particles. The l -values were determined by comparing the measured ( 3 He, α) cross sections with that obtained in previous (d, t) experiment to the same nuclei, and by the ratio of the ( 3 He, α) cross section measured at 60° and 90°. Only one strong 13 2 + state was observed in each nucleus. This is readily explained by the strong Coriolis coupling between the N = 6 Nilsson orbitals. The previously unknown 11 2 9 2 − [514] state is assigned in both nuclei.

Angular distributions for the 160Gd(d,t) 159Gd reaction

Abstract The angular distributions for triton groups from the 160 Gd(d,t) reaction have been measured at a deuteron energy of 12.1 meV. The Nilsson assignments which were known for a considerable number of levels in 159 Gd made it possible to intercompare the distributions for selected groups with l =0, 1, 2, 3, 4, 5 and 6. An optical-model triton potential was found which gave a good fit to the data at forward angles. Deviations at backward angles indicate that the cross sections depend on the total angular momentum j of the transferred neutron.

Shapes, electromagnetic properties and enhanced E1 strength in 169Lu

Abstract Rotational bands in 169 Lu previously observed via (p, 3n) and (α, 4n) reactions were extended by 8–14 units of angular momentum using the 154 Sm( 19 F, 4n) reaction and the Nordball detector array. By analysis of γγ coincidence relations and γ-ray angular correlations we have established the [541] 1 2 − , α = + 1 2 band to 57 2 h , the [514] 9 2 − bands to 47 2 > the [404] 7 2 + bands to 53 2 h and the [411] 1 2 [su+ , α = − 1 2 to 47 2 ( 55 2 ) h . The bands belonging to the [411] 1 2 + and [402] 5 2 + configurations with α = + 1 2 appear to be rather mixed in the low spin region. One of these bands is established to 45 2 ( 49 2 ) units of spin. The transitions interconnecting the signature partners, in the bands based on the [514] 9 2 − and [404] 7 2 + Nilsson orbitais, as well as in and between the strongly mixed [411] 1 2 + and [402] 5 2 + bands are compared to particle-rotor model calculations. By DSAM analysis, lifetimes and thereby transition quadrupole moments for the band built on the configuration h 9 2 [541] 1 2 − , α = + 1 2 could be extracted. The abnormal alignment pattern at the ν i 13 2 crossing for the h 9 2 [541] 1 2 − ban analysed in terms of a difference in both deformation and neutron pairing compared to the other less polarizing configurations. The influence of octupole modes on the strength of observed [411] 1 2 + ⇒[541] 1 2 − E 1 transitions as well as on observed spin-flip, [514] 9 2 − ⇒[404] 7 2 + , E1 transitions is investigated theoretically and compared to the experimental data.

Energy levels of 155Gd and 157Gd populated by the (d, d′) reaction

Abstract The inelastic scattering of deuterons from 155 Gd and 157 Gd has been studied. The data supplement the information previously obtained about the low-lying levels in these isotopes from (d, p) and (d, t) reactions. The (d, d) spectra were recorded at a deuteron energy of 12 MeV in a high-resolution magnetic spectrograph at 60°, 90° and 125°. The inelastic scattering cross sections are discussed in terms of collective vibrational excitations and the Coriolis coupling of single-particle states.

Angular distributions for the 156Gd(d, t)155Gd reaction

Abstract The angular distributions for triton groups from the 156 Gd(d, t) reaction have been measured at a deuteron energy of 12.1 MeV. The distributions were compared with similar distributions for the 160 Gd(d, t) reaction which had been measured earlier. On this basis, it was possible to establish or confirm the Nilsson assignments for a number of levels in the 155 Gd nucleus. Special attention was paid to the energy levels at 87 keV ( l = 2), 105 keV (doublet l = 2 and l = 4), 119 keV ( l = 5) and 214 keV ( l = 6) and their relations to the Nilsson model. It is discussed how the strong Coriolis coupling of even parity bands can account for the observed energy levels and neutron transfer cross sections.

Probing the limits of complete spectroscopy in 164Yb

Abstract High spin states of 164Yb have been populated using the 152Sm(16O,4n) reaction. Analysis has been made using γγ coincidences and, for the first time in a large detector array, angular correlations. The experimental level scheme has been extended to include a total of 15 decay cascades, for some of which the spins have been measured. Extensive cranked shell model calculations have been performed to map the quasiparticle rotational bands in a window, reaching up to 1 MeV above the yrast line, in the spin-energy plane. The experimental data are compared with the calculated bands, and most of the experimental bands are interpreted in terms of quasiparticle excitations. It is also found that the number of experimentally detected bands is in good agreement with the calculated number of bands in the observed spin-energy region.

Elastic deuteron scattering on the even Nd isotopes

Abstract Elastic scattering cross sections for 12 MeV deuterons on the even isotopes of Nd, 142 ≦ A ≦ 150, have been measured from 15° to 150°, using a solid state counter in connection with a magnetic spectrograph. The results have been analysed in terms of the optical model. The optical model parameters were extracted using an optical model automatic search code. A systematic behaviour of the optical model parameters, going from the spherical 142 Nd to the deformed 150 Nd, was found if search on four parameters, U , W , a and a ′, was done.

High spin structure in the odd-odd nucleus124Cs

High spin states in the odd- odd nucleus124Cs have been investigated within theNordball collaboration. In the yrast cascade which is determined as a πh11/2 ⊗ νh11/2 configuration, a rather large signature splitting in the ratios, B(M1)/B(E2), has been observed. Furthermore, signature inversion is suggested in the lower spin part of the yrast band.