Search

The $\stackrel{P\vec}{p}p\ensuremath{\rightarrow}p{K}^{+}\mathrm{\ensuremath{\Lambda}}$ reaction has been measured with the COSY-TOF detector at a beam momentum of $2.7\phantom{\rule{0.16em}{0ex}}\mathrm{GeV}/c$. The polarized proton beam enables the measurement of the beam analyzing power by the asymmetry of the produced kaon $({A}_{N}^{K})$. This observable allows the $p\mathrm{\ensuremath{\Lambda}}$ spin triplet scattering length to be extracted for the first time model independently from the final state interaction in the reaction. The obtained value is ${a}_{t}=(\ensuremath{-}2.{55}_{\ensuremath{-}1.39}^{+0.72}{}_{\mathrm{stat}.}\ifmmode\pm\else\textpm\fi{}0.{6}_{\mathrm{syst}.}\ifmmode\pm\else\textpm\fi{}0.{3}_{\mathrm{theo}.})\mathrm{fm}$. This value is compatible with theoretical predictions and results from model-dependent analyses.

High-spin states in the neutron-rich nuclei 172,173Yb have been populated in a 170Er(7Li,(p,d,t)xn) incomplete-fusion reaction and the emitted γ-radiation was detected with the GASP array. The signature partners of the 7/2+[633] rotational band of the odd-N 173Yb isotope have been newly established and were observed up to spin values of (45/2+) and (43/2+), respectively. The ground-state band of the even-even nucleus 172Yb has been observed up to a spin value of (22+). No band crossings were found in these bands. To explain this observation, it is proposed that the static pair field is absent, considering that the neutron odd-even mass differences reach for these nuclei very small values and that the band crossing is absent in cranked shell modell calculations without pairing. The results indicate, however, that strong dynamic correlations are still present.

Matière Nucléaire; International audience; The gamma decay of the nuclei 124,125Ba has been investigated with the EUROBALL array, using the reaction 64Ni+64 Ni at E_{beam} = 255 and 261 MeV. Six new E1 transitions have been found in the nucleus 125Ba, suggesting a significant role of octupole correlations in the origin of its parity doublets. The pi = 3-level of the nucleus 124Ba has been identified for the first time. Its excitation energy is in very good agreement with a prediction based on a microscopic model including octupole interactions.

Excited states in 110Sn and 111Sn nuclei have been investigated using in-beam γ-ray spectroscopic methods. An 16O beam with an energy of 60-80MeV was used to bombard a 98Mo target. On the basis of the relative excitation functions, γ-ray angular distributions, γ-γ and γ-time distributions, γ-ray multiplicity and total energy data, the level schemes of 110Sn and 111Sn have been studied and extended up to Eexc ∼ 11.5MeV, I = 24ℏ, and Eexc ∼ 11.1MeV and I = (51/2)ℏ, respectively. An extension of the intruder, g.s. and negative-parity bands, as well as 5 new band-like structures are proposed in 110Sn. The nature of newly introduced collective band 8 as well as 10+ states fed in the decay of the collective band is discussed. In the 111Sn nucleus an intruder band based on the 23/2- state has been reinvestigated and the extension of the g.s. band and second negative-parity band is given. Evidence for neutron-core coupling in 111Sn is found. The structure and systematics of excited states in light Sn isotopes is discussed.

For a level scheme investigation of 144Gd an experiment with the \(\gamma\)-spectrometer EUROBALL III has been carried out and lifetimes have been measured with the \(\gamma\)-spectrometer GASP using the Doppler-shift attenuation method. The high-spin states have been populated in these experiments by means of the 100Mo(48Ti,4n) reaction at 215 MeV and the 114Cd(36S,6n) reaction at E = 182 MeV, respectively. The known quadrupole band has been modified and a new one has been established. Reduced E2 transition probabilities B(E2) were determined for seven members of these quadrupole bands. They show values between \(\approx 60\) and 130 W.u. and this considerable enhancement gives evidence for a significant nuclear deformation. A \((\pi h_{11/2})^2 \otimes (\nu h_{11/2})^{-2}\) configuration may be assigned to one of the quadrupole bands according to total Routhian surface calculations. The spin dependence of the B(E2) values has been explained by IBM calculations involving high-spin quasiparticle excitations.

High-spin states in the odd-odd nucleus 172Lu have been populated in a 170Er(7Li, 5n) reaction and the emitted \(\gamma\)-radiation was detected with the GASP array. Two sequences of a new identical band have been observed with the transition energies in the favoured and unfavoured sequences being identical within \(\approx 3\) keV at low spins and \(\approx 1\) keV at high spins over the whole observed spin range. Aninterpretation as a pseudo-spin singlet band of \(\pi 1/2^- [541] \otimes \nu 1/2^- [\widetilde{420}]\) configuration is proposed. It represents the best example of a pseudo-spin singlet band in normal deformed nuclei known until now.

High-spin states in 142Gd have been populated by means of the 99Ru(48Ti, 2p3n) reaction at 240 MeV and investigated with the γ-spectrometer EUROBALL III and the charged-particle detector array ISIS. The features of four dipole bands have been determined and compared with tilted-axis cranking model calculations indicating that they are magnetic rotational bands. A transition from regular to irregular bands has been found approaching N = 82 demonstrating that this is a general phenomenon in nuclei near a double-shell closure.

The level scheme of 143Gd has been extended to E = 8.7MeV (I = 53/2+) in an experiment with the GASP γ-ray spectrometer and the 100Mo(48Ti,5n) fusion reaction. Most of the level scheme shows single particle character. A strongly populated cascade consisting of ten stretched E2 transitions and another structure with weak M1 and strong E2 shows an indication of a collective character.

A superdeformed band has been discovered in 143Gd consisting of 15 transitions. It does not show the band crossing observed in the neighbouring heavier Gd isotopes and it is degenerate with the superdeformed band in 143Eu. In contrast to other degenerate bands at superdeformed shape, the configurations of the bands are quite different here. They result from the exchange of a ν64 with a π[404]9/2 configuration. In addition, a collective band has been observed which adopts a well-deformed triaxial shape at high spins according to calculations. The transition from highly to superdeformed shapes proceeds via triaxial shapes.

High-spin states in 180Os have been populated by means of the 150Nd(36S,6n) reaction at 177 MeV and studied with the γ-spectrometers OSIRIS and GASP. Eight known bands have been extended to higher spins and a new strongly coupled band has been discovered. Configuration assignments of the bands have been carried out in the framework of the tilted-axis cranking model utilizing experimental ratios of reduced transition probabilities B( M1 ) B( E2 ) . The investigation of the alignment behaviour of the bands revealed that besides the well-known first band crossing caused by the alignment of an i 13 2 quasineutron pair, a second band crossing occurs in four of the bands. The crossing frequency is ⩾ 0.38 MeV and the alignment gain is fairly small, ranging between 2 and ⩾4 ℏ;. The crossing can consistently be explained as a two-quasineutron (ν 7 2 − [514]) 2 alignment. This crossing has been observed for the first time.

Five superdeformed (SD) bands have been identified in 144Gd with the GASP array using the reaction 100 Mo + 48 Ti . The J(2) moments of inertia of the four excited SD bands are flat as a function of rotational frequency, indicating the blocking of the N = 6 proton crossing observed in the yrast SD band. According to cranked shell model calculations, the excited bands have two-quasiproton configurations with one proton in the N = 6 orbital and the other in each signature partner of the [404]9 2 + or [411]3 2 + orbitals, lying above the Z = 64 gap. The interpretation of the excited SD bands in terms of proton excitations points to the high stability of the N = 80 shell closure at SD shapes. The population of the yrast SD band as a function of the beam energy has been also investigated. Our data shows that the intensity of the yrast SD band is not configuration dependent, being comparable to that of yrast SD bands in the neighboring nuclei. By comparing experimental and theoretical alignments, spins and configurations are assigned to all observed SD bands in the A = 140–150 region.

The study of superdeformation in nuclei around the nucleus 144Gd, which can be considered as doubly-closed at superdeformed shape, provided detailed knowledge about the structure of superdeformed bands in this region. The chain of Gd isotopes showing superdeformation could be extended to 143Gd. Since highly-deformed bands are known in 139,141Gd, it appears that the transition between the regions of superdeformed nuclei with A ≈ 150 and of highly-deformed nuclei with A ≈ 130 is rather sharp and takes place around N = 78 as theoretically predicted. In 144Gd four excited superdeformed bands have been found in addition to the yrast superdeformed band. They form two pairs of signature partner bands of π6 1 π[404]9 2ν7 0 and π6 1 π[411]3 2ν7 0 configurations. In 145Gd for the first time two crossings have been observed in a superdeformed band, which are assigned to the alignment of an i 13 2 proton pair and a subsequent crossing of the i 13 2 [642]5 2 and i 11 2 [651]1 2 neutron orbitals, respectively.

Measurements of the pp → pK + Λ reaction at T p = 2.28 GeV have been carried out at COSY-TOF. In addition to the Λp FSI and N * resonance excitation effects a pronounced narrow structure is observed in the Dalitz plot and in its projection on the pΛ invariant mass. The strongly asymmetric structure appears at the pp → NK + Σ threshold and is interpreted as the ΣN cusp effect. The observed width of about 20 MeV/c 2 is substantially broader than anticipated from previous measurements as well as theoretical predictions. Angular distributions of this cusp structure are shown to be dissimilar to those in the residual pK + Λ channel, but similar to those observed in the pK + Σ 0 channel.

The possibility to determine the pLambda scattering length from the final-state interaction in the reaction pp->pKLambda is investigated experimentally. From a transversely polarized measurement, the K analyzing power (A_N) which, in principle, allows one to extract the spin triplet scattering length is studied. An unexpected energy dependence of the forward/backward symmetric part of A_N is found. The influence of N*-resonances on the pLambda invariant mass spectrum is investigated by exploiting the large acceptance for the process pp->pKLambda->pKppi and is found to be the main source of uncertainty for determining the pLambda scattering length.

High-spin states in186Os have been populated by the186W(4He,4n)-reaction at 55MeV. The emittedγ-radiation was detected with the OSIRIS spectrometer. The yrast band, for which the nucleus has a prolate shape, was found to terminate atIπ=18+. Theγ-ray intensity is then distributed between several irregular sequences. Different to other cases of band termination, the minimum in the total routhian surface corresponding to a collective shape is calculated to disappear in this spin region, although the available spin of the valence nucleons is far from being exhausted. A different structure, which is dominated by non-collective states becomes yrast.

High-spin states in the nuclei 181, 182Os have been populated in the 150 Nd( 36 S ,x n ) reactions and studied with the ESSA30 array. The nucleus 181Os has also been studied at the NBI tandem accelerator using the 167Er(18O,4n) reaction. The previously known bands in both nuclei have been extended to higher spins and two new side bands have been found in 181Os. In the latter nucleus the ground state has been established to have I π = 1 2 − . The extraction of the ratios of reduced transition probabilities B(M1) B(E2) from branching and E2 M1 mixing ratios permitted configuration assignments for most of the bands in both nuclei. The analysis has been carried out within the semiclassical vector model for M1 radiation. The positive-parity yrare sequences in 182Os and the band based on the I π = K π = 23 2 − state in 181Os have been interpreted as t-bands arising from a rotation about a tilted axis. The alignment behaviour and the crossing frequencies are for most of the bands consistent with predictions of the cranked shell model.

High-spin states in 144 Gd have been investigated through the 108 Pd( 40 Ar, 4n) reaction. An extended level scheme is proposed. A ridge structure has been observed in a γγ coincidence matrix, consistent with energy spacings in the superdeformed bands of neighbouring nuclei. Several discrete high-spin sequences have been observed. They are interpreted in the context of cranked-Strutinsky-type calculations in terms of different coexisting shapes.

Charged-particle-γ-ray coincidences were utilized to study4He-induced break-up fusion reactions on159Tb at 25.5 MeV/A beam energy. In coincident γ-ray spectra the electric giant dipole resonance (GDR) built on highly excited states in Dy isotopes was observed. A pronounced splitting of the GDR was evident at a nuclear temperature ofT≈2 MeV which can correspond to different nuclear shapes. Consistent with available systematics a prolate deformation could be suggested in agreement with results obtained at lowerT; however, the onset of a phase transition to an oblate shape cannot be excluded. The widths of GDR components, similar to the results obtained recently from incomplete-fusion reactions with heavy ions, are as small as those of the GDR built on the ground state.

Cross-sections and γ-ray fold distributions have been measured for the 97Mo+51V, 100Mo+48Ti and 114Cd+36S reactions at energies of 238, 215 and 182 MeV of the 51V, 48Ti and 36S projectiles, respectively. For the 97Mo(51V, α2n 142Eu reaction channel a double-humped fold distribution has been observed. This fold distribution can only be understand if an incomplete-fusion reaction mechanism associated with the α-particle emission is assumed. The 97Mo(51V, α n 143Eu reaction channel represents an incomplete-fusion reaction channel as well and its single-humped fold distribution can be described on the same footing as that of the α2n channel. The fold distributions associated with xn and pxn channels can be explained assuming complete-fusion reactions. For the calculations in terms of an incomplete-fusion reaction mechanism a narrow angular momentum window, ranging from ≈ 68 to 82ℏ has been assumed for the 97Mo(51V, αn and α2n reaction channels. The complete-fusion reaction mechanism is considered to be negligible in this angular-momentum range.

Two new isomers have been observed in180Os. A high-K isomer withI, K ≧20 and a half-life ofT1/2=12+4 ns have been established. It deexcites via two transitions into the 18+ level of the yrare band indicating an unusually smallK-hindrance factor. Evidence for an isomer withI, K>16 and a half-life ofT1/2=41±10 ns was found. A half-life of 17±3 ns was measured for the previously known 7− state at 1862 keV. The decay scheme of the previously known 7− isomer at 1928 keV has been extended and a revised version is presented.

Two discrete superdeformed bands have been found in 146Gd. The superdeformed yrast band has an average quadrupole moment of 12±2 eb and shows a band crossing with an alignment of ≈ at a rotational frequency of 0.65 MeV. No crossing has been observed for the excited superdeformed band. Configuration assignments are discussed for 146–148Gd considering (i) the crossing behaviour of the superdeformed bands and (ii) the existence of degenerate and average superdeformed bands. Arguments are given that the [651 1 2 ] and [642 5 2 ] single-particle states are involved in the band crossing.

High-spin states in the oblate-deformed nuclei195Hg and196Hg were populated in the198Pt(α, xn) reaction and investigated by in-beamγ-ray spectroscopy using six Compton-suppressed Ge detectors. The level schemes of both nuclei are extended considerably. The level structure is interpreted within the framework of the cranked shell model. Good agreement is obtained between model predictions and experimental results.

High-spin states in 146 Nd and 148 Sm have been populated using the 3 C+ 136 Xe and 22 Ne+ 130 Te compund nucleus reactions. Alternating parity bands built on the ground state are observed to spin I = (19) and I = (27) in 146 Nd and 148 Sm respectively. Analysis of the data done in terms of the reflection-asymmetric mean-field approach suggests that both nuclei become octupole-unstable at medium spins. The observed enhancement of E1 rates supports this prediction. In 148 Sm also a structure with simplex quantum number s = −1 is observed. At medium spins the reflection-asymmetric structures coexist with reflection-symmetric configurations. The decrease of the electric dipole moment observed for the N = 86 isotones between Z = 62 and Z = 64 is explained by the transition from static to dynamical octupole correlations.

For a level scheme investigation of ^{142}Gd an experiment with the $\gamma$-spectrometer EUROBALLIII has been carried out and lifetimes have been measured with EUROBALL IV using the Doppler-shift attenuation method. The high-spin states have been populated in these experiments by means of the ^{99}Ru(^{48}Ti, 2p3n) reaction at a beam energy of 240MeV and the ^{114}Sn(^{32}S, 2p2n) reaction at 160MeV, respectively. Reduced E2 transition probabilities B(E2) were determined for 15 members of four quadrupole bands. For the interpretation of the positive-parity even-spin quadrupole bands, calculations in the cranked Nilsson-Strutinsky as well as interacting boson models have been performed. From the former calculations it was concluded that the high-spin states of the (+ , 0)_{1} band in ^{142}Gd represent a triaxial nucleus rotating around the longest principal axis.

Lifetimes have been measured for a dipole band in 139Sm using DSAM. The deduced B(M1) and B(E2) values as well as B(M1)/B(E2) ratios are compared with calculations in the framework of the TAC (Tilted Axis Cranking) and SPAC (Shears mechanism with Principal Axis Cranking) models. The dipole band in 139Sm can be considered as a magnetic rotational band with a prolate or triaxial nuclear deformation.

An investigation of γ‐ray fold distributions has been carried out for the 97Mo(51V,zα yp xn) reaction. For the α2n channel leading to 142Eu a double‐humped fold distribution was found. An explanation in terms of an incomplete‐fusion reaction mechanism is proposed.

High-spin states in 180 Re have been populated by the (α, 5n) and ( 14 N, 4n) reactions and studied using the γ spectrometer OSIRIS. Seven bands have been identified to high spins and four isomers have been observed. Configuration assignments are based on g K factors, extracted from branching and mixing ratios, alignments and rotational spacings. Two bands seem to be built on singlet and triplet states of the same configuration. Their energetical order in the level scheme is inverted with respect to the predictions of the Gallagher-Moszkowski coupling rules. The band crossing features of the bands can be explained taking into account blocking of i 13 2 orbitals and shape changes. The present results confirm that the crossings known in the 1 2 − [541] bands in 179,181 Re result from the rotation alignment of an i 13 2 quasineutron pair.

High-spin states in Ba-124 were investigated in two experiments using the Ni-64(Ni-64, 4n)Ba-124 reaction at three different beam energies. In-beam gamma-ray coincidences were measured with the Eur ...

The gamma decay of the nuclei Ba-124,Ba-125 has been investigated by means of the EUROBALL spectrometer, coupled to the DIAMANT array of charged-particle detectors, using the reaction Ni-64 + Ni-64 ...

International audience; A breakthrough was recently obtained in the analysis of the so-called Hyper-Long-HyperDeformed (HLHD) experiment made at the EUROBALL-IV γ-detector array (EB). The 64Ni + 64Ni ⇒ 128Ba* fusion reaction was studied at Ebeam = 255 and 261 MeV, reaching the highest angular momentum that the compound nuclei can accommodate. To date no discrete HD rotational bands have been identified. However, rotational patterns in the form of ridge-structures in three-dimensional (3D) rotational mapped spectra are identified with dynamic moments of inertia J(2) ranging from 71 to 1112 MeV-1 in 12 different nuclei selected by charged particle- and/or γ-gating. The four nuclei, 118Te, 124Cs, 125Cs and 124Xe found with moment of inertia J(2)≥100 2 MeV-1, are most likely hyperdeformed, the remaining nuclei with smaller values of J(2), are considered to be superdeformed, in qualitative agreement with recent theoretical calculations.

For a level scheme investigation of 142Gd an experiment with the γ -spectrometer EUROBALLIII has been carried out and lifetimes have been measured with EUROBALL IV using the Doppler-shift attenuation method. The high-spin states have been populated in these experiments by means of the 99Ru(48Ti, 2p3n) reaction at a beam energy of 240MeV and the 114Sn(32S, 2p2n) reaction at 160MeV, respectively. Reduced E2 transition probabilities B(E2) were determined for 15 members of four quadrupole bands. For the interpretation of the positive-parity even-spin quadrupole bands, calculations in the cranked Nilsson-Strutinsky as well as interacting boson models have been performed. From the former calculations it was concluded that the high-spin states of the (+ , 0)1 band in 142Gd represent a triaxial nucleus rotating around the longest principal axis.

High-spin states in the odd-odd nucleus 172Lu have been populated in a 170Er(7Li,5n) reaction at 51 MeV and the emitted $\gamma$ -radiation was detected with the GASP array. A new semidecoupled band with the proposed $\pi 1/2^-[541] \otimes \nu 7/2^ + [633]$ configuration has been established exhibiting a signature inversion. A systematic study of the signature inversion in odd-odd nuclei of the rare-earth region is presented. The variation of the inversion spin remains nearly constant for nuclei with the same N-Z, increases with N for an isotopic chain and decreases with Z for an isotonic chain. On the basis of the systematics a change of the spins by $1\hbar$ is proposed for the semidecoupled bands in 180Re, 182,184Ir and 184,186Au.

High-spin states in the odd-proton nucleus 173Lu have been populated in a 170Er(7Li,4n) reaction and the emitted \(\gamma\)-radiation was detected with the GASP array. The favoured and unfavoured sequences of the \(\pi 1/2^- [541]\) band have been considerably extended. The favoured sequence does not show any indication of a band crossing up to a rotational frequency of \(\approx\) 0.45 MeV. This is the largest crossing frequency ever observed for 1/2- [541] bands of odd-proton nuclei with \(67 \leq Z \leq 77\) and \(90 \leq N \leq 106\). Previous Cranked Shell Model (CSM) calculations underestimate the crossing frequency by 100 keV.

The decay of the ${K}^{\ensuremath{\pi}}{=8}^{\ensuremath{-}}$ isomer in ${}^{132}\mathrm{Ce}$ with an excitation energy of 2340.2 keV has been investigated using the ${}^{120}\mathrm{Sn}{(}^{16}\mathrm{O}{,4n)}^{132}\mathrm{Ce}$ reaction. A half-life of 9.4\ifmmode\pm\else\textpm\fi{}0.3 ms was determined. Two new decay paths have been found in the deexcitation of this isomer. The hindrance factors for the $E1,$ $M2,$ and $E3$ transitions deexciting the isomer have been determined. The decay properties of the ${8}^{\ensuremath{-}}$ isomers in the $N=74$ isotones are discussed. A band mixing mechanism involving the ground state and $s$ band seems to be responsible for the behavior of the reduced hindrance factors of the $E1$ transitions deexciting the ${K}^{\ensuremath{\pi}}{=8}^{\ensuremath{-}}$ isomers in these isotones. A $K$ mixing, characteristic of the axially asymmetric nuclei, may account for the reduced hindrance factors of the $E3$ transitions to the ${5}_{\ensuremath{\gamma}}^{+}$ states in ${}^{130}\mathrm{Ba}$ and ${}^{132}\mathrm{Ce}.$

Mean lifetimes have been measured for superdeformed bands of 145Gd with the Doppler-shift attenuation method. The extracted quadrupole moments of the yrast and first excited superdeformed bands are Q 0 =11.8±0.8 e b and Q 0 =13.2±1.0 e b, respectively. The configuration assignments based on the quadrupole moments are π61π[404]9/2ν[514]9/2ν70 for the yrast superdeformed band and π62ν[642]5/2ν70 for the first excited superdeformed band between the two known crossings.

The nuclei ${}^{138}\mathrm{Nd}$ and ${}^{139}\mathrm{Nd}$ have been studied at very high spins via the ${}^{48}\mathrm{Ca}{+}^{94}\mathrm{Zr}$ reaction. Several new rotational bands were observed, four in ${}^{138}\mathrm{Nd}$ and two in ${}^{139}\mathrm{Nd}.$ The ${J}^{(2)}$ moments of inertia calculated from the observed $\ensuremath{\gamma}$-ray energies are very small and almost constant, indicating that these bands are triaxial. Cranked Nilsson-Strutinsky calculations reproduce the general behavior of the bands, supporting this interpretation and suggesting an approximately constant $\ensuremath{\gamma}$ value of $\ensuremath{\sim}+35\ifmmode^\circ\else\textdegree\fi{}$ over a large spin range up to the highest observed spins. These bands and a few similar bands in other nuclei of the $N\ensuremath{\approx}80$ region are a unique example of almost undisturbed triaxial bands.

A mean lifetime measurement using the Doppler shift attenuation method has been performed at GASP in order to measure the quadrupole moment of the yrast superdeformed band of ${}^{144}\mathrm{Gd}$. The extracted intrinsic quadrupole moment above the backbending, ${Q}_{0}{=13.7}_{\ensuremath{-}0.9}^{+1.1} e$ b, is in nice agreement with cranked shell model predictions. To fit the data properly below the backbending a smaller ${Q}_{0}$ value is required ${(11.6}_{\ensuremath{-}1.0}^{+1.4})e$ b. This is consistent with the predicted lower deformation in the second well for the configuration without high-$N$ $(\ensuremath{\pi}N=6$ and $\ensuremath{\nu}N=7)$ intruder orbitals occupied.

Excited states in $^{145}\mathrm{Nd}$ and $^{147}\mathrm{Sm}$ nuclei have been studied using heavy-ion induced reactions. Level schemes of both nuclei are very similar to the level scheme of $^{149}\mathrm{Gd}$. In analogy to the $^{149}\mathrm{Gd}$ isotone most of the observed excitations are interpreted as single-particle neutron excitations with octupole vibrations coupled to them. Candidates for double octupole-phonon states were identified in both nuclei. \textcopyright{} 1996 The American Physical Society.

The nuclear structure of 145Gd has been investigated via the 114Cd(36S,5n) reaction. Three superdeformed bands have been discovered, consisting of 17, 16 and 10 transitions, respectively. The first excited superdeformed band shows two band crossings which are assigned to the subsequent alignment of an i 13 2 proton pair and a crossing of the i 13 2 and i 11 2 neutron orbitals, respectively. Such a double band crossing has been observed for the first time. The second excited superdeformed band is assigned as the signature partner of the previous band but shows no band crossing in the observed frequency range. The band crossing behaviour of the SD bands has been described theoretically.

Excited states of 130Ba have been studied by means of in-beam γ-ray spectroscopy and electron-spectroscopy via the reaction 120Sn(13C, 3n). Spin and parity assignments have been made for 28 new levels. A comparison with a cranking-model calculation shows that the negative-parity band based on the 5− state is a two-quasiproton band.

The N = 78 isotones 140Sm and 142Gd have been studied with α-particle- and HI-induced reactions. In both nuclei two close-lying 10+ isomers at ∼ 3.2 MeV have been established, and from the feeding E2 cascades they are characterized as the prolate ν h 11 2 −2 and the oblate π h 11 2 2 excitations. A third E2 cascade feeding into the 142Gd 8+ state is interpreted as the continuation of the collective ground state sequence that might assume the properties of a perfect deformed rotor for spins above 10.

High spin states in /sup 83/Br and in /sup 85/Rb were studied via the reactions /sup 82/Se(/sup 6/Li,..cap alpha..n..gamma..)/sup 83/Br, /sup 82/Se(/sup 7/Li,..cap alpha..2n..gamma..)/sup 83/Br, /sup 82/Se(/sup 6/Li,3n..gamma..)/sup 85/Rb, and /sup 82/Se(/sup 7/Li,4n..gamma..)/sup 85/Rb at beam energies of 25 to 36 MeV. In-beam ..gamma.. techniques were used to collect the data. Level schemes were constructed and spin and parity assignments were deduced. Thirty four ..gamma.. rays could be placed in two level schemes. Three new levels with spins up to 17/2, 19/2 h could be established for /sup 83/Br and thirteen for /sup 85/Rb with spins up to 29/2 h. Strongly populated yrast bands were found in both nuclei.

Two-dimensional \ensuremath{\gamma}-ray energy correlations have been measured at high spins in $^{146}\mathrm{Gd}$ with the anti-Compton spectrometer array OSIRIS. Pronounced ridges have been found consisting of stretched E2 transitions. The separation of the ridges gives a dynamical moment of inertia 2${\mathrm{\ensuremath{\theta}}}_{\mathrm{band}}^{(2)}$=(150\ifmmode\pm\else\textpm\fi{}6)${\mathrm{\ensuremath{\Elzxh}}}^{2}$/MeV, suggesting a superdeformation with an axis ratio c/a=1.7 (${\ensuremath{\beta}}_{2}$\ensuremath{\approxeq}0.6). The quadrupole moment of the superdeformed nucleus is ${Q}_{0}$${=11}_{\mathrm{\ensuremath{-}}4}^{+14}$ e\ensuremath{\cdot}b. .AE

High-spin states in179Re have been populated by the165Ho(18O, 4n) and170Er(14N,5n) reactions. A level scheme is constructed from the studies ofγγ-coincidences using anti-Compton spectrometer arrays. The previously known 5/2+[402], 1/2− [541] and 9/2− [514] bands have been extended to 35/2+, 45/2− and 39/2−, respectively. In addition a 1/2+ [660] band, a three-quasiparticle band and two isomers were established. Furthermore several level sequences were identified decaying into the 5/2+ [402] and 1/2− [541] bands. This allowed to determine the excitation energy of the 9/2− member of the latter band. The band crossing features of the bands have been explained as the rotation alignment of ani13/2 quasineutron pair taking into account shape changes.

High-spin states in186Pt have been populated by the188Os (α, 6n) reaction and were investigated with the OSIRIS spectrometer. A shape coexistence at high spins was established in the nucleus186Pt, which lies on the border between light prolate and heavy oblate Pt nuclei. Two bands corresponding to predominantly prolate shapes and one band of predominantly oblate shape have been observed. For prolate shapes a (π h9/2)2 alignment and for oblate shapesa (vi13/2)2 alignment has been found.

Excited states of 120 Xe have been studied by in-beam γ-ray spectroscopy using the 110 Cd( 13 C, 3n) and 111 Cd( 12 C, 3n) reactions. The yrast band was observed up to the 14 + level, showing backbending at the 12 + state. A γ-band and two new negative-parity bands were found. The low-lying levels of 120 Xe could be described by the IBA-1 hamiltonian plus a triaxial degree of freedom.

The use of large detector arrays allows to measure γ-γ angular correlations and to determine spins and multipolarities, even of weak and unresolved transitions. The method utilizing directional correlations of γ-rays deexciting oriented states (DCO ratio method) has been described and applied to experimental data on 178 W taken with the γ-γ coincidence spectrometer OSIRIS. The spin of the 35 ns isomer in 178 W has been established to be 14.

$^{84}\mathrm{Sr}$ has been investigated by means of conventional in-beam gamma-ray spectroscopy with the reactions $^{76}\mathrm{Ge}$($^{12}\mathrm{C}$,$4n$) and $^{81}\mathrm{Br}$($^{6}\mathrm{Li}$,$3n$). Lifetimes of 10 levels have been measured by the recoil distance Doppler shift technique. Four positive and at least two negative parity bands have been found. The energies of the ground state band and quasigamma band as well as the $E2$ transition strengths are compared with theoretical values obtained from the proton-neutron interacting boson model. A relatively long lived ${8}^{+}$ state has been found, to which we assign the ${(\ensuremath{\nu}{g}_{\frac{9}{2}})}^{\ensuremath{-}2}$ configuration.NUCLEAR REACTIONS $^{76}\mathrm{Ge}$($^{12}\mathrm{C}$,$4n\ensuremath{\gamma}$), $E=48\ensuremath{-}60$ MeV; $^{81}\mathrm{Br}$($^{6}\mathrm{Li}$,$3n\ensuremath{\gamma}$), $E=19\ensuremath{-}32$ MeV, measured ${E}_{\ensuremath{\gamma}}$, ${I}_{\ensuremath{\gamma}}$, $\ensuremath{\gamma}\ensuremath{\gamma}$ coincidence, $\ensuremath{\gamma}$ angular distribution, recoil distance Doppler shift; $^{84}\mathrm{Sr}$ deduced levels, $J$, $\ensuremath{\pi}$, $\ensuremath{\tau}$. Enriched targets, Ge(Li) detectors.

Levels in 146,148Nd have been populated in the 150 Nd (α, α′ x n ) reactions. Cascades of enhanced E1 transitions have been observed. B( E 1) B( E 2) branching ratios, of the order of 10−6 fm−2 as well as the presence of low energy negative-parity bands indicate strong octupole effects. Shell correction type calculations suggest an explanation in terms of octupole correlations at medium spins.

The decay scheme of $^{83}\mathrm{Rb}$ was studied by gamma-ray spectroscopy with the $^{81}\mathrm{Br}(\ensuremath{\alpha}, 2n)^{83}\mathrm{Rb}$, $^{70}\mathrm{Zn}(^{16}\mathrm{O}, p2n)^{83}\mathrm{Rb}$, $^{74}\mathrm{Ge}(^{12}\mathrm{C}, p2n)^{83}\mathrm{Rb}$, and $^{80}\mathrm{Se}(^{6}\mathrm{Li}, 3n)^{83}\mathrm{Rb}$ reactions. New energy levels and spins and parities were established. A stretched spin band built on the isomeric $\frac{9}{{2}^{+}}$ level at 42.3 keV, a $\frac{5}{{2}^{\ensuremath{-}}}$ ground state quasirotational band, and a three-quasiparticle band were found.NUCLEAR REACTIONS $^{81}\mathrm{Br}(\ensuremath{\alpha}, 2n)$, ${E}_{\ensuremath{\alpha}}=19\ensuremath{-}25$ MeV, $^{80}\mathrm{Se}(^{6}\mathrm{Li}, 3n)$, ${E}_{^{6}\mathrm{Li}}=23\ensuremath{-}29$ MeV, measured ${E}_{\ensuremath{\gamma}}$, ${I}_{\ensuremath{\gamma}}$, $\ensuremath{\gamma}\ensuremath{-}\ensuremath{\gamma}$-coincidence, $\ensuremath{\gamma}$-angular distribution, $^{70}\mathrm{Zn}(^{16}\mathrm{O}, p2n)^{83}\mathrm{Rb}$, ${E}_{^{16}\mathrm{O}}=52$ MeV, $^{74}\mathrm{Ge}(^{12}\mathrm{C}, p2n)^{83}\mathrm{Rb}$, ${E}_{^{12}\mathrm{C}}=35\ensuremath{-}49$ MeV, measured ${E}_{\ensuremath{\gamma}}$, $^{83}\mathrm{Rb}$ deduced levels, $J$, $\ensuremath{\pi}$. Enriched targets, Ge(Li).