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We report on four recent results concerning the population and the decay of superdeformed states, namely the structure of excited superdeformed states in 194Hg, the search for fine structure of the last superdeformed transitions in 194Pb, the primary decay-out strength analysis in 194Hg and, as a consequence of this, the possibility of using the decay-out as a tool to study order-to-chaos properties of normally deformed states.

High-spin states of 194 Pb have been populated by the reaction 184 W( 16 O, 6n) at 113 MeV beam energy and studied using the EUROGAM-1 array. The level scheme has been extended up to spin of 33 ℏ and excitation energy of 11.1 MeV. The high-spin part of the level scheme is dominated by bands of dipole transitions. New dipole bands have been observed and the configurations of their band heads are discussed. Besides the well-known coupling of the K π =11 − two-proton state to several νi 13/2 rotation-aligned neutron states, the K π =8 + two-proton state is also involved. Such a coupling is identified for the first time in a lead isotope. Moreover, the K π =11 − two-proton state is coupled to the rotation-aligned proton pair ( πh 11/2 ) 2 . Thus many multiparticle configurations involving all the high- j subshells located around the proton and neutron Fermi levels, πh 11/2 , πh 9/2 , πi 13/2 , and νi 13/2 have been identified in this nucleus.

A brief introductory survey of gamma-ray detector arrays and in-beam electron spectrometers developed during the last three lustra is followed by a broad discussion of the general requirements for single and multiple in-beam e-gamma spectrometers. A detailed analysis is made of a few important tools for reducing the low-energy electron background (i.e. simultaneous E-Bp selection, true and random coincidence rates, EM static fields around the target region). This survey and discussion are illustrated by the results of several in-beam e-gamma measurements dealing with nuclear spectroscogic investigations of a few medium and heavy nuclei. (C) 1999 Elsevier Science B.V. All rights reserved.

The main features of nuclear targets, recoil ion catchers and reaction chambers used in nuclear spectroscopic investigations involving in-beam multi-e-gamma spectrometers are discussed. The relative importance of the F-ray background due to the accelerated ion-target and the recoil-ion-target interaction is estimated. Its impact on the prompt low-energy electron measurements is stressed. Finally a few general features of the interplay between accelerated ion beams, targets and recoil ion catchers particularly relevant for these measurements are broadly discussed and illustrated with typical examples of in-beam e-gamma studies. (C) 1998 Elsevier Science B.V. All rights reserved.

A few accelerated ion beam requirements for in-beam e-gamma spectroscopy are briefly reviewed as well as several features of the MP Tandem accelerator of IPN-Orsay and the accelerated ion-beam transport devices leading to the experimental area of in-beam e-gamma spectroscopy. In particular, the main capabilities of the ion-sources, the ion pulsing system, the ion stripping and stabilizing devices as well as the versatility of the ion beam transport system are discussed from the point of view of the different kinds of in-beam e-gamma experiments performed in that area. (C) 1998 Elsevier Science B.V. All rights reserved.

Three superdeformed bands have been observed in ${}^{191}$Au using the EUROGAM II multidetector array. The previously known yrast superdeformed band has been extended up to very high rotational frequencies and two new excited bands have been assigned to this nucleus. These bands behave as signature partners and display characteristics which suggest they could be based either on the $\ensuremath{\pi}$ [532]3/2 orbital alone or on that orbital plus the $\ensuremath{\pi}$ [530]1/2 orbital, which become the $[\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{431}]$3/2,1/2 doublet in the pseudospin formalism.

The nucleus195Pb has been populated with the184W+16O reaction at 113 MeV. Two dipole γ-ray cascades have been observed using the EUROGAM spectrometer. A comprehensive level scheme related to these structures has been established. Multiparticle configurations are attributed to these high-spin structures from detailed comparison with the neighbouring nuclei,193Hg,194Pb and195Tl. Band crossings due to i13/2 neutron pair breaking are observed in195Pb at about the same frequencies as in the isotone193Hg.

The decay-out spectrum of the superdeformed yrast band in {sup 192}Hg comprises a quasicontinuum, from which about 50 weak discrete transitions of energy between 1 and 3.2MeV are resolved. The fluctuations of the one-dimensional quasicontinuum spectrum are studied with the fluctuation analysis method, which shows that of the order of a few thousand different transitions are available in the first step of the decay-out cascades. The experimental effective number of transitions is compared to schematic theoretical calculations. {copyright} {ital 1996 The American Physical Society.}

The six superdeformed bands in {sup 193}Pb have been studied with the EUROGAM 2 {gamma}-ray spectrometer using the {sup 168}Er({sup 30}Si,5{ital n}){sup 193}Pb reaction. The results are discussed in terms of cranked-Hartree-Fock-Bogolioubov-Lipkin-Nogami calculations. From the @FF {sup (2)} moment of inertia behavior as function of the rotational frequency and the {ital M}1 and {ital E}2 decay competition of the superdeformed states, the bands are interpreted as three pairs of signature partners based on quasineutron excitations. Dipole transitions linking two signature partner superdeformed bands have been observed and, for the first time in lead isotopes, the branching ratio {ital B}({ital M}1)/{ital B}({ital E}2)=0.15{plus_minus}0.04 {mu}{sup 2}{sub {ital N}}/{ital e}{sup 2}b{sup 2} has been extracted. {copyright} {ital 1996 The American Physical Society.}

From the observed competition between $M1$ and $E2$ $\ensuremath{\gamma}$ transitions deexciting the states of the two signature partner yrast superdeformed bands in $^{193}\mathrm{Tl}$, the ${i}_{\frac{13}{2}}$ ($\ensuremath{\Omega}=\frac{5}{2}$) intruder proton orbital is found to have $\frac{({g}_{K}\ensuremath{-}{g}_{R})K}{{Q}_{0}}=0.138\ifmmode\pm\else\textpm\fi{}0.008$. A model dependent value of ${g}_{s}^{\mathrm{eff}}=(0.7\ifmmode\pm\else\textpm\fi{}0.2){g}_{s}^{\mathrm{free}}$ is deduced. A saturation of the ${\mathcal{T}}^{2}$ moments of inertia, at rotational frequency $\ensuremath{\hbar}\ensuremath{\omega}g0.32$ MeV, is observed for the two bands. This feature is discussed in terms of exhausted quasineutron alignment in the presence of substantially reduced quasiproton alignment due to Pauli blocking.

For the first time, two excited superdeformed (SD) bands have been observed in the double closed shell superdeformed nucleus $^{192}\mathrm{Hg}$. One of the SD bands exhibits a pronounced peak in the dynamic moment of inertia which is interpreted as a crossing between two excited SD configurations involving the N=7 intruder and the [512]5/2 orbitals. This is only the second occurrence of such a crossing in a SD nucleus around A=190. The second excited SD band has near identical transition energies to an excited SD band in $^{191}\mathrm{Hg}$.

Recent data from the EUROGAM array have revealed dipole transitions linking signature partner superdeformed bands in 194Tl and 195Tl nuclei. Measurements of the decay branching ratios, taken together with the average quadrupole moment of the neighboring superdeformed nuclei, enable the absolute M1 strengths to be determined. From these data and using the strong coupling model, we find that two SD bands in 195Tl are due to the 81st proton being in the [642]5/2+ orbital and four from the six SD bands in 194Tl correspond to a configuration where the intrinsic spins of the single proton and single neutron are aligned.

Dipole transitions linking the superdeformed Yrast signature-partner bands in 195Tl have been observed using the EUROGAM 1 spectrometer. From the measurements of the photon decay branching ratios, taken together with the average quadrupole moment measured in neighbouring superdeformed nuclei, we find that the two signature partner superdeformed bands involve the excitation of the 81 st proton into the i 13 2 Ω= 5 2 intruder orbital

A new superdeformed band is reported in 193Hg which has properties that are consistent with it being based on the unfavoured N = 7 (π, α) = (−, +12) intruder orbital. The signature splitting at hω = 200 keV of this intruder orbital and its favoured (−, −12) partner is estimated to be 160±30 keV, which is in agreement with cranked mean field calculations. This band completes the set of low-lying quasi-neutron orbitals predicted to be at the N = 113 superdeformed Fermi-surface. The previously known superdeformed bands in 193Hg have been extended to higher rotational frequencies, hω ⩾ 0.40 MeV.

The complete spectrum of [gamma] rays following the decay of superdeformed (SD) states in [sup 192]Hg has been extracted. The spectrum, which comprises a quasicontinuous component and sharp lines, reveals the decay mechanism and defines the excitation energies of the SD band. The decay of SD states results from the coupling between a cold, ordered SD system with a hot, chaotic one with normal deformation.

The192Hg nucleus was populated in the160Gd(36S, 4n) reaction at a beam energy of E=159 MeV. Emittedγ-rays were detected with the EUROGAM array comprising 43 Compton-suppressed large volume Ge detectors. The level scheme of192Hg has been extended up to an excitation energy of E=10.4 MeV and spin I=34 ħ. Two new structures, made of competing ΔI=1 and ΔI=2 transitions have been observed and their connexions with the low-lying levels established. Their lowest levels are located at 6.304 MeV and 6.879 MeV excitation energy. The experimental results are compared with mean-field HF+BCS calculations. It is proposed that the new structures originate from deformation-aligned quasi-proton excitations π(i13/2 * h9/2)K=11 andπ (h9/2) K=8 2 , coupled to rotation-aligned quasi-neutron ν(i13/2)n and quasi-proton π(h11/2)2 excitations.

Two regular dipole gamma -ray cascades have been observed in 194Pb. A comprehensive level scheme related to these structures has been built and first members of rotational bands built on K=8 and K=11 two-proton oblate states have been identified. From the excitation energies, spin values, behaviours of the moments of inertia and alignments, and from the comparison with the isotone 192Hg, multiparticle configurations can be attributed to three high-spin structures of 194Pb built respectively on the 4966 keV, 4334 keV and 6198 keV levels: ( pi 9/2(505) pi 13/2(606))(vi13/2)2, ( pi 9/2(505) pi 13/2(606))(vf5/2vi13/2), ( pi 9/2(505) pi 13/2(606)) (vf5/2(vi13/2)3). Within this interpretation, the regular dipole bands correspond to the presence of two or three i13/2 decoupled neutrons.

The level scheme of 147Tb has been extended up to 13.8 MeV excitation energy and spin I=67/2 using the 120Sn(31P,4n) reaction. Evidence for a new octupole band built upon an excited multi-particle-hole state has been found. The high spin levels are interpreted in the framework of DIPM model and presents an evolution towards sizeable oblate shape at the highest spins.

The location of nuclear closed shells, as evidenced through discontinuities in binding energy and one- and two-particle separation energy systematics, remains one of the simplest tests of global nuclear models. How shell gaps evolve, whether with increasing mass, increasing neutron:proton ratio or increasing deformation, is still uncertain, and it has recently been suggested that one must go beyond a static meanfield picture to include the effects of dynamic fluctuations in the nuclear shape even in the ground state. The identification of key properties which may distinguish between competing approaches is thus vital. Comparison of the binding energies of superdeformed nuclei in the A ≈ 190 region shows that two-proton separation energies are higher in the superdeformed state than in the normal state, despite the probably lower Coulomb barrier and lower total binding energy. Possible reasons for this difference are discussed. This somewhat counterintuitive result provides a critical test for global nuclear models.

Relative intensities of the yrast and the first excited superdeformed bands in $^{151}\mathrm{Tb}$ have been accurately measured, with the EUROGAM spectrometer. It is shown that he excited band depopulates at the same freqeuncy and spin as its identical band in the isotone $^{152}\mathrm{Dy}$ whereas the yrast band deexcites at higher rotational frequency and spin even though it is much lower in excitation energy. A classification of superdeformed bands in the A\ensuremath{\sim}150 mass region indicates that the decay-out mechanism is strongly affected by neutron pairing correlations and the occupancy of high-N intruder orbitals.

Dipole transitions linking signature partner superdeformed bands in 193Hg have been observed. Measurements of the photon decay branching ratios, taken together with the average superdeformed quadrupole moment measured in neighboring nuclei, enable the absolute M1 strengths to be determined. From these data, using the strong coupling model, we find (gK-gR)K/Q0=-0.14±0.01 (e b)−1, gK=-0.65±0.14 with Ω=2.8±0.8. These data are consistent with the superdeformed neutron orbital being [512]5/2− as predicted by cranked Woods-Saxon calculations.

A subset of the Eurogam array has been used to investigate the decay out of the superdeformed (SD) band in 194Pb. Two new band members and a new decay pattern into the low lying states at normal deformation (ND) have been established for this band. In the level scheme at normal deformation, the linking transitions between the previously known floating ΔI = 1 sequence and the lower states have been established for the first time. In this talk we will also report on the preliminary results of the search for the linking transitions between the SD and ND states in 192Hg with the fully operational EUROGAM array.

High-spin states in Tl-198 were studied using the Au-197(alpha, 3n) reaction. The level scheme was considerably extended including two new bands and several non-yrast levels. One of the new bands is possibly a chiral partner to the yrast pi h(9/2) circle times vi(13/2)(-1) band. Two-quasiparticle-plus-triaxial-rotor model calculations suggest an aplanar orientation of the total angular momenta for these bands, thus supporting possible chirality.

Some important physical factors influencing in-beam e-γ measurements are briefly discussed. The close implication between target and beam properties including the reaction products on high resolution in-beam electron spectroscopy is worked out. The influence of the target properties on their Doppler broadening of an electron line analyzed by axial symmetric spectrometers is discussed in detail. A few examples of the target influence on prompt in-beam electron spectra are also presented in the perpendicular geometry, while the important role of electron background reduction techniques is stressed in the forward collinear geometry.

Two excited superdeformed bands observed in , which have an identical energy relationship with the even-even core, are suggested to be two members of the pseudo-spin doublet .

A candidate for chiral bands was found in Tl-198 for the first time in a mass region of oblate (or nonaxial with gamma >= 30 degrees) deformed nuclei. Two bands show very similar quasiparticle alignments, moments of inertia, and B(M1)/B(E2) ratios. They have a relative excitation energy of about 500 keV and different patterns of energy staggering. Calculations using the two-quasiparticle-plus-triaxial-rotor model with residual proton-neutron interaction included show that a triaxial deformation with gamma similar to 44 degrees agrees very well with all the experimental observations. Furthennore, considerable energy staggering for both partner bands was calculated for this pi h(9/2) circle times vi(13/2)(-1) configuration at gamma - 30 degrees, suggesting that chiral bands may have substantial energy staggering. (Less)

Excited superdeformed bands have been observed in the {ital N}=86 isotones {sup 150}Gd and {sup 151}Tb. The properties of these bands were found to closely resemble those of the yrast superdeformed bands in their {ital Z}+1 {ital N}=86 isotones ({sup 151}Tb and {sup 52}Dy) such that, on average, the transition energies are identical to an accuracy of 1:1000. It is proposed that these excited superdeformed bands are based on single-proton excitations from the (301)1/2 orbital into the (651)3/2 intruder orbital and thus they are the first obsrevation of proton excitations in superdeformed nuclei.

Spin and parity values of the states of two dipole bands in 194Pb have been determined from internal conversion and linear polarisation measurements. The multiparticle configurations assigned previously to these dipole bands are discussed within these results.

Excited states in $^{191}$Pt have been populated using the reaction $^{186}$W + $^{11}$B at 85MeV beam energy. Gamma-ray coincidences were measured using the EUROGAM-II spectrometer array. The level scheme has been extended considerably. Evidence for favoured structures of highly triaxial shape with $\gamma \sim$ -90° coexisting with oblate structures has been obtained by comparison with total Routhian surface and cranked shell model calculations. The presence of proton excitations in both positive- and negative-parity states has been confirmed.

The excitation energies and spins of the levels in the yrast superdeformed band of {sup 191}Hg have been determined from two single-step {gamma} transitions and the quasicontinuum spectrum connecting the superdeformed and normal-deformed states. The results are compared with those from theoretical mean-field calculations with different interactions. A discussion of pairing in superdeformed states is also included.

The level scheme of Au-190 was extended up to high spin using gamma spectroscopy with the Eurogam-II array and internal conversion measurements with the electron- gamma spectrometer of Orsay. Sever ...

The level scheme of Au-191 was considerably extended to high spin using gamma spectroscopy with the Eurogam-II array and internal conversion measurements with the Orsay electron spectrometer. Several bands that appear as strongly coupled were associated with low- Omega configurations in Au-191 . Using total routhian surface and cranked shell model calculations it was shown that these bands have a rotation-aligned nature and are most likely generated by the nonaxiallity of the nucleus induced by the odd proton. The predictions for the presence of such bands in Au-191 and in the oblate nuclei in the Pt-Au-Hg region found excellent agreement with the experimental data, as well as the predictions for their alignments and band-crossing frequencies in Au-191 .

Excited isomeric states ${I}^{\ensuremath{\pi}}{=20}^{+}$ have been identified for the first time in odd-odd ${}^{190,192}\mathrm{Au}$ nuclei. Two independent measurements of their half-lives were performed, using the recoil shadow anisotropy method with the Eurogam-II data, and using the time distribution of K-electron lines from the Orsay electron-spectrometer data. Half-lives of $7.0\ifmmode\pm\else\textpm\fi{}0.3$ and $5.4\ifmmode\pm\else\textpm\fi{}0.3$ ns were obtained for these isomers in ${}^{190}\mathrm{Au}$ and ${}^{192}\mathrm{Au},$ respectively, by the latter measurements. The $\ensuremath{\pi}{h}_{11/2}^{\ensuremath{-}1}\ensuremath{\bigotimes}\ensuremath{\nu}{i}_{13/2}^{\ensuremath{-}2}{h}_{9/2}^{\ensuremath{-}1}$ configuration was assigned to these isomeric states. A shape transition towards highly triaxial deformation with $\ensuremath{\gamma}\ensuremath{\sim}\ensuremath{-}90\ifmmode^\circ\else\textdegree\fi{}$ is suggested by total Routhian surface calculations, which could be the cause for their relatively hindered decay.

Superdeformed bands in the mass A=190 region decay suddenly, over a few states, at relatively low spin and high excitation energy. The decay path is very fragmented and only in a few cases have one-step or two-step decays been seen. Thus, only three superdeformed bands have so far been linked to the normal states they decay to. Most of the {gamma} rays from the decay form an unresolved quasicontinuum spectrum. This paper describes the extraction of the total quasicontinuum decay spectrum that connects the superdeformed and normal yrast states. It also demonstrates that the excitation energy and spins of superdeformed bands can be determined by analyzing this total decay spectrum. The analysis method is first tested in {sup 194}Hg, which is one of the few cases where the excitation energy and spin of the yrast superdeformed band are known, and is then applied to the yrast superdeformed band in {sup 192}Hg, where no one-step decays have been seen thus far. fe ndash

An isomer has been observed in the stable nuclide ${}^{153}\mathrm{Eu},$ which primarily decays via a 919-keV gamma ray to the ${17/2}^{+}$ level of the ground-state band. The structure of the isomer has been investigated using an array of eight germanium detectors and an electron spectrometer. The K-shell internal-conversion coefficient of the 919-keV transition has been measured to be $9.8(2.4)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$ establishing that this transition has electric-dipole character. This measurement, and the observed decays of the isomer, indicate that the isomer has spin and parity ${19/2}^{\ensuremath{-}}.$ Using timing measurements against a pulsed beam, the half-life of the isomer has been measured to be 475(10) ns: this suggests high purity for the K quantum number and associated highly K-forbidden decays. The gamma-gamma coincidence data have revealed a rotational band built upon the isomer. The properties of the rotational band are consistent with the configurations $\ensuremath{\nu}[651]3/2\ensuremath{\bigotimes}\ensuremath{\nu}[505]11/2\ensuremath{\bigotimes}\ensuremath{\pi}[413]5/2,$ and $\ensuremath{\nu}[402]3/2\ensuremath{\bigotimes}\ensuremath{\nu}[505]11/2\ensuremath{\bigotimes}\ensuremath{\pi}[413]5/2,$ or a mixture of both.

The present work reports on a study of high spin states in 190Pt On the basis of TRS calculation, an interpretation is proposed for the new structures as well as for the previously known 10- isomer.

Pseudospin symmetry has been invoked as a possible explanation for the {open_quotes}quantized alignment{close_quotes} observed in some superdeformed {open_quotes}identical{close_quotes} bands. The clearest case involves the 1/2[301] orbital (a pseudospin singlet, {tilde {Lambda}}=0), where pseudospin alignment provides an explanation for some identical bands in the mass-150 region. Pseudospin doublets ({Omega}={tilde {Lambda}}{plus_minus}1/2) can also generate quantized alignments and such an explanation, with {tilde {Lambda}}=1, has recently been proposed for the band in {sup 191}Au identical to {sup 192}Hg. The present work examines whether the data on the normally deformed nuclei support such an interpretation and concludes that pseudospin alignment is plausible for states with {tilde {Lambda}}=0 or 1. {copyright} {ital 1998} {ital The American Physical Society}

The nucleus 193Pb was populated via the 168Er(30Si,5n) reaction at a beam energy of 159 MeV and studied with the EUROGAM II spectrometer. Five new dipole Δ I = 1 cascades have been found. These structures have been connected to the level scheme which has been considerably extended up to a spin of ħ and an excitation energy of about 8 MeV. Angular distribution coefficients, a2, have been measured and confirm the dipole character of the in-band transitions. B(M1)/B(E2) ratios have been extracted for the two most intense cascades. The 193Pb dipole bands are discussed in comparison with those known in odd lead isotopic series and the structure of the band heads is analyzed in terms of microscopic HF+BCS calculations. The proposed configurations are based on a high-K two quasiproton excitation, π ([505]9/2t? ⊗ [606]13/2+)K=11t-, coupled to one or three rotation aligned quasineutrons involving the i13/2, p3/2, f5/2 and/or h{9/2} subshells. The main difference, compared with the heavier lead isotopes, is the presence of large Ω orbitals from the ν (i13/2) shell near the Fermi surface which are responsible for the increasing band-head spin as A decreases.

The EUROGAM array has been used to investigate the decay out of the yrast superdeformed (SD) band in 194 Pb. Six single step decays from the lowest observed SD states to low-lying states at normal deformation (ND) have been identified. From this observation, the excitation energy of the SD band in 194 Pb is established at 4877 ± 1.5 keV for the 6 + SD state. The most probable spins and parities of all members of the SD band are also deduced assuming that the SD states have even spin and positive parity.

An excited superdeformed (SD) band has been observed in 192Hg with the UROGAM spectrometer. It is interpreted as a two quasi-neutron excitation in the 192Hg SD nucleus. Nuclear level lifetimeshave been measured using the Dopple-shift attenuation method. An average transition quadrupole moment of 19.5 ± 1.5 b has been obtained which is similar to the value measured in the yeast SD band. These results indicate that the deformation in the 192Hg SD nucleus is stable despite changes in the occupancy of high-N-orbitals.

A controversy has arisen over the existence, or not, of a superdeformed rotational band in192Pb. We have carried out an experiment using the168Er(3OSi, 6n)192Pb reaction at 159 MeV and have observed the coincidentγ rays in the EUROGAM 2 spectrometer. We confirm the original result of Henry et al. that a superdeformed band exists in192Pb.

The main features of the interplay between the target structure and the accelerated ion beam characteristics suitable for an in-beam e-gamma measurement are discussed in detail. In particular, the different types of ''spurious'' electron (and photon) spectra overlapped with in-beam internal conversion electrons (and discrete gamma-rays) are reviewed as well as the most efficient experimental methods used for their attenuation. Furthermore, the general characteristics of particle beams, targets and electron spectrometers required for prompt and delayed in-beam e, gamma and e-gamma measurements are also compared. Moreover, the relative magnitude of the electron line Doppler broadening corresponding to the perpendicular and the collinear geometry is briefly discussed and illustrated by a few in-beam e-gamma studies of Pm and Eu isotopes produced by accelerated ions (H-2(1) and Li-7(3)) bombarding very thin Nd(+C) backed targets. Finally the most recent developments made at Orsay towards multi e-gamma detector assemblies lead to a broad discussion concerning the most suitable targets to be inserted within such instrumental arrangements.

Excited states in the 150, 151, 152 Tb isotopes have been investigated using the 130Te(27 Al, xn) reaction and the EUROGAM array. The theoretical interpretation of the level schemes has been performed in the framework of the deformed independent particle model. The feeding patterns of the normal-deformed states by the superdeformed bands in 150, 151 Tb istopes have also been established. The results indicate that the decay-out mechanism of the bands is not of purely statistical nature, but depends on the configurations of both normal- and superdeformed states.

The level structure of the 152Ho nucleus below the 47 ns isomer has been established studying, by the catcher recoil method, the delayed γ-rays following the 120Sn(37Cl, 5n) reaction. The conversion-electron measurements, carried out from the 141Pr(16O, 5n) reaction (also by a recoil method) lead to reliable spin and parity assignments for the yrast levels. Three yrast isomers have been located at 3.02 MeV ( I π = 19 − , T 1 2 = 8.4 μs) , 4.88 MeV (24+, 5 ns) and 6.00 MeV (28−, 47 ns). The B(E3) value 0.92 ± 0.03 W.u., obtained for the 734 keV, E3 transition deexciting the 19− isomer, is typical of a single-particle transition. Its interpretation involves the j − 1 state ( 9 2 − ) of the (π h 3 11 2 ) multiplet coupled to the aligned state of the three valence neutrons. The 47 ns isomer appears as the expected fully aligned state of the six valence particles. Configurations are proposed for most of the observed structures.

High-spin states of 149Tb have been investigated using the 122Sn(31P, 4n) reaction at beam energies of 140 and 150 MeV. Measurements of γγ coincidences and DCO ratios with the Château de Cristal array allowed the level scheme to be extended up to spin 75 2 h and E ∗ = 13 MeV Experiments performed with an eγ spectrometer led to the determination of transition conversion coefficients. The level scheme is interpreted in the frame of a deformed independent particle model.

Excited states in the nucleus150Tb have been investigated up to spin 39ħ and 13 MeV excitation energy using the130Te(27Al, 7n) reaction and the EUROGAM array. The theoretical interpretation of the observed states has been performed in the framework of the deformed independent particle model. The analysis of the decay out of the yrast superdeformed band indicates that normal-deformed states with spins between 24ħ and 28ħ are fed.

Excited states in the nucleus 151 Tb have been investigated up to spin 91/2 ħ and energy 16.5 MeV using the 130 Te( 27 Al, 6n) reaction and the EUROGAM array. The theoretical interpretation of the level scheme has been performed in the framework of the deformed independent particle model. The feeding patterns of the normal-deformed states by both the yrast and first excited superdeformed bands have also been established. The results indicate that the decay-out mechanism of the bands is not of purely statistical nature, but depends on the configurations of both normal- and superdeformed states.