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Isomer decays, β–γ and electron–γ spectroscopy, α–γ fine structure studies, and Coulomb excitation are cases of nuclear structure experiments where the ideal detector is a compact, highly segmented, very efficient germanium (Ge) detector box. In order to develop such a structure, we are working on the R&D of large, segmented, high-purity planar Ge strip detectors (HPGeDSSD) which form the walls of such a box. We have developed a 92 mm×92 mm×20 mm HPGeDSSD, which has 16×16 orthogonal strips of 5 mm width. We are in the process of designing a focal plane detector for the Argonne fragment mass analyzer which consists of a five-sided box, each side having a HPGeDSSD backed by a large segmented clover HPGe detector. MCNP simulations indicate this detector would have an efficiency of ∼60% for 122 keV gamma rays and ∼15% for 1.33 MeV radiation, which is ideal for studying the decays of nuclei far from stability that are usually produced with very low cross-sections.

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.

An experiment aimed at studying high-spin states in 190 Hg was performed with the Eurogam II array. The data have revealed the presence of cascades of magnetic dipole transitions with some unexpected properties. Unlike the M1 bands previously observed in the heavier Hg isotopes, these structures have extremely large B(M1)/B(E2) ratios. The observation of a third dipole band with much lower B(M1)/B(E2) values in the same spin/excitation energy regime suggests that the bands may represent configurations occurring in different minima in the potential energy surface. Configuration-dependent Cranked Nilsson–Strutinsky calculations predict the presence of a minimum in the nuclear potential energy surface at a deformation of e≈0.2, γ≈−90°, occurring when a proton is excited across the Z=82 shell-gap into an h9/2 orbital. It is suggested that the bands exhibiting anomalously large B(M1)/B(E2) ratios may be associated with this minimum.

A technique for producing a high-quality radioactive 56 Ni (T 1/2 =6.1 d ) beam via the two-accelerator method has been developed. Beam intensities of 2×107 56Ni/s were extracted from the ion source and 2×104 56Ni/s were delivered to the target. For a study of neutron transfer reactions in inverse kinematics, a high-efficiency detection system was built consisting of a large solid angle (2.8 sr), high-granularity Si detector array for measuring the outgoing protons in coincidence with the heavy reaction products identified with respect to mass A and nuclear charge Z in the focal plane of a recoil mass separator.

In a series of measurements with Gammasphere, striking differences were found between the yrast and negative parity bands in ${}^{238--240}\mathrm{Pu}$ and those in ${}^{241--244}\mathrm{Pu}$. These differences can be linked to variations with mass of the strength of octupole correlations. At the highest spins, ${}^{238--240}\mathrm{Pu}$ are found to exhibit properties associated with stable octupole deformation, suggesting that a transition with spin from a vibration to stable deformation may have occurred.

New high-K isomers are populated in {sup 180,181,182}Hf nuclei via inelastic excitation and transfer reactions, using pulsed {sup 238}U beams on Hf targets. The new data explore K-hindrances for different multipolarities and the role of residual spin-spin interactions for multi-quasiparticle (qp) configurations at the neutron-rich edge of the {beta}-stability line. The mapping of 4-qp K-isomers in the A {approx} 180 region is extended into neutron-rich territory.

Yrast states of Sb-106 have been investigated in the Fe-54(Ni-58, alpha pn) reaction using in-beam gamma-spectroscopic methods and in the Cr-50(Ni-58,pn) reaction performing delayed gamma and conversion electron studies. A new isomeric state was found at 103 keV with t(1/2) = 232(21) ns. The number of start's and transitions in the proposed level scheme have been doubled. The experimental results are discussed within the framework of the shell model. [S0556-2813(99)08502-7].

The strength distribution of the γ rays in the decay-out from superdeformed (SD) states is investigated by applying the maximum likelihood method, with special emphasis on the influence of the lower threshold given by experimental conditions. Clear graphical solutions are found, and a careful estimation of the dispersion in the values of the number of degrees of freedom and of the average strength of the most likely χ 2 distribution is carried out. For the 194 Hg nucleus, 41 primary transitions from the decay-out of SD states are identified above 2600 keV. It is concluded that they represent the strongest 10% of the transitions selected stochastically from a Porter-Thomas distribution. This would support the scenario of a statistical decay of SD states via coupling to a compound state at normal deformation. However, the occurrence of several very strong direct one-step transitions as previously observed in 194 Hg has a very small probability of the order of 10 −4 . This may indicate special selection rules governing the decay. However, based on the absence of strong primary transitions from SD states in adjacent nuclei, the situation in 194 Hg is viewed as a very lucky incidence.

High-spin states in the doubly-odd nuclei {sup 154,156}Tb have been populated in two separate experiments using the {sup 36}S+{sup 124}Sn reaction at different beam energies (160 and 175 MeV). The yrast structures of both nuclei were extended to much higher spin (I{le}48{h_bar}) than previously known and several quasiparticle alignments have been identified. These include the second neutron alignment and a clear delineation of the second proton crossing in {sup 156}Tb. Systematics of these crossings for odd-Z nuclei and comparisons with results of cranked shell model calculations are discussed. thinsp {copyright} {ital 1999} {ital The American Physical Society}

High-spin states in {sup 97,98}Rh (Z=45) were populated via the {sup 65}Cu({sup 36}S,xn){sup 97,98}Rh (x=4,3) fusion-evaporation reactions. More than 40 additional transitions have been identified and placed in the decay schemes of these nuclei. The level scheme of {sup 97}Rh has been extended up to tentative spins of J{sup {pi}}=39/2{sup +},37/2{sup {minus}}, and the placement of some of the previously known transitions has been revised. The level structure of {sup 97}Rh indicates a single-particle nature and the observed levels are reproduced well by spherical shell-model calculations. The level scheme of {sup 98}Rh has been extended up to spins J{approximately}20{h_bar} and up to an excitation energy of {approximately}10 MeV. The low-spin structure of {sup 98}Rh (J{le}10{h_bar}), appears to indicate also a single-particle structure, as supported by the stretched coupling scheme [{sup 97}Rh(J{sup {prime}}){circle_times}{nu}(d{sub 5/2})={sup 98}Rh (J)]. {copyright} {ital 1998} {ital The American Physical Society}

In-beam \ensuremath{\gamma} rays have been observed in the neutron-deficient isotopes ${}^{170,171,172}\mathrm{Pt}$ using the recoil-decay tagging technique. The yrast transition sequence proposed for ${}^{172}\mathrm{Pt}$ indicates that the ${0}^{+}$ bandhead of the deformed intruder band is situated about 900 keV above the weakly deformed ground state, i.e., its excitation energy has risen by about 300 keV compared to ${}^{174}\mathrm{Pt}.$ The measured energy of the ${2}^{+}\ensuremath{\rightarrow}{0}^{+}$ transition in ${}^{170}\mathrm{Pt}$ supports an even larger increase in the excitation energy of the intruder configuration with the departure from the middle of the 82--126 major neutron shell. Furthermore, a band with transition energies almost identical to those found in ${}^{172}\mathrm{Pt}$ has been assigned to ${}^{171}\mathrm{Pt}$ and was interpreted as corresponding to a rotationally aligned ${i}_{13/2}$ neutron orbital coupled to the core excitations.

gamma-ray spectroscopy of the high-spin states of the neutron-deficient nucleus Pb-187 has been conducted with the Gd-155(Ar-36,4n) reaction. A cascade of three transitions was deduced from gamma-gamma coincidence data gated by detection of recoiling evaporation residues in a gas-filled recoil separator. In an earlier, separate experiment, two of these gamma rays were positively identified with Pb-187 by recoil-gamma coincidence measurements with a high-resolution, recoil mass spectrometer. From comparison with similar sequences in heavier odd-A lead isotopes, the cascade in Pb-187 is associated with the sequence of three E2 transitions from the yrast 25/2(+) level to a low-lying 13/2(+) isomer. The variation of excitation energy with mass number of the levels concerned suggests that their structure can be associated with weak coupling of an odd i(13/2) neutron to states in the spherical well. However, the possibility that they are influenced by mixing with states in the prolate-deformed well cannot be discounted. [S0556-2813(98)00411-7].

The reactions {sup 152}Sm({sup 7}Li,4n) at 45 MeV and {sup 124}Sn({sup 36}S,p4n) at 165 MeV were used to study high-spin states of the N=90 nucleus {sup 155}Tb. Previously known bands have been greatly extended in spin (I{approx}45{h_bar}) and a new decoupled sequence was identified. Several band crossings or quasiparticle alignments have been observed in each of the structures, and as a result a configuration assignment has been given to the new band. B(M1)/B(E2) transition strength ratios have been extracted from the data and comparisons were made with theoretical predictions. A comprehensive analysis of the signature splitting in the energy levels and B(M1)/B(E2) ratios for the {pi}h{sub 11/2} bands of the A{approx}160 region has been performed. Possible interpretations for the observed trends in the signature splitting of these structures are discussed. {copyright} {ital 1998} {ital The American Physical Society}

Two superdeformed bands of 10 transitions each have been found in {sup 189}Tl extending the mass 190 region of superdeformation down to neutron number N=108. The new bands can be interpreted as signature partners and are proposed to be based on a proton i{sub 13/2} ({Omega}=5/2) configuration, in analogy with the yrast superdeformed band structures in the heavier odd-mass Tl isotopes. The dynamic moments of inertia of all these bands show no noticeable differences as function of N, consistent with an essentially constant quadrupole deformation from the center of the island to its edges. {copyright} {ital 1998} {ital The American Physical Society}

The nucleus {sup 102}Sn, which is the lightest Sn isotope with known excited states, was investigated with the {sup 50}Cr({sup 58}Ni,{alpha}2n) reaction using delayed in-beam {gamma}-ray and conversion-electron spectroscopy. The experimental setup was designed to study the decay of {micro}s-long isomeric states by placing {gamma}-ray and electron detectors behind the focal plane of the Fragment Mass Analyzer at the Argonne National Laboratory. A 44 keV conversion-electron line corresponding to the (6{sup +}){yields}(4{sup +}) transition in {sup 102}Sn was identified and a half-life of 0.62{sup +0.43}{sub -0.19} {micro}s was measured for the (6{sup +}) state. From the available experimental information neutron effective charges from 1.6 to 2.3 e were deduced, based on the comparison with different shell-model calculations.

The highest-spin discrete states ( I ∼60 ℏ and E x ∼30 MeV) in normal deformed nuclei have been observed in the rare-earth isotope 156 Dy using the 124 Sn( 36 S,4n) reaction in conjunction with the GAMMASPHERE spectrometer. The positive parity yrast sequence appears to evolve smoothly from a prolate (collective) towards an oblate (non-collective) shape, in contrast to the sudden shape change observed in the isotone 158 Er. Terminating states are identified in the negative parity sequences at I π =52 − and 53 − and specific multi-particle-hole configurations are assigned by comparison with cranked Nilsson-Strutinsky calculations. An order of magnitude increase in the interaction strength between close lying high-spin weakly collective structures is determined compared with that found in the lower-spin strongly collective domain. These results give valuable insight into the interplay between collective and terminating structures, and their competition for yrast status in the 40−60 ℏ spin range.

Five superdeformed (SD) bands have been observed in ${}^{149}\mathrm{Tb},$ using the Gammasphere spectrometer. The measurement was performed with a backed target to obtain lifetime information from a Doppler-shift attenuation method analysis. It is proposed that the yrast SD band corresponds to the ${}^{148}\mathrm{Gd}(\mathrm{yrast})\ensuremath{\bigotimes}\ensuremath{\pi}{6}^{3}$ intruder configuration. The first excited band (band 2) is found to be identical to the ${}^{150}\mathrm{Tb}$ yrast SD band. Band 3 is proposed to correspond to the $\ensuremath{\pi}[301]1/2(\ensuremath{\alpha}=\ensuremath{-}1/2)\ensuremath{\rightarrow}[651]3/2(\ensuremath{\alpha}=\ensuremath{-}1/2)$ proton-hole excitation coupled to the $\ensuremath{\pi}{6}^{4}\ensuremath{\nu}{7}^{1}(\ensuremath{\nu}[651]{1/2)}^{\ensuremath{-}1}$ intruder configuration. Bands 4 and 5, the weakest SD bands seen in the present work, show similarities with band 3 and are most likely associated with a similar intruder configuration.

The high-spin level structures of {sup 94,95}Mo (N=52,53) have been investigated via the {sup 65}Cu({sup 36}S, {alpha}p2n){sup 94}Mo and {sup 65}Cu({sup 36}S, {alpha}pn){sup 95}Mo reactions at 142 MeV. The level schemes have been extended up to spin J{approx}19{h_bar} and excitation energies E{sub x}{approx}12 MeV. Spherical shell-model calculations have been performed and compared with the experimental energy levels. The level structure of {sup 94}Mo exhibits a single-particle nature and the higher-angular-momentum states are dominated by the excitation of a g{sub 9/2} neutron across the N=50 shell gap. The level sequences observed in {sup 95}Mo have been interpreted on the basis of the spherical shell model and weak coupling of a d{sub 5/2} or a g{sub 7/2} neutron to the {sup 94}Mo core. {copyright} {ital 1998} {ital The American Physical Society}

New high-spin isomers in 175 Lu, 181 Ta and 186 W target nuclei have been strongly excited by pulsed 238 U beams. The use of inelastic excitation opens up an uncharted region in the neutron-rich K-isomer landscape. First results establish the key role of multi-quasiparticle configurations in the high-angular-momentum structure.

Quadrupole moments of the six known superdeformed (SD) bands of {sup 193}Hg and the yrast SD band of {sup 192}Hg have been determined by a Doppler-shift-attenuation-method measurement utilizing the gammasphere array. The quadrupole moments of all {sup 193}Hg SD bands were found to be similar, suggesting the active single-particle orbitals in the mass-190 region exhibit only small shape-driving effects. Additionally, there is evidence for an unexpected difference in the quadrupole moments of SD bands in {sup 192}Hg and {sup 193}Hg. {copyright} {ital 1998} {ital The American Physical Society}

Superdeformation studies in {sup 189,191,192}Tl at Gammasphere are discussed. New results on {sup 191}Tl are the observation of interband transitions between the signature partner E2 bands and the measurement of an average quadrupole moment (Q{sub 0} = 18 {+-} 1 eb) for these superdeformed structures. These data enable them to derive absolute M1 strengths and confirm that the 81st proton occupies the [642]5/2 orbital. Tentative data for one superdeformed sequence in {sup 189}Tl are consistent with the prediction of a decrease in quadrupole deformation for the lightest nuclei at the limit of this island of superdeformation.

The single-particle character of states outside the doubly magic (radioactive) nucleus {sup 56}Ni has been determined through a measurement of the (d,p) neutron transfer reaction using inverse kinematics. From the spectroscopic factors of the low-lying states in {sup 57}Ni , the astrophysically interesting yield for the {sup 56}Ni( p,{gamma}) reaction to the mirror nucleus {sup 57}Cu has been calculated, utilizing charge symmetry. The rate for this reaction in the temperature range typical of novae, supernovae, and x-ray bursts is found to be more than 10 times higher than previously assumed. {copyright} {ital 1998} {ital The American Physical Society}

Lifetime measurements with the Doppler shift attenuation method have been performed for the two superdeformed (SD) bands of 142Sm. The inferred transition quadrupole moments, Q0, are 11.7±0.1 eb for the yrast SD band and 13.2+0.8−0.7 eb for the excited SD band. These results are consistent with expectations from mean-field calculations, and indicate that the proposed additivity of contributions of individual orbitals to Q0 is valid for SD nuclei over an extended mass range in the vicinity of 152Dy.

The high-spin level structures of {sup 96,97,98}Ru (Z=44) have been investigated using the {sup 65}Cu({sup 36}S,pxn){sup 96,97,98}Ru (x=4,3,2) reactions. About 130 new transitions have been observed and unambiguously placed in the decay schemes of these nuclei. The level schemes have been extended up to spin J{approx}22{endash} 34{h_bar}, and excitation energies E{sub x}{approx}20{minus}24 MeV. Spherical shell model calculations have been performed and theoretical level energies compared with experimental values. Calculations using {sup 88}Sr as the core give a reasonable agreement for the observed energy levels up to J{le}16{h_bar} (the maximum angular momentum possible within this restricted model space). The higher angular momentum states are dominated by the {nu}(g{sub 9/2}){sup {minus}1} configuration, associated with breaking of the N=50 core. The experimental indications for this `core breaking` are (i) the observation of {gamma} rays with energies E{sub {gamma}}{approx} 2 MeV at intermediate spins and (ii) the fragmentation of {gamma}-ray intensity into a number of branches. A cascade of E2 transitions of nearly equal transition energies has been observed in {sup 98}Ru after the core breaking (J{ge}16{h_bar}), possibly manifesting vibrational behavior. {copyright} {ital 1998} {ital The American Physical Society}

An excited superdeformed band in {sup 194}Hg , observed to decay directly to both normal-deformed and superdeformed yrast states, is proposed to be a K{sup {pi}}=2{sup {minus}} octupole vibrational band, based on its excitation energies, spins, and likely parity. The transition energies are identical to those of the yrast superdeformed band in {sup 192}Hg , but originate from levels with different spins and parities. The evolution of transition energies with spin suggests that cancellations between pairing and particle alignment are partly responsible for the identical transition energies. {copyright} {ital 1997} {ital The American Physical Society}

The Doppler-shift attenuation method was used to measure lifetimes of superdeformed (SD) states for both the yrast and the first excited superdeformed band of 190Hg. Intrinsic quadrupole moments Q o were extracted. For the first time, the dipole transition rates have been extracted for the inter-band transitions which connect the excited SD band to the yrast states in the second minimum. The results support the interpretation of the excited SD band as a rotational band built on an octupole vibration.

One-step decay transitions linking the superdeformed (SD) bands 1 and 3 in194Hg to yrast levels are discussed. Inter-band transitions between bands 1 and 3 have also been identified. For the first time, the spin, parity and excitation energy have been determined for two SD bands in the same nucleus. The low excitation energy of the excited band supports the view that it is based on an octupole excitation. It is believed that Porter-Thomas fluctuations play a major role in determining the strength of the one-step transitions as suggested by the fact that only one other SD band has been linked in theA=190 mass region (194Pb) at the present time. When Porter-Thomas fluctuations prevent the observation of one-step or two-step linking transitions, as e.g. in the case of192Hg, the analysis of the quasi-continuous part of the decay-out spectrum provides an alternative method for the determination of the excitation energy and spin of an SD band. This method is discussed in detail.

In-beam γ-ray transitions in 181Hg, the lightest odd-A Hg isotope known thus far, have been identified from fragment mass-γ and γ-γ coincidence measurements. Five prolate deformed rotational bands were placed in the level scheme. A decoupled band built on the strongly prolate deformed 1 2 − [521] ground state was observed up to 29 2 − . A 5 2 − [512] configuration is suggested for a pair of strongly coupled bands displaying no signature splitting. The other two bands are also signature partner bands. They are populated with the largest intensity and exhibit splitting. They have been associated with the mixed neutron i 13 2 orbitals and are proposed to decay to an i 13 2 isomeric state associated with an oblate state.

Excited states have been observed for the first time in the neutron-deficient {sup 176,178}Hg nuclei using the recoil-decay tagging (RDT) technique in which prompt {gamma} rays are associated with a particular isotope through a correlation with the characteristic ground state {alpha} decay. Below N=102, the excitation energy of a rotational band built on a prolate shape ({beta}{sub 2}{approximately}0.25) increases with decreasing mass to the point where there is no longer any evidence for its presence at low spin in {sup 176}Hg. The data are in qualitative agreement with recent mean field calculations. {copyright} {ital 1997} {ital The American Physical Society}

Gamma rays from the decay of states in the proton unstable nucleus {sup 147}Tm were observed for the first time following the {sup 92}Mo({sup 58}Ni,p2n){sup 147}Tm reaction at 260 MeV. Prompt {gamma} rays were detected with an array of Compton-suppressed Ge detectors, placed in front of the fragment mass analyzer at the ATLAS accelerator, and were assigned to individual reaction channels on an event-by-event basis using the recoil-decay tagging method. Gamma-ray transitions were associated with both the proton decay of the {pi}h{sub 11/2} ground state and the {pi}d{sub 3/2} isomeric state in {sup 147}Tm, even though the cross sections for populating these states were only {approx} 16 {mu}b and 2 {mu}b, respectively. The level scheme which was constructed for {sup 147}Tm is discussed and compared with the level structures for lighter N=78 isotones. {copyright} {ital 1997} {ital The American Physical Society}

High-precision lifetime measurements have been performed in superdeformed (SD) bands of {sup 192,194}Hg with the Doppler-shift attenuation method. Intrinsic quadrupole moments Q{sub 0} were extracted for three SD bands in {sup 194}Hg and for the yrast SD band in {sup 192}Hg. Within experimental uncertainties, all four SD bands have equal Q{sub 0} values. These results provide constraints on differences in Q{sub 0} values between the {open_quotes}identical{close_quotes} SD bands {sup 194}Hg(3) and {sup 192}Hg(1). {copyright} {ital 1997} {ital The American Physical Society}

Excitations in {sup 192}Po have been studied via in-beam {gamma}-ray spectroscopy following the {sup 164}Er + 164 MeV {sup 32}S reaction. The experiment was performed at the ATLAS facility using ten Compton-suppressed Ge detectors and the Fragment Mass Analyzer. The {alpha} decay of {sup 192}Po has been used to identify prompt {gamma}-ray transitions by means of the recoil decay tagging technique. The first three excited states of {sup 192}Po were established. The particle-core model has been successfully used to model these excitations and the quasiparticle random phase approximation has been applied to extract microscopic wave functions of the 2{sub 1}{sup +} states. {copyright} {ital 1997} {ital The American Physical Society}

Four new superdeformed bands have been observed with the Gammasphere array and have been assigned to the {sup 195}Hg nucleus. Two of the bands are interpreted as signature partners most likely based on N{sub osc}=6 neutron quasiparticles coupled to a superdeformed core, while the other two appear to be based on a j{sub 15/2} intruder orbital. These four bands do not exhibit a simple, {open_quotes}identical bands{close_quotes} relationship to other superdeformed bands in this mass region. {copyright} {ital 1997} {ital The American Physical Society}

The presence of {Delta}{ital I}=2 staggering in the three known superdeformed (SD) bands of {sup 194}Hg has been reexamined in a new experiment with Gammasphere. A relative precision of better than 60eV was achieved for most transition energies. Staggering plots were extracted and their statistical significance was analyzed. No clear evidence was found for an extended regular {Delta}{ital I}=2 staggering in the three SD bands of {sup 194}Hg. However, statistically significant deviations from a smooth reference were observed in the two excited SD bands. Different scenarios are discussed but no firm conclusion about the origin of the observed deviations can be drawn. {copyright} {ital 1996 The American Physical Society.}

The fully energy-damped yields for the {sup 36}Ar + {sup 12}C and {sup 20}Ne + {sup 28}Si reactions at E{sub c.m.}=47.0 MeV and 45.5 MeV, respectively, are explored using particle-particle-{gamma} coincidence data. These reactions reach a similar excitation energy of E{sub CN}*=59.5 MeV in the {sup 48}Cr compound nucleus as was obtained in an earlier particle-particle coincidence study of the {sup 24}Mg + {sup 24}Mg reaction. The overall mass and total kinetic energy distributions of the fission fragments are found to be well reproduced by statistical-model calculations. These calculations are also found to reproduce structure seen in the excitation-energy spectra for the {sup 20}Ne + {sup 28}Si and {sup 24}Mg + {sup 24}Mg exit channels for all three reactions. In previous excitation-function measurements, strong heavy-ion resonance behavior has been observed in elastic and inelastic cross sections for the {sup 24}Mg + {sup 24}Mg system. There has been speculation that peaks observed in the corresponding excitation-energy spectra at more negative Q values may also be a consequence of this resonance phenomenon. The observation of very similar behavior with the asymmetric-mass entrance channels makes it less likely, though, that the peaks arise from any special configuration of the compound system. Instead, anmore » analysis of the {gamma}-ray data and the results of statistical-model calculations support the conclusion that most of the observed high-lying structure can be accounted for in terms of statistical fission from a fully energy- and shape-equilibrated compound nucleus. For the {sup 24}Mg + {sup 24}Mg entrance channel, however, comparisons with the statistical model indicate a reduction of high-angular-momentum partial cross sections, leading to the {sup 24}Mg + {sup 24}Mg fission channel. For the first time, we are able to deduce the nature of the competition between the resonance and statistical-fission mechanisms in this mass region.« less

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.}

Superdeformed (SD) states of {sup 190}Hg have been studied with the Eurogam Phase 2 {gamma}-ray spectrometer using the {sup 160}Gd({sup 34}S,4{ital n}) reaction. Two new excited SD bands have been found and identified as belonging to this nucleus, bringing the total number of SD bands in {sup 190}Hg to 4. One of the new bands has a dynamic moment of inertia that is very similar to that of the yrast SD band of {sup 190}Hg and most other SD bands in the {ital A}{approximately}190 region. In contrast, the other band has a dynamic moment of inertia which is mainly constant as a function of rotational frequency and exhibits a dramatic increase at the lowest frequencies. The observed dynamic moments of inertia are compared with the results of random phase approximation calculations based on the cranked shell model. Finally, the known excited SD band has been extended towards lower frequencies and new transitions have been found linking this band to the yrast SD band. The extracted {ital B}({ital E}1) values of the new linking transitions give further support for the possible octupole vibrational character of this band. {copyright} {ital 1996 The American Physical Society.}

Four superdeformed bands have been confirmed in {sup 192}Tl. Two of these bands have I{sup (2)} dynamic moments of inertia which are nearly constant with rotational frequency {h_bar}{omega}. The other two bands show the characteristic rise of I{sup (2)} with increasing {h_bar}{omega} seen in most superdeformed bands of the {ital A} = 190 region of superdeformation. From comparisons with the odd-{ital A} neighbors, it was found that the alignments of these bands relative to a {sup 192}Hg core can be accounted for from the additive contributions of the assigned quasiproton and quasineutron orbitals. {copyright} {ital 1996 The American Physical Society.}

Discrete {gamma} rays directly connecting states of a superdeformed (SD) band in {sup 194}Hg to the yrast states have been discovered. Thus, the excitation energies and spins of all members of the lowest SD band are established for the first time, together with their likely parity. The SD band decays from its 10{sup +} and 12{sup +} states, which lie 4204.8 and 4407.4 keV above the normal-deformed yrast states of the same spins. {copyright} {ital 1996 The American Physical Society.}

Prompt, in-beam γ rays following the reaction Yb170 + 142 MeV Si28 were measured at the ATLAS facility using 10 Compton-suppressed Ge detectors and the Fragment Mass Analyzer. Transitions in Po194 were identified and placed using γ-ray singles and coincidence data gated on the mass of the evaporation residues. A level spectrum up to J10 was established. The structure of Po194 is more collective than that observed in the heavier polonium isotopes and indicates that the structure has started to evolve toward the more collective nature expected for deformed nuclei. © 1995 The American Physical Society.

Two new superdeformed (SD) bands have been observed in Tb-150 using the reaction P-31 + Sn-124 and the GAMMASPHERE detector array. These new bands are interpreted as being excited SD configurations ...

A new superdeformed band has been identified in {sup 191}Hg bringing the total number of bands observed in this nucleus to four. The new band has properties similar to those of a superdeformed band reported recently in {sup 193}Hg. Both bands are believed to be built on the unfavored signature of the {ital j}{sub 15/2} intruder configuration. Comparisons between the data and cranked Woods-Saxon calculations highlight the strengths and weaknesses of theory in describing high-{ital N} orbitals at large deformation.

An experiment using the Eurogam phase II \ensuremath{\gamma}-ray spectrometer confirms the existence of an excited superdeformed (SD) band in $^{190}\mathrm{Hg}$ and its very unusual decay into the lowest SD band over 3--4 transitions. The energies of the transitions linking the two SD bands have been firmly established, and their angular distributions are consistent with a dipole character. Comparisons with calculations using random-phase approximation indicate that the excited SD band can be interpreted as an octupole-vibrational structure.

A superdeformed band has been found in the [sup 154]Dy ([ital N]=88) nucleus. The dynamic moment of inertia is identical to that of the yrast superdeformed band of [sup 152]Dy and the transition energies are similar to those of an excited superdeformed band in [sup 153]Dy. It is proposed that the two valence neutrons above the [ital N]=86 shell gap occupy the deformation-driving [514]9/2 orbital.

The region of nuclei with mass {approximately} 190 was studied extensively over the last few years following the discovery of superdeformation in {sup 190}Hg. More recently, considerable interest in the neutron-deficient Pb isotopes developed with the discover of a number of bands at high spin connected by dipole transitions in both even {sup 192-200}Pb and odd {sup 197-201}Pb nuclei. The majority of the dipole bands are regular in character (i.e. transition energies increase smoothly with spin) while the remaining bands are referred to as irregular in character, due to the fact that the transition energies do not increase smoothly with spin. The properties of the dipole bands were interpreted in terms of high-K, moderately-deformed oblate states built on configurations involving high-J, shape-driving quasiproton excitations coupled to rotation-aligned quasineutrons. It was suggested that the difference between the regular and irregular dipole sequences is related to the deformation where the irregular sequences are thought to be less collective than their regular counterparts.

The low-lying level structure of the neutron-deficient isotope [sup 202]Rn has been studied for the first time, using the [sup 181]Ta([sup 27]Al,6[ital n]) and [sup 192]Pt([sup 16]O,6[ital n]) reactions. Gamma-ray transitions between excited states in [sup 202]Rn were identified by mass tagging using a recoil mass separator, the Argonne Fragment Mass Analyzer, and by observation of coincident x rays. Transitions in [sup 203]Rn were also identified. The level scheme deduced from these data is consistent with the systematics of light radon isotopes below the [ital N]=126 shell closure and with theoretical calculations indicating that the ground-state shape should not be strongly deformed at [ital N]=116.

An excited superdeformed (SD) band has been observed in 190 Hg which decays to the lowest-energy (yrast) SD band rather than to the less deformed states as observed in most known SD bands in the A ∼ 150 and A ∼ 190 regions. The most plausible interpretation of this very unusual decay pattern associates this band with a collective structure built on an octupole-vibrational phonon in the SD well.

High spin states in the very neutron-deficient isotopes 185Tl and 187Tl have been identified from γ-γ coincidence measurements performed with the reactions 154Gd(35Cl, 4n) and 159Tb(32S, 4n). Unambigous mass assignments were obtained using a Fragment Mass Analyzer and the reactions 154Gd(36Ar, p4n and 155Gd(36Ar, p3n). Struvtures are observed corresponding to both an i 13 2 proton coupled to a prolate deformed core, and also h 9 2 and i 13 2 protons coupled to an oblate defo rmed core. The proposed 13 2 + [606] intrinsic states are isometric, with meanlives of 12±2 ns in 185Tl and 1.0±0.2 ns in 187Tl. Eq uilibrium deformation calculations for the excitation energies of intrinsic states reproduce general trends, but overestimate the bandhead energies of high-j states.