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The magnitudes and signs of twenty eight E2 and three M1 matrix elements involving 17 low-lying excited states in 104Ru have been measured by Coulomb excitation using 208Pb, 136Xe and 58Ni ions. The completeness of the set of E2 matrix elements is sufficient to extract, directly from the data, the expectation values of the intrinsic-frame E2 moments that provide considerable insight into the underlying collectivity. The measured E2 properties strongly correlate with macroscopic quadrupole collective degrees of freedom. Detailed comparison of the experimental results and theoretical microscopic calculations within the general quadrupole collective Bohr Hamiltonian are presented. Very good agreement of calculations and experiment is achieved without any parameters fitted to the 104Ru experimental data. Results of phenomenological γ-unstable and γ-rigid models are also given.

GRETINA is a high precision gamma-ray detector for nuclear spectroscopy experiments, which is currently being developed. It consists of a number of highly segmented coaxial germanium detectors arranged in a close-packed configuration. GRETINA uses digital signal processing electronics and pulse shape analysis to determine the energy and position of each individual interaction resulting from the gamma-ray absorption. Gamma-ray tracking is then used to reconstruct the gamma-ray scattering sequence. This results in high efficiency, peak-to-total ratio and position resolution. Particularly, the capability of reconstructing the position of the interaction with resolution at the level of a few millimeters is a fundamental requirement and is important to understand and quantify limiting factors of position resolution. This paper reports on the effects of neutron damage on pulse shape and on its impact on position resolution. Simulation results show that even a relatively heavily damaged detector maintains high position resolution. Only for neutron flux >6 × 109 neutron/cm2, the position resolution becomes worse than 1 mm, which is the achievable limit.

Fast neutrons damage the lattice structure of germanium γ-radiation detectors and introduce hole traps. This results in a reduction of charge collection efficiency and a degradation of the energy resolution of the detector. For tracking detectors that use pulse shapes to determine the position of γ-ray interactions, it is important to study the effect of neutron damage on pulse shapes and to quantify the achievable position resolution. In this work, the effect of neutron damage on energy, position and time resolution has been calculated for both an n-type and a p-type detector, and a method for correcting the energy loss using the information on the position of the interaction has been tested. Calculations indicate that the energy resolution of a neutron-damaged n-type detector is superior to that of a similarly damaged p-type detector, while the position resolution does not depend on the detector type. For both n- and p-type coaxial detectors the detectable degradation of energy resolution occurs at a much lower neutron flux than the degradation of position resolution: in practice, a measurable effect of neutron damage on position resolution is never reached before annealing is required for recovering energy resolution.

A gamma-ray energy tracking array (GRETA) is a new concept for the detection of gamma radiation. In such an array, the individual interactions of all the gamma rays are identified by their energies and positions. Then, using tracking algorithms based on the properties of gamma ray interactions, the scattering sequences are reconstructed. GRETA will give high peak efficiency, peak-to-background ratio, and position resolution. Recent research and development efforts have demonstrated that the construction of a gamma ray tracking array is feasible, and a plan for constructing a US array GRETINA is in place.

High-spin states in 112Pd were studied using prompt γ-ray spectroscopy with Gammasphere following heavy-ion-induced fission in the reaction 18O + 208Pb at 91 MeV. A new 8+ level at 2638 keV was discovered with transitions connecting it to the yrast band and the quasi-gamma band. The three, now established, closely spaced 8+ states indicate a mixing between the ground-state band, s-band, and quasi-gamma band. Several high-spin structures with likely negative parity have been extended to higher spin and it is proposed that they are based on the νh 11/2(g 7/2 d 5/2) and νh 11/2(s 1/2 d 3/2) configurations.

High-spin states in 197Pb and 198Pb were populated in the 186W(18O ,x n) reactions. In-beam γ -ray coincidences were measured in two experiments using the Gammasphere and the Eurogam II spectrometer arrays, respectively. In both nuclei new bands of enhanced magnetic dipole transitions were found and the known cascades were partly reordered and extended to higher spins. In most cases, γ -ray transitions connecting the magnetic rotational bands to lower-lying states have been identified. Configuration assignments are suggested for the bands. The systematic behavior confirms the shears mechanism. An effective interaction between the main high-spin proton and neutron orbitals is derived.

High-spin states have been studied in neutron-rich nuclei produced in deep-inelastic collisions between a pulsed beam of Pb ions and a U target. The structure of nuclei such as Hg, Pb and Bi has revealed new information on the couplings of single-particle states to each other and to the octupole-vibrational phonon, essential input to the nuclear shell model. In addition, the first observations of high-spin states in U, U and U are compared to recent results for neighbouring plutonium nuclei.

A superdeformed rotational band has been identified in ${}^{36}\mathrm{Ar}$, linked to known low-spin states, and observed to its high-spin termination at ${I}^{\ensuremath{\pi}}{\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}16}^{+}$. Cranked Nilsson-Strutinsky and spherical shell model calculations assign the band to a configuration in which four $\mathrm{pf}$-shell orbitals are occupied, leading to a low-spin deformation ${\ensuremath{\beta}}_{2}\ensuremath{\approx}0.45$. Two major shells are active for both protons and neutrons, yet the valence space remains small enough to be confronted with the shell model. This band thus provides an ideal case to study the microscopic structure of collective rotational motion.

Measured- and simulated-pulse shapes in electrically segmented coaxial Ge detectors have been investigated. Three-dimensional position sensitivities have been determined experimentally and theoretically in a 36-fold segmented Ge detector. By using the two-dimensional segmentation in conjunction with pulse-shape analysis, a position sensitivity of better than 1 mm can be obtained in three dimensions at an energy of 374 keV. This is achieved by analyzing the shape of net charge signals of segments containing interactions and of transient image charge signals of neighboring segments. The ability to locate interactions in three-dimensions is one of the crucial properties in the proposed γ-ray energy tracking array (GRETA). The concept of γ-ray tracking will not only increase the efficiency in detecting γ radiation but also enables the localization and characterization of unknown γ-ray sources with much higher accuracy than is possible with current instruments.

A working, two-dimensionally segmented Ge detector is one of the crucial elements in the development of GRETA – a next-generation 4π germanium detector array that uses three-dimensional positions and energies to of individual interactions of γ rays in the detector to reconstruct the full energies and direction vectors of the individual γ rays by employing tracking algorithms. The three-dimensional position and the energy of interactions will be determined by using a two-dimensionally segmented Ge detector along with pulse-shape analysis of the signals. The current prototype is a 36-fold segmented HP-Ge detector in a closed-ended coaxial geometry. Preamplifiers with a compact design, low noise, and very good response properties have been built and implemented. An integrated noise level of about 5 keV has been measured for the segment channels. The average energy resolution of this detector was measured to be 1.14 and 1.93 keV at 60 and 1332 keV, respectively. Using pulse-shape analysis, a three-dimensional position sensitivity of 0.2 to 0.5 mm (R.M.S) has been obtained at 374 keV, dependent on the position and the direction. The results represent a major step towards the feasibility of a γ-ray tracking detector.

We present a new analysis of the pairing vibrations around 56Ni, with emphasis on odd-odd nuclei. This analysis of the experimental excitation energies is based on the subtraction of average properties that include the full symmetry energy together with volume, surface and Coulomb terms. The results clearly indicate a collective behavior of the isovector pairing vibrations and do not support any appreciable collectivity in the isoscalar channel., Comment: RevTeX, two-column, 5 pages, 4 figures

Lifetimes of states in the two strongest superdeformed (SD) bands in 193Tl were measured using the Doppler-shift attenuation method. The reaction 176Yb(23Na,6n)193Tl at a beam energy of 129 MeV was used and γ-rays were detected by the Gammasphere array. Quadrupole moments of 18.3(10) eb and 17.4(10) eb were extracted for SD bands 1 and 2, respectively, using the fractional Doppler-shifts of the SD transitions. The previously reported linking transitions of these SD bands to normal deformed near yrast levels could not be confirmed. No other candidates for linking transitions could be established.

We present a new concept for c-ray detector arrays. An example, called GRETA (Gamma-Ray Energy Tracking Array), consists of highly segmented HPGe detectors covering 4p solid angle. The new feature is the ability to track the scattering sequence of incident c-rays and in every event, this potentially allows one to measure with high resolution the energy deposited, the location (incident angle) and the time of each c-ray that hits the array. GRETA will be of order of 1000 times more powerful than the best present arrays, such as Gammasphere or Euroball, and will provide access to new physics. ( 1999 Published by Elsevier Science B.V. All rights reserved.

We discuss a γ-ray tracking algorithm that has been developed for the proposed gamma-ray energy tracking array (GRETA). This algorithm has been designed so as to maximize the resolving power for detecting high-multiplicity γ-ray events. The conceptual basis for this algorithm will be presented. In addition, Monte Carlo simulated data will be used to assess performance over a large range of relevant parameters. A discussion of the potential γ-ray polarimeter performance of GRETA is also presented.

Lifetimes of states in a rotational-like $M1$ band in ${}^{110}\mathrm{Cd}$ have been determined through a Doppler-shift attenuation method measurement performed with the Gammasphere array. The deduced $B(M1)$ values, which agree well with the predictions of the tilted axis cranking model, clearly confirm that it has the character of a shears band. Using a semiclassical scheme of the coupling of two long $j$ vectors we deduce information on the strength and form of the effective interaction between the constituent nucleons. These results are the first definitive evidence of the shears mechanism and ``magnetic rotation'' in this mass region.

We present a model study of the competition between the shears mechanism and the rotation of the core. This is done in the framework of a classical solution of a Particles-plus-Rotor Model. The competition is governed by the relative strength of the residual interaction between the blades in the shears and the rotational energy of the core. The results are summarized in terms of a “phase-diagram” of these two modes of rotation that is applicable for all mass regions. We find that in order for the shears mechanism to dominate, the deformation of the core has to be ϵ ≲0.12.

Light-actinide nuclei in the octupole deformed region have been populated using multi-nucleon transfer from Th. The energy level schemes of several thorium isotopes with A = 228-234 have been extended up to and negative parity states have been observed for the first time in Th. A systematic study of the difference in alignment between the positive- and negative-parity bands in thorium nuclei in this mass region shows that Th behave like octupole vibrators, in contrast with Th, which are octupole-deformed in character. An intrinsic electric dipole moment has been measured for the first time in Th. The small value obtained is consistent with the vibrational description of this nucleus.

High-spin spectroscopy of Rn, Ra and Th isotopes has been performed. The nuclei have been populated using multi-nucleon transfer reactions involving a 232 Th target and a 136 Xe projectile. This type of reaction offers the only mechanism for populating high-spin states in many of these nuclei. Interleaving bands with opposite parities have been observed to high spin ( ∼28 h ) in 218,220,222 Rn, 222,224,226,228 Ra and 228,230,234 Th. A systematic study of the rotational alignment properties of octupole bands in radon, radium and thorium isotopes reveals information concerning the role of the octupole phonon and the onset of stable octupole deformation with increasing rotational frequency. Measurement of the magnitude of the intrinsic electric dipole moment, D 0 , provides additional information concerning the strength of octupole interactions in these nuclei.

The Doppler shift attenuation method has been used to determined the transition quadrupole moment of a triaxial band belonging to the γ-soft nucleus,133Ce. Doppler broadened lineshape (DBLS) analysis has revealed the magnitude of theQt value, to be ∼ 2.4 eb. This contribution provides new information of (i) the transition quadrupole moment of this band (ii) the life-times of in-band and sidefeeding transition and (iii) the relative deformations of coexisting nuclear shapes.

An experiment designed to populate two-phonon vibrational states in {sup 208}Pb by Coulomb excitation was performed with a {sup 136}Xe beam at a bombarding energy of 650 MeV. The {gamma} rays from the decay of the excited states were measured with Gammasphere and scattered particles were detected in the compact heavy-ion counter CHICO. We have not been able to observe any state close to the expected harmonic energy of 5.2 MeV. However, we were able to extract the B(E3,3{sub 1}{sup {minus}}{r_arrow}6{sub 1}{sup +}) value for the lowest known 6{sup +} state at 4.424 MeV based on measured {gamma}-ray intensities. About 20{percent} of the expected total E3 strength can be found in this state, suggesting a large fragmentation of this second octupole phonon state in {sup 208}Pb. Upper limits for the B(E3) strength were determined for higher-lying, but unseen, 6{sup +} states ranging from 15{percent} of the harmonic value at 5.2 MeV to 100{percent} at 6.0 MeV. {copyright} {ital 1998} {ital The American Physical Society}

Lifetimes of states in at least one of the M1 bands in each nucleus from 193−197 Pb have been determined through Doppler-Shift Attenuation Method experiments performed with the Gammasphere array. The nuclei were populated under similar conditions allowing accurate relative measurements of the state lifetimes. The deduced B(M1) values display the characteristic decrease with increasing angular momentum which is a clear signature of the shears mechanism. Combined with the recent results for 198,199 Pb an impressive body of evidence now exists which supports the interpretation of these structures as examples of a new mode of nuclear behavior: `magnetic rotation'.

We present a technique for operating the Gammasphere segmented Ge detectors as γ-ray polarimeters. Using γ-rays of known polarization, we have measured the polarization sensitivity, Q ( E γ ), of these detectors in the energy range E γ =0.4–1.4 MeV. The experimentally obtained value of Q ranges from 5% at 415 keV to 4% at 1368 keV. The magnitude and energy dependence of Q ( E γ ) has also been determined theoretically by means of a Monte Carlo simulation, and the agreement between experiment and theory is within 20% over the energy range measured. In order to investigate the potential for operating Gammasphere as a γ-ray polarimeter in a high background environment (one which is typical of high-spin nuclear structure studies), we also discuss data that we have analyzed from the 176 Yb ( 26 Mg, 5n) 197 Pb reaction at E =135 MeV. Although the polarimeter performance of Gammasphere is seen to be relatively poor, we are still able to demonstrate, by way of γ-ray polarization measurements, that “Shears Band 1” in 197 Pb should have negative parity.

Subpicosecond lifetimes of states near the bandhead of an M1 band in {sup 198}Pb have been measured with the recoil-distance Doppler-shift technique using the Gammasphere array and the Cologne plunger. The deduced B(M1) values are in agreement with the predictions of the tilted axis cranking (TAC) model. Their spin dependence continues the trend set by recently published B(M1) values for the high spin states in this band. The emerging picture gives strong support to the concept of {open_quotes}magnetic rotation,{close_quotes} an alternative mode for the generation of rotational spectra in nuclei. {copyright} {ital 1998} {ital The American Physical Society}

Lifetimes have been measured for states in five superdeformed yrast bands in 193−196 Pb using the Gammasphere spectrometer array. Centroid shifts and lineshapes of transitions showing attenuated Doppler shifts have been analyzed. Transition quadrupole moments are deduced for the five bands including, for the first time, bands of two odd-A Pb isotopes. The quadrupole moments are found to be remarkably similar for the yrast bands in 194 Pb (band 1), 195 Pb (bands 1 and 2) and 196 Pb (band 1) (Q t ≈20 b). However, for 193 Pb a smaller value, Q t =17.3(7) b, is obtained. This can be explained in terms of the occupation of the neutron N = 7 intruder orbitals.

By deriving the angle between the proton and neutron spin vectors ${j}_{\ensuremath{\pi}}$ and ${j}_{\ensuremath{\nu}}$ in the shears bands in ${}^{198,199}\mathrm{Pb},$ we present a semiclassical analysis of the $B(M1)$ and $B(E2)$ transition probabilities as a function of the shears angle. This provides a semiempirical confirmation of the shears mechanism proposed by Frauendorf using the tilted-axis-cranking model. In addition, we propose that the rotational-like behavior observed for these bands may arise from a residual proton-neutron interaction.

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}

High-spin states in 195 Hg have been investigated using the GAMMASPHERE Ge-detector array in its early implementation phase. The level scheme has been extended up to an excitation energy of about 10 MeV and a spin of 71 2 ħ. Three new dipole band structures have been added for which B( M1 , ΔI = 1) B( E2 , ΔI = 2) branching ratios were determined to be of the order of 2 ( μ n eb ) 2 . Possible quasiparticle excitations responsible for these structures are discussed.

The quadrupole moments and deformations have been measured for six superdeformed bands in Gd-150. The results indicate evidence for deformation driving properties of both the high-hi intruder and a ...

The nucleus {sup 168}Yb, and its near neighbors, have been studied at the very highest angular momenta using the full Gammasphere array. The experiment was performed in order to search for evidence for the existence of hyperdeformed states, which have predicted nuclear axis ratios of {approx}3:1. After exhaustive searching for both discrete and continuum {gamma} rays associated with a hyperdeformed shape, using a wide variety of different analysis techniques, no evidence for the existence of hyperdeformation has been found. This search of unprecedented sensitivity has been carried out with the full Gammasphere, and was performed on arguably the best candidate nucleus. A maximum achievable observational limit of {approx}0.02{percent} of the {sup 168}Yb channel has been calculated for this particular experiment, using Monte Carlo simulations of the response of Gammasphere. {copyright} {ital 1997} {ital The American Physical Society}

We report on an experiment to search for the decay of two-phonon octupole vibrational states in ${}^{208}\mathrm{Pb}$ with GAMMASPHERE. A beam of ${}^{154}\mathrm{Sm}$ at a bombarding energy of 1 GeV was used to excite ${}^{208}\mathrm{Pb}$ via quasielastic as well as via deep-inelastic processes. To be independent of the lifetime of the two-phonon state a thin target was used, requiring the measurement of the position of the scattered particles to correct for the Doppler shift of the emitted \ensuremath{\gamma} rays. Scattered particles were detected by a silicon-strip detector covering forward angles. We did not observe any discrete \ensuremath{\gamma} transition in the expected energy range of 2\char21{}3 MeV down to a limit of 20% and 4% of the intensity in the ${5}^{\ensuremath{-}}\ensuremath{\rightarrow}{3}^{\ensuremath{-}}$ transition for quasielastic and deep-inelastic processes, respectively.

We have used the Ca-48+Yb-176 reaction to study the population of high-spin states in neutron-rich nuclei by deep-inelastic reactions. Using Gammasphere, we observed gamma transitions from nuclei s ...

Research and development is proceeding on a new /spl gamma/-ray detector array for nuclear physics: the Gamma-Ray Energy Tracking Array (GRETA). This array will consist of a spherical shell of highly segmented Ge detectors. By obtaining the energy and position of each interaction point, high efficiency and peak-to-total ratios can be obtained as compared with existing arrays. Here we discuss the computer algorithms that are needed to process the raw data and maximize the performance of the array. The results of these algorithms on Monte Carlo simulated data are presented.

The yrast superdeformed band in {sup 194}Pb has been populated using the {sup 174}Yb({sup 25}Mg,5n){sup 194}Pb reaction at E{sub beam}=130 MeV. Decay {gamma} rays were detected using the GAMMASPHERE array at the 88-Inch Cyclotron. Twelve {gamma}-ray transitions have been observed directly linking three members of the {sup 194}Pb yrast superdeformed band to low-lying normal deformed levels. Anisotropy measurements indicate that these linking decays include E1, M1, and mixed M1/E2 multipolarities. The radiative widths deduced are very inhibited, typically B(E1){approximately}10{sup {minus}8} Weisskopf units (W.u.) and B(M1){approximately}10{sup {minus}5} W.u. Without recourse to {ital a priori} assumptions J{sup {pi}}=6{sup +} and E{sub x}=4878.4(3) keV have been unambiguously assigned to the lowest-lying observed superdeformed state (the state populated by the 170-keV intraband transition). The intensity of the observed primaries accounts for 21(2){percent} of the superdeformed band population. {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}

Lifetimes of the 14{sup +}, 12{sup +}, 10{sup +} states and, for the first time, the 8{sup +} state in the yrast superdeformed (SD) band of {sup 194}Pb were measured at Gammasphere with the recoil-distance Doppler-shift method. Constant transition quadrupole moments with an average of 18.8 (11) eb were found at the bottom of the SD band. The decay out of the SD band can be viewed as governed by a small admixture of normal deformed (ND) states to the SD wave function which is assessed for the 8{sup +} and 10{sup +} SD states based on a simple mixing model. The electromagnetic properties of the ND states involved in the decay out are extracted for the first time by investigating the decay strength of the discrete linking transitions. Despite the large intensity of observed linking transitions, the new data show that the decay out of the SD band is statistical in nature. {copyright} {ital 1997} {ital The American Physical Society}

Lifetimes of states in four of the M1 bands in {sup 198,199}Pb have been determined through a Doppler-shift attenuation method measurement performed using the Gammasphere array. The deduced B(M1) values, which are a sensitive probe of the underlying mechanism for generating these sequences, show remarkable agreement with tilted axis cranking (TAC) calculations. The results represent clear evidence for a new concept in nuclear excitations: {open_quotes}magnetic rotation.{close_quote}{close_quote} {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}

High-precision lifetime measurements have been performed in superdeformed (SD) bands of 151,152 Dy and 151 Tb with the Doppler-shift attenuation method. Differences found in the quadrupole moments Q 0 of the yrast SD bands are understood in terms of shape polarization effects by the high- N intruder orbitals. Q 0 moments are also presented for three excited SD bands in 151 Dy. Recent calculations can account for most of the observations.

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.}

Four bands of enhanced dipole transitions, with weak crossovers, have been observed in Pb-195. Three of these bands are connected to the spherical levels. in addition, the spherical level scheme ha ...

E2 collective properties for the low-lying states in 186,188,190,192 Os and 194 Pt have been investigated experimentally by means of Coulomb excitation using 3.3–4.8 MeV/nucleon 40 Ca, 58 Ni, 136 Xe and 208 Pb beams. The deexcitation γ rays following Coulomb excitation were detected in coincidence with the scattered particles. Levels with excitation energies up to 3–4 MeV of the ground-state, γ and 4 + collective bands as well as excited 0 + states were populated in each nucleus studied. A semiclassical Coulomb-excitation least-squares search code GOSIA was used to extract E2 matrix elements from the measured γ-ray yields. For each nucleus studied, a unique and almost complete set of E2 matrix elements for the low-lying states has been determined, which includes both the magnitudes and signs of the transitional and diagonal matrix elements. The completeness of the set of measured E2 matrix elements makes it possible to determine the intrinsic quadrupole deformation for the low-lying states in these nuclei via a model-independent method. The results indicate clearly that the E2 properties for the low-lying states in these nuclei are correlated well using only the quadrupole collective degrees of freedom. The extracted E2 matrix elements are compared with the prediction of various collective models such as the asymmetric rigid rotor model, the γ-soft model of Leander, and the IBA-2 model. These particular models do not reproduce the data satisfactorily, however the general trends of the data are consistent with the descriptions of γ-soft type collective models through a prolate to oblate shape-transition region. That the enhanced B (E2) values between the I ,quasi- K π = 4,4 + state and members of the I ,quasi- K π = 2,2 + band are well reproduced by the γ-soft model is consistent with the interpretation of the I ,quasi- K π = 4,4 + state being a two-phonon γ-vibration excitation.

The quadrupole moments {ital Q}{sub 0} of five superdeformed bands in {sup 131,132}Ce have been established using the Doppler-shift attenuation method; for the first time, we can compare relative deformations of yrast and excited bands in different nuclei to an accuracy of {approx_equal}(57){percent}. Four of the five bands have very similar deformations, while the excited band in {sup 131}Ce has a somewhat larger quadrupole moment. Important new information is presented on the shape-driving force of the {nu}{ital i}{sub 13/2} orbital, the stability of the second minimum with respect to particle excitations, the relative deformations of identical bands, the nature of the sidefeeding, and the time scale of the decay process. {copyright} {ital 1996 The American Physical Society.}

Three experiments using the (174) Yb(Mg-25,5n)Pb-194 reaction have been undertaken at the Early Implementation of Gammasphere to study the decay of known superdeformed states in Pb-194. A single di ...

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.}

The decay of the superdeformed (SD) band in Nd-135 was studied with the early implementation of gamma-sphere. The results suggest that the SD band ''terminates'' at spin 25/2. This termination is e ...

The collective structure of the even-even nuclei 76,80,82 Se has been studied using Coulomb excitation with 16 O, 48 Ti and 208 Pb ions. About 20 E2 matrix elements were determined in each isotope. The measured matrix elements are compared with the predictions of simple geometric and algebraic collective models. The E2 properties and energy level spectra of the 76,80,82 Se nuclei exhibit features characteristic of anharmonic vibrational collective motion. Although the simplest collective vibrational models exhibit the general features of the data, they do not reproduce the fine details. The influence of a number of physical effects on the data was investigated. These include Coulomb-nuclear interference, mutual excitation and the effect due to the semiclassical approximation of the Coulomb-excitation formalism.

We have studied via in-beam gamma-ray spectroscopy Po-196 and Po-198, which are the first neutron-deficient Po isotopes to exhibit a collective low-lying structure. The ratios of yrast state energi ...

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.

Four new superdeformed bands have been observed in $^{195}\mathrm{Pb}$, the first time superdeformation has been observed in an odd-A Pb nucleus. Two of the bands have a dynamic moment of inertia that is nearly constant as a function of \ensuremath{\Elzxh}\ensuremath{\omega}. This is the first time that bands with such behavior have been observed in an odd-A nucleus in the A\ensuremath{\approxeq}190 region and it is interpreted as the result of the blocking of the alignment of neutron pairs.