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Three strongly coupled sequences have been established in Te-110,Te-112 up to high spins. They are interpreted in terms of deformed structures built on proton 1-particle-1-hole excitations that reach termination at I similar to 40h. This is the first observation of smooth terminating dipole structures in this mass region. Lifetime measurements have allowed the extraction of experimental B(M 1; 1 -> I - 1) and B(E2; I -> I - 2) reduced transition rates for one of the dipole bands in Te-110. The results support the deformed interpretation. (c) 2006 Elsevier B.V. All rights reserved.

Excited states have been identified in the very neutron-deficient 122Ce nucleus. This is the first observation of this nucleus and its excited states. The ground-state rotational band has been observed up to spin 14 ℏ. The band has been assigned to 122Ce by detecting gamma rays in coincidence with evaporated charged particles and neutrons. The E ( 2 1 + ) value suggests a rather large ground-state deformation of β 2 = 0.35 , in good agreement with Hartree–Fock–Bogoliubov (HFB) mean-field calculations. The aligned angular momentum of the band has been studied and is compared with those of the neighboring even–even cerium isotopes, and to Woods–Saxon cranking calculations. The non-observation of the π ( h 11 / 2 ) 2 alignment until at least 0.4 MeV/ℏ is consistent with the extracted value of β 2 .

The effects introduced by 4π charged-particle detector arrays such as the Microball on lifetime measurements by Doppler-shift attenuation techniques are discussed. The effect originates from the lower efficiency for detecting charged particles at backward angles. Procedures for correcting for such “bias” are described.

High-spin states in the neutron-deficient isotope Cd-104 were populated using the Cr-50(Ni-58,4p)Cd-104 reaction at a beam energy of 250 MeV The level scheme has been extended using triple gamma-ray coincidences to a spin of 29h and an excitation energy of 18.2 MeV. Several collective structures involving the excitation of h(11/2) neutrons have been observed to spins approaching 30h. The high-spin structure has been compared to the results of cranked Nilsson-Strutinsky calculations.

Excited states have been identified in the very neutron-deficient 112 Xe nucleus. The ground-state band has been observed up to spin 12 ℏ, and a negative-parity side band has been observed up to 13 ℏ. The bands have been assigned to 112 Xe by detecting gamma rays in coincidence with evaporated charged particles and neutrons. The energy of the 2 + 1 state in 112 Xe is lower than would be expected from both calculations and from systematics of the neighboring xenon isotopes, which indicates a larger than expected ground-state deformation. The observations of a low-lying 3 − state and large deduced B (E1) values are suggestive of increased octupole correlations, which may explain the apparently large ground-state deformation. Constrained Hartree–Fock+BCS calculations have been performed which show qualitative agreement with the trend in deformation of the very neutron-deficient xenon isotopes.

Two excited well-deformed bands have been observed in the semi-magic nucleus Ni-58. One of the bands was observed to partially decay by emission of a prompt discrete alpha particle that feeds the 2949 keV 6(+) spherical yrast state in the daughter nucleus Fe-54. This constitutes the first observation of prompt alpha emission from states lying in the deformed secondary minimum of the nuclear potential. gamma -ray linking transitions via several parallel paths establish the spin. parity, and excitation energy of this deformed band in Ni-58.

New sideband partners of the yrast bands built on the $\ensuremath{\pi}{h}_{11/2}\ensuremath{\nu}{h}_{11/2}$ configuration were identified in ${}_{55}\mathrm{Cs}$, ${}_{57}\mathrm{La}$, and ${}_{61}\mathrm{Pm}$ $N\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}75$ isotones of ${}^{134}\mathrm{Pr}$. These bands form with ${}^{134}\mathrm{Pr}$ unique doublet-band systematics suggesting a common basis. Aplanar solutions of 3D tilted axis cranking calculations for triaxial shapes define left- and right-handed chiral systems out of the three angular momenta provided by the valence particles and the core rotation, which leads to spontaneous chiral symmetry breaking and the doublet bands. Small energy differences between the doublet bands suggest collective chiral vibrations.

A high-spin rotational band with 11 gamma -ray transitions has barn observed in Tc-91. The dynamical moment of inertia as well as the transition quadrupole moment of 8.1(-1.4)(+1.9) eb measured for this band show the characteristics of a superdeformed band. However, the shape is more elongated than in the neighbouring A = 80-90 superdeformed nuclei. Theoretical interpretations of the band within the cranked Strutinsky approach based on two different Woods-Saxon potential parameterisations are presented. Even though an unambiguous configuration assignment proved difficult, both calculations indicate a larger deformation and at least three additional high-N intruder orbitals occupied compared to the lighter SD nuclei. (C) 2000 Elsevier Science B.V. All rights reserved.

Comparative measurements of the lifetimes of yrast superdeformed (SD) states in ${}^{80--83}\mathrm{Sr}$, ${}^{83}\mathrm{Y}$, and ${}^{84}\mathrm{Zr}$ have been performed using the Doppler-shift attenuation method. Thus, the transition quadrupole moments ( ${Q}_{t}$) of these structures have been determined accurately. The yrast SD bands in ${}^{80--83}\mathrm{Sr}$ possess ${Q}_{t}\ensuremath{\sim}3.5e\mathrm{b}$, while the ${}^{83}\mathrm{Y}$ and ${}^{84}\mathrm{Zr}$ cases display ${Q}_{t}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}4.4e\mathrm{b}$ and $5.6e\mathrm{b}$, respectively. Intruder orbital assignments based on these results demonstrate a previously unnoticed transition in the structure of the SD bands when the proton number changes from $Z\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}38$ to $Z\ensuremath{\ge}39$.

High-spin states in Mo-88 were studied using the GAMMASPHERE germanium detector array in conjunction with the MICROBALL CsI(TI) charged-particle detector system. Three gamma-ray cascades with dynamic moments of inertia showing similar characteristics to superdeformed rotational bands observed in the neighbouring A = 80 region have been identified and assigned to the nucleus Mo-88. The quadrupole moment of the strongest band, deduced by the Residual Doppler Shift Method, corresponds to a quadrupole deformation of beta(2) approximate to 0.6. This confirms the superdeformed nature of this band. The experimental data are interpreted in the framework of total routhian surface calculations. All three hands are assigned to two-quasi-particle proton configurations at superdeformed shape.

A superdeformed band consisting of a cascade of ten gamma-ray transitions has been identified and assigned to the nucleus Tc-89, close to the proton dripline. The quadrupole moment of the band (Q(t) = 6.7(-2.3)(+3.0) eb, as measured by the Residual Doppler Shift Method) as well as a large dynamic moment of inertia point to a highly elongated shape. With a relative population of approximately 15% of the gamma-ray flux in the Tc-89 exit channel, thp band is among the most intense superdeformed bands observed to date.

High-spin states of the mass A = 39 mirror pair K-39 and Ca-39 were investigated via the fusion-evaporation reaction Si-28+O-16 at 125 MeV beam energy. The GAMMASPHERE array in conjunction with the 4 pi charged-particle detector array MICROBALL and neutron detectors was used to detect gamma rays in coincidence with evaporated light particles. The results of the first high-spin study of the T-z = -1/2 nucleus Ca-39 are discussed in terms of mirror symmetry and compared to spherical shell-model calculations in the 1d(3/2)-1f(7/2) configuration space.

A superdeformed rotational structure is reported in the stable nucleus Zn-68. It has a transition quadrupole moment (Q(t)) of 2.5(-0.4)(+0.7) e b (beta(2) approximate to 0.4), as measured by the residual Doppler shift method. Theoretical calculations suggest that two different configurations are possible candidates for this band. One is built without h(11/2) neutrons, as seen in superdeformed bands in the A similar to 60 region, while the other involves one h(11/2) neutron in analogy with superdeformed bands in the A similar to 80 region. The second of these candidate configurations is preferred, thus establishing a new, neutron-rich (relative to the line of beta stability) region of superdeformation with Z similar to 30 and N similar to 38. (Less)

The quadrupole moments of three decoupled bands in the odd-odd nuclei {sup 130}Pr and {sup 132}Pr were measured using the Doppler shift attenuation method in the bombardment of {sup 105}Pd with {sup 35}Cl at 173 MeV. The {pi}h{sub 11/2}{circle_times}{nu}(f{sub 7/2},h{sub 9/2}) configuration was assigned to these structures on the basis of the observed in-band properties and relative deformations. New information is presented on the shape-driving behavior of the 1/2{sup {minus}}[541] (f{sub 7/2},h{sub 9/2}) intruder neutron orbital, whose involvement in a particular configuration leads to quadrupole deformation values which are intermediate between those known for normally deformed and so-called superdeformed bands in this mass region. {copyright} {ital 1999} {ital The American Physical Society}

The doubly magic superdeformed band in the N = Z nucleus Zn-60 has been identified. Linking transitions connecting this band to the yrast line provide the first spin, parity, and excitation energy measurements for superdeformed states in the A similar to 60 region. The stretched-E2 character and relatively large B(E2) values of these transitions suggest a nonstatistical decay-out process.

High-spin states in Kr-78 were studied using the Ni-58(Na-23,3p) reaction at 70 MeV and the Ni-58(Si-23,alpha 4p) reaction at 130 MeV. Prompt gamma-gamma coincidences were measured using the Pitt-FSU detector array and the GAMMASPHERE-MICROBALL array. Results from these experiments have led to 26 new excitation levels, some of which have been grouped into 3 new bands. Spins were assigned based on directional correlations of oriented nuclei. Two of the new negative-parity bands appear to form a signature-partner pair based on a two-quasineutron structure, in contrast to the previously known two-quasiproton negative-parity bands. A forking has been observed at the 24(+) state in the yrast band, which calculations suggest may result from an unpaired crossing. The available evidence suggests oblate shapes in the yrast band coexist with prolate shapes in the negative-parity bands. [S0556-2813(99)04602-6]. (Less)

High-spin states in Nb-85 were studied using the GAMMASPHERE Ge detector array and the MICROBALL charged-particle detector system. Three gamma-ray cascades with collective rotational characteristics were observed. One of the bands exhibits a forking at the top, most likely reflecting the termination of one branch into a favoured non-collective, near spherical state. The data are interpreted in terms of cranked Strutinsky-type calculations. (C) 1999 Elsevier Science B.V.

High-spin states have been populated in the neutron-deficient {sup 135,136}Sm nuclei via the {sup 105}Pd({sup 35}Cl,pxn) reaction at a beam energy of 180 MeV. Transitions within the Sm nuclei were enhanced by using the Microball charged particle array and {gamma}-ray de-excitation was studied using Gammasphere. A new highly deformed band has been observed in the data and assigned to {sup 136}Sm. Comparison of the properties of the new band with Woods-Saxon cranking calculations suggests that it is built upon a {nu}(i{sub 13/2}){sup 2} configuration. The band shows evidence for an interaction at {h_bar}{omega}{approximately}0.7 MeV. This has tentatively been interpreted as resulting from a crossing between the {alpha}=+1/2 signatures of the [532]5/2 and [541]1/2 proton orbitals. The previously known {nu}i{sub 13/2} intruder band in {sup 135}Sm was also observed and extended to higher rotational frequency. Both structures show good agreement with extended total Routhian surface calculations. {copyright} {ital 1998} {ital The American Physical Society}

We observe for the first time rotational bands of enhanced deformation (ED) in 127 Pr and 128 Pr, and suggest that these bands are built upon πg9/2 ( [404] 9 2 ) in 127 Pr and on the πg9/2νh11/2 orbitals in 128 Pr. These are the lightest isotopes of Pr for which ED bands have been observed. A contrasting trend in the dynamical moments of inertia ( J (2) ) versus N is observed at low frequencies for the “normal-deformed” πh11/2 and “enhanced-deformed” πg9/2 bands of 127 – 131 Pr both experimentally and in self-consistent Woods-Saxon calculations. The trends in J (2) and β2 are correlated with a decreasing probability for pair scattering into the deformation-driving νh9/2/f7/2 ( [541] 1 2 ) orbital.

Gamma rays in the N=Z + 1 nucleus Y-79 were identified using the reaction Si-28(Fe-54, p2n)Y-79 at a 200 MeV beam energy and an experimental setup consisting of an array of Ge detectors and the Recoil Mass Spectrometer at Oak Ridge National Laboratory. With the help of additional gamma-gamma coincidence data obtained with Gammasphere, these gamma rays were found to form a strongly coupled rotational band with rigid-rotor-like behavior. Results of conventional Nilsson-Strutinsky cranked shell model calculations, which predict a deformation of beta(2)similar to 0.4, are in excellent agreement with the properties of this band. Similar calculations for the neighboring N=Z and N=Z + 1 nuclei are also in good agreement with experimental data. This suggests that the presence of the putative T=0 neutron-proton pairing does not significantly affect such simple observables as the moments of inertia of these bands at low spins. [S0556-2813(98)50612-7].

Results are presented of a systematic survey of {Delta}I=4 bifurcation in 19 superdeformed bands in A{approximately}150 Eu and Gd nuclei. The majority of bands show no sign of this regular oscillation in energy levels. The statistical significance of the few examples that exhibit the effect is examined. {copyright} {ital 1998} {ital The American Physical Society}

High-spin states in the odd-$A{ }^{113}\mathrm{Sn}$ nucleus have been investigated with the ${}^{100}\mathrm{Mo}{(}^{18}\mathrm{O}, 5n)$ reaction at 94 MeV using the Chalk River $8\ensuremath{\pi}$ array. Three decoupled $(\ensuremath{\Delta}I=2)$ rotational bands extending to spins $I$ in the range $(63/2--69/2)\ensuremath{\Elzxh}$ have been identified and connected to known low-lying states. Experimental observations for the most extended band have been interpreted as evidence for smooth band termination. Theoretical calculations performed within a configuration-dependent shell-correction approach suggest that all three bands are built upon deformed two-particle--two-hole proton excitations across the $Z=50$ shell gap.

Eight superdeformed bands have been observed in the nuclei {sup 147,148}Eu. Some of these are identical to bands in the Z+1 nuclei {sup 148,149}Gd, and are interpreted as having the same single-particle configurations with the exception of a hole in one of the [301]1/2 proton orbitals. Some of the bands in {sup 147}Eu exhibit either upbends or downbends in their moments of inertia which are related to the crossing of {pi}6{sup 1} and {pi}6{sup 3} proton intruder configurations. These results constitute the first evidence of this crossing. {copyright} {ital 1998} {ital The American Physical Society}

An excited well-deformed rotational band has been observed in the N = Z odd-odd nucleus Cu-58. The first excited state in this band decays via gamma emission to the spherical states associated with the first minimum in the potential, thus providing for its unambiguous assignment to Cu-58. I, contrast, its bandhead decays via emission of a prompt 2.4(1) MeV proton to an excited state in the daughter nucleus Ni-57. This is the first observation of proton decay from states associated with a deformed secondary minimum in the potential. Self-consistent Hartree-Fock calculations reproduce well both the large collectivity of this band and the general trend of its moment of inertia.

The high-spin structure of ${}^{111}$In has been investigated with $\ensuremath{\gamma}$-ray spectroscopic methods using the ${}^{96}$Zr${(}^{19}$F,4$n)$ reaction with thin and backed targets. A comprehensive level scheme has been constructed which exhibits interesting collective as well as novel single-particle excitations. Unambiguous evidence of proton particle-hole excitations is found for the first time in a $Zl$50 nucleus in the form of decoupled bands involving proton ${g}_{7/2}{(d}_{5/2})$ and ${h}_{11/2}$ orbitals above the $Z$=50 spherical shell gap. The high-spin structure of ${}^{111}$In also involves the recently discovered magnetic rotation mechanism which is manifest as high-spin $\ensuremath{\Delta}I$=1 bands with no signature splitting and large $B(M1)$ strengths, but only a small associated deformation.

Two sets of strongly coupled rotational bands have been identified in Zn-62. These bands have been observed up to the terminating states of their respective configurations. Lifetime measurements indicate that the transition quadrupole moments in these bands decrease as termination is approached. These results establish the first terminating states of rotational bands in the A similar to 60 mass region and confirm the predicted loss of collectivity associated with smooth band termination.

High-spin states of a number of nuclei near Ni-56 have been studied by means of the Si-28(Ar-36,x alpha ypzn) reaction. The GAMMASPHERE array in conjunction with light charged particle and neutron detectors were used to identify and cleanly select the fusion-evaporation products. In addition to significantly extending the level schemes of many previously known N = Z nuclei from Fe-52 to Cu-58, excited states in the one-neutron-hole nucleus Ni-55 and high-spin rotational bands in the vicinity of the doubly-magic Ni-56 have been established for the first time. Spherical-fp shell model and cranked Hartree-Fock calculations employing several Skyrme-type effective interactions have been used to interpret these data. The calculated moments of inertia of the rotational bands show considerable sensitivity to the details of the effective interactions.

Four new superdeformed bands have been found in the nucleus {sup 86}Zr. The good agreement between experiment and configuration-dependent shell correction calculations suggests that three of the bands have triaxial superdeformed shapes. Such unique features in mass A{approximately}80 superdeformed bands have been predicted, but not observed experimentally until now. A fourth band in {sup 86}Zr is interesting due to a fairly constant and unusually high dynamic moment of inertia. Possible interpretations of this structure are discussed. {copyright} {ital 1998} {ital The American Physical Society}

Lifetimes of a superdeformed band in Sr-82 were measured with the centroid shift method. The measured average quadrupole moment of this band corresponds to a quadrupole deformation of beta(2) approximate to 0.49, which is slightly smaller than both the theoretical prediction, and the measured deformation of the SD band in the neighboring isotone Zr-84. Lifetimes of high spin states of three normally deformed rotational bands in Sr-82 were also measured with the Doppler shift attenuation method technique. The quadrupole moments of these normally deformed bands show a decrease at the highest spins, supporting the predicted band terminations.

Four superdeformed bands are reported in Sr-80, extending known superdeformation in the Sr-38 series down to N = 42. The characteristics of these bands are discussed. Residual Doppler shifts were measured and average transition quadrupole moments (Q(t)) inferred for these new bands, These Q(t) values are compared to Q(t) values obtained for previously identified superdeformed bands in Sr81-83. The low Q(t) of 2.7(-0.6)(+0.7) eb obtained for the yrast band in Sr-80 indicates a reduction in the deformation of yrast superdeformed bands in the series Sr80-83 with decreasing N, and possibly the onset of triaxiality in superdeformed shapes. (C) 1997 Elsevier Science B.V.

An experiment was performed with the Gammasphere Ge-detector array, and the Microball charged particle detector, to search for transitions involved in the decay from the yrast superdeformed band in Eu-143. Sum spectra in coincidence with single, double, and triple gates on SD transitions were produced to search for previously reported two-step links between the superdeformed and the near-yrast ND levels. The sum spectra contained no evidence of peaks corresponding to sums of two-step linking transitions. Several discrete gamma rays were observed in coincidence with the yrast SD band. One previously reported single-step transition at 3361 keV was confirmed to decay out of the SD band.

Two strongly coupled bands with large dynamic moment of inertia values have been observed for the first time in the neutron-deficient odd-odd nucleus ${}^{130}$Pr using Gammasphere and the Microball charged-particle detector array. These bands involve the important ${g}_{9/2}$[404]9/2 proton orbital. This new information on ${}^{130}$Pr coupled with Projected Shell Model calculations provide valuable insight on rotational alignment processes taking place in this mass region, the size of the $N$=72 deformed shell gap, and the position of the ${i}_{13/2}$[660]1/2 neutron intruder orbital at the boundary of the $A$=135 superdeformed region.

A high-spin rotational cascade of six gamma rays has been observed in Zn-62. The quadrupole moment of 2.7(-0.5)(+0.7) e b measured for this band corresponds to a deformation beta(2) = 0.45(-0.07)(+0.10). The properties of this band are in excellent agreement with calculations that predict high-spin superdeformed bands in Zn-62 with deformations beta(2) = 0.41-0.49. These results establish a new region of superdeformation for nuclei with neutron and proton numbers N, Z approximate to 30-32.

Collective structures have been investigated via $\ensuremath{\gamma}$-ray studies in ${}^{117,119}$Sb. Previously observed strongly coupled $(\ensuremath{\pi}{g}_{9/2})$${}^{\ensuremath{-}1}$ bands in both nuclei involving 1p-1h proton excitations across the $Z=50$ gap have been extended, and an alignment of ${h}_{11/2}$ neutrons identified. New negative-parity strongly coupled bands based on this proton configuration have also been observed in both nuclei. Decoupled bands involving 2p-2h excitations across the gap have been observed in ${}^{119}$Sb, similar to those presented earlier for ${}^{117}$Sb. These bands are interpreted as due to the coupling of a low-$K$ valence proton to the $(\ensuremath{\pi}{g}_{7/2}{d}_{5/2}{)}^{2}\ensuremath{\bigotimes}(\ensuremath{\pi}{g}_{9/2}{)}^{\ensuremath{-}2}$ deformed state of the respective ${}_{50}$Sn core nuclei. Anomalies in the expected ${h}_{11/2}$ neutron crossing of these bands are discussed.

The fusion-evaporation reaction {sup 58}Ni({sup 32}S,2{alpha}p) has been used to study the neutron-deficient isotope {sup 81}Y. Multiple particle {gamma}-ray coincidences have been detected by the GAMMASPHERE array combined with the MICROBALL charged-particle detector system. Gamma-ray spectra with an improved resolution have been achieved from an event-by-event determination of the nucleus recoil momentum, thus allowing a precise Doppler-shift correction. In this way a resolution enhancement by a factor 2 was obtained for a 1 MeV {gamma} line. During the analysis an E{sub {gamma}}-E{sub {gamma}} matrix as well as an E{sub {gamma}}-E{sub {gamma}}-E{sub {gamma}} cube have been used to extend the previously known level scheme to higher spin (I{approx}(57)/(2)) and excitation energy (E{sub x}{approx}17MeV). More than 100 new {gamma} rays and 80 new levels have been added to the level scheme and six new bands have been established. The interpretation of these bands in terms of the cranking model and their comparison with similar bands in neighboring nuclei is discussed. {copyright} {ital 1997} {ital The American Physical Society}

High-spin states in Kr-77 were identified via analysis of prompt gamma-gamma coincidences in the Ni-58(Si-29,2 alpha 2p) reaction at 128 MeV at the Gammasphere facility. Evaporation channel selecti ...

The high-spin structure of odd-odd {sup 86}Nb was studied with the early implementation of GAMMASPHERE using 36 Compton-suppressed Ge detectors and the MICROBALL, a 95-element full-sphere charged-particle detector array. High-spin states were populated using the {sup 58}Ni({sup 32}S,3pn) reaction at 135 MeV with beams from the 88-Inch Cyclotron at Lawrence Berkeley National Laboratory. A number of bands were observed up to spins as high as (31{sup {minus}}). The yrast positive-parity band shares many characteristics with the {pi}g{sub 9/2}{circle_times}{nu}g{sub 9/2} bands in other odd-odd f-p-g shell nuclei. These similarities include the behavior of the moments of inertia, the magnitude and phase of the signature splitting and its phase reversal near the 10{sup +} state, and the strong alternations in the B(M1)/B(E2) strengths. The moments of inertia in the lowest pair of negative-parity bands start out with a sharp upbend and then gradually fall back to the rigid-body value. New positive- and negative-parity bands appear in the quasiparticle alignment region and eventually become yrast. Some additional positive-parity states around spin 17{h_bar} are candidates for fully or nearly fully aligned shell-model-like configurations. {copyright} {ital 1997} {ital The American Physical Society}

High-spin states of T-z = 1 nuclei were studied with the reactions Ni-58(Si-28,3 alpha)Kr-74,Ni-58(Si-28,2 alpha)Sr-78, and Ni-58(Si-28,2p2n)Zr-82 at 130 MeV beam energy. The Gammasphere array in conjunction with the 4 pi charged-particle detector array Microball was used to detect gamma rays in coincidence with evaporated light charged particles. The known pi = +, alpha = 0 yrast bands were extended to I = 28 (h) over bar at 20 MeV excitation energy. For all three nuclei, a number of positive- and negative-parity sidebands were established; altogether 15 new rotational bands were found. The data are discussed using the pairing-and-deformation self-consistent total Routhian surface (TRS) model: High-spin structures of Kr-74 and Sr-78 are governed by the shell gaps at large prolate deformation while Zr-82 seems to exhibit shape coexistence. Nearly identical bands were established which may be explained as arising from the fp orbits acting as spectators at very elongated shapes. The experimental data in these T-z = 1 nuclei are in good agreement with predictions of the TRS model using conventional T = 1 like-nucleon pairing correlations. (Less)

{Delta}I=4 bifurcation has been observed in two superdeformed bands, the newly discovered yrast superdeformed band of {sup 148}Eu, and a previously known excited band in {sup 148}Gd. Both of these bands have moments of inertia that are identical to the yrast band of {sup 149}Gd, the first superdeformed band in which this bifurcation was observed. This first observation of {Delta}I=4 bifurcation in identical superdeformed bands provides a crucial test of recent models. {copyright} {ital 1997} {ital The American Physical Society}

Second minimum structures have been observed for the first time in the doubly odd nucleus ${}_{59}^{132}$Pr. Two new bands are interpreted as based on the $\ensuremath{\pi}{g}_{9/2}[404]9/2\ensuremath{\bigotimes}\ensuremath{\nu}{i}_{13/2}[660]1/2$ configuration and a third as the $\ensuremath{\pi}{h}_{11/2}[532]5/2\ensuremath{\bigotimes}\ensuremath{\nu}{i}_{13/2}[660]1/2$ configuration. Signature splitting effects observed in the $\ensuremath{\pi}{(g}_{9/2}{)}^{\ensuremath{-}1}$ bands provide new information regarding the positive parity proton orbitals at large deformation. Results from the extracted $B(M1)/B(E2)$ ratios are consistent with a large deformation for the $\ensuremath{\pi}{(g}_{9/2}{)}^{\ensuremath{-}1}$ bands.

Four superdeformed bands have been observed in ${}^{87}\mathrm{Nb}$. Transition quadrupole moment measurements on three of the bands confirm superdeformed shapes. Two of the bands were observed to mutually interact, and cross transitions between them have been observed. This is the first time such behavior has been observed in mass 80 superdeformed bands. Once this interaction is accounted for, a second crossing appears in one of the bands. This crossing is interpreted as evidence for the occupation of the ${i}_{13/2}$ superintruder orbital, making ${}^{87}\mathrm{Nb}$ the lightest nucleus by far in which the shape-driving properties of this orbital can be studied.

Two superdeformed (SD) bands extending over eight to eleven transitions have been identified in Zr-83, The quadrupole moment of the more intense band was determined by the Residual Doppler Shift Method and is consistent with a quadrupole deformation of beta(2) approximate to 0.5. The large quadrupole moment and population intensity of the yrast SD band (approximate to 5%) in Zr isotopes relative to their isotones in Sr and Y nuclei suggest the presence of a large SD shell gap at proton number Z = 40, At the decay-out points, the Routhians of the SD bands reapproach that of the positive parity normally-deformed states which may be the reason why both of these bands feed mainly (approximate to 85%) into the positive-parity yrast band.

The response of the Ge detector array Gammasphere to γ-rays, both individually and in cascades, has been modeled with the Monte Carlo code GEANT 3. The effects on the performance of Gammasphere of including an auxiliary detector, the Microball, are investigated. The use of the existing Ge detectors and BGO suppression detectors as a γ-ray multiplicity and total γ-ray energy spectrometer is explored, and its total energy - multiplicity ( H , k ) response is simulated in detail. The utility of the Hevimet collimators in spectroscopic studies, as opposed to the use of the available ( H , k ) information, is discussed.

A 4π multidetector light-charged particle and light fragment detection spectrometer is described. It consists of 95 CsI(T1) scintillators closely packed to cover the angular range 4.0°–172°, arranged in 9 rings with increasing forward segmentation. The device is optimally designed to be used in conjunction with Gammasphere. The scintillator light is collected by silicon photodiodes that provide high quantum efficiency and minimal mass. The signals are processed through a charge sensitive preamplifier followed by a slow shaper. Particle identification for 1,2,3 H, 3,4 He ions and Li, Be and B ions is accomplished by pulse shape discrimination. The geometry, construction, energy calibration, gain stability, associated integrated electronics and the data acquisition system are discussed. The capabilities of this spectrometer as a channel selecting device in conjunction with Gammasphere are discussed. A second version of the device with thicker scintillators, that can stop more energetic charged particles and is useful for reaction mechanism studies, is also described.

Intruder rotational bands have been investigated to high frequency in $_{51}^{109}\mathrm{Sb}$. Five decoupled (\ensuremath{\Delta}I=2) bands extending to rotational frequencies above 1.4 MeV/\ensuremath{\Elzxh} have been observed. At the highest frequencies, the ${\mathit{J}}^{(2)}$ dynamic moments of inertia for four of these bands are seen to decrease steadily to unexpectedly low values, ${\mathit{J}}^{(2)}$ \ensuremath{\sim} 10 ${\mathrm{\ensuremath{\Elzxh}}}^{2}$ ${\mathrm{MeV}}^{\mathrm{\ensuremath{-}}1}$. These four bands, which are interpreted as being based on deformed 2p-2h proton excitations across the Z=50 closed-shell gap, achieve the so-called ``smooth band termination'' following alignment of the valence nucleons outside of $^{100}\mathrm{Sn}$. In addition, two strongly coupled (\ensuremath{\Delta}I=1) bands have been observed, which are related to 1p-1h proton excitations across the gap. \textcopyright{} 1996 The American Physical Society.

A search was undertaken to look for evidence of hyperdeformation in Gd-146,Gd-147. Three experiments employing Gammasphere for gamma-ray detection coupled with the Microball for channel selection via charged particle detection were carried out with increasing detection sensitivity and statistics. No definitive evidence for band structures that could be assigned to hyperdeformation could be found. Candidates previously reported are shown not to have properties consistent with a band structure.

High-spin states have been studied in neutron-deficient {sup 132}Nd, produced in the {sup 105}Pd({sup 35}Cl,{alpha}{ital p}3{ital n}{gamma}) reaction, using the Gammasphere {gamma}-ray spectrometer in conjunction with the Microball charged-particle detector array. Three new, weakly populated rotational bands have been found, which are believed to be associated with a superdeformed (second minimum) prolate shape. Comparison of the properties of these bands with Woods-Saxon cranking calculations suggests that they are built upon negative-parity neutron configurations that involve only one intruder orbital ({nu}{ital i}{sub 13/2}) from the {ital N}=6 shell. One of the bands has been linked into the normally deformed states allowing an estimation of the spin, parity, and excitation energy of the band. {copyright} {ital 1996 The American Physical Society.}

High-spin states in Mo-86 were studied by means of the fusion evaporation reaction Ni-58(S-32,2p2n) Mo-86 at 135 MeV beam energy. Charged-particle-gamma gamma and -gamma gamma gamma coincidences recorded with the early implementation of the GAMMASPHERE array and the MICROBALL charged-particle detection system were used to largely extend the level scheme of the T-tau=1 nucleus Mo-86 to a possible spin of I=24h at 13 MeV excitation energy. The excitation scheme is compared to neighboring nuclei. There is evidence for enhanced shell-model influence in the 4 quasiparticle region (I=12-16h). The observed (pi=+,alpha=0) sequence at spin I greater than or equal to 16 h appears to be associated with a triaxial collective rotational band. This interpretation is supported by calculations within the configuration-dependent shell-correction approach with the cranked Nilsson potential. (Less)