Search

Deep-inelastic collisions of a 208Pb beam on a 208Pb target were performed using the ATLAS accelerator at Argonne National Laboratory. The Gammasphere detector array was used for the detection of prompt and delayed gamma-rays of the reaction products.207Tl is one proton away from the 208Pb doubly-magic nucleus. Its low-energy level structure is dominated by the single proton-hole states πs1/2−1, πd3/2−1 and πh11/2−1. The 11/2− state is isomeric with T1/2 = 1.33(11) s. The reaction partner of 207Tl is 209Bi, which has arelatively well established level scheme compared to 207Tl. Cross-coincidences between these two nuclei were used to confirm or establish levels above the 11/2− isomeric state in 207Tl. These states are obtained via breaking of the neutron core. Angular correlation analysis was performed on known transitions in 208Pb, proving the applicability of this method for multipolarity assignment.

High-spin properties of the nucleus 169Hf have been studied through the fusion evaporation reaction 96Zr(76Ge,3n)169Hf at a beam energy of 310 MeV. The known rotational bands have been extended considerably and 6 new bands have been established, four of which form coupled bands with pronounced M1 connections. Quasiparticle assignments are suggested for the new band structures, and it appears that coupling to vibrational degrees of freedom plays a role. Both coupled bands involve the excitation of quasiprotons. In the region of highest spin, a large alignment gain is interpreted in terms of a mixed crossing where an h 9/2 and an h 11/2 quasiproton provide the two signatures of the aligning configuration.

Excited states in the proton-unbound 173,175,177 Au nuclei were identified for the first time. Level structures associated with three different shapes were observed in 175 Au. While the yrast lines of 175 Au and 177 Au consist of a prolate band built upon the intruder 1/2 + [660] ( i 13/2 ) proton orbital, no sign of collectivity was observed in the lighter 173 Au isotope. Implications for the deformation associated with these structures are discussed with a focus on shape co-existence in the vicinity of the proton-drip line.

Three superdeformed (SD) bands have been found in 168Hf. Lifetime measurements revealed a large quadrupole moment, Q t ∼11.4 e b , for the strongest band (TSD1). Theoretical calculations using the Ultimate Cranker code predict high-spin SD minima (ϵ2∼0.43) with stable triaxial deformations of γ∼+20° and γ∼−15°. The measured Qt value suggests that band TSD1 corresponds, most likely, to a deformation with a positive γ value. This constitutes the first evidence for triaxial superdeformation in an even proton system.

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.

The domain of nuclei situated far from the line of b stability has always been an arena of numerous experimental pursuits and a testing ground for new theoretical models. With radioactive beams on the horizon, the physics of nuclei with an excess of neutrons or protons has become one of the focal points of nuclear physics. These nuclei define the very limits of nuclear existence and will be susceptible to phenomena associated with low binding energy, such as halos, skins, or mixing between bound and continuum states. The proton separation energy decreases with decreasing neutron number. Proton-rich nuclei, which have a negative proton separation energy and are, thus, situated beyond the proton drip-line, can spontaneously emit protons. The proton decay rate is governed by the energy and orbital angular momentum of the emitted proton. It also depends on the wave function of the proton-decaying state, which is determined by the shape of the nuclear potential and by residual interactions between valence nucleons. Most of the known proton emitters have decay rates consistent with the assumption of a spherical potential. The recent experimental

The majority of experiments performed during the 2-year long stay of GAMMAS-PHERE at the Argonne National Laboratory aimed to study proton-rich nuclei far from the line of stability at and beyond the proton drip-line. A high reaction channel selectivity was required to assign in-beam {gamma}-ray transitions to weakly populated exotic nuclei in the presence of background from strong reaction channels. In many of the experiments this was achieved by using the Argonne fragment mass analyzer to separate heavy-ion fusion-evaporation reaction products from scattered beam and disperse them according to their mass-over-charge-state ratio. For medium mass and heavy a and proton emitters the Recoil-Decay Tagging method was implemented. In-beam {gamma}-ray transitions were observed in several proton emitters between Z=50 and Z=82. Among others, rotational bands were assigned to {sup 141}Ho and {sup 131}Eu. A quadruple deformation of {beta}=0.25(4) was deduced for the ground state in {sup 141}Ho from the extracted dynamic moment of inertia. Based on observed band crossings and signature splittings the 7/2{sup {minus}} [523] and 1/2{sup +}[411] configurations were proposed for the ground state and the isomeric state, respectively. Comparison with particle-rotor calculations indicates, however, that {sup 141}Ho may have significant hexadecapole deformation and could be triaxial.

Excited states of nuclei near the doubly-magic nucleus Sn-100 were studied with the Ni-58+Cr-50 reaction. The experimental setup consisted of the GAMMASPHERE array augmented with light charged-particle and neutron detectors. Excited states were identified for the first time in the proton emitting nucleus Sb-105. Excitations across the N=Z=50 doubly closed shell were observed in Cd-99 and In-101. Some results of large-scale shell-model calculations are discussed.

P. Chowdhury”, I. Shestakova”, R. D’Alarcaoa, C.J. Pearsonb, Z. Podolyakb, P.M. Walkerb, C. Wheldonb, D.M. Cullenc, I. Ahmadd, M.P. Carpenterd, R.V.F. Janssensd, T.L. Khood, F.G. Kondevd, C.J. Listerd, D. Seweryniakd and I. Wiedenhoeverd aDepartment of Physics, University of Massachusetts, Lowell, MA 01854, USA bDepartment of Physics, University of Surrey, Guildford GU2 5XH, UK ‘Department of Physics, Oliver Lodge Laboratory, University of Liverpool, Liverpool L69 7ZE, UK dArgonne Na tl ‘o nal Laboratory, Argonne, IL 60439, USA New multi-quasiparticle K-isomers have been investigated in neutron-rich hafnium nu- clei via inelastic and transfer reactions with a pulsed 238U beam on a lsoHf target. The emphasis of this presentation is on the specific techniques of isolating and characteriz- ing isomers with 2~s half-lives and low cross-sections in the transfer channels using the Gammasphere array. 1. THE PHYSICS Quantum numbers associated with special symmetries of the nuclear wave-function in- vite investigation regarding their limits of validity. One that has received considerable attention now for a number of years is K, the

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.

Rotational states assigned to a Kπ = ({5}+) band in 18071Lu109 have been populated in the decay of a t1/2≥1 ms, two-quasiparticle isomer. Delayed γ-ray and x-ray coincidences were observed with the Gammasphere array following the deep-inelastic reaction 23892U + 18072Hf. Gamma-ray coincidence and intensity data, comparisons with the level structure of the neighbouring odd-odd isotone, a g-factor analysis and theoretical predictions of multi-quasiparticle states, all support the assignment of the new band to the neutron-rich nucleus 180Lu.

For many nuclei beyond the proton drip line in the Z > 72, N > 82 region, both proton and α emission are energetically allowed. In the case of some proton emitters, there are α-decay chains emanating from both parent and daughter nuclei. This means that if the mass excess of one member of an α-decay chain is known, then the mass excesses for all members of both chains can be obtained. In addition, proton separation energies may be derived for nuclei in the α-decay chain of the proton emitter. The method of time- and space-correlations also allows the identification of isomeric states in these nuclei. As an example, a large number of mass excesses and proton separation energies for ground and metastable states have been derived from Q α and Q p values obtained from the proton emitters 165,166,167Ir, 171Au, 177Tl and their daughters.

The spontaneous fission of 252 Cf has been studied via γ  γ  γ coincidences and γ  γ-light charged particle coincidences with Gammasphere. The yields of correlated Mo-Ba pairs in binary fission with 0–10 neutron emission have been remeasured with an uncompressed γγγ coincidence data. The previous hot fission mode with 8–10 neutron emission seen in the Mo-Ba split is found to be smaller than earlier results but still present. New 0n binary SF yields are reported. By gating on the light charged particles detected in ΔE-E Si detectors and γγ coincidences with Gammasphere, the relative yields of correlated pairs in alpha ternary fission with zero to 6n emission are observed for the first time. A number of correlated pairs are identified in ternary fission with 10 Be as the LCP. We observed only cold, 0n 10 Be and little, if any, hot, xn 10 Be channel.

High-spin states in Te-122 were populated in the reaction Se-82(Ca-48, alpha 4n) Te-122 at a beam energy of 200 MeV and gamma-ray coincidences weremeasured with the Gammasphere spectrometer. The previously known level scheme was extended to considerably higher spin. Maximally aligned states and several high-energy transitions feeding into some of these levels were observed. In addition, seven collective high-spin bands were discovered for the first time in this nucleus. The experimental results are compared with cranked Nilsson-Strutinsky model calculations and possible configuration assignments to the new high-spin structures are discussed.

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.

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.

The entry distribution in angular momentum and excitation energy for the formation of {sup 254}No has been measured after the {sup 208}Pb( {sup 48}Ca, 2 n) reaction at 215 and 219 MeV. This nucleus is populated up to spin 22({Dirac_h}/2{pi}) and excitation energy (greater-or-similar sign)6 MeV above the yrast line, with the half-maximum points of the energy distributions at {approx}5 MeV for spins between 12({Dirac_h}/2{pi}) and 22({Dirac_h}/2{pi}) . This suggests that the fission barrier is (greater-or-similar sign)5 MeV and that the shell-correction energy persists to high spin. (c) 2000 The American Physical Society.

Cross sections for the 44Ti(alpha,p)47V reaction which significantly affects the yield of 44Ti in supernovae were measured in the energy range 5.7 MeV

Reactions with a heavy projectile incident on a light target can be used for the efficient in-flight production of secondary radioactive beams. An overview of this technique is given using data on 17F beams produced via the p(17O, 17F)n and d(16O, 17F)n reactions. With primary 16,17O beam currents of 100 pnA, intensities of up to 2×106 17F/s on target were achieved. Using this beam, the p(17F, α) 14O reaction was measured.

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.

The superdeformed nucleus 193 Pb has been studied following a heavy-ion fusion-evaporation reaction with the Gammasphere spectrometer array. Three new superdeformed bands, two of them probably signature partners, have been observed, bringing the total number of superdeformed bands known in this nucleus to nine. An estimate of the g -factor associated with one of the previously known pairs of strongly coupled excited bands has been made, confirming their configuration. The properties of the bands are compared with the results of cranked shell model calculations; good agreement is found and configurations are assigned to each band. The two new signature partner bands are suggested to be based on the two signatures of the [512]5/2 neutron orbital. The third new band is probably based on the 7 3 intruder orbital. In addition, the high-energy region of the spectrum in coincidence with the yrast superdeformed bands has been carefully studied. The current data provide no evidence for the previously reported transitions linking the superdeformed and normal-deformed states with energies around 2.2 – 2.4 MeV.

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.

The strength distribution of the primary γ rays in the decay from superdeformed (SD) states is investigated by applying the maximum likelihood method. For the 194 Hg nucleus, 41 primary transitions 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 “one-step linking” transitions is found to have a very small probability. 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.

Ground and isomeric proton and alpha decay branches are reported for the new isotope ${}^{177}\mathrm{Tl},$ produced by bombarding a ${}^{102}\mathrm{Pd}$ target with a 370 MeV beam of ${}^{78}\mathrm{Kr}$ ions. The ground state is assigned as a $\ensuremath{\pi}{s}_{1/2}$ configuration and the high spin isomer is assigned as a $(\ensuremath{\pi}{h}_{11/2}{)}^{\ensuremath{-}1}$ configuration. The ground-state proton decay of ${}^{171}\mathrm{Au}$ has been identified for the first time, produced by bombarding a ${}^{96}\mathrm{Ru}$ target with ${}^{78}\mathrm{Kr}$ ions. The ${}^{171}\mathrm{Au}$ ground state is also assigned as a $\ensuremath{\pi}{s}_{1/2}$ configuration. Spectroscopic factors, masses, and proton separation energies are derived using these new proton decay measurements. New ground-state $\ensuremath{\alpha}$ decays for ${}^{169}\mathrm{Ir}$ and ${}^{173}\mathrm{Au}$ are also reported.

A method has been developed that can provide beams of many short-lived nuclei of interest in nucleosynthesis along the rp process path. With a {sup 17}F beam (T{sub 1/2}=64 s ) the excitation function of the {sup 17}F( p,thinsp{alpha}){sup 14} O reaction was measured to determine properties of excited states in {sup 18}Ne . These states influence the rate of the {sup 14}O( {alpha},thinspp){sup 17} F reaction which is important for understanding energy generation and nucleosynthesis in x-ray bursts. The present direct measurements yield a pattern of resonances and cross sections which differ substantially from previous estimates. {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.

Excited states in the proton-unbound nucleus {sup 109}I were populated using the {sup 54}Fe({sup 58}Ni,p2n) reaction at a beam energy of 220 MeV. Gamma rays in {sup 109}I were identified using the recoil-decay tagging technique. The analysis of proton-correlated {gamma}{gamma} coincidence data produced the yrast decay sequence in {sup 109}I, which can be tentatively assigned as built on the h{sub 11/2} proton state based on systematic trends in the neighboring isotopes. This sequence is completely different from that reported previously. A comparison of the h{sub 11/2} band in {sup 109}I with those in heavier iodines shows that {sup 109}I continues the trend of decreasing quadrupole deformation with decreasing neutron number.

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 GDR in 164 Er at 62 MeV excitation energy has been studied in coincidence with the evaporation residues, selected using the Argonne fragment mass analyzer (FMA). The statistical model fit to the data indicate that 164 Er ∗ has a prolate shape with deformation similar to the ground state.

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}

The ground-state band of the Z=102 isotope {sup 254}No has been identified up to spin 14, indicating that the nucleus is deformed. The deduced quadrupole deformation, {beta}=0.27 , is in agreement with theoretical predictions. These observations confirm that the shell-correction energy responsible for the stability of transfermium nuclei is partly derived from deformation. The survival of {sup 254}No up to spin 14 means that its fission barrier persists at least up to that spin. {copyright} {ital 1999} {ital The American Physical Society }

The yrast states of the beta-stable nucleus have been studied using the reaction at a beam energy of 65 MeV. Transitions in this nucleus were identified unambiguously using high-efficiency recoil-gated gamma-ray spectra obtained from the AYEBALL gamma-ray array in conjunction with the Argonne fragment mass analyser coupled to a split anode ionization chamber. The decay scheme is presented and it is hoped that such a study will shed light on the competition between core breaking and population of the neutron intruder orbitals in the generation of high angular momentum states in this region.

The time evolution of the decay of high-spin, normal deformed structures in 193,194 Hg was studied by measuring, in the Gammasphere array, the Doppler shift attenuation of selected transitions depopulating various bands. The data suggest that a fraction of states feeding selective yrast levels is non-collective in nature and show resemblance to A = 150 nuclei where shape polarizing effects have been linked to particles occupying high- j orbitals.

The excited states of the self-conjugate, odd-odd system, Ga have been investigated following the fusion-evaporation reaction at a beam energy of 65 MeV. Identification of candidate transitions in this nucleus were made using the AYEBALL -ray array following the selection of the recoil products with the Argonne fragment mass analyser (FMA) and a split anode ionization chamber. Spin assignments have been made on the basis of measured directional correlations from oriented states (DCO ratios). The resulting level scheme is presented and candidates for T = 1 and T = 0 structures suggested.

The average g factors of high spin, high-excitation energy, quasicontinuum structures in {sup 194,193}Hg were measured by observing the precessions of the angular distributions of {gamma}-ray transitions in several normal-deformation bands that coalesce in the decay of the entry distribution of states. The average g factors of the states leading to the three main bands in the {sup 193,194}Hg isotopes were: {l_angle}g({sup 193}Hg){r_angle}=+0.19(1) and {l_angle}g({sup 194}Hg){r_angle}=+0.26(1), respectively. These average g factors are smaller than the average of the g factors of the high energy states in the three superdeformed bands of {sup 194}Hg, {l_angle}g(SD; {sup 194}Hg){r_angle}=+0.41(8). While the nucleus in the superdeformed well behaves like a rigid rotor, the present results demonstrate the important role played by multiple, quasiparticle neutron configurations in the structure of normal-deformation, highly-excited nuclear states.

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}

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}

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 average g factors of the high-energy states of the three superdeformed bands in ${}^{194}\mathrm{Hg}$ were determined directly in a transient field experiment. The reaction ${}^{150}\mathrm{Nd}{(}^{48}\mathrm{Ca}{,4n)}^{194}\mathrm{Hg}$ at a beam energy of 203 MeV was used to provide recoiling reaction product nuclei with sufficient velocity to traverse a gadolinium ferromagnetic layer. The resulting g factors $g(\mathrm{SD}1)=0.36(10),$ $g(\mathrm{SD}2)=0.41(20),$ and $g(\mathrm{SD}3)=0.71(26)$ are in agreement with cranked Hartree-Fock calculations as well as with the picture of a rigid rotation for which $g=Z/A.$