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The fusion-evaporation reaction 32S+28Si at 125-MeV beam energy was used to populate excited states in 55Fe. Combining the Gammasphere spectrometer with ancillary devices including the Microball CsI(Tl) array and a shell of neutron detectors, a comprehensive level scheme could be derived. The experimental results are compared with theoretical results from shell-model calculations. Taking into account isospin-symmetry breaking terms is found to considerably improve the shell-model description for 55Fe. This motivated a predictive case study of near-yrast states in the mirror nucleus 55Cu.

The $\ensuremath{\beta}$ decay of the isomeric and ground state of $^{50}\mathrm{Sc}$ to the semimagic nucleus $_{22}^{50}\mathrm{Ti}_{28}$ has been studied using a $^{50}\mathrm{Ca}$ beam delivered to the GRIFFIN $\ensuremath{\gamma}$-ray spectrometer at the TRIUMF-ISAC facility. $\ensuremath{\beta}$-decay branching ratios are reported to 16 excited states with a total of 38 $\ensuremath{\gamma}$-ray transitions linking them. These new data significantly expand the information available over previous studies. Relative intensities are measured to less than 0.001 $%$ that of the strongest transition with the majority of $\ensuremath{\gamma}$-ray transitions observed here in $\ensuremath{\beta}$ decay for the first time. The data are compared with shell-model calculations utilizing both phenomenologically derived interactions employed in the $pf$ shell as well as a state-of-the-art ab initio-based interaction built in the valence-space in-medium similarity renormalization-group framework.

Excited states in the neutron-rich nucleus Fe 68 were populated using a Be 9 ( Co 68 , 68 Fe + γ ) X charge-exchange reaction at 95 MeV/u. The new γ -ray transitions reported here for the first time complement data from β -decay studies and nucleon knockout reactions. In comparison to shell-model calculations with the LNPS effective interaction, two candidate states for the 6 1 + level emerge. The distinct population pattern of excited states and the magnitude of the cross section, σ inc = 0.51 ( 6 ) mb, make this reaction a promising one for future in-beam γ -ray spectroscopy. Reaction calculations with nuclear structure input from a new, locally optimized Hamiltonian, f 7 j 4 a , together with general considerations for heavy-ion-induced charge-exchange reactions appear consistent with most of the observations, although challenges remain.

Background: Neutron-rich nuclei in the $\mathrm{A}\ensuremath{\approx}140--160$ mass region provide valuable information on nuclear structure such as quadrupole- and octupole-shape coexistence and the evolution of the collectivity. These nuclei have also a nuclear engineering interest because they contribute to the total decay heat after a fission burst. The information concerning $^{145}\mathrm{La}$ is very limited.Purpose: The study of low-spin states in $^{145}\mathrm{La}$ will provide a more detailed level scheme and enable the determination of the half-lives of the excited states.Methods: Low-spin excited states in $^{145}\mathrm{La}$ have been investigated from the $^{145}\mathrm{Ba}\phantom{\rule{4pt}{0ex}}{\ensuremath{\beta}}^{\ensuremath{-}}$ decay. The $^{145}\mathrm{Ba}$ nuclei were directly produced by photofission in the ALTO facility or obtained from the ${\ensuremath{\beta}}^{\ensuremath{-}}$ decay of $^{145}\mathrm{Cs}$ also produced by photofission. Gamma spectroscopy and fast-timing techniques were used.Results: A new level scheme was proposed including 67 excited levels up to about 3 MeV and 164 transitions. Half-lives in the few-nanosecond range were measured for the first excited states. Configurations for levels up to $\ensuremath{\approx}600$ keV were discussed.Conclusions: The available information on the low-spin states of $^{145}\mathrm{La}$ has been modified and considerably extended. The analysis of the properties of the first excited states, such as excitation energies, decay modes, log $\mathit{\text{ft}}$ values, reduced transition probabilities, and Weisskopf hindrance factors, has enabled the identification of the first members of the bands corresponding to the ${g}_{7/2},$ ${d}_{5/2},$ and ${h}_{11/2}$ proton configurations.

The fusion-evaporation reaction $^{28}\mathrm{Si}+^{40}\mathrm{Ca}$ at 122 MeV beam energy was used to populate excited states in the $N=Z+1$ nucleus $^{63}\mathrm{Ga}$. With the combination of the Gammasphere spectrometer and the Microball CsI(Tl) charged-particle detector array, the level scheme of $^{63}\mathrm{Ga}$ was extended by more than a factor of two in terms of number of $\ensuremath{\gamma}$-ray transitions and excited states, excitation energy $({E}_{x}g30\phantom{\rule{0.16em}{0ex}}\mathrm{MeV})$, and angular momentum $(Ig30\phantom{\rule{0.16em}{0ex}}\ensuremath{\hbar})$. Nine regular sequences of states were newly established in the high-spin part of the level scheme. The majority of these rotational band structures could be connected to the previously known part of the level scheme by high-energy $\ensuremath{\gamma}$-ray transitions in the energy range ${E}_{\ensuremath{\gamma}}=4--6\phantom{\rule{0.16em}{0ex}}\mathrm{MeV}$. Low-spin states were assessed by shell-model calculations. The high-spin rotational bands were interpreted and classified by means of cranked Nilsson-Strutinsky calculations.

Background: In the "island of inversion", ground states of neutron-rich $sd$-shell nuclei exhibit strong admixtures of intruder configurations from the $fp$ shell. The nucleus $^{30}$Mg, located at the boundary of the island of inversion, serves as a cornerstone to track the structural evolution as one approaches this region. Purpose: Spin-parity assignments for excited states in $^{30}$Mg, especially negative-parity levels, have yet to be established. In the present work, the nuclear structure of $^{30}$Mg was investigated by in-beam $\gamma$-ray spectroscopy mainly focusing on firm spin-parity determinations. Method: High-intensity rare-isotope beams of $^{31}$Mg, $^{32}$Mg, $^{34}$Si, and $^{35}$P bombarded a Be target to induce nucleon removal reactions populating states in $^{30}$Mg. $\gamma$ rays were detected by the state-of-the-art $\gamma$-ray tracking array GRETINA. For the direct one-neutron removal reaction, final-state exclusive cross sections and parallel momentum distributions were deduced. Multi-nucleon removal reactions from different projectiles were exploited to gain complementary information. Results: With the aid of the parallel momentum distributions, an updated level scheme with revised spin-parity assignments was constructed. Spectroscopic factors associated with each state were also deduced. Conclusions: Results were confronted with large-scale shell-model calculations using two different effective interactions, showing excellent agreement with the present level scheme. However, a marked difference in the spectroscopic factors indicates that the full delineation of the transition into the island of inversion remains a challenge for theoretical models.

The beta-decay of Zn-81 to the neutron magic N = 50 nucleus Ga-81, with only three valence protons with respect to Ni-78, was investigated. The study was performed at the ISOLDE facility at CERN by means of gamma spectroscopy. The 81Zn half-life was determined to be T-1/2 = 290(4) ms while the beta-delayed neutron emission probability was measured as P-n = 23(4)%. The analysis of the beta-gated gamma-ray singles and gamma-gamma coincidences from the decay of Zn-81 provides 47 new levels and 70 new transitions in Ga-81. The beta(-)n decay of Zn-81 was observed and a new decay scheme into the odd-odd Ga-80 nucleus was established. The half-lives of the first and second excited states of Ga-81 were measured via the fast-timing method using LaBr3(Ce) detectors. The level scheme and transition rates are compared to large-scale shell-model calculations. The low-lying structure of (81)Gais interpreted in terms of the coupling of the three valence protons outside the doubly magic Ni-78 core.

Author(s): Rudolph, D; Ragnarsson, I; Andreoiu, C; Bentley, MA; Carpenter, MP; Charity, RJ; Clark, RM; Ekman, J; Fahlander, C; Fallon, P; Reviol, W; Sarantites, DG; Seweryniak, D | Abstract: The fusion-evaporation reaction S32+Si28 at 125 MeV beam energy was used to populate high-spin states in the semimagic N=28 nuclei Mn53 and Fe54. With a combination of the Gammasphere spectrometer and ancillary devices including the Microball CsI(Tl) array, extensive high-spin level schemes are derived. They exhibit rotational-like collective structures and competing single-particle excitations. The experimental results are compared with predictions from shell-model calculations, for which the inclusion of isopin-symmetry-breaking terms is found to improve the description. An interpretation of the high-spin states is put forward using cranked Nilsson-Strutinsky calculations, indicative of contributions from collective excitations beyond some 8-MeV excitation energy and highlighting the importance of the g9/2 intruder orbital in this energy range.

The fusion-evaporation reaction 28Si + 40Ca at 122 MeV beam energy was used to populate high-spin states in the odd-odd N = Z nucleus 62Ga. With the combination of the Gammasphere spectrometer and the Microball CsI(Tl) charged-particle detector array the decay scheme of 62Ga was extended beyond 10 MeV excitation energy. The onset of band structures was observed. These high-spin rotational states are interpreted and classified by means of cranked Nilsson-Strutinsky calculations.

The decays of the β-delayed neutron emitters I137 and Rb95 have been studied with the total absorption γ-ray spectroscopy technique. The purity of the beams provided by the JYFLTRAP Penning trap at the ion guide isotope separator on-line facility in Jyvaskyla allowed us to carry out a campaign of isotopically pure measurements with the decay total absorption γ-ray spectrometer, a segmented detector composed of 18 NaI(Tl) modules. The contamination coming from the interaction of neutrons with the spectrometer has been carefully studied, and we have tested the use of time differences between prompt γ rays and delayed neutron interactions to eliminate this source of contamination. Due to the sensitivity of our spectrometer, we have found a significant amount of β intensity to states above the neutron separation energy that deexcite by γ rays, comparable to the neutron emission probability. The competition between γ deexcitation and neutron emission has been compared with Hauser-Feshbach calculations, and it can be understood as a nuclear structure effect. In addition, we have studied the impact of the β-intensity distributions determined in this work on reactor decay heat and reactor antineutrino spectrum summation calculations. The robustness of our results is demonstrated by a thorough study of uncertainties and with the reproduction of the spectra of the individual modules and the module-multiplicity gated spectra. This work represents the state-of-the-art of our analysis methodology for segmented total absorption spectrometers.

The neutron-rich isotopes 211;213Tl, beyond the N = 126 shell-closure, have been studied for the first time in isomer γ-ray decay, exploiting the fragmentation of a primary uranium beam at the FRS-RISING (FRagment Separator-Rare ISotopes INvestigation at GSI) setup at GSI. The observed isomeric states in 211;213Tl show a deviation from the seniority-like scheme of 209Tl. The possible interpretation of the data is discussed on the basis of energy-level systematics and shell-model calculations.

A dedicated spectroscopic study of the β decay of 127Cd was conducted at the IGISOL facility at the University of Jyvaskyla. Following high-resolution mass separation in a Penning trap, β-γ-γ coincidences were used to considerably extend the decay scheme of 127In. The β-decaying 3/2+ and 11/2- states in 127Cd have been identified with the 127Cd ground state and the 283-keV isomer. Their respective half-lives have been measured to 0.45(+12-8)s and 0.36(4) s. The experimentally observed β feeding to excited states of 127In and the decay scheme of 127In are discussed in conjunction with large-scale shell-model calculations.

Short-lived α-decaying nuclei "northeast" of 208Pb in the chart of nuclides were studied using the reaction 48Ca+243Am with the decay station TASISpec at TASCA, GSI Darmstadt. Decay energies and times from pile-up events were extracted with a tailor-made pulse-shape analysis routine and specific α-decay chains were identified in a correlation analysis. Decay chains starting with the even-even 220Ra and its odd-A neighbors, 219Fr, and 219,221Ra, with a focus on the 219Ra→215Rn decay, were studied by means of α-γ spectroscopy. A revised α-decay scheme of 219Ra is proposed, including a new decay branch from a previously not considered isomeric state at 17 keV excitation energy. Conclusions on nuclear structure are drawn from the experimental data, aided by Geant4 simulations and a discussion on theoretical calculations. (Less)

We report on the in-beam gamma spectroscopy of Sn102 and Cd100 produced via two-neutron removal from carbon and CH2 targets at about 150 MeV/nucleon beam energy. New transitions assigned to the decay of a second 2+ excited state at 2470(60) keV in Sn102 were observed. Two-neutron removal cross sections from Sn104 and Cd102 have been extracted. The enhanced cross section to the 22+ in Sn102 populated via the (p,p2n) reaction is traced back to an increase of shell-model structure overlaps, consistent with the hypothesis that the proton-induced two-deeply bound-nucleon removal mechanism is of direct nature.

The half-lives of $^{135}$La and $^{132}$La were determined via gamma spectroscopy and high-precision ionization chamber measurements. The results are 18.930(6) h for $^{135}$La and 4.59(4) h for $^{132}$La compared to the previously compiled values of 19.5(2) h and 4.8(2) h, respectively. The new results represent an improvement in the precision and accuracy of both values. These lanthanum isotopes comprise a medically interesting system with positron emitter $^{132}$La and Auger electron emitter $^{135}$La forming a matched pair for internal diagnostics and therapeutics. The precise half-lives are necessary for proper evaluation of their value in medicine and for a more representative tabulation of nuclear data.

The ground-state rotational band of the neutron-deficient californium (Z = 98) isotope 244Cf was identified for the first time and measured up to a tentative spin and parity of I I-pi = 20(+). The observation of the rotational band indicates that the nucleus is deformed. The kinematic and dynamic moments of inertia were deduced from the measured gamma-ray transition energies. The behavior of the dynamic moment of inertia revealed an up-bend due to a possible alignment of coupled nucleons in high-j orbitals starting at a rotational frequency of about (h) over bar (omega) = 0.20 MeV. The results were compared with the systematic behavior of the even-even N = 146 isotones as well as with available theoretical calculations that have been performed for nuclei in the region.

An experimental scheme combining the mass resolving power of a Penning trap with contemporary decay spectroscopy has been established at GSI Darmstadt. The Universal Linear Accelerator (UNILAC) at GSI Darmstadt provided a $^{48}\mathrm{Ca}$ beam impinging on a thin $^{170}\mathrm{Er}$ target foil. Subsequent to velocity filtering of reaction products in the Separator for Heavy Ion reaction Products (SHIP), the nuclear ground state of the $5n$ evaporation channel $^{213}\mathrm{Ra}$ was mass-selected in SHIPTRAP, and the $^{213}\mathrm{Ra}$ ions were finally transferred into an array of silicon strip detectors surrounded by large composite germanium detectors. Based on comprehensive geant4 simulations and supported by theoretical calculations, the spectroscopic results call for a revision of the decay path of $^{213}\mathrm{Ra}$, thereby exemplifying the potential of a combination of a mass-selective Penning trap device with a dedicated nuclear decay station and contemporary geant4 simulations.

We searched for the bound state of the neutron-rich Lambda-hypernucleus H-6(Lambda), using the Li-6(pi(-), K+)X double charge-exchange reaction at a pi-beam momentum of 1.2 GeV/c at J-PARC. A total of 1.4 x 10(12) pi(-) was driven onto a Li-6 target of 3.5-g/cm(2) thickness. No event was observed below the bound threshold, i.e., the mass of H-4(Lambda) + 2n, in the missing-mass spectrum of the Li-6(pi(-), K+) X reaction in the 2 degrees < theta(pi K) < 20 degrees angular range. Furthermore, no event was found up to 2.8 MeV/c(2) above the bound threshold. We obtained the double-differential cross section spectra of the Li-6(pi(-), K+)X reaction in the angular range of 2 degrees < theta(pi K) < 14 degrees. An upper limit of 0.56 nb/sr (90% C.L.) was obtained for the production cross section of the H-6(Lambda) hypernucleus bound state. In addition, not only the bound state region, but also the Lambda continuum region and part of the Sigma(-) quasifree production region of the Li-6(pi(-), K+) reaction were obtained with high statistics. The present missing-mass spectrum will facilitate the investigation of the Sigma(-) -nucleus optical potential for Sigma(-) -He-5 through spectrum shape analysis.

The beta decay of Tc-100 has been studied by using the total absorption gamma-ray spectroscopy technique at the Ion Guide Isotope Separator On-Line facility in Jyvaskyla. In this work the new Decay Total Absorption gamma-ray Spectrometer in coincidence with a cylindrical plastic beta detector has been employed. The beta intensity to the ground state obtained from the analysis is in good agreement with previous high-resolution measurements. However, differences in the feeding to the first-excited state as well as weak feeding to a new level at high excitation energy have been deduced from this experiment. Theoretical calculations performed in the quasiparticle random-phase approximation framework are also reported. Comparison of these calculations with our measurement serves as a benchmark for calculations of the double beta decay of Mo-100.

An experiment focused on the study of shape coexistence and new high-spin structures in $^{195}\mathrm{Bi}$ has been performed. The nucleus is in a transitional region of the bismuth isotope chain. A large number of new states have been found, resulting in a significant extension of the previously known level scheme. Several new collective structures have been identified. A strongly coupled rotational band built upon the $13/{2}^{+}$ isomeric state was extended up to ${I}^{\ensuremath{\pi}}=(49/{2}^{+})$ and an energy of 5706 keV. The ${I}^{\ensuremath{\pi}}=31/{2}^{+}$ member of the $\ensuremath{\pi}{i}_{13/2}$ band was also found to feed a new long-lived isomeric state with an excitation energy of 2616 keV and a spin and parity of ${I}^{\ensuremath{\pi}}=29/{2}^{+}$. The half-life of the $29/{2}^{+}$ isomeric state was determined to be $1.49(1)\phantom{\rule{0.28em}{0ex}}\ensuremath{\mu}\mathrm{s}$. It decays via the emission of 457-keV $E2$ and 236-keV $E1$ transitions, respectively. A low-energy 46-keV $E2$ transition has been identified to depopulate the ($29/{2}^{\ensuremath{-}}$) isomeric state, with a measured half-life of ${T}_{1/2}=614(5)\phantom{\rule{0.28em}{0ex}}\mathrm{ns}$. This transition allows the excitation energy of the isomeric state to be determined as 2381 keV. The feeding patterns of both $29/{2}^{+}$ and ($29/{2}^{\ensuremath{-}}$) isomeric states have also been described. This is the first time collective structures have also been observed up to high spins and excitation energies in the neutron-deficient $^{195}\mathrm{Bi}$ nucleus. Evidence for the manifestation of shape coexistence in $^{195}\mathrm{Bi}$ is also discussed.

The neutron-rich nucleus \nucleus{200}{Pt} is investigated via in-beam \gamma-ray spectroscopy in order to study the shape evolution in the neutron-rich platinum isotopes towards the N = 126 shell closure. The two-neutron transfer reaction \nucleus{198}{Pt}(\nucleus{82}{Se}, \nucleus{80}{Se})\nucleus{200}{Pt} is used to populate excited states of \nucleus{200}{Pt}. The Advanced Gamma Ray Tracking Array (AGATA) demonstrator coupled with the PRISMA spectrometer detects \gamma rays coincident with the \nucleus{80}{Se} recoils, the binary partner of \nucleus{200}{Pt}. The binary partner method is applied to extract the \gamma-ray transitions and build the level scheme of \nucleus{200}{Pt}. The level at 1884\,keV reported by Yates et. al [Phys. Rev. C 37, 1889] was confirmed to be at 1882.1\,keV and assigned as the (6^+_1) state. An additional \gamma ray was found and it presumably de-excites the (8^+_1) state. The results are compared with state-of-the-art beyond mean-field calculations, performed for the even-even \nucleus{190-204}{Pt} isotopes, revealing that \nucleus{200}{Pt} marks the transition from the \gamma-unstable behaviour of lighter Pt nuclei towards a more spherical one when approaching the N=126 shell closure.

The structure of $^{70}$Ge has been studied through in-beam gamma ray spectroscopy. A new band structure is identified that leads to forking of the ground-state band into two excited bands. Band structures have been investigated using the microscopic triaxial projected shell model approach. The observed forking is demonstrated to result from almost simultaneous band crossing of the two neutron aligned and the \gamma-band built on this two-quasiparticle configuration with the ground-state band.

Forty-six decay chains, assigned to the decay of 288-115, were produced using the 243Am(48Ca,3n)288-115 reaction at the Lawrence Berkeley National Laboratory 88-in. cyclotron. The resulting series of α decays were studied using α-photon and α-x-ray spectroscopies. Multiple α-photon coincidences were observed in the element 115 decay chain members, particularly in the third- and fourth-generation decays (presumed to be 280Rg and 276Mt, respectively). Upon combining these data with those from 22 288-115 decay chains observed in a similar experiment, updated level schemes in 276Mt and 272Bh (populated by the α decay of 280Rg and 276Mt, respectively) are proposed. Photons were observed in the energy range expected for K x rays coincident with the α decay of both 280Rg and 276Mt. However, Compton scattering of higher-energy γ rays and discrete transitions are present in the K x-ray region preventing a definitive Z identification to be made based on observation of characteristic K x-ray energies. (Less)

Excited states in the highly neutron-deficient nucleus W-162 have been investigated via the Mo-92(Kr-78, 2 alpha) W-162 reaction. Prompt gamma rays were detected by the JUROGAM II high-purity germa ...

We have studied the β decay of the Tz=−1, f7/2 shell nuclei Ni54, Fe50, Cr46, and Ti42 produced in fragmentation reactions. The proton separation energies in the daughter Tz=0 nuclei are relatively large (≈4–5 MeV) so studies of the γ rays are essential. The experiments were performed at GSI as part of the Stopped-beam campaign with the RISING setup consisting of 15 Euroball Cluster Ge detectors. From the newly obtained high precision β-decay half-lives, excitation energies, and β branching ratios, we were able to extract Fermi and Gamow-Teller transition strengths in these β decays. With these improved results it was possible to compare in detail the Gamow-Teller (GT) transition strengths observed in beta decay including a sensitivity limit with the strengths of the Tz=+1 to Tz=0 transitions derived from high resolution (3He,t) reactions on the mirror target nuclei at RCNP, Osaka. The accumulated B(GT) strength obtained from both experiments looks very similar although the charge exchange reaction provides information on a broader energy range. Using the “merged analysis” one can obtain a full picture of the B(GT) over the full Qβ range. Looking at the individual transitions some differences are observed, especially for the weak transitions. Their possible origins are discussed. (Less)

Reduced transition strengths of the deexciting transitions from the first two excited states in 33Ar were measured in a relativistic Coulomb excitation experiment at the GSI Helmholtz center. The radioactive ion beam was produced by fragmentation of a primary 36Ar beam on a 9Be target followed by the selection of the reaction product of interest via the GSI Fragment Separator. The 33Ar beam hit a secondary 197Au target with an energy of approximately 145 MeV/nucleon. An array of high-purity germanium cluster detectors and large-volume BaF2 scintillator detectors were employed for γ -ray spectroscopy at the secondary target position. The Lund-York-Cologne Calorimeter was used to track the outgoing ions and to identify the nuclear reaction channels. For the two lowest energy excited states of 33Ar the reduced transition strengths have been determined. With these first results the Tz = −3/2 nucleus 33Ar is now, together with 21Na (Tz = −1/2), the only neutron-deficient odd-A sd shell nucleus in which experimental transition strengths are available. The experimental values are compared to results of shell-model calculations which describe simultaneously mirror-energy differences and transition-strength values of mirror pairs in the sd shell in a consistent way

The structure of the neutron-rich bismuth isotope 217Bi has been studied for the first time. The fragmentation of a primary 238U beam at the FRS-RISING setup at GSI was exploited to perform γ-decay spectroscopy, since μs isomeric states were expected in this nucleus. Gamma rays following the decay of a t1/2=3 μs isomer were observed, allowing one to establish the low-lying structure of 217Bi. The level energies and the reduced electric quadrupole transition probability B(E2) from the isomeric state are compared to large-scale shell-model calculations.

Complete and incomplete fusion cross sections for the $^{9}\mathrm{Be}$ $+\phantom{\rule{0.16em}{0ex}}^{181}\mathrm{Ta}$ system were measured at near barrier energies, using the offline gamma ray spectroscopy method. The results were compared with coupled channel calculations that do not take into account the coupling of the breakup channel, using a double folding potential as bare potential. A complete fusion suppression of the order of 35% was found, at energies above the barrier, whereas the total fusion cross sections are in agreement with the calculations. The ratio between incomplete fusion and total fusion at energies above the Coulomb barrier was found to be $32\ifmmode\pm\else\textpm\fi{}1%$. At sub-barrier energies one observes some enhancement of total fusion cross section.

The shape transition in the neutron-rich Os isotopes is studied by investigating the neutron-rich 196Os nucleus through in-beam γ-ray spectroscopy using a two-proton transfer reaction from a 198Pt target to a 82Se beam. The beam-like recoils were detected and identified with the large-acceptance magnetic spectrometer PRISMA, and the coincident γ rays were measured with the advanced gamma tracking array (AGATA) demonstrator. The de-excitation of the low-lying levels of the yrast-band of 196Os were identified for the first time. The results are compared with state-of-the-art beyond-mean-field calculations, performed for the even-even 188-198Os isotopes. The new results suggest a smooth transition in the Os isotopes from a more axial rotational behavior towards predominately vibrational nuclei through triaxial configurations. An almost perfect γ-unstable/triaxial rotor yrast band is predicted for 196Os which is in agreement with the experimentally measured excited states

Complete and incomplete fusion of an ${}^{16}\mathrm{O}$ projectile with an ${}^{115}\mathrm{In}$ target is studied. Forward recoil range distributions of several evaporation residues were measured at 105 MeV beam energy. The recoil catcher activation technique followed by offline gamma ray spectroscopy was used. The disentanglement of the complete and incomplete fusion processes was done in terms of full and partial linear momentum transfer from the projectile to the target nucleus. Results indicate the occurrence of incomplete fusion involving the breakup of ${}^{16}\mathrm{O}$ into ${}^{4}$He + ${}^{12}$C and/or ${}^{8}$Be + ${}^{8}$Be followed by fusion of one of the fragments with the target nucleus ${}^{115}\mathrm{In}$. The complete fusion contributions deduced from the recoil range distribution data were found to be consistent with the predictions of the theoretical model code pace4. An attempt was also made to separate out the relative contributions of complete and incomplete fusion components from the analysis of the measured recoil range distribution data. The study indicates that the incomplete fusion contribution increases with the projectile energy and the mass asymmetry of the interacting partners. The projectile structure effect also plays an important role in the underlying reaction dynamics.

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.

Low-spin states in ${}^{124,126,128,130}\mathrm{Ba}$ fed by the $\mathrm{EC}/{\ensuremath{\beta}}^{+}$ decay of their La parents have been investigated by means of the \ensuremath{\gamma}-\ensuremath{\gamma} angular correlation measurement coupled with an isotope separator on-line. The spin of the first excited ${0}^{+}$ states ${(0}_{2}^{+})$ were unambiguously established, and higher-excited ${0}^{+}$ states were newly identified. The energy of the ${0}_{2}^{+}$ state in ${}^{124}\mathrm{Ba}$ previously assigned was revised upward. Resultingly, the level energy of the ${0}_{2}^{+}$ state in neutron-deficient Ba nuclei takes a minimum at $N=72$ and then gradually increases toward neutron midshell $(N=66),$ while the level energy of the ${0}_{3}^{+}$ state rapidly decreases with decreasing neutron number. From an extrapolation of these ${0}^{+}$ energies, it is highly expected that the energy relation between the ${0}_{2}^{+}$ and ${0}_{3}^{+}$ state would invert at ${}^{122}\mathrm{Ba}$ or at more deformed Ba nuclei. This energy inversion is interpreted as the evolution of the ${0}_{2}^{+}$ state in \ensuremath{\gamma}-soft nuclei toward the two-phonon \ensuremath{\gamma}-vibrational ${0}^{+}$ state in axially-symmetric deformed nuclei, while the ${0}_{3}^{+}$ state toward the \ensuremath{\beta}-vibrational ${0}^{+}$ state.

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.

Neutron-rich nuclei ${}^{147,149,151}$Ce have been studied via the prompt $\ensuremath{\gamma}$-ray spectroscopy of ${}^{248}$Cm fission fragments. A partial level scheme for ${}^{151}$Ce is presented for the first time, along with the high-spin structure in ${}^{147,149}$Ce. A rapidly changing yrast structure with neutron number is observed and it is suggested that bands in ${}^{147}$Ce and ${}^{151}$Ce are built on the $\ensuremath{\nu}{i}_{13/2}$ Nilsson state. The level scheme of ${}^{149}$Ce displays two bands with quite similar transition energies. There is no experimental evidence for octupole deformation in any of the three nuclei.

High-spin states in {sup 162}Lu and {sup 164}Lu have been studied by means of in-beam {gamma}-ray spectroscopy techniques using the multidetector array GASP. The excited states have been populated through the {sup 139}La({sup 28}Si,5n){sup 162}Lu and {sup 139}La[{sup 29(30)}Si,4(5)n]{sup 164}Lu reactions. Level schemes were constructed for both nuclei. Configurations for the rotational bands have been discussed. Alignments, band crossing frequencies, and B(M1)/B(E2) ratios have been analyzed in the framework of the cranking model. The systematic evolution of the signature inversion in the {pi}h{sub 11/2}{circle_times}{nu}i{sub 13/2} structure is reviewed. {copyright} {ital 1997} {ital The American Physical Society}

{beta} decay of the T{sub z}={minus}1/2 nuclide {sup 71}Kr has been studied at the ISOLDE PSB Facility at CERN. {sup 71}Kr ions were produced in spallation reactions in a Nb foil using the 1 GeV proton beam and studied by means of {beta}-delayed proton, {beta}- and {gamma}-ray spectroscopy. The half-life and the {beta}-decay energy of {sup 71}Kr were determined using the decay of protons and positrons. These results: T{sub 1/2}=100{plus_minus}3ms and Q{sub EC}=10.14{plus_minus}0.32MeV and the first observation of the {beta} branch to the 207 keV level in {sup 71}Br makes the extension of the systematics of Gamow-Teller matrix elements of mirror nuclei up to A=71 possible. The Gamow-Teller strength of the same magnitude as that of the fp-shell mirror nuclei is observed for the ground-state transition. {copyright} {ital 1997} {ital The American Physical Society}

Precision measurements of superallowed Fermi β-decay allow for stringent tests of the magnitude of isospin-symmetry-breaking effects in nuclei, the validity of the conserved vector current hypothesis, and the unitarity of the Cabibbo-Kobayashi-Maskawa (CKM) quark-mixing matrix. A high-precision measurement of the branching ratio for the superallowed β+ decay of 74Rb has been performed at the Isotope Separator and ACcelerator (ISAC) facility at TRIUMF. The 8π spectrometer, an array of 20 HPGe detectors, was used to detect γ-rays emitted following the Gamow-Teller and non-analogue Fermi β-decays of 74Rb. PACES, an array of 5 Si(Li) detectors, was used to detect emitted conversion electrons, while half of SCEPTAR, a close-packed array of 10 plastic scintillators, was used to detect emitted β particles. In this experiment, 23 excited states were identified in 74Kr which were populated following the β-decay of 74Rb. A total of 58 γ-rays were identified following the 8.241(4)x108 detected β-particles. An observed non-superallowed branching ratio of 0.396(7)% was determined from the intensity of the identified γ-rays, while the unobserved non-superallowed intensity was calculated to be 0.05(5)%, leading to a superallowed branching ratio of 99.55(5)%. The superallowed branching ratio is now the most precise experimental quantity in the determination of the superallowed ft-value of 74Rb. Combining the half-life and Q-value with the superallowed branching ratio measured in this work leads to a superallowed ft-value of 3082.6(66) s. Finally, comparisons between the superallowed ft-value, the world average Ft-value, and the non-analogue Fermi branching ratio are made to provide future guidance in the refinement of the theoretical models required to describe the crucial isospin-symmetry-breaking term in superallowed β-decay.

Short lived neutron rich nuclei including 93 Br, 93 Kr and 94 Kr were produced in proton induced fission of 238 U at the HRIBF in Oak Ridge. Their beta decay was studied by means of a high resolution on line mass separator and beta gamma spectroscopy methods. The half life of 93Br T1/2 = 152(8) ms and delayed branching ratio of Pn = 53-8+11 may be compared to the previously reported values of T1/2 = 102(10) ms and Pn = 68(7)%. At the same time the half life of 94Kr T1/2 = 227(14) ms and B delayed branching ratio of Pn = 1.9+0.6 0.2 % of 93Kr are in very good agreement with literature values. The decay properties of 93Br include four new gamma transitions following beta delayed neutron emission.

The neutron rich nuclei {sup 61,63}Co have been studied using the reactions {sup 16}O({sup 48}Ca,{ital p}2{ital n}){sup 61}Co and {sup 18}O({sup 48}Ca,{ital p}2{ital n}){sup 63}Co at a bombarding energy of 110 MeV. Discrete {gamma} rays from the channels of interest were investigated using prescaled {gamma} singles, charged-particle{endash}{gamma}, neutron{endash}charged-particle{endash}{gamma}, and charged-particle{endash}{gamma}{endash}{gamma} coincidence techniques. Decay schemes, with level spins deduced from two-point angular distribution data, are presented together with some approximate information on apparent state lifetimes. The experimental results are compared with previous light ion data for these systems and with theoretical shell model predictions. These data represent the first study of medium to high spin states in these nuclei. {copyright} {ital 1996 The American Physical Society.}

The level structures of the neutron-rich {sup 104}Mo and {sup 108}Mo nuclei have been investigated by observing prompt {gamma} rays emitted in the spontaneous fission of {sup 248}Cm with the EUROGAM spectrometer. Levels with spins up to 12{h_bar} have been observed and {gamma} branching obtained. The data can be satisfactorily described when {sup 104,108}Mo are considered as axially symmetric nuclei: in {sup 104}Mo, rotational bands based on the ground state, the one-phonon and the two-phonon {gamma}-vibrational states and a quasiparticle state have been observed, whereas in {sup 108}Mo the information is limited to the yrast band and the one phonon {gamma} band. {copyright} {ital 1996 The American Physical Society.}

Excited states of the {sup 125}La and {sup 127}La nuclei were populated following {sup 112}Sn({sup 16}O,{ital p}2{ital n}) and {sup 112}Cd({sup 19}F,4{ital n}) fusion-evaporation reactions, respectively, and investigated using methods of in-beam {gamma}-ray spectroscopy. Five collective bands in {sup 125}La, and eleven collective bands in {sup 127}La were observed. The spin and/or parity assignments of excited states in these nuclei were based on angular-correlation and linear-polarization measurements. The experimental data are discussed and compared to the results of self-consistent total-Routhian-surface calculations including quadrupole pairing. {copyright} {ital 1996 The American Physical Society.}

We have measured the complete fusion, incomplete fusion, and the one-neutron stripping reaction for the ${}^{9}$Be+${}^{186}$W system, at energies not too much above the Coulomb barrier. The online and offline gamma ray spectroscopy methods were used for the derivation of the cross sections. A large value of one-neutron stripping cross section has been observed. The comparison of the data with coupled channel calculations without taking into account the breakup and transfer channels show the usual complete fusion suppression. The possible suppression of the total fusion is discussed.

The cross sections for the {sup 58}Ni({ital n},{ital p}){sup 58}Co{sup {ital m},{ital g}} reactions were measured in the neutron energy range 2.1--14.8 MeV using the activation technique in combination with high-resolution gamma-ray spectroscopy. Neutrons were produced via the {sup 2}H({ital d},{ital n}){sup 3}He and {sup 3}H({ital d},{ital n}){sup 4}He reactions using solid TiD, TiT, and deuterium gas targets. The isomeric cross section ratio was determined in the 5.38--12.2 MeV range and at 14.8 MeV neutron energy. Statistical model calculations taking into account precompound effects were performed for the formation of the isomeric and ground states of the {sup 58}Co. The calculational results based on the ``back-shifted`` level density model agree well with the measured excitation functions and render possible the selection of the most probable values of isomeric cross section ratios among the discrepant data obtained around 2 and 14 MeV neutron energies.

The near-yrast spectrum of the N=84 isotope $^{144}\mathrm{Nd}$ has been studied using the $^{130}\mathrm{Te}$${(}^{18}$O,4n) reaction at a lab energy of 85 MeV and the techniques of \ensuremath{\gamma}-ray spectroscopy. Sixteen new states and 23 new \ensuremath{\gamma} rays were placed in the level scheme. Most of the yrast and near-yrast negative-parity states have been interpreted in terms of empirical shell-model configurations. However, the interpretation of a sequence of states from J=17--24 in terms of the ${\mathit{h}}_{11/2}^{3}$${\mathit{g}}_{7/2}^{\mathrm{\ensuremath{-}}1}$${\mathit{d}}_{5/2}^{\mathrm{\ensuremath{-}}6}$ proton configuration is problematic because the observed energies cannot be satisfactorily reproduced with empirical shell-model calculations.

The reaction {sup 168}Er({ital d},2{ital n}{gamma}) and conventional in-beam {gamma}-ray spectroscopy have been used to assign, for the first time, many {gamma}-ray transitions to {sup 168}Tm. On the basis of {gamma}-{gamma} coincidence data, some of these observed {gamma} rays are identified as transitions between the low-spin members of rotational bands in {sup 168}Tm, specifically, those with {ital K}{sup {pi}}=3{sup +}, (3{sup {minus}}), and (4{sup {plus_minus}}).

With prompt \ensuremath{\gamma}-ray and x-ray spectroscopy on fission fragments, several new transitions in $^{109,111}\mathrm{Ru}$ have been identified. Angular correlation analysis of several of the new transitions yield evidence of a stretched E2 band structure. Qualitative Nilsson model arguments, systematics, and triaxial rotor+particle calculations support our hypothesis that the observed band is built on the unique parity \ensuremath{\nu}${\mathit{h}}_{11/2}$ orbital.

Excited states of the neutron deficient nucleus $^{109}\mathrm{Te}$ were identified for the first time in the $^{54}\mathrm{Fe}$${(}^{58}$Ni,2pn) reaction by in-beam \ensuremath{\gamma}-spectroscopic methods. The nordball detector array, equipped with a charged-particle and a neutron detector system for reaction channel identification, was used to detect the evaporated particles and \ensuremath{\gamma} rays. A level scheme was constructed on the basis of \ensuremath{\gamma}\ensuremath{\gamma}-coincidence relations, and the angular momenta of the states were determined from the measured angular correlation intensity ratios. Two favored bands built on the \ensuremath{\nu}${\mathit{g}}_{7/2}$ and \ensuremath{\nu}${\mathit{h}}_{11/2}$ neutron quasiparticle states were identified. The structure of the nucleus is discussed in the framework of the particle-vibration coupling model using the interacting boson-fermion formalism up to spin 27/2. The negative parity sequence is compared to Total Routhian Surface calculations.