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To control non-native species, resource managers may import and introduce biocontrol agents. Like accidentally introduced insects, biocontrol agents must overcome several abiotic and biotic obstacles to establish successfully. They can also have varying efficacy and negative or positive impacts on native species and ecosystems. Given the similarities between accidentally introduced insects and biocontrol agents, researchers studying these organisms can more effectively communicate and actively link data to improve overall understanding and management of non-native species within the framework(s) of invasion theory. To assess interdisciplinarity between invasion ecologists and biocontrol practitioners that study insects in forests, we identified 102 invasion ecology and 90 biocontrol articles published from 2006 to 2018. These articles helped us determine which broad disciplines (invasion ecology, biocontrol, other control, other ecological, and nonecological) and publication formats (e.g., journals and books) the authors cited most. We found 1) invasion ecologists primarily cite other invasion ecology research; 2) biocontrol researchers cite biocontrol and invasion ecology research; 3) both disciplines primarily cited peer-reviewed journal articles; and 4) there was 65–70% overlap in the top 20 journals cited in primary invasion ecology and biocontrol literature. Though we found some cross-communication, it is currently mostly unidirectional, whereby invasion ecology informs biocontrol. We identify and discuss three areas—1) ecological principles governing success or failure of introduced species, 2) the invasion process, and 3) negative impacts on native species—for which the disciplines possess substantial overlap to demonstrate that biocontrol agents can provide invasion ecologists with an unconventional model to study the mechanisms of species invasion.

A long‐standing goal of invasion biology is to identify factors driving highly variable impacts of non‐native species. Although hypotheses exist that emphasize the role of evolutionary history (e.g., enemy release hypothesis & defense‐free space hypothesis), predicting the impact of non‐native herbivorous insects has eluded scientists for over a century.Using a census of all 58 non‐native conifer‐specialist insects in North America, we quantified the contribution of over 25 factors that could affect the impact they have on their novel hosts, including insect traits (fecundity, voltinism, native range, etc.), host traits (shade tolerance, growth rate, wood density, etc.), and evolutionary relationships (between native and novel hosts and insects).We discovered that divergence times between native and novel hosts, the shade and drought tolerance of the novel host, and the presence of a coevolved congener on a shared host, were more predictive of impact than the traits of the invading insect. These factors built upon each other to strengthen our ability to predict the risk of a non‐native insect becoming invasive. This research is the first to empirically support historically assumed hypotheses about the importance of evolutionary history as a major driver of impact of non‐native herbivorous insects.Our novel, integrated model predicts whether a non‐native insect not yet present in North America will have a one in 6.5 to a one in 2,858 chance of causing widespread mortality of a conifer species if established (R 2 = 0.91) Synthesis and applications. With this advancement, the risk to other conifer host species and regions can be assessed, and regulatory and pest management efforts can be more efficiently prioritized., This research is the first to empirically support historically assumed hypotheses about the importance of evolutionary history as a major driver of impact of non‐native herbivorous insects. We discovered that evolutionary history between native and novel hosts, life history traits of the novel host, and the evolutionary relationship between non‐native and coevolved insects on a shared host were more predictive of impact than traits of the invading insect. Our novel, integrated model predicts whether a non‐native insect not yet present in North America will have a one in 6.5 to a one in 2,858 chance of causing widespread mortality of a conifer species if established.

Understanding the successes and failures of nonnative species remains challenging. In recent decades, researchers have developed the enemy release hypothesis and other antagonist hypotheses, which posit that nonnative species either fail or succeed in a novel range because of the presence or absence of antagonists. The premise of classical biological control of invasive species is that top-down control works. We identify twelve existing hypotheses that address the roles that antagonists from many trophic levels play during plant and insect invasions in natural environments. We outline a unifying framework of antagonist hypotheses to simplify the relatedness among the hypotheses, incorporate the role of top-down and bottom-up influences on nonnative species, and encourage expansion of experimental assessments of antagonist hypotheses to include belowground and fourth trophic level antagonists. A mechanistic understanding of antagonists and their impacts on nonnative species is critical in a changing world.

Millions of people around the globe are suffering from energy poverty, particularly the inhabitants of Africa and South-East Asia. Electrification through national grids is cost-prohibitive with limited power generation sources in the third world countries. The low-voltage, low-power islanded DC microgrids are a practical option for rural electrification. In this paper, the detailed network loss analysis of four different microgrid architectures is performed using the modified Newton-Raphson power flow for DC systems. These architectures include, 1) Centralized generation centralized storage (CGCS), 2) Centralized generation distributed storage (CGDS), 3) Distributed generation centralized storage (DGCS), and 4) Distributed generation distributed storage (DGDS), which are implemented with both radial and ring interconnection schemes using time-varying load demand and dynamic PV generation. The comparative analysis on these architectures is performed with multiple conductor sizes and different low-voltage levels which indicates that distributed architecture with ring interconnection is more efficient and reliable in comparison to other architectures and interconnection schemes due to its high efficiency, low voltage drop, and reduced distribution losses. This analysis will be useful in optimal planning and designing of new and upgrading of existing low voltage DC (LVDC) microgrid systems systems.

Benthic microorganisms transported into the water column potentially influence biogeochemical cycles and the pelagic food web structure. In the present study six gas-releasing vent sites in the Coal Oil Point seep field (California) were investigated, and the dislocation of microorganisms from the sediment into the water column via gas bubbles released from the seabed was documented. It was found that the methanotrophs transport efficiency was dependent on the volumetric gas flow, with the highest transport rate of 22.7 × 103 cells mLgas−1 at a volumetric gas flow of 0.07 mLgas s−1, and the lowest rate of 0.2 × 103 cells mLgas−1 at a gas flow of 2.2 mLgas s−1. A simple budget approach showed that this bubble-mediated transport has the potential to maintain a relevant part of the water-column methanotrophs in the seep field. The bubble-mediated link between the benthic and pelagic environment was further supported by genetic analyses, indicating a transportation of methanotrophs of the family Methylomonaceae and oil degrading bacteria of the genus Cycloclasticus from the sediment into the water column. These findings demonstrate that the bubble-mediated transport of microorganisms influences the pelagic microbial abundance and community composition at gas-releasing seep sites.

A novel and emerging eastern white pine (Pinus strobus L.) dieback phenomenon is occurring in the Southern Appalachian Mountains in the eastern United States. Symptomatic eastern white pine trees exhibit canopy thinning, branch dieback, and cankers on the branches and bole. These symptoms are often associated with the presence of a scale insect, Matsucoccus macrocicatrices Richards (Hemiptera: Matsucoccidae), and a fungal pathogen, Caliciopsis pinea Peck (Coryneliales: Coryneliaceae). We determined the extent, range, and severity of dieback of 2,061 eastern white pine trees from 40 sites in Georgia, North Carolina, South Carolina, Tennessee, Virginia, and West Virginia. We also evaluated associations between eastern white pine health and abiotic (aspect, elevation, latitude, precipitation, slope, and temperature) and biotic (eastern white pine basal area and density, relative stand density, and presence of C. pinea and M. macrocicatrices) factors. Our results indicate that trees ≥2.54 cm DBH had an average health rating of 3.57 (1 = healthy tree, 5 = dead tree), with 57% being in the 4–5 health rating groups. Eastern white pine dieback was positively associated with presence of C. pinea, and negatively associated with mean annual temperature and tree size. Sawtimber (≥22.86 cm) were healthier than poletimber (12.70–22.61 cm) and sapling sized trees (2.54–12.45 cm). Further, C. pinea incidence was positively correlated with eastern white pine density and M. macrocicatrices. The insect-pathogen complex was present in all six states and 80% of the sites. If eastern white pine dieback continues, effective management practices will be needed to conserve and maintain this economically and ecologically important pine species in the eastern United States.

Matsucoccus macrocicatrices Richards (Hemiptera: Matsucoccidae) is the only species within this genus that feeds and reproduces on eastern white pine (Pinus strobus L.), and at the time of its description, was not observed or known to cause serious damage. With eastern white pine dieback occurring extensively throughout the Appalachian Mountains, researchers are now in search of the contributors to this dieback phenomenon. Since its recent discovery (2007) far outside its historical range, M. macrocicatrices, and cankers associated with Caliciopsis pinea Peck, are regularly present on symptomatic trees throughout the range of eastern white pine. Little is known about the relationship between M. macrocicatrices and the fungal cankers commonly found on eastern white pines expressing dieback symptoms. For this study, we evaluated the relationships between both focal organisms and the extent of dieback symptoms on tree seedlings to identify contributing factors affecting symptomatic trees. We assessed the insect-pathogen complex on 270 eastern white pine seedlings from nine states that include the Appalachian Mountain range. There were positive correlations between M. macrocicatrices and seedling dieback, cankers and seedling dieback, and M. macrocicatrices and cankers in both the southern and northern portions of the Appalachians. About 95% of the observed M. macrocicatrices cysts and shells were associated with cankers, especially C. pinea-dominated cankers, which were exceptionally abundant on severely affected seedlings. The most prevalent fungi isolated from cankers without apparent fruiting bodies of C. pinea were in the genus Phaeomoniella. Trials were conducted to test the pathogenicity of C. pinea and other fungal isolates. Of the 15 fungal species tested, C. pinea was the only pathogenic species that formed girdling cankers on eastern white pine seedlings. We postulate that there is a facultative relationship between M. macrocicatrices and C. pinea, forming an insect-pathogen complex that is contributing to eastern white pine dieback and significantly impacting its regeneration dynamics in North America.

Mn is one of the most abundant redox-sensitive metals on earth. Some microorganisms are known to use Mn(IV) oxide (MnO2) as electron acceptor for the oxidation of organic compounds or hydrogen (H2), but so far the use of sulfide (H2S) has been suggested but not proven. Here we report on a bacterial isolate which grows autotrophically and couples the reduction of MnO2 to the oxidation of H2S or thiosulfate (S2O32−) for energy generation. The isolate, originating from the Black Sea, is a species within the genus Sulfurimonas, which typically occurs with high cell numbers in the vicinity of sulfidic environments [Y. Han, M. Perner, Front. Microbiol. 6, 989 (2015)]. H2S and S2O32− are oxidized completely to sulfate (SO42−) without the accumulation of intermediates. In the culture, Mn(IV) reduction proceeds via Mn(III) and finally precipitation of Ca-rich Mn(II) carbonate [Mn(Ca)CO3]. In contrast to Mn-reducing bacteria, which use organic electron donors or H2, Fe oxides are not observed to support growth, which may either indicate an incomplete gene set or a different pathway for extracellular electron transfer.

Cyanobacterial blooms regularly occur in the Baltic Sea during the summer months, with filamentous, heterocystous Nodularia spumigena and Dolichospermum sp. and the coccoid picocyanobacterium Synechococcus spp. as important species. Under calm conditions, N. spumigena accumulate at the surface, whereas Dolichospermum sp. and Synechococcus sp. remain at the subsurface, in the upper water layer. This vertical separation allows co-occurring species to compete for the same resources. The factors that determine the vertical distribution within blooms, however, are mostly unknown. The present study examined the growth rates of these three cyanobacterial species in a two-factorial experiment, with temperature (16 and 24 °C) and radiation (38 and 150 μmol photons m−2 s−1) conditions mimicking those at the water surface and directly below. To determine whether interactions between the three species influenced their growth rates (and therewith also their vertical distribution), paired and multi-species cultures were established. In the single-species cultures, the autecological preferences of the species matched the assumed natural occurrence in bloom events: N. spumigena grew best under high and Dolichospermum sp. and Synechococcus sp. under low light conditions (maximum growth rates at the preferred conditions: μ = 0.48 ± 0.017, 0.88 ± 0.092, and 0.67 ± 0.012, respectively). High temperatures were tolerated by N. spumigena, but inhibited the growth of Dolichospermum sp. and Synechococcus sp. These results suggested that the factors resulting in the vertical separation of species within a bloom are species-specific: N. spumigena responded predominantly to irradiance and only slightly to temperature, Dolichospermum sp. was intensely affected by temperature and less by irradiance, and Synechococcus sp. responded more strongly to irradiance than to temperature. The interactions in paired and multi-species cultures revealed beneficial and detrimental effects, depending on species composition and abiotic conditions. Under the environmental conditions in which the three species occur, however, similar interactions resulted in no or only slight inhibition. Our observations demonstrate how autecological preferences together with the avoidance of negative interactions determine the vertical distribution of cyanobacteria during bloom events in the Baltic Sea.

Assessing the ecological and economic impacts of non-native species is crucial to providing managers and policymakers with the information necessary to respond effectively. Most non-native species have minimal impacts on the environment in which they are introduced, but a small fraction are highly deleterious. The definition of ‘damaging’ or ‘high-impact’ varies based on the factors determined to be valuable by an individual or group, but interpretations of whether non-native species meet particular definitions can be influenced by the interpreter’s bias or level of expertise, or lack of group consensus. Uncertainty or disagreement about an impact classification may delay or otherwise adversely affect policymaking on management strategies. One way to prevent these issues would be to have a detailed, nine-point impact scale that would leave little room for interpretation and then divide the scale into agreed upon categories, such as low, medium, and high impact. Following a previously conducted, exhaustive search regarding non-native, conifer-specialist insects, the authors independently read the same sources and scored the impact of 41 conifer-specialist insects to determine if any variation among assessors existed when using a detailed impact scale. Each of the authors, who were selected to participate in the working group associated with this study because of their diverse backgrounds, also provided their level of expertise and uncertainty for each insect evaluated. We observed 85% congruence in impact rating among assessors, with 27% of the insects having perfect inter-rater agreement. Variance in assessment peaked in insects with a moderate impact level, perhaps due to ambiguous information or prior assessor perceptions of these specific insect species. The authors also participated in a joint fact-finding discussion of two insects with the most divergent impact scores to isolate potential sources of variation in assessor impact scores. We identified four themes that could be experienced by impact assessors: ambiguous information, discounted details, observed versus potential impact, and prior knowledge. To improve consistency in impact decision-making, we encourage groups to establish a detailed scale that would allow all observed and published impacts to fall under a particular score, provide clear, reproducible guidelines and training, and use consensus-building techniques when necessary.

Energy poverty is a big enigma, that needs to be considered for millions of people suffering in remote rural communities without electricity access. As the grid extension is cost prohibitive, the renewable energy sources (RES) are an optimal solution for off-grid communities. In this paper, a hybrid microgrid system is designed and simulated in Hybrid Optimization of Multiple Energy Resources (HOMER) based on the estimated load demand and available energy resources. Three different rural villages from Ethiopia, Uganda, and Brazil are considered for a comparative performance analysis based on the least cost of energy (LCOE). Two different dispatch strategies, i.e., i) Load following and ii) Cycle charging are modeled with the different scheduled operation of the diesel generator and bio generator. The solar and wind resource data are obtained from the National Solar Radiation Database (prediction of the worldwide database) [1] and the National Renewable Energy Laboratories (NREL) [2] respectively. The results of sensitivity analysis, techno-economic analysis and cost optimization based on LCOE verify the feasibility of the proposed microgrid system.

Redox-sensitive mobilization of nutrients from sediments strongly affects the eutrophic state of the central Baltic Sea; a region associated with the spread of hypoxia and almost permanently anoxic and sulfidic conditions in the deeper basins. Ventilation of these basins depends on renewal by inflow of water enriched in oxygen (O2) from the North Sea, occurring roughly once per decade. Benthic fluxes and water column distributions of dissolved inorganic nitrogen species, phosphate (PO43-), dissolved inorganic carbon (DIC), sulfide (HS-) and total oxygen uptake (TOU) were measured along a depth gradient in the Eastern Gotland Basin (EGB). Campaigns were conducted during euxinic conditions of the deep basin in Aug./Sept. 2013 and after two inflow events in July/Aug. 2015 and March 2016 when O2 concentrations in deep waters reached 60 µM. The intrusion of O2-rich North Sea water into the EGB led to an approximate 33 % and 10 % reduction of the seabed PO43- and ammonium (NH4+) release from deep basin sediments. Post-inflow, the deep basin sediment was rapidly colonized by HS- oxidizing bacteria tentatively assigned to the family Beggiatoaceae, and HS- release was completely suppressed. The presence of a hypoxic transition zone (HTZ) between 80 and 120 m water depth was confirmed not only for euxinic deep-water conditions during 2013 but also for post-inflow conditions. Because deep-water renewal did not ventilate the HTZ, where PO43- and NH4+ fluxes were highest, high seabed nutrient release there was relatively unchanged. Extrapolation of the in situ nutrient fluxes indicated that, overall, the reduction in PO43- and NH4+ release in response to deep-water renewal can be considered as minor, reducing the internal nutrient load by 2 and 12 % only, respectively. Infrequent inflow events thus have a limited capacity to sustainably reduce internal nutrient loading in the EGB and mitigate eutrophication.

Long-term precipitation records from the extremely arid northern coast of Chile (18°S–30°S) were analysed to assess changes occurring at different time scales. Results are presented here along with a discussion on changes in the temperature and cloudiness regimes in order to offer a more comprehensive overview of the climate evolution in this extremely arid region. Apart from a significant influence of ENSO on the rainfall regime, characterized by a tendency for more frequent rainfall events during El Nino episodes, changes at the decadal time scale were identified in association with the Interdecadal Pacific Oscillation (IPO). Thus, the warm IPO-phase is associated with increased precipitation, while the opposite occurs during the cold IPO-phase. Changes occurring at the interannual and decadal time scales are superimposed on a long-term precipitation decline during the 20th century. Apart from the intensified dryness, the temperature records show a positive long-term trend resulting mainly from an abrupt warming in the mid-1970s, principally associated with a marked upwards shift of the minimum daily temperature, coinciding with the change from the cold to the warm phase of the IPO. However, the period following this step-like warming has been characterized by a persistent cooling trend, most evident in the maximum daily temperature, which is coherent with a negative trend in the sea surface temperature over a large oceanic region off the coast of northern Chile. In the northernmost region, this behaviour in the temperature regime was accompanied by a strong decrease in cloudiness since the 1970s. The negative trend in rainfall and the decrease in the total cloud cover are certainly important factors that could explain the coastal vegetation decline over the past decades in the coastal region north of 24°S. Copyright © 2011 Royal Meteorological Society

High-spin states from the three-quasiparticle (3qp) configuration $\pi$ g $_{9/2}\nu$ h11/2 2 in the neutron-rich 49In isotopes have been studied in the framework of shell model calculation. The two-body residual interactions needed for such calculations have been extracted from the level schemes of neighbouring nuclei. In particular, the evolution of the proton-neutron $\pi g_{9/2}\nu h_{11/2}$ interaction has been analyzed as a function of the neutron number. When the gradual filling of the $\nu h_{11/2}$ sub-shell is taken into account, the results of the 3qp configuration calculations are found to be very close to the experimental positive-parity yrast states located above 2 MeV excitation energy in $^{113\mbox{--}121}$ In. Moreover, several long-lived isomeric states with positive parity are predicted in 123,125,127In.

High-spin states in 108,110Pd isotopes are studied by $\gamma$ -ray spectroscopy of heavy-ion-induced fission. The Pd isotopes are produced in the fission channel of the 31P + 176Yb reaction at beam energy 152 MeV. The prompt $\gamma$ -rays are detected with the EUROBALL4 multidetector array. The yrast states of 108,110Pd have been observed above the region of the first backbend. The level scheme of 108Pd was extended with a new negative-parity band. The yrast sequence in 110Pd is observed up to spin I = 14 + and negative-parity bands have also been identified. The backbending in these even-mass Pd isotopes is associated with the alignment of the neutron (h 11/2)2 pair. The negative-parity states arise from two neutron configurations $\nu h_{11/2} \otimes \nu g_{7/2}$ and $\nu h_{11/2} \otimes \nu d_{5/2}$ and they are interpreted in the frame of two-quasiparticle + rotor model as semidecoupled bands. The observed experimental staggering in the $\gamma$ -bands of 108,110Pd supports the theoretical predictions for $\gamma$ -instability of their shapes.

Measurements of g-factors of excited states in barium and cerium fission fragments have been performed using time-integral perturbed angular correlations between secondary-fragment gamma rays. Larmor precession angles have been obtained for the first I-pi = 2(+) states in Ba-144,Ba-146 and Ce-146,Ce-148 as well as for the 9/2(-) state at 117 keV in Ba-143, the 7/2(-) state at 114 keV in Ba-145 and the first 4(+) state in Ce-150. The deduced g-factor fur the 2(+) state in Ba-146 provides substantiating evidence for a downward trend in 2(+) g-factors with increasing neutron number, in line with Interacting Boson Model predictions for the neutron-rich barium isotopes, assuming the quenching of the Z = 64 shell gap for N>88. The static hyperfine fields for implanted barium and cerium isotopes are found to be opposite in sign. These results constitute the first use of secondary-fragment gamma-ray emission in the determination of g-factors of excited states in fission fragments. (C) 1999 Elsevier Science B.V. All rights reserved.

Excited levels in the {sup 109}Tc nucleus, populated in the spontaneous fission of {sup 248}Cm, have been studied using the EUROGAM2 array. In {sup 109}Tc we have found a new band corresponding to the {pi}5/2{sup -}[303] configuration and a three-quasiparticle band with I{sup {pi}}=(15/2{sup -}) band-head level at 1749.5 keV. The structure of the 1749.5-keV level probably involves the {l_brace}{pi}5/2{sup +}[422]{nu}(5/2{sup -}[532],5/2{sup +}[413]){r_brace}{sub 15/2}{sup -} prolate configuration. The quasiparticle-rotor model calculations performed in this work show that the odd-proton configurations observed in {sup 107}Tc and {sup 109}Tc are consistent with the scheme of proton excitations in a prolate triaxial potential. Significant differences between the degree of triaxiality observed for positive- and negative-parity excitations may be due to blocking of the triaxial shape by the odd proton populating negative-parity orbitals. The properties of the new 494.5-, 1440.7-, and 1748.8-keV levels found in {sup 109}Tc may indicate a change toward an oblate shape in this nucleus.

Lifetimes of excited states have been measured for the positive-parity rotational bands in neutron-rich Ba-142,Ba-144 as well as the 7(-) and 9(-) states of the negative-parity band in Ba-144 using the differential Doppler shift method. The deduced quadrupole moment, Q(t), of the positive-parity band decreases with angular momentum and overall shows good agreement with earlier measurements. The measured lifetimes of 7(-) and 9(-) states are used to determine the electric dipole moment, D-0=0.17(3) and 0.09(1) e fm, respectively, in the negative-parity octupole band of Ba-144.

Levels in 115Pd and 117Pd nuclei, populated in the spontaneous fission of 248Cm were studied by means of prompt gamma spectroscopy using the EUROGAM2 array of Anti-Compton spectrometers. Negative-parity, I = 9/2 excitations were identified, which are associated with the long-lived isomers in these nuclei, reported previously as 11/2- excitations. The new data indicate spin and parity 3/2 + for ground states in 115Pd and 117Pd instead of 5/2 + proposed in previous works. This result implicates changes of spin assignments to other levels in both nuclei.

A T 1/2 = 16(2) ns isomeric level, populated in the spontaneous fission of $^{248}$Cm, has been found in $^{101}$Zr at 941.8 keV in a measurement of prompt $\gamma$-rays using the EUROGAM2 array. The level is interpreted as a K-isomer corresponding to the 9/2[404] neutron-hole excitation. The quadrupole moment, Q0 = 3.6(4) eb, deduced for the new band indicates a large deformation of $\beta_2$=0.38(4), which is produced by a specific shape-coexistence mechanism. This is another observation of the $\nu$9/2[404] orbital in the mass A $\sim$ 100 region, confirming the presence of the effect reported first in our previous work. The 9/2[404] neutron-hole excitation is also confirmed in the $^{97}$Sr nucleus and the deformation $\beta_2$=0.44(2) is determined for this configuration. The properties of the 9/2[404] neutron orbital and its influence on the onset of deformation in the A $\sim^100 region are discussed.

The $^{111}$Ru nucleus, populated in the spontaneous fission of $^{248}$Cm has been studied by means of prompt gamma spectroscopy using the EUROGAM2 array. Spin and parity assignments, based on angular correlations, linear polarization, and conversion coefficient measurements differ from those available in the literature. New bands are reported, which incorporate $\gamma$ transitions seen previously but not placed in the scheme of $^{111}$Ru or placed incorrectly. The bands are interpreted as neutron excitations into subshells originating predominantly from the h 11/2, g 7/2 and s 1/2 spherical orbitals. The s 1/2 band, strongly mixed with the d 3/2, d 5/2 and g 7/2 configurations, is observed for the first time in this region.

The ground-state band in 110Mo has been observed for the first time. The band, comprising six levels, has been populated in the spontaneous fission of 248Cm and studied by means of prompt \(\gamma\)-ray spectroscopy using the EUROGAM2 array. The ratio \(E_{\rm exc}(4^ + )/ E_{\rm exc}(2^ + )\) suggests that the deformation of 110Mo is smaller than that in 108Mo but may stabilize at higher neutron number, where an oblate shape is expected. The new data suggests that the deformation of Sr and Zr isotopes decreases above neutron number N = 64.

A new band, populated by the spontaneous fission of 248Cm and studied by means of prompt γ-ray spectroscopy using the EUROGAM2 array, was observed in 99Zr. The 1038.8 keV band head with a half-life T 1/2 = 54(10) ns is interpreted as a K-isomer, corresponding to the 9/2[404] neutron-hole excitation. It is the first observation of this orbital in the mass A ∼ 100 region. The quadrupole moment, Q 0 = 3.9(3) eb deduced for the new band indicates a large deformation of β = 0.41, which is produced by a specific shape-coexistence mechanism, known in other regions and now found in the A ∼ 100 nuclei.

The 115, 117, 119, 121In nuclei have been produced as fission fragments in three reactions induced by heavy ions: 12C + 238U at 90MeV bombarding energy, 18O + 208Pb reaction at 85MeV, and 31P + 176Yb at 152MeV. Their level schemes have been built from gamma-rays detected using the EUROBALL III and IV arrays. High-spin states of 117, 119, 121In nuclei have been identified for the first time. Moreover, isomeric states lying around 2.5MeV have been established in 119, 121In from the delayed coincidences between the fission fragment detector SAPhIR and the gamma array. Most of the observed states can be described by coupling a proton g 9/2 hole to a Sn core, while the intruder band based on an orbital from the π[g 7/2/d 5/2] sub-shells behaves as the ground-state band of neighbouring Cd isotopes.

Excited states in the 134Sb nucleus, populated in the β−-decay of 134Sn, have been studied at the mass separator OSIRIS. The 134Sn activity was produced via fast neutron-induced fission of 238U target. A main result was the discovery of a very low-lying first-excited state of 134Sb, at 13 keV, which has led to a strong revision of the level scheme. The new results are compared with different theoretical calculations and with the known data for the analogous neutron and proton two-particle nucleus in the 208Pb region. On the basis of this comparison, the energy of the (πg 7/2νf 7/2)7− isomer is estimated to be about 250 keV, some 100 keV lower than previously reported.

Excited states in the nucleus {sup 133}Sb, populated in spontaneous fission of {sup 248}Cm, were studied with EUROGAM2. Medium-spin structure, described as the {nu}(f{sub 7/2}h{sub 11/2}{sup -1}) multiplet of the {sup 132}Sn core coupled to the odd proton in the g{sub 7/2} orbital, has been identified in this nucleus. Levels corresponding to the octupole excitations of the {sup 132}Sn core were also identified. Some uncertainties concerning isomeric decays in {sup 133}Sb, observed in previous works, have been resolved. (c) 2000 The American Physical Society.

High-spin states in 113-116Cd have been investigated with the fusion-fission reaction 28Si +176Yb at 145 > MeV. The experiment has been performed with the Eurogam2 array. New rotational bands based on two quasi-particle states have been observed for even-even cadmium isotopes. A new level scheme based on the 11/2− isomeric state is proposed for 115Cd and the one of 113Cd has been extended to spin (31/2−). The decoupled bands identified in both odd-A nuclei are interpreted as being built upon a low-Ωh11/2 quasi-neutron configuration. Microscopic Hartree-Fock + BCS calculations confirm the prolate deformation in this mass region especially for the odd cadmium isotopes.

Excited states in the neutron-rich, N=84 nuclei 134Sn, 136Te and 138Xe, populated in the spontaneous fission of 248Cm, were studied to medium spins using the EUROGAM2 array. OXBASH code calculations support the experimental identification of maximum aligned configurations in these isotopes. Empirical shell model calculations agree with the proposed excitation energy of the neutron h9/2 excitation in the 132Sn region. A discrepancy between the observed and calculated excitation energy of the Iπ= 12+ level in 136Te indicates possible admixtures of collective excitations in this nucleus. Clear signs of collective excitations are observed in 138Xe.

The low-spin collective excitations of even-even Pd nuclei in the A ≈ 110 mass region indicate a structural transition from an anharmonic vibrator to a gamma-soft rotor. This observation is supported by recent calculations of the potential energy surfaces using different types of mean field approaches. In particular, prolate-to-oblate shape transition has been predicted at 111Pd [1]. Experimental evidence for a shape change or shape coexistence can be obtained by high-spin studies of these transitional nuclei. Band crossings in the odd-N Pd nuclei are especially important to understand the origin of the alignments. No band structures built on the low-lying states were known in heavier odd Pd nuclei (A≥109). High-spin states in these nuclei cannot be populated using fusion-evaporation reactions. The heavier neutron-rich 112,114,116Pd nuclei have been studied from spontaneous fission of 252Cf [2]. In this work the less neutron-rich Pd nuclei have been produced as fission fragments following the fusion reactions 28Si + 176Yb at 145 MeV. The 28Si beam was provided by the Vivitron accelerator in Strasbourg. Gamma rays were recorded with the EUROGAM2 array [3]. The level schemes were constructed by examining γ- spectra extracted from two and three dimensional matrices.

A study of the $\ensuremath{\gamma}$-ray decay of low-lying excited states in fragments produced in the spontaneous fission of ${}^{252}\mathrm{Cf}$ has revealed a significant correlation between the angles of emission of the ${2}_{1}^{+}\ensuremath{\rightarrow}{0}_{1}^{+}$ transitions of complementary fragment pairs. Calculations of the amount of dealignment that is needed to reproduce the measured ${a}_{2}$ values, and a comparison with the results of previous fragment-$\ensuremath{\gamma}$ angular distribution measurements, suggests that at scission there may be significant population of $m\ensuremath{\ne}0$ substates associated with the projection of the fragment spin vector on the fission axis. Fragments from the spontaneous fission of ${}^{248}\mathrm{Cm}$ emit ${2}_{1}^{+}\ensuremath{\rightarrow}{0}_{1}^{+} \ensuremath{\gamma}$ rays that show markedly reduced interfragment correlations, suggesting that either a larger role is played by the relative angular momentum of the fragments, or that the dealignment introduced by the neutron emission and statistical $\ensuremath{\gamma}$ decay to the ${2}_{1}^{+}$ state is larger in ${}^{248}\mathrm{Cm}$ than ${}^{252}\mathrm{Cf}$ fission.

Actinides with $N\ensuremath{\sim}132$ present the best explored region of pear shape nuclei. Still almost no spectroscopic information is available for the heaviest elements, $Z=91--98,$ which are predicted to be octupole instable. The lack of data for the latter nuclei results from the high fission probability encountered in the heavy-ion reactions used to populate them. In order to overcome this handicap, an $\ensuremath{\alpha}$-decay tagging technique was used to identify $\ensuremath{\gamma}$ rays in ${}^{223}\mathrm{Pa}$ produced through the ${}^{208}\mathrm{Pb}{(}^{19}\mathrm{F},4n)$ reaction. A new value of 4.9(4) ms for the half-life of ${}^{223}\mathrm{Pa}$ was obtained as a by-product.

The 107,109Rh nuclei have been produced as fission fragments following the fusion reaction 28Si +176Yb at 145 MeV bombarding energy and studied with the Eurogam2 array. In both nuclei three new rotational bands with the odd proton occupying the πg9/2, πp1/2 and π(g7/2/d5/2) sub-shells have been observed. In 107Rh, two other bands involving strong M1 transitions have been identified at excitation energy larger than 2 MeV. They can be interpreted in terms of three quasiparticle excitations. In addition new structures consisting of four transitions, built on states located at low excitation energy (680 keV in 107Rh and 642 keV in 109Rh), point out the importance of triaxial deformation in these two isotopes.

In this paper we present research that has been carried out using the Euroball and Eurogam arrays to detect γ rays emitted from spontaneously fissioning 248Cm and 252Cf. The paper focuses on three sub-areas of current activity, namely, the measurement of yields of secondary fragment pairs, the measurement of state lifetimes at around spin 10, and recent measurements of g-factors of excited states in fission fragments.

About eighty nuclei in the A≈100 mass region have been observed as fission fragments following the fusion evaporation 28,30Si+176Yb at 145 MeV bombarding energy. These nuclei have been identified from their γ-ray cascades detected with the EUROGAM2 array. The level schemes of several stable or neutron-rich nuclei have been extended to higher spins. From coincidences between transitions in complementary fragments, γ-rays de-exciting new high-spin states of hitherto unexplored isotopes can be assigned and some aspects of the fission mechanism can be studied.

The high-spin state structure of the nucleus 221 Ac was investigated by means of the 209 Bi( 14 C, 2n) reaction at 63 and 65 MeV. Measurements consisted of in-beam γγ coincidences using the Château de Cristal multidetector array and of e − γ coincidences. Two alternating parity bands could be established in 221 Ac up to spin 35 2 h . Almost all of the states may be regrouped into parity doublets and the origin of these doublets is discussed.

High-spin states of doubly odd 218 Ac1 129 have been investigated using in-beam α, γ and conversion electron spectroscopy techniques through the 209 Bi( 12(13) C,3(4)n) fusion-evaporation reactions. The level scheme of 218 Ac shows three interconnected, alternating parity structures, each one linked by strong El transitions. Two of these bands are strikingly similar to the known scheme of the isotone 217 Ra and this analogy is shown to persist for the pair 220 Ac, 219 Ra. The relation between the structure of 218 Ac and its neighbors is thoroughly discussed showing that the first signals of octupole collectivity appear for N = 129.

Excited states of220Ac have been investigated by means of the209Bi(14C,3n) reaction and using the “Château de Cristal” gamma ray facility. The observation of bands with alternating parity states reveals the reflection asymmetric nuclear shape of220Ac. The extracted B(E1)/B(E2) ratios display a clear spin dependence.

An alpha-particle and gamma-ray investigation of 215Fr was performed by means of the reaction 208Pb(11B, 4n). Gamma-ray angular distributions, gamma - gamma and alpha - gamma coincidences time centroid shifts and pulsed-beam isomeric decay rates were measured. Excited states were observed up to spins of about 47/2 and 3.5 MeV excitation energy. An interpretation of the results is given in terms of a particle-hole analysis based on the Woods-Saxon single-particle potential.

Two- and three-nucleon stripping reactions induced by 480 MeV /sup 12/C have been studied on /sup 12/C, /sup 16/O, /sup 28/Si, /sup 40/Ca, and /sup 54/Fe target nuclei. Discrete levels are fed with cross sections up to 1 mbsr for d-transfer reactions and 1 order and 2 orders of magnitude less for 2p- and /sup 3/He-transfer reactions, respectively. These reactions preferentially populate high spin states with stretched configurations. Several spin assignments were known from transfer reactions induced by lighter projectiles at incident energies well above the Coulomb barrier. In the case of two-nucleon transfer reactions, the energy of these states is well reproduced by crude shell model calculations. Such estimates are of use in proposing spins of newly observed states especially as the shapes of the measured angular distributions are independent of the final spin of the residual nucleus.

One-proton and one-neutron stripping reactions induced by a 480 MeV $^{12}\mathrm{C}$ beam bombarding a $^{208}\mathrm{Pb}$ target have been studied using a high resolution energy loss magnetic spectrometer. The reactions are governed by two selection rules which are naturally contained in the one-step exact finite range distorted wave Born approximation formalism. Relative intensities of the populated states are well reproduced by this formalism as well as the absolute values of the cross sections. Comparisons with the results of one-nucleon stripping reactions induced by a $^{16}\mathrm{O}$ beam on a $^{208}\mathrm{Pb}$ target at 793 MeV incident energy are also presented; in this latter case the absolute cross section values are not reproduced.

High-spin states in 54Mn were populated in the 52Cr( alpha ,pn gamma ) reaction. Using angular distribution, linear polarisation and gamma - gamma coincidence measurements, the following unambiguous spin and parity assignments were obtained: Ex, Jpi ; 1073 keV, 6+; 1784 keV, 7+; 1925 keV, 7+; 2857 keV, 8+; and 3244, (9)+. In addition a new level was observed at an excitation energy of 3939 keV. The experimental data show evidence for low-lying intruder states as predicted by a recent shell-model calculation.

The lifetimes of the 235 keV, 2− state and 350 keV, 4+ state in44Sc have been measured via the44Ca(p, n)44Sc reaction with a pulsed proton beam. The time integral perturbed angular distribution technique with an external field was used to measure the precession angles of the 2− and 4+ states populated by the30Si(16O,pnγ)44Sc reaction. The following values for the mean-lives andg-factors were obtained: τ(2−)=8.83(33) ns, g(2−)=0.30(13) and τ(4+)=4.52(27)ns, g(4+)=0.90(12). The results for the 2− state support a rotational description of the negative parity states in44Sc. The magnetic moment of the 4+ state is compared to shell model predictions.

One-proton and one-neutron stripping reactions induced by a 793 MeV 16 O beam bombarding a 208 Pb target have been studied at the GANIL facility using a high resolution energy-loss magnetic spectrometer. The reactions are governed by two semi-classical selection rules which are naturally contained in the one-step EFR-DWBA formalism. Relative intensities of the populated states are well reproduced by this formalism which, on the other hand, fails to correctly predict absolute cross section values.

Gamma-rays in coincidence with the α-particles from the decay of the ground-state of 218Th have been observed in the 206Pb( 16O, 4n) reaction. A tentative decay scheme of 218Th is proposed.

The electromagnetic decays of the negative parity states in 45Sc up to an excitation energy of 2107 keV have been investigated via the 42Ca(α, pγ)45Sc reaction at a bombarding energy of 10.5 MeV. Reaction produced protons were detected in an annular silicon detector at an average angle of 171°. Gamma-ray spectra were measured with a Ge(Li) detector at angles 105° ≥ θ ≥ 0°. Spins and lifetimes of the levels as well as branching and mixing ratios of their decay γ-rays have been obtained from proton-gamma angular correlation measurements. Reduced electromagnetic transition matrix elements have been extracted for a number of observed transitions. Calculations based on the strong coupling model have been performed. The results are compared with experiment.

Levels in 45Sc have been investigated through the 42Ca(α, pγ) reaction. Gamma-ray spectra in coincidence with backscattered protons were recorded with a Ge(Li) detector positioned at angles 105° ≧ θ ≧ 0°. The data corresponding to the members of the proposed K π = 3 2 + band were analysed and led to the following results for excitation energies (keV), spins, parities and lifetimes (ps): 543.3, 5 2 + , 9.2 −3.3 +6.8 ; 974.8, 7 2 + , 3.2 −0.7 +0.8 ; 1433.8, 9 2 + , 7.8 −2.2 +4.3 ; 2031.6, 11 2 + , 1.6 −0.5 +0.8 and 2563.3, 9 2 + , 11 2 + , 13 2 + , 2.0 −0.6 +0.9 . Multipole mixing ratios and γ-ray branching ratios were also obtained from the data, and reduced electromagnetic transition matrix elements have been deduced. Results for other positive parity states are also presented.

The interacting multiboson model (IMBM) introduced earlier (1987), in its spdf boson case, is applied to a new experiment on the vibrational nucleus88218Ra130. It is shown to describe in a natural way, with the essential participation of pf bosons, both the ground yrast bands with positive and negative parity, and the peculiar side yrare bands with the same space pi and opposite spin (-)I parity. So this experiment together with its boson interpretation can be viewed as evidence for the existence of combined dipole-octupole correlations in nuclei.

One-proton and one-neutron stripping reactions induced by a 793 MeV16O beam bombarding a208Pb target have been studied at the GANIL facility using a high resolution energy loss magnetic spectrometer. The reactions are governed by two semi classical selection rules which are naturally contained in the one-step EFR-DWBA formalism. Relative intensities of the populated states are well reproduced by this formalism which, on the other hand, fails to predict correctly absolute cross section values.