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The spectra of the isotopes of Zn, Ge and Se in the A = 60 – 80 region of the nuclear landscape display interesting spectral variations with N and Z. At first we study these structures empirically. The state-wise deformation status of each isotope is deduced using the power index formula. The average value of the power index displays the variation with neutron number N. The linear plot of B ( E 2 , 0 1 + → 2 1 + ) versus [ 1 / E ( 2 1 + ) ] for a given Z gives further information on the spectral variation with N. The level energy spectra are used to study the role of the excited bands in the phase transitions and the possible shape co-existence. The common spectral features of the three isotopic chains and some unique features are pointed out from our study and the role of the Nilsson single particle orbits is discussed. A comparison with recent works for Ge and Se isotopes reveals the importance of our empirical studies vis-a-vis the high efficiency experiments and different theoretical interpretations of the shape changes with N and Z and spin.

New transitions in neutron-rich Y100 have been identified in a Be9+U238 experiment with mass and Z gates to provide full fragment identification. These transitions and high spin levels of Y100 have been investigated by analyzing the high statistics γ-γ-γ and γ-γ-γ-γ coincidence data from the spontaneous fission of Cf252 at the Gammasphere detector array. Two new bands, 14 new levels, and 23 new transitions have been identified. The Kπ=4+ new band decaying to a 1s isomeric state is assigned to be the high-K Gallagher-Moszkowski (GM) partner of the known Kπ=1+ band, with the π5/2[522] - ν3/2[411] configuration. This 4+ band is also proposed to be the pseudospin partner of the new Kπ=5+ band with a 5+π5/2[422] - ν5/2[413] configuration, to form a π5/2[422] - ν[3125/2,3/2] neutron pseudospin doublet. Constrained triaxial covariant density-functional theory and quantal particle rotor model calculations have been applied to interpret the band structure and available electromagnetic transition probabilities and are found to be in good agreement with experimental values.

The light $$Z=54$$ Xe isotopes in the $$A=130$$ region, have been studied in the last 4 decades, in experiment and in theory. For ( $$N < 82$$ ) region, the evolution of the nuclear structure between the analytical symmetries U(5) and O(6) with neutron number N, is shown to be different for $$N=60\hbox {--}68$$ and $$N=70\hbox {--}78$$ . Here we focus on the lighter mass group. The shape transition between U(5) and O(6) symmetry is studied in terms of the variation in quadrupole deformation with N, the variation of the $$\upgamma $$ -band and the growth of the $$K^{{\uppi }} \quad =0_{\mathrm {2}}^{\mathrm {+}}$$ band and $$0_{\mathrm {3}}^{\mathrm {+}}$$ state. The effect of increasing triaxiality varying with N is illustrated. This variation is also reflected in the B(E2) values and the interband E2 transitions. Also, the role of neutrons filling the Nilsson single particle orbits in changing the spectra is studied. The sd interacting boson model IBM-1 is used to reproduce this spectral evolution. The study of the shape change between the analytical symmetries leads to the underlying basic physics.

New transitions in neutron rich $^{100}$Y have been identified in a $^9$Be+$^{238}$U experiment with mass- and Z- gates to provide full fragment identification. These transitions and high spin levels of $^{100}$Y have been investigated by analyzing the high statistics $\gamma$-$\gamma$-$\gamma$ and $\gamma$-$\gamma$-$\gamma$-$\gamma$ coincidence data from the spontaneous fission of $^{252}$Cf at the Gammasphere detector array. Two new bands, 14 new levels and 23 new transitions have been identified. The $K^{\pi}=4^+$ new band decaying to an 1s isomeric state is assigned to be the high-$K$ Gallagher-Moszkowski (GM) partner of the known $K^{\pi}=1^+$ band, with the $\pi 5/2[522] \otimes \nu 3/2[411]$ configuration. This 4$^+$ band is also proposed to be the pseudo spin partner of the new $K^{\pi}=5^+$ band with a 5$^{+}$ $\pi 5/2[422] \otimes \nu 5/2[413]$ configuration, to form a $\pi 5/2[422] \otimes \nu [312$ $5/2,3/2]$ neutron pseudospin doublet. Constrained triaxial covariant density functional theory and quantal particle rotor model calculations have been applied to interpret the band structure and available electromagnetic transition probabilities and are found in good agreement with experimental values.

A search for production of the superheavy elements with atomic numbers 119 and 120 was performed in the 50Ti+249Bk and 50Ti+249Cf fusion-evaporation reactions, respectively, at the gas-filled recoil separator TASCA at GSI Darmstadt, Germany. Over four months of irradiation, the 249Bk target partially decayed into 249Cf, which allowed for a simultaneous search for both elements. Neither was detected at cross-section sensitivity levels of 65 and 200 fb for the 50Ti+249Bk and 50Ti+249Cf reactions, respectively, at a midtarget beam energy of Elab=281.5 MeV. The nonobservation of elements 119 and 120 is discussed within the concept of fusion-evaporation reactions including various theoretical predictions on the fission-barrier heights of superheavy nuclei in the region of the island of stability. peerReviewed

Background: A puzzle has arisen recently caused by the apparent shift in maximum deformation from the expected $^{66}\mathrm{Dy}$ isotopic chain to the ${}_{60}\mathrm{Nd}$ isotopic chain in the $82lNl126$ and $50lZl82$ midshell region.Purpose: This work provides data for two specific nuclei with odd neutron numbers, $^{155}\mathrm{Nd}$ and $^{163}\mathrm{Gd}$, useful for constraining parameters in models that seek to answer the six proton shift in maximum deformation.Method: Data from the spontaneous fission of $^{252}\mathrm{Cf}$ were taken by the Gammasphere detector array at Lawrence Berkeley National Laboratory to observe the excited states of $^{155}\mathrm{Nd}$ and $^{163}\mathrm{Gd}$.Results: The structure of $^{163}\mathrm{Gd}$ has been expanded with the addition of two new levels and three new $\ensuremath{\gamma}$ rays, which are found to be consistent with previously published calculations and the structure of $^{165}\mathrm{Dy}$. In $^{155}\mathrm{Nd}$, nine new levels and 12 new $\ensuremath{\gamma}$ rays are observed. The spins and parities of the previously known levels in $^{155}\mathrm{Nd}$ have been reassigned from a $\ensuremath{\nu}3/{2}^{\ensuremath{-}}[521]$ ground state configuration to a $\ensuremath{\nu}5/{2}^{+}[642]$ isomeric configuration by comparison of these newly observed levels with levels in $^{153}\mathrm{Nd}$ and $^{155}\mathrm{Sm}$.Conclusion: Further experimentation is required to determine the energy of the newly reassigned $\ensuremath{\nu}5/{2}^{+}[642]$ level in $^{155}\mathrm{Nd}$ with respect to the suspected $\ensuremath{\nu}3/{2}^{\ensuremath{-}}[521]$ ground state. Additionally, more experiments should be conducted to further determine the structure of neutron rich nuclei, rarely produced in the spontaneous fission of $^{252}\mathrm{Cf}$, such as $^{163}\mathrm{Gd}$.

Background: Neutron-rich nuclei in the mass region around A=160 have been and will continue to be of interest for the study of nuclear structure because of the rapid onset of deformation between 88 and 90 neutrons. The observation of detailed changes in nuclear structures within this mass region has provided and will continue to provide insight into the nuclear force. Purpose: Investigations of γ rays emitted following Eu163 β-decay to Gd163 have been performed for evaluation of the nuclear structure of Gd163. Method: Data were collected at the LeRIBSS station of the Holifield Radioactive Ion Beam Facility at Oak Ridge National Laboratory with an array of four Clover HPGe detectors for γ-rays and two plastic scintillators for β detection. The γ rays were identified as belonging to Gd163 via mass selection and γ-γ-β, x-ray-γ, or γ-γ coincidences. Results: In total 107 new γ-ray transitions were observed in Gd163 from 53 newly identified levels. Conclusions: The structure of Gd163 has been identified for the first time. This structure has been evaluated in comparison to projected shell model, and potential energy surface calculations with good agreement.

Level structures in the neutron-rich ^{144}Ba nucleus have been reinvestigated by measuring prompt γ rays in the spontaneous fission of ^{252}Cf. The previous s=+1 octupole band structure with reflection asymmetric shape has been expanded, and a side quadrupole band structure based on a 3^{+} state with reflection symmetric shape is identified. Thus, the results show the coexistence of reflection asymmetric and symmetric shapes in ^{144}Ba. This is a first identification of such a shape coexistence structure in a nuclear structure. The other structural characteristics are discussed.

We reinvestigated the neutron multiplicity yields of Ba-Mo, Ce-Zr, Te-Pd, and Nd-Sr from the spontaneous fission of $^{252}\mathrm{Cf}$ by (i) using both $\ensuremath{\gamma}\ensuremath{-}\ensuremath{\gamma}\ensuremath{-}\ensuremath{\gamma}\ensuremath{-}\ensuremath{\gamma}$ and $\ensuremath{\gamma}\ensuremath{-}\ensuremath{\gamma}\ensuremath{-}\ensuremath{\gamma}$ coincidence data, (ii) using up to date level scheme structures, and (iii) crosschecking analogous energy transitions in multiple isotopes, we have achieved higher precision than previous analyses. Particular attention was given to the Ba-Mo pairs where our results clearly confirm that the Ba-Mo yield data have a second hot fission mode where 8--10, and now 11 neutron evaporation channels are observed. These are the first observations of the 11 neutron channel. These 8--11 neutron channels are observed for the first time in the Ce-Zr pairs, but are not observed in other fission pairs. The measured intensities of the second mode in Ba-Mo and Ce-Zr pairs are $\ensuremath{\sim}1.5(4)%$ and $\ensuremath{\sim}1.0(3)%$, respectively. These high neutron number evaporation modes can be an indication of hyperdeformation and/or octupole deformation in $^{143--145}\mathrm{Ba}$ and in $^{146,148}\mathrm{Ce}$ at scission to give rise to such high neutron multiplicities.

Level structures in the neutron-rich ^{144}Ba nucleus have been reinvestigated by measuring prompt γ rays in the spontaneous fission of ^{252}Cf. The previous s=+1 octupole band structure with reflection asymmetric shape has been expanded, and a side quadrupole band structure based on a 3^{+} state with reflection symmetric shape is identified. Thus, the results show the coexistence of reflection asymmetric and symmetric shapes in ^{144}Ba. This is a first identification of such a shape coexistence structure in a nuclear structure. The other structural characteristics are discussed.

From γ-γ-γ and γ-γ-γ-γ coincidence studies of spontaneous fission of 252Cf, new high spin states in 148Ce were identified. The octupole bands with s = + 1 and s = − 1 are expanded with spins with 28+ and 18−, respectively. Importantly, a 1γ vibrational band has been established up to 14+ and a 1β vibrational band up to 6+. The levels in γ and β bands in 148Ce are compared systematically to those in neighboring 150Nd and 152Sm isotones. This comparison informs the role of deformation and shape transition in this mass region. New 3− and 5− members of the s = + 1 octupole band were observed.

Collective rotational bands were observed for the first time in neutron-rich odd–odd [Formula: see text]La by means of [Formula: see text]-[Formula: see text]-[Formula: see text] and [Formula: see text]-[Formula: see text]-[Formula: see text]-[Formula: see text] coincidence measurements of prompt fission [Formula: see text] rays from [Formula: see text]Cf using multi-detector array Gammasphere. Similarity between the yrast band of [Formula: see text]La and those of neighboring [Formula: see text]La, [Formula: see text]Ce was found and interpreted as quasiparticle excitations. PES calculations suggested triaxial deformation for the ground state of 142La. Considerable triaxial and near zero octupole deformations were deduced for the yrast band of [Formula: see text]La by the TRS model calculations. The band-crossing observed in the yrast band of [Formula: see text]La was interpreted to be caused by alignment of the (h[Formula: see text])2 proton pair, and the crossing frequency was best reproduced by the TRS calculations taking into account triaxial deformations. In contrast to the interpretations for the band crossing of [Formula: see text]La, alignments of the (i[Formula: see text])2 neutron pair were found to be responsible for the band-crossing of the yrast band in the neighboring even-N [Formula: see text]La, and triaxial degree of freedom was found to play a more significant role than octupole deformations in the nucleus, although its [Formula: see text] values deduced are large.

The heaviest currently known nuclei, which have up to 118 protons, have been produced in 48Ca induced reactions with actinide targets. Among them, the element tennessine (Ts), which has 117 protons, has been synthesized by fusing 48Ca with the radioactive target 249Bk, which has a half-life of 327 d. The experiment was performed at the gas-filled recoil separator TASCA. Two long and two short α decay chains were observed. The long chains were attributed to the decay of 294Ts. The possible origin of the short-decay chains is discussed in comparison with the known experimental data. They are found to fit with the decay chain patterns attributed to 293Ts. The present experimental results confirm the previous findings at the Dubna Gas-Filled Recoil Separator on the decay chains originating from the nuclei assigned to Ts.

The Kr isotopes lying in between the lighter isotopes of (Zn, Ge and Se) and the heavier isotopes of (Sr and Zr) in the [Formula: see text]–80 region exhibit very interesting spectral features. The spectra of [Formula: see text]Kr isotopes display a striking contrast from those of Zn, Ge and Se isotopes. The role of spherical and oblate and prolate deformed subshell gaps at specific [Formula: see text] and [Formula: see text] and the resulting re-inforcement are strikingly evident in these contrasting features, with variation in [Formula: see text] or [Formula: see text]. The evolution of the spectral features in Kr isotopes with [Formula: see text] as reflected in the quadrupole deformation, [Formula: see text]-band structures, [Formula: see text]0 decay, [Formula: see text]2) values, [Formula: see text]-softness of the nuclear core and odd–even staggering in [Formula: see text]-bands is studied to explore the role of the under lying nuclear interactions. The correlations with odd–[Formula: see text] isotopes are explored. The shape co-existence displayed in some Kr isotopes is studied. The large deformation observed in the ground bands of [Formula: see text]Kr, as exhibited in the [Formula: see text]2) values, is especially interesting.

High spin band structures of neutron-rich $^{152--158}\mathrm{Pm}$ isotopes have been obtained from the measurement of prompt $\ensuremath{\gamma}$ rays of isotopically identified fragments produced in fission of $^{238}\mathrm{U}+^{9}\mathrm{Be}$ and detected using the VAMOS++ magnetic spectrometer and EXOGAM segmented Clover array at GANIL and also from the high statistics $\ensuremath{\gamma}\text{\ensuremath{-}}\ensuremath{\gamma}\text{\ensuremath{-}}\ensuremath{\gamma}$ and $\ensuremath{\gamma}\text{\ensuremath{-}}\ensuremath{\gamma}\text{\ensuremath{-}}\ensuremath{\gamma}\text{\ensuremath{-}}\ensuremath{\gamma}$ data from the spontaneous fission of $^{252}\mathrm{Cf}$ using Gammasphere. The excited states in $^{157}\mathrm{Pm}$ and those above the isomers in even-$A$ Pm isotopes $^{152,154,156,158}\mathrm{Pm}$ have been identified for the first time. The spectroscopic information on the rotational band structures in odd-$A$ Pm isotopes has been extended considerably to higher spins and the possibility of the presence of reflection asymmetric shapes is explored. The configuration assignments are based on the results of cranked relativistic Hartree-Bogoliubov calculations. From the systematics of bands in odd-$A$ Pm isotopes and weak population of opposite parity bands, octupole deformed shapes in neutron-rich Pm isotopes beyond $N=90$ seem unlikely to be present.

The search for new decay chains of oganesson isotopes is presented. The experiment utilized the Dubna Gas Filled Recoil Separator and a highly segmented recoil-decay detection system. The signals from all detectors were analyzed in parallel by digital and analog data acquisition systems. For the first time, a target of mixed californium (51% Cf249, 13% Cf250, and 36% Cf251) recovered from decayed Cf252 sources was produced and irradiated with an intense Ca48 beam. The observation of a new decay chain of Og294 is reported. The prospects for reaching new isotopes Og295,296 are discussed.

E2/M1 mixing ratios have been measured for transitions from states in the $\gamma$ vibrational bands ( $ I^{+}_{\gamma}$ ) to states in the ground state bands ( $I^{+}$ or $ [I-1]^{+}$ ) of the neutron rich, even-even, deformed isotopes, 102, 104, 106, 108Mo, 108, 110, 112Ru, and 112, 114, 116Pd, including from states as high as $ 9^{+}_{\gamma}$ . These measurements were done using the GAMMASPHERE detector array, which, at the time of the experiment, had 101 working HPGe detectors, arranged at 64 different angles. A 62 $\mu$ Ci source of 252Cf was placed inside GAMMASPHERE yielding $5.7\times 10^{11}$ $\gamma$ - $\gamma$ - $\gamma$ and higher coincidence events. The angular correlations between the transitions from the $\gamma$ -bands to the ground bands, and the pure E2 transitions within the ground band were then measured. These angular correlations yielded the mixing ratios, demonstrating that these transitions are pure or nearly pure E2, in agreement with theory. In order to correct for possible attenuation due to the lifetime of the intermediate state in these correlations, the g-factors of the intermediate states needed to be known. Therefore, the g-factors of the 2+ states in the ground state band have been measured.

The paper reviews the systematic studies of triaxial deformations, new mode excitations and shape evolutions with regard to triaxial deformation in the neutron-rich nuclei with Z = 41-46, A~100-116.

High spin states of neutron-rich 146,147La have been reinvestigated by $\gamma$ - $\gamma$ - $ \gamma$ and $\gamma$ - $\gamma$ - $\gamma$ - $\gamma$ coincidence data from a 252Cf spontaneous fission experiment by using Gammasphere. Thirty-two new transitions in 146La are observed. Two new bands in 146La have been established. One of them is proposed to be the octupole parity partner of the previously known band. Twenty new transitions in 147La are observed. The ground state band of 147La has been established with a proposed $ 5/2^+$ band-head. Angular correlation of cascades has been used to study the spins and parities of the states. The B(E1)/B(E2) ratios and dipole moments of bands in 146, 147La have been measured.

After a successful production of isotopes of element 116 in the reaction 48Ca + 248Cm, the reaction 54Cr + 248Cm → 302120* was investigated at the velocity filter SHIP at GSI, Darmstadt, aiming to search for isotopes of element 120. One chain of events was observed, which is not created by chance with high probability. Parts of the chain agree with model predictions and measured data from a decay chain which could start at the isotope 299120. In a complementary study, model dependent shell-correction energies and related heights of fission barriers were deduced from measured Qα values. The results are compared with predictions of macroscopic-microscopic models. The consequences for calculations of crosssections are discussed.