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Two new excited bands built on the πh11/2 configuration have been identified in Nd135 in addition to the known πh11/2 band. The energy spectra of the excited bands and the available electromagnetic transition probabilities are in good agreement with theoretical results obtained using quasiparticle-plus-triaxial-rotor model calculations. The properties of the bands identify them as tilted precession bands instead of wobbling bands. Our results give a new insight into the interpretation of the low-lying bands in odd-A mass nuclei, and can stimulate future studies to address the nuclear triaxiality.

The neutron-deficient gold (Z=79) isotopes in the vicinity of the neutron midshell N=104 provide prolific examples of shape coexistence and isomerism at low excitation energy. They can be probed via a number of different experimental techniques. In this study, two new isomeric states with half-lives of 294(7) and 373(9) ns have been observed in the neutron-deficient odd-odd nuclide Au178 (N=99) in an experiment at the RITU gas-filled separator at JYFL, Jyvaskyla. This result was achieved due to the use of a segmented planar germanium detector with a high efficiency at low energies. By applying the recoil-decay tagging technique, they were assigned to decay to two different long-lived α-decaying states in Au178.

Fine structure in the α decay of Th90221, populating excited states in Ra88217, was studied using αγ-coincidence spectroscopy. Two α-decay branches from Th221 have been newly observed, with Eα(keV)[bα(%)]=7951(8)[0.14(3)] and 8247(3)[1.51(12)], together with three previously known branches. Also, two new states in Ra217 were identified at E = 177 and 227 keV. The ground-state configurations of the odd-A, N = 131 transitional isotones above Pb208 are interpreted from their α-decay fine structure systematics and considered in terms of predictions using spherical shell and reflection-asymmetric models.

The odd-Z Md251 nucleus was studied using combined γ-ray and conversion-electron in-beam spectroscopy. Besides the previously observed rotational band based on the [521]1/2− configuration, another rotational structure has been identified using γ-γ coincidences. The use of electron spectroscopy allowed the rotational bands to be observed over a larger rotational frequency range. Using the transition intensities that depend on the gyromagnetic factor, a [514]7/2− single-particle configuration has been inferred for this band, i.e., the ground-state band. A physical background that dominates the electron spectrum with an intensity of ≃60% was well reproduced by simulating a set of unresolved excited bands. Moreover, a detailed analysis of the intensity profile as a function of the angular momentum provided a method for deriving the orbital gyromagnetic factor, namely gK=0.69−0.16+0.19 for the ground-state band. The odd-Z Md249 was studied using γ-ray in-beam spectroscopy. Evidence for octupole correlations resulting from the mixing of the Δl=Δj=3 [521]3/2− and [633]7/2+ Nilsson orbitals were found in both Md249,251. A surprising similarity of the Md251 ground-state band transition energies with those of the excited band of Lr255 has been discussed in terms of identical bands. Skyrme-Hartree-Fock-Bogoliubov calculations were performed to investigate the origin of the similarities between these bands.

Decay spectroscopy of No250 has been performed using digital electronics and pulse-shape analysis of the fast nuclear decays for the first time. Previous studies of No250 reported two distinct fission decay lifetimes, related to the direct fission of the ground state and to the decay of an isomeric state but without the possibility to determine if the isomeric state decayed directly via fission or via internal electromagnetic transitions to the ground state. The data obtained in the current experiment allowed the puzzle to finally be resolved, attributing the shorter half-life of t1/2=3.8±0.3μs to the ground state and the longer half-life t1/2=34.9−3.2+3.9μs to the decay of an isomeric state. No250 becomes, thus, one of a very few examples of very heavy nuclei with an isomeric state living considerably longer than its ground state. This phenomenon has important consequences for the nuclear-structure models aiming to determine the borders of the island of stability of superheavy elements.

© 2019 American Physical Society. An analysis technique has been developed in order to mitigate energy summing due to sequential short-lived α decays from nuclei implanted into a silicon detector. Using this technique, α-decay spectroscopy of the N=130 isotones Ra218 (Z=88) and Th220 (Z=90) has been performed. The energies of the α particles emitted in the Ra218→Rn214 and Th220→Ra216 ground-state-to-ground-state decays have been measured to be 8381(4) keV and 8818(13) keV, respectively. The half-lives of the ground states of Ra218 and Th220 have been measured to be 25.99(10) μs and 10.4(4) μs, respectively. The half-lives of the ground states of the α-decay daughters, Rn214 and Ra216, have been measured to be 259(3) ns and 161(11) ns, respectively. Fine structure in the α decay of Ra218 has been observed for the first time, populating the 695-keV 21+ state in Rn214. The fine-structure α decay has an α-particle energy of 7715(40) keV and branching ratio bα=0.123(11)%.

The structure of low-spin states originating from shape-coexisting configurations in $^{68}_{40}$Ni$_{28}$ was directly probed via the two-neutron transfer reaction $^{66}$Ni$(t,p)^{68}$Ni in inverse kinematics using a radioactive ion beam on a radioactive target. The direct feeding to the first excited 0$^+$ state was measured for center-of-mass angles 4°–16° and amounts to an integral of 4.2(16)% relative to the ground state. The observed difference in feeding of the 0$^+$ states is explained by the transfer of neutrons, mainly in the $pf$ shell below $N=40$ for the ground state, and across $N=40$ in the $g_{9/2}$ orbital for the 0$_2^+$, based on second-order distorted-wave Born approximation calculations combined with state-of-the-art shell-model two-nucleon amplitudes. However, the direct feeding to the 2$_1^+$ state [29(3)%] is incompatible with these calculations.

The Tz=−32 nucleus 21Mg has been studied by Coulomb excitation on 196Pt and 110Pd targets. A 205.6(1)-keV γ-ray transition resulting from the Coulomb excitation of the 52+ ground state to the first excited 12+ state in 21Mg was observed for the first time. Coulomb excitation cross-section measurements with both targets and a measurement of the half-life of the 12+ state yield an adopted value of B(E2;52+→12+)=13.3(4) W.u. A new excited state at 1672(1) keV with tentative 92+ assignment was also identified in 21Mg. This work demonstrates a large difference in the B(E2;52+→12+) value between T=32, A=21 mirror nuclei. The difference is investigated in the shell-model framework employing both isospin conserving and breaking USD interactions and using modern ab initio nuclear structure calculations, which have recently become applicable in the sd shell. (Less)

In the study of the odd-$Z$, even-$N$ nuclei $^{243}$Es and $^{249}$Md, performed at the University of Jyv\"askyl\"a, the fusion-evaporation reactions $^{197}$Au($^{48}$Ca,2$n$)$^{243}$Es and $^{203}$Tl($^{48}$Ca,2$n$)$^{249}$Md have been used for the first time. Fusion-evaporation residues were selected and detected using the RITU gas-filled separator coupled with the focal-plane spectrometer GREAT. For $^{243}$Es, the recoil decay correlation analysis yielded a half-life of $24 \pm 3$s, and a maximum production cross section of $37 \pm 10$ nb. In the same way, a half-life of $26 \pm 1$ s, an $\alpha$ branching ratio of 75 $\pm$ 5%, and a maximum production cross section of 300 $\pm$ 80 nb were determined for $^{249}$Md. The decay properties of $^{245}$Es, the daughter of $^{249}$Md, were also measured: an $\alpha$ branching ratio of 54 $\pm$ 7% and a half-life of 65 $\pm$ 6 s. Experimental cross sections were compared to the results of calculations performed using the KEWPIE2 statistical fusion-evaporation code.

The first 2+ and 3- states of the doubly magic nucleus Sn132 are populated via safe Coulomb excitation employing the recently commissioned HIE-ISOLDE accelerator at CERN in conjunction with the highly efficient MINIBALL array. The Sn132 ions are accelerated to an energy of 5.49 MeV/nucleon and impinged on a Pb206 target. Deexciting γ rays from the low-lying excited states of the target and the projectile are recorded in coincidence with scattered particles. The reduced transition strengths are determined for the transitions 0g.s.+→21+, 0g.s.+→31-, and 21+→31- in Sn132. The results on these states provide crucial information on cross-shell configurations which are determined within large-scale shell-model and Monte Carlo shell-model calculations as well as from random-phase approximation and relativistic random-phase approximation. The locally enhanced B(E2;0g.s.+→21+) strength is consistent with the microscopic description of the structure of the respective states within all theoretical approaches. The presented results of experiment and theory can be considered to be the first direct verification of the sphericity and double magicity of Sn132. (Less)

The level structure of Nd136 has been investigated using the Mo100(Ar40,4n) reaction and the JUROGAM II+RITU+GREAT setup. The level scheme has been extended significantly. Many new bands have been identified both at low and high spin, among which are five nearly degenerate bands interpreted as chiral partners. Excitation energies, spins, and parities of the previously known bands are revised and firmly established, and some previously known bands have been revised. Configurations are assigned to the observed bands based on cranked Nilsson-Strutinsky calculations. The band structure of Nd136 is now clarified and the various types of single-particle and collective excitations are well understood.

Fine structure in the a decay of high-spin isomers in Lu-155( 25/2(-)) and Hf-156(8(+))has been studied for the first time using alpha gamma- coincidence analysis. Three new a decays from Lu-155(25 ...

A multiparticle spin-trap isomeric state having a half-life of 179(4) ns and lying 2601 keV above the yrast 10(+) state in Lu-156 has been discovered. The Lu-156 nuclei were produced by bombarding ...

Lifetimes of the first excited 2(+) and 4(+) states in the extremely neutron -deficient nuclide Pt-172 have been measured for the first time using the recoil-distance Doppler shift and recoil-decay tagging techniques. An unusually low value of the ratio B(E2: 4(1)(+) -> 2(1)(+)/B(E2: 2(1)(+) -> 0(gs)(+)) = 0.55(19) was found, similar to a handful of other such anomalous cases observed in the entire Segre chart. The observation adds to a cluster of a few extremely neutron -deficient nuclides of the heavy transition metals with neutron numbers N approximate to 90-94 featuring the effect. No theoretical model calculations reported to date have been able to explain the anomalously low B(E2: 4(1)(+) -> 2(1)(+)/B(E2: 2(1)(+) -> 0(gs)(+)) ratios observed in these cases. Such low values cannot, e.g., be explained within the framework of the geometrical collective model or by algebraic approaches within the interacting boson model framework. It is proposed that the group of B(E2: 4(1)(+) -> 2(1)(+)/B(E2: 2(1)(+) -> 0(gs)(+)) ratios in the extremely neutron-deficient even-even W, Os, and Pt nuclei around neutron numbers N approximate to 90-94 reveal a quantum phase transition from a seniority-conserving structure to a collective regime as a function of neutron number. Although a system governed by seniority symmetry is the only theoretical framework for which such an effect may naturally occur, the phenomenon is highly unexpected for these nuclei that are not situated near closed shells.

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.

Using fusion-evaporation reactions, a gas-filled recoil separator, recoil-gating technique and recoil-isomer decay tagging technique we have extended the level scheme of At-203 (N = 118) significan ...

The very neutron-deficient isobars Pb-179 and Tl-179 have been produced using the fusion-evaporation reactions Pd-104(Kr-78,xpyn), where x = 2. The gas-filled separator RITU was employed to transpo ...

The evolution of collectivity with spin along the yrast line in the neutron-deficient nucleus $^{112}\mathrm{Te}$ has been studied by measuring the reduced transition probability of excited states in the yrast band. In particular, the lifetimes of the ${4}^{+}$ and ${6}^{+}$ excited states have been determined by using the recoil distance Doppler-shift method. The results are discussed using both large-scale shell-model and total Routhian surface calculations.

The structure of the low- and medium-spin levels of the $^{211}\mathrm{Po}$ nucleus have been studied with in-beam $\ensuremath{\gamma}$-ray spectroscopy with the $^{208}\mathrm{Pb}(\ensuremath{\alpha},n)^{211}\mathrm{Po}$ fusion-evaporation reaction. The level scheme was further extended with levels of the configurations $\ensuremath{\pi}{({h}_{9/2})}_{{2}^{+}\ensuremath{-}{4}^{+}}^{2}\ensuremath{\bigotimes}\ensuremath{\nu}{g}_{9/2}$, $\ensuremath{\pi}{({h}_{9/2})}_{{8}^{+}}^{2}\ensuremath{\bigotimes}\ensuremath{\nu}{g}_{9/2}$, $\ensuremath{\pi}{({h}_{9/2})}_{{2}^{+}\ensuremath{-}{4}^{+}}^{2}\ensuremath{\bigotimes}\ensuremath{\nu}{i}_{11/2}$, $\ensuremath{\pi}{({h}_{9/2})}_{{2}^{+}\ensuremath{-}{4}^{+}}^{2}\ensuremath{\bigotimes}\ensuremath{\nu}{j}_{15/2}$, $\ensuremath{\pi}{({h}_{9/2}{f}_{7/2})}_{{8}^{+}}\ensuremath{\bigotimes}\ensuremath{\nu}{g}_{9/2}$, and $\ensuremath{\pi}{({h}_{9/2})}_{{0}^{+}}^{2}\ensuremath{\bigotimes}\ensuremath{\nu}{({g}_{9/2})}_{{0}^{+}}^{2}{({s}_{1/2})}^{\ensuremath{-}1}$. The single-particle neutron states $\ensuremath{\nu}{d}_{5/2}$ and $\ensuremath{\nu}{s}_{1/2}$ were also identified. Furthermore, a number of states feeding the low-spin structures were added.

Excited states in the proton-unbound nuclide $^{177}$Au were populated in the $^92}$Mo($^{88}$Sr, p2n) reaction and identified using the Jurogam-II and GREAT spectrometers in conjunction with the RITU gas-filled separator at the University of Jyvaskyla Accelerator Laboratory. A strongly coupled band and its decay path to the 11/2−α-decaying isomer have been identified using recoil-decay tagging. Comparisons with cranked Hartree-Fock-Bogoliubov (HFB) calculations based on Skyrme energy functionals suggest that the band has a prolate deformation and is based upon coupling the odd 1h11/2 proton hole to the excited 02+ configuration in the $^{178}$Hg core. Although these configurations might be expected to follow the parabolic trend of core Hg(02+) states as a function of neutron number, the electromagnetic decay paths from the strongly coupled band in $^{177}$Au are markedly different from those observed in the heavier isotopes above the midshell. This indicates that a significant change in the structure of the underlying A+1Hg core occurs below the neutron midshell.

Lifetimes of the first excited 2(+) states in the extremely neutron- deficient W-162 and W-164 nuclei have been measured using the recoil distance Doppler shift technique. Experimental B(E2) data f ...

A newly observed isomeric intruder ${\textonehalf{}}^{+}$ state $[{T}_{\textonehalf{}}=3.5(6)\phantom{\rule{0.16em}{0ex}}\mathrm{ms}]$ is identified in $^{203}\mathrm{At}$ using a gas-filled recoil separator and fusion-evaporation reactions. The isomer is depopulated through a cascade of $E3$ and mixed $M1/E2$ transitions to the ${9/2}^{\ensuremath{-}}$ ground state, and it is suggested to originate from the $\ensuremath{\pi}{({s}_{\textonehalf{}})}^{\ensuremath{-}1}$ configuration. In addition, the structures above the ${\textonehalf{}}^{+}$ state in $^{203}\mathrm{At}$ and $^{197}\mathrm{At}$ are studied using in-beam $\ensuremath{\gamma}$-ray spectroscopy, recoil-decay tagging, and recoil-isomer decay tagging methods. The ${\textonehalf{}}^{+}$ state is fed from ${3/2}^{+}$ and ${5/2}^{+}$ states, and the origin of these states are discussed.

Excited states in the neutron-deficient N = 84 nuclide Lu-155 have been populated by using the Pd-102(Ni-58, alpha p) reaction. The Lu-155 nuclei were separated by using the gas-filled recoil ion t ...

The structure of neutron-rich 96,98Sr nuclei was investigated by low-energy safe Coulomb excitation of radioactive beams at the REX-ISOLDE facility, CERN, with the MINIBALL spectrometer. A rich set of transitional and diagonal E2 matrix elements, including those for non-yrast structures, has been extracted from the differential Coulomb-excitation cross sections. The results support the scenario of a shape transition at N = 60, giving rise to the coexistence of a highly deformed prolate and a spherical configuration in 98Sr, and are compared to predictions from several theoretical calculations. The experimental data suggest a significant contribution of the triaxal degree of freedom in the ground state of both isotopes. In addition, experimental information on low-lying states in 98Rb has been obtained.

The recoil-β tagging technique has been used in conjunction with the 40 Ca(32 S ,2n) reaction at a beam energy of 88 MeV to identify transitions associated with the decay of the 2 + and, tentatively, 4 + states in the nucleus 70 Kr. These data are used, along with previously published data, to examine the triplet energy differences (TED) for the mass 70 isobars. The experimental TED values are compared with shell model calculations, performed with the JUN45 interaction in the fpg model space, that include a J = 0 isospin nonconserving (INC) interaction with an isotensor strength of 100 keV. The agreement is found to be very good up to spin 4 and supports the expectation for analog states that all three nuclei have the same oblate shape at low-spin. The A = 70 results are compared with the experimental and shell model predicted TED and mirror energy differences (MED) for the mass 66 and 74 systems. The comparisons clearly demonstrate the importance of the isotensor INC interaction in replicating the TED data in this region. Issues related to the observed MED values and their interpretation within the shell model are discussed.

The extremely neutron-deficient isotope $^{178}\mathrm{Pb}$ has been produced. The GREAT spectrometer at the focal plane position of the gas-filled separator RITU was used to study the $\ensuremath{\alpha}$ decay of $^{178}\mathrm{Pb}$ and its $\ensuremath{\alpha}$-decay chain through $\ensuremath{\alpha}\text{\ensuremath{-}}\ensuremath{\alpha}$ correlations. The $\ensuremath{\alpha}$ decay was measured to have an energy and half-life of ${E}_{\ensuremath{\alpha}}$= 7610(30) keV and ${t}_{1/2}=0.{21}_{\ensuremath{-}0.08}^{+0.21}$ ms, respectively. The half-life is consistent with recent theoretical calculations using the Coulomb and proximity potential model. The $\ensuremath{\alpha}$-decay reduced width and hindrance factor for $^{178}\mathrm{Pb}$ were deduced and correspond to an unhindered $\mathrm{\ensuremath{\Delta}}l$ = 0 transition. In addition, the mass excess of $^{178}\mathrm{Pb}$ and the $\ensuremath{\alpha}$-decay $Q$ value were calculated from the experimental results and compared to theoretical values.

The lifetime of the $(11/{2}^{+})$ state in the band above the proton-emitting $(3/{2}^{+})$ state in $^{113}\mathrm{Cs}$ has been measured to be $\ensuremath{\tau}=24(6)$ ps from a recoil-decay-tagged differential-plunger experiment. The measured lifetime was used to deduce the deformation of the states using wave functions from a nonadiabatic quasiparticle model to independently calculate both proton-emission and electromagnetic $\ensuremath{\gamma}$-ray transition rates as a function of deformation. The only quadrupole deformation, which was able to reproduce the experimental excitation energies of the states, the electromagnetic decay rate of the $(11/{2}^{+})$ state and the proton-emission rate of the $(3/{2}^{+})$ state, was found to be ${\ensuremath{\beta}}_{2}=0.22(6)$. This deformation is in agreement with the earlier proton emission studies which concluded that $^{113}\mathrm{Cs}$ was best described as a deformed proton emitter, however, it is now more firmly supported by the present measurement of the electromagnetic transition rate.

The electromagnetic structure of 140Sm was studied in a low-energy Coulomb excitation experiment with a radioactive ion beam from the REX-ISOLDE facility at CERN. The 2+ and 4+ states of the ground-state band and a second 2+ state were populated by multistep excitation. The analysis of the differential Coulomb excitation cross sections yielded reduced transition probabilities between all observed states and the spectroscopic quadrupole moment for the 2+ 1 state. The experimental results are compared to large-scale shell model calculations and beyond-mean-field calculations based on the Gogny D1S interaction with a five-dimensional collective Hamiltonian formalism. Simpler geometric and algebraic models are also employed to interpret the experimental data. The results indicate that 140Sm shows considerable γ softness, but in contrast to earlier speculation no signs of shape coexistence at low excitation energy. This work sheds more light on the onset of deformation and collectivity in this mass region. 15 pages, 12 figures ispartof: Physical Review C vol:93 issue:5 status: published

States in the N = 28 nucleus Ar-46 have been studied by a two-neutron transfer reaction at REX-ISOLDE (CERN). A beam of radioactive Ar-44 at an energy of 2.16 AMeV and a tritium-loaded titanium target were used to populate Ar-46 by the H-3(Ar-44, p) two-neutron transfer reaction. Protons emitted from the target were identified in the T-REX silicon detector array. The excitation energies of states in Ar-46 have been reconstructed from the measured angles and energies of recoil protons. Angular distributions for three final states were measured and based on the shape of the differential cross section an excited state at 3695 keV was identified as J(pi) = 0(+). The angular differential cross section for the population of different states are compared to calculations using a reaction model employing both sequential and direct transfer of two neutrons. Results are compared to shell-model calculations using state-of-the-art effective interactions.

The levels in Sn-129 populated from the beta(-) decay of In-129 isomers were investigated at the ISOLDE facility of CERN using the newly commissioned ISOLDE Decay Station (IDS). The lowest 1/2(+) state and the 3/2(+) ground state in 129Sn are expected to have configurations dominated by the neutron s(1/2) (l = 0) and d(3/2) (l = 2) single-particle states, respectively. Consequently, these states should be connected by a somewhat slow l-forbidden M1 transition. Using fast-timing spectroscopy we havemeasured the half-life of the 1/2(+) 315.3-keV state, T-1/2 = 19(10) ps, which corresponds to a moderately fast M1 transition. Shell-model calculations using the CD-Bonn effective interaction, with standard effective charges and g factors, predict a 4-ns half-life for this level. We can reconcile the shell-model calculations to the measured T-1/2 value by the renormalization of the M1 effective operator for neutron holes.

Excited states in the neutron-deficient nuclides(74)(162)W(88) and W-164(74)90 were investigated by using the gamma-ray spectrometer Jurogam. A change in structure is apparent from the first rotational alignments in W-162 and W-164, whose rotationally aligned bands are interpreted as nu(h(9/2))(2) and nu(i(13/2))(2) configurations, respectively. The level schemes have been extended using recoil (-decay) correlations with the observation of excited collective structures. Configuration assignments have been made on the basis of comparisons of the deduced aligned angular momentum, as a function of rotational frequency, with the predictions of the cranked shell model.

Neutron-rich {96,98}Sr isotopes have been investigated by safe Coulomb excitation of radioactive beams at the REX-ISOLDE facility. Reduced transition probabilities and spectroscopic quadrupole moments have been extracted from the differential Coulomb excitation cross sections. These results allow, for the first time, the drawing of definite conclusions about the shape coexistence of highly deformed prolate and spherical configurations. In particular, a very small mixing between the coexisting states is observed, contrary to other mass regions where strong mixing is present. Experimental results have been compared to beyond-mean-field calculations using the Gogny D1S interaction in a five-dimensional collective Hamiltonian formalism, which reproduce the shape change at N=60.

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 ...

Despite that it is more than 100 years since the atomic nucleus was first dis- covered by Ernest Rutherford and coworkers, many of its features still elude our understanding. The fact that the fundamental interactions between the nuclear constituents; nucleons, and ultimately quarks, are not yet known in detail, and the complexity of the nuclear many-body system compound the great challenges facing theoretical interpretations of experimental data. It is therefore important to focus on distinct phenomena where experimental mea- surements can be compared with theoretical predictions, providing stringent tests of theory. One such area is the nuclear phenomenology of collective excitations related to rotations and vibrations of the nucleus as a whole, and how such modes of excitation may develop from the interactions between a few nucleons occupying single-particle orbits outside closed shells.This thesis is devoted to experimental studies of excited states in the 99Tc, 162W, and 166Re nuclei. These nuclei lie in “transitional” regions of the Segre chart, where collective excitation mechanisms start becoming important when adding valence nucleons outside closed neutron and proton shells. Such nuclei are important for testing state-of-the-art theoretical models. The excited states of the nuclei studied in the present work were populated using heavy-ion fusion-evaporation reactions. Prior to the present work, high-spin data were still lacking in 99Tc since in the previous works [1–5] excited states were only populated up to around 3 MeV. Two collective bands have been extended to intermediate angular momentum states in the present work. The experimental results were compared with the systematics of other technetium isotopes, evaluating electromagnetic characteristics based on semiclassical calculations and the particle-rotor model. The 162W and 166Re nuclei are situated in the very neutron-deficient 160-170 mass region, requiring special techniques for identifying their excited-state structures. The level scheme of 162W was first reported by Dracoulis et al. in 1993 [6], where the first excited 2+ state was assigned to be 450 keV above the ground state. However, the lack of selectivity made the γ-ray identification for higher energy levels of 162W uncertain. In this work, the highly selective recoil-decay tagging technique was used to uniquely identify γ-ray transitions from excited states in 162W and to construct its level scheme. In addition, the experimental setup enabled a precise determination of the half-life of the α-decaying ground state of 162W. The α-formation probability for 162W was extracted from the measurement of the half-life and systematical comparisons with the neighboring nuclei were performed. Two rotational-like bands were identified in 166Re for the first time and the lifetimes of the lowest three excited states in band (1) were measured using the recoil distance Doppler shift method. The results were compared with theoretical calculations based on a semiclassical approach, the particle-rotor model, and the tilted axis cranking model in a relativistic mean field approach. The microscopic mechanisms (configuration and alignment, etc) of the rotational bands were interpreted under the framework of total Routhian surface predictions and cranked shell model calculations.

The lifetime of the 2(+) --> 0(g.s.)(+) transition in the neutron-deficicient nucleus Te-112 has been measured for the first time using the DPUNS plunger and the recoil distance Doppler shift te ...

It was shown that the evolution of the $B(E2;{2}_{1}^{+}\ensuremath{\rightarrow}{0}_{1}^{+})$ values in $N$ = 80 isotones from Te to Nd is affected by the underlying subshell structure. This manifests itself in the observation of the local suppression of the $B(E2)$ value at $Z=58$ with respect to the neighboring nuclei $^{136}\mathrm{Ba}$ and $^{140}\mathrm{Nd}$. To investigate this shell sensitivity toward the $Z=64$ subshell gap, the $B(E2;{2}_{1}^{+}\ensuremath{\rightarrow}{0}_{1}^{+})$ value of the unstable nucleus $^{142}\mathrm{Sm}$ was measured utilizing the projectile Coulomb excitation technique. The radioactive ion beam (RIB) experiment was performed at the REX-ISOLDE facility at CERN. The $B(E2)$ value of $32\phantom{\rule{0.16em}{0ex}}(4)\phantom{\rule{0.16em}{0ex}}\mathrm{W}.\mathrm{u}.$ reflects the impact of the $\ensuremath{\pi}(1{g}_{7/2}\phantom{\rule{0.16em}{0ex}}2{d}_{5/2})$ subshell closure at $Z=64$ with respect to a linear scaling of collectivity with valence proton number.

Gamma rays from excited states feeding a proton-emitting isomeric-state in Lu-151 have been observed for the first time. Comparison with state-of-the-art nonadiabatic quasiparticle calculations indicates an oblately deformed, 3/2(+) proton-emitting state with a quadrupole deformation of beta(2) = -0.11. The calculations suggest an increase in quadrupole deformation, to beta(2) = -0.18, with increasing spin which is understood in terms of the mixing of Nilsson states at the Fermi surface. It is also shown that the proton decay half-life is consistent with that from a 3/2(+) state with a quadrupole deformation of beta(2) = -0.12.

Excited states in the neutron-deficient nuclei ${}_{75}^{163}{\mathrm{Re}}_{88}$ and ${}_{75}^{165}{\mathrm{Re}}_{90}$ were populated in the ${}^{106}{\mathrm{Cd}(}^{60}\mathrm{Ni},\phantom{\rule{0.16em}{0ex}}p2n\ensuremath{\gamma})$ and ${}^{92}{\mathrm{Mo}(}^{78}\mathrm{Kr}$, $3p2n\ensuremath{\gamma})$ fusion-evaporation reactions at bombarding energies of 270 and 380 MeV, respectively. \ensuremath{\gamma} rays were detected at the target position using the JUROGAM spectrometer while recoiling ions were separated in-flight by the RITU gas-filled recoil separator and implanted in the GREAT spectrometer. The energy level schemes for $^{163}\mathrm{Re}$ and $^{165}\mathrm{Re}$ were identified using recoil-decay correlation techniques. At low spin, the yrast bands of these isotopes consist of signature partner bands based on a single $\ensuremath{\pi}{h}_{11/2}$ quasiproton configuration. The bands display large energy splitting consistent with the soft triaxial shape typical of transitional nuclei above $N=82$. The configurations of the excited states are proposed within the framework of the cranked shell model.

The excited states of $^{201}\mathrm{At}$ were studied and an isomeric $29/{2}^{+}$ state $[{T}_{\textonehalf{}}=3.39(9)\phantom{\rule{0.28em}{0ex}}\ensuremath{\mu}\mathrm{s}]$ was identified by using a fusion-evaporation reaction, a gas-filled recoil separator, and recoil gating techniques. The $29/{2}^{+}$ state is suggested to originate from the $\ensuremath{\pi}({h}_{9/2})\ensuremath{\bigotimes}|^{200}\mathrm{Po};{11}^{\ensuremath{-}}\ensuremath{\rangle}$ configuration, and it decays through the 269- and 339-keV $E2$- and $E3$-type transitions, respectively. Moreover, a cascade of magnetic dipole transitions that is suggested to originate from a shears band was observed by using recoil-gated $\ensuremath{\gamma}\ensuremath{-}\ensuremath{\gamma}(\ensuremath{-}\ensuremath{\gamma})$ coincidence techniques.

Background: Shell-model calculations crucially depend on the residual interaction used to approximate the nucleon-nucleon interaction. Recent improvements to the empirical universal $sd$ interaction (USD) describing nuclei within the $sd$ shell yielded two new interactions---USDA and USDB---causing changes in the theoretical description of these nuclei.Purpose: Transition matrix elements between excited states provide an excellent probe to examine the underlying shell structure. These observables provide a stringent test for the newly derived interactions. The nucleus $^{26}\mathrm{Na}$ with 7 valence neutrons and 3 valence protons outside the doubly-magic ${}^{16}\mathrm{O}$ core is used as a test case.Method: A radioactive beam experiment with $^{26}\mathrm{Na}$ (${T}_{1/2}=1,07s$) was performed at the REX-ISOLDE facility (CERN) using Coulomb excitation at safe energies below the Coulomb barrier. Scattered particles were detected with an annular Si detector in coincidence with $\ensuremath{\gamma}$ rays observed by the segmented MINIBALL array. Coulomb excitation cross sections of the beam have been obtained by normalization to the well known Coulomb excitation cross sections of the $^{104}\mathrm{Pd}$ target.Results: The observation of three $\ensuremath{\gamma}$-ray transitions in $^{26}\mathrm{Na}$ together with available spectroscopic data allows us to determine $E2$- and $M1$-transitional matrix elements. Results are compared to theoretical predictions.Conclusion: The improved theoretical description of $^{26}\mathrm{Na}$ could be validated. Remaining discrepancies between experimental data and theoretical predictions indicate the need for future experiments and possibly further theoretical improvements.

Excited states in the neutron-deficient nucleus $_{72}^{161}\mathrm{Hf}_{89}$ have been populated using the $^{118}\mathrm{Sn}(^{48}\mathrm{Ti},5n)^{161}\mathrm{Hf}$ and $^{110}\mathrm{Pd}(^{56}\mathrm{Fe},5n)^{161}\mathrm{Hf}$ fusion-evaporation reactions at 240 and 270 MeV, respectively. The level scheme for $^{161}\mathrm{Hf}$ has been extended with the observation of new band structures and an ${I}^{\ensuremath{\pi}}=(13/{2}^{+})$ isomeric state with a half-life of 4.8(2) $\ensuremath{\mu}\mathrm{s}$ has been identified. The decay path from this isomer to the $(7/{2}^{\ensuremath{-}})$ ground state is established. The yrast band, based on the $(13/{2}^{+})$ isomeric state, is extended up to $(73/{2}^{+})$ and side band structures are identified up to $(69/{2}^{\ensuremath{-}})$ and $(55/{2}^{\ensuremath{-}})$. Quasiparticle assignments for these rotational structures are made on the basis of their alignment properties and Woods-Saxon cranked shell-model calculations.