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Decay spectroscopy of the odd-proton nuclei $^{249}$Md and $^{251}$Md has been performed. High-K isomeric states were identified for the first time in these two nuclei through the measurement of their electromagnetic decay. An isomeric state with a half-life of 2.8(5) ms and an excitation energy $\ge 910$ keV was found in $^{249}$Md. In $^{251}$Md, an isomeric state with a half-life of 1.4(3) s and an excitation energy $\ge 844$ keV was found. Similarly to the neighbouring $^{255}$Lr, these two isomeric states are interpreted as 3 quasi-particle high-K states and compared to new theoretical calculations. Excited nuclear configurations were calculated within two scenarios: via blocking nuclear states located in proximity to the Fermi surface or/and using the quasiparticle Bardeen–Cooper–Schrieffer method. Relevant states were selected on the basis of the microscopic-macroscopic model with a deformed Woods–Saxon potential. The most probable candidates for the configurations of K-isomeric states in Md nuclei are proposed. Decay spectroscopy of the odd-proton nuclei $^{249}$Md and $^{251}$Md has been performed. High-$K$ isomeric states were identified for the first time in these two nuclei through the measurement of their electromagnetic decay. An isomeric state with a half-life of $2.8(5)$ ms and an excitation energy $\geq 910$ keV was found in $^{249}$Md. In $^{251}$Md, an isomeric state with a half-life of $1.4(3)$ s and an excitation energy $\geq 844$ keV was found. Similarly to the neighbouring $^{255}$Lr, these two isomeric states are interpreted as 3 quasi-particle high-$K$ states and compared to new theoretical calculations. Excited nuclear configurations were calculated within two scenarios: via blocking nuclear states located in proximity to the Fermi surface or/and using the quasiparticle Bardeen-Cooper-Schrieffer method. Relevant states were selected on the basis of the microscopic-macroscopic model with a deformed Woods-Saxon potential. The most probable candidates for the configurations of $K$-isomeric states in Md nuclei are proposed.

International audience; Prolate-oblate shape coexistence close to the ground state in the strongly-deformed proton-rich A≈120 nuclei is reported for the first time. One of the four reported bands in 119Cs, built on a 11/2− state at 670 keV, consists of nearly degenerate signature partners, and has properties which unequivocally indicate the strongly-coupled πh11/2[505]11/2− configuration associated with oblate shape. Together with the decoupled πh11/2[541]3/2− band built on the 11/2− prolate state at 110 keV, for which a half-life of T1/2=55(5)μs has been measured, the new bands bring evidence of shape coexistence at low spin in the proton-rich strongly deformed A≈120 nuclei, a phenomenon predicted since long time, but not yet observed. Calculations using the particle-number conserving cranked shell model and two dimensional tilted axis cranking covariant density functional theory support and well reproduce the observed oblate and prolate coexisting low-energy states in 119Cs.

The very neutron-deficient strongly deformed Cs 119 nucleus has been studied using the Ni 58 ( Zn 64 , 3 p ) reaction and the JUROGAM 3 γ -ray detector array coupled to the MARA recoil-mass separator setup. The excitation energies of all observed bands have been determined, spins and parities have been firmly assigned to most of the observed states. The previously known and the newly identified rotational bands have been extended to very high spin and excitation energy. The configurations of the observed bands are discussed using the particle number conserving cranked shell model. The present study establishes the largest set of rotational bands observed in the proton-rich A ≈ 120 mass region.

Using a fusion-evaporation reaction and a gas-filled recoil separator, an isomeric state [T12=83(8)μs] with a most likely spin and parity of 132+ has been identified in Th211. The isomeric state is mainly depopulated via a hindered internal M2 transition [B(M2)=0.0025(5) W.u.], but also a weak α-decay branch of 4(3)% was observed. The present observations fit well to the systematic pattern set by the previously identified states of the same spin and parity in this region of the nuclear chart.

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.

Lifetime measurements in $$^{178}$$ 178 Pt with excited states de-exciting through $$\gamma $$ γ -ray transitions and internal electron conversions have been performed. Ionic charges were selected by the in-flight mass separator MARA and measured at the focal plane in coincidence with the $$4_1^+\rightarrow 2_1^+$$ 4 1 + → 2 1 + $$257\,$$ 257 keV $$\gamma $$ γ -ray transition detected using the JUROGAM 3 spectrometer. The resulting charge-state distributions were analysed using the differential decay curve method (DDCM) framework to obtain a lifetime value of 430(20) ps for the $$2_1^+$$ 2 1 + state. This work builds on a method that combines the charge plunger technique with the DDCM analysis. As an alternative analysis, ions were selected in coincidence with the $$^{178}$$ 178 Pt alpha decay ($$E_{\mathrm {alpha}} = 5.458(5)$$ E alpha = 5.458 ( 5 ) MeV) at the focal plane. Lifetime information was obtained by fitting a two-state Bateman equation to the decay curve with the lifetime of individual states defined by a single quadrupole moment. This yielded a lifetime value of 430(50) ps for the $$2_1^+$$ 2 1 + state, and 54(6) ps for the $$4_1^+$$ 4 1 + state. An analysis method based around the Bateman equation will become especially important when using the charge plunger method for the cases where utilising coincidences between prompt $$\gamma $$ γ rays and recoils is not feasible.

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.

Experimental signatures of moderately enhanced octupole correlations at high spin in 136 Nd are indicated for the first time. The extracted dipole moments of two negative-parity bands are only two times smaller than those of the lanthanide nuclei with N ≈ 90 which present well-established octupole correlations. Calculations using the cranked quasiparticle random phase approximation and a model of quadrupole-octupole rotations with octupole vibrations reveal the structure of the bands and the enhanced octupole correlations at high spin in 136 Nd .

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.

The extremely neutron-deficient isotopes 177,179Au were studied by means of in-beam ?-ray spectroscopy. Specific tagging techniques, ?-decay tagging in 177Au and isomer tagging in 179Au, were used for these studies. Feeding of positive-parity, nearly spherical states, which are associated with 2d3/2 and 3s1/2 proton-hole configurations, from the 1i13/2 proton-intruder configuration was observed in 177Au. Such a decay path has no precedent in odd-Au isotopes and it is explained by the effect of mixing of wave functions of the initial state. © 2020, 262010 2/0129/17 Science and Technology Facilities Council, STFC European Research Council, ERC: 203481 Academy of Finland: 131665 Agentúra na Podporu V?skumu a V?voja, APVV: APVV-15-0225, The authors express their gratitude to the staff of the Accelerator Laboratory at the University of Jyväskylä for their excellent technical support. This work has been supported by the EU-FP7-IA project ENSAR (No. 262010 ), the Academy of Finland (CoE in Nuclear and Accelerator Based Physics, grant to T.G., Contract No. 131665 ), the European Research Council through the project SHESTRUCT (Grant Agreement No. 203481 ), the UK Science and Technology Facilities Council , the Slovak Research and Development Agency under Contract No. APVV-15-0225 , and the Slovak Grant Agency VEGA (Contract No. 2/0129/17 ).

© 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)%.

CITATION: Majola, S. N. T., et al. 2019. Spectroscopy of low-spin states in 157Dy : Search for evidence of enhanced octupole correlations. Physical Review C, 100(6):034322, doi:10.1103/PhysRevC.100.034322.

International audience; Three new highly-deformed (HD) bands are identified in Nd136 and the highly deformed band of Nd137 is extended at higher spin by four transitions, revealing a band crossing associated with the occupation of the second νi13/2 intruder orbital. Extended cranked Nilsson-Strutinsky calculations are performed for all HD bands observed in Nd134, Nd136, and Nd137, achieving for the first time a consistent interpretation of all HD bands in the Nd nuclei. The new interpretation has significant consequences, like the change of parity of the yrast HD bands of Nd134 and Nd136, and the involvement of two negative-parity neutron intruder orbitals in the configurations of most HD bands. The present experimental results and their theoretical interpretation represent an important step forward in the understanding of the second-minimum excitations in the Nd nuclei.

International audience; Multipolarity measurements are presented for transitions in the deformed odd-mass nucleus$^{167}$ Yb in support of tentative spin assignments and level interpretations based upon the cranked-Nilsson model. Internal-conversion coefficients were measured with the SAGE (Silicon And GErmanium) spectrometer confirming several E2 transition assignments. The array of high-purity germanium detectors enabled the recording of high-multiplicity events from which $\gamma\gamma\gamma$ and $\gamma\gamma e^{-}$ data sets were extracted and the technique of high-fold $\gamma$ -ray gating was demonstrated to cleanly isolate transitions of interest.

Grahn, Tuomas/0000-0002-6255-2279; Herzan, Andrej/0000-0002-6736-7638; Cullen, Dave/0000-0002-0041-1606; Barber, Liam/0000-0002-7409-9352; Keatings, James Michael/0000-0003-4271-8021; SAYGI, BAHADIR/0000-0001-5406-506X; Greenlees, Paul/0000-0002-5986-5274; Spagnoletti, Pietro/0000-0002-7674-989X; Parr, Edward/0000-0001-6204-4461; Bondili, S Nara Singh/0000-0002-4096-2429, WOS: 000494939000022, This letter reports lifetime measurements of excited states in the odd-N nucleus W-163 using the recoil-distance Doppler shift method to probe the core polarising effect of the i(13/2) neutron orbital on the underlying soft triaxial even-even core. the ratio B(E2:21/2(+) -> 17/2(+))/B(E2:17/2(+) -> 13/2(+)) is consistent with the predictions of the collective rotational model. the deduced B(E2) values provide insights into the validity of collective model predictions for heavy transitional nuclei and a geometric origin for the anomalous B(E2) ratios observed in nearby even-even nuclei is proposed. (C) 2019 the Authors. Published by Elsevier B.V., UK Science and Technology Facilities CouncilScience & Technology Facilities Council (STFC) [ST/P004598/1, ST/L005670/1, ST/L005794/1]; Scientific and Technological Research Council of Turkey (TUBITAK)Turkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK) [117F508]; EU HORIZON2020 programme "Infrastructures" [654002]; Academy of Finland under the Finnish Centre of Excellence Programme (Nuclear and Accelerator Based Physics Programme at JYFL); Science and Technology Facilities CouncilScience & Technology Facilities Council (STFC) [1643549] Funding Source: researchfish, This work has been supported by the UK Science and Technology Facilities Council under grants ST/P004598/1, ST/L005670/1 and ST/L005794/1; the Scientific and Technological Research Council of Turkey (TUBITAK Project No: 117F508); the EU HORIZON2020 programme "Infrastructures", project number: 654002 (ENSAR2) and by the Academy of Finland under the Finnish Centre of Excellence Programme (Nuclear and Accelerator Based Physics Programme at JYFL). the UK/France (STFC/IN2P3) Loan Pool and GAMMAPOOL network are acknowledged for the HPGe escapesuppressed detectors of the JUROGAM II array.

WOS: 000406755100001, Lifetimes of excited states in the yrast band of the neutron-deficient nuclide W-166 have been measured utilizing the DPUNS plunger device at the target position of the JUROGAM II gamma-ray spectrometer in conjunction with the RITU gas-filled separator and the GREAT focal-plane spectrometer. Excited states in W-166 were populated in the Mo-92(Kr-78, 4p) reaction at a bombarding energy of 380 MeV. The measurements reveal a low value for the ratio of reduced transitions probabilities for the lowest-lying transitions B(E2; 4(+)-> 2(+)) / B(E2; 2(+)-> 0(+)) = 0.33(5), compared with the expected ratio for an axially deformed rotor (B-4/2 = 1.43)., EURONS (European Commission)European Commission Joint Research Centre [RII3-CT-2004-506065]; Academy of Finland under the Finnish Centre of Excellence Programme (Nuclear and Accelerator Based Physics) [213503]; UK Science and Technology Facilities CouncilScience & Technology Facilities Council (STFC); Academy of FinlandAcademy of Finland [131665], This work has been supported through EURONS (European Commission Contract No. RII3-CT-2004-506065), the Academy of Finland under the Finnish Centre of Excellence Programme 2006-2011 (Nuclear and Accelerator Based Physics Contract No. 213503), and the UK Science and Technology Facilities Council. The UK/France (STFC/IN2P3) Loan Pool and GAMMAPOOL network are acknowledged for the EUROGAMdetectors of JUROGAMII. T.G. acknowledge the support of the Academy of Finland (Contract No. 131665).

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.

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.

The new neutron-deficient nuclei 240 Es and 236 Bk were synthesised at the gas-filled recoil separator RITU. They were identified by their radioactive decay chains starting from 240 Es produced in the fusion–evaporation reaction 209 Bi( 34 S,3n) 240 Es. Half-lives of 6 ( 2 ) s and 22 − 6 + 13 s were obtained for 240 Es and 236 Bk, respectively. Two groups of α particles with energies E α = 8.19 ( 3 ) MeV and 8.09 ( 3 ) MeV were unambiguously assigned to 240 Es. Electron-capture delayed fission branches with probabilities of 0.16 ( 6 ) and 0.04 ( 2 ) were measured for 240 Es and 236 Bk, respectively. These new data show a continuation of the exponential increase of ECDF probabilities in more neutron-deficient isotopes.

A study of Sm 154 through γ -ray and internal conversion electron coincidence measurements was performed using the Silicon And GErmanium spectrometer (SAGE). An upper limit for the ρ 2 ( E 0 ; 2 2 + → 2 1 + ) and measurement of the ρ 2 ( E 0 ; 4 2 + → 4 1 + ) monopole transitions strengths were determined. The extracted transition strength for each is significantly lower than that predicted by either the Bohr and Mottelson β -vibration description or the interacting boson model. Hence, the long standing interpretation of these states as a collective band built on the 0 2 + state, which is conventionally assigned as a Bohr and Mottelson β vibration is questionable.

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 triple $\ensuremath{\alpha}$-decay chain $^{114}\mathrm{Ba}\ensuremath{\rightarrow}^{110}\mathrm{Xe}\ensuremath{\rightarrow}^{106}\mathrm{Te}\ensuremath{\rightarrow}^{102}\mathrm{Sn}$ has been directly observed for the first time, following the $^{58}\mathrm{Ni}(^{58}\mathrm{Ni},2n)$ reaction. Implantation of $^{114}\mathrm{Ba}$ nuclei into a double-sided silicon-strip detector has allowed their $\ensuremath{\alpha}$ decays to be correlated in position and time with the $\ensuremath{\alpha}$ decays of the daughter $(^{110}\mathrm{Xe})$ and granddaughter $(^{106}\mathrm{Te})$ nuclei. In total, 17 events have been assigned to the $^{114}\mathrm{Ba}\ensuremath{\rightarrow}^{110}\mathrm{Xe}\ensuremath{\rightarrow}^{106}\mathrm{Te}\ensuremath{\rightarrow}^{102}\mathrm{Sn}$ triple $\ensuremath{\alpha}$-decay chain. The energy of the $^{114}\mathrm{Ba} \ensuremath{\alpha}$ decay has been measured to be ${E}_{\ensuremath{\alpha}}=3480$(20) keV, which is 70 keV higher than the previously measured value, and the half-life of $^{114}\mathrm{Ba}$ has been measured with improved accuracy, to be ${380}_{\ensuremath{-}110}^{+190}$ ms. A revised ${Q}_{^{12}\mathrm{C}}$ value of 19 035(45) keV for $^{114}\mathrm{Ba}$ is presented.

The $\ensuremath{\alpha}$ decay of $^{222}\mathrm{Th}$ populating the low-lying ${J}^{\ensuremath{\pi}}={3}^{\ensuremath{-}}$ state, and also a proposed ${1}^{\ensuremath{-}}$ state, in $^{218}\mathrm{Ra}$ has been observed. The observations suggest an excitation energy of 853 keV for the ${1}^{\ensuremath{-}}$ state, which is 60 keV above the ${3}^{\ensuremath{-}}$ state. The hindrance factors of these $\ensuremath{\alpha}$ decays give a possible boundary to the region of ground-state octupole deformation in the light-actinide nuclei. The relative positions of the ${J}^{\ensuremath{\pi}}={1}^{\ensuremath{-}}$ and ${3}^{\ensuremath{-}}$ states suggest they are produced by an octupole-vibrational mechanism, as opposed to $\ensuremath{\alpha}$ clustering or rotations of a reflection-asymmetric octupole-deformed shape.

Excited states in the neutron-deficient odd-odd proton-unbound nuclide $^{158}\mathrm{Ta}$ have been investigated in two separate experiments. In the first experiment, $^{166}\mathrm{Ir}$ nuclei were produced in the reactions of 380 MeV $^{78}\mathrm{Kr}$ ions with an isotopically enriched $^{92}\mathrm{Mo}$ target. The $\ensuremath{\alpha}$-decay chain of the ${9}^{+}$ state in $^{166}\mathrm{Ir}$ was analyzed. Fine structure in the $\ensuremath{\alpha}$ decay of the ${9}^{+}$ state in $^{162}\mathrm{Re}$ established a 66 keV difference in excitation energy between the lowest-lying ${9}^{+}$ and ${10}^{+}$ states in $^{158}\mathrm{Ta}$. Higher-lying states in $^{158}\mathrm{Ta}$ were populated in the reactions of 255 MeV $^{58}\mathrm{Ni}$ ions with an isotopically enriched $^{102}\mathrm{Pd}$ target. Gamma-ray decay paths that populate, depopulate, and bypass a ${19}^{\ensuremath{-}}$ isomeric state have been identified. The general features of the deduced level scheme are discussed and the prospects for observing proton emission branches from excited states are considered.

WOS: 000371740600004, Lifetimes of excited states in the neutron-deficient odd-odd nucleus Re-166 have been measured for the first time using the recoil distance Doppler-shift method. The measured lifetime for the (8(-)) state; tau = 480 (80) ps, enabled an assessment of the multipolarities of the gamma rays depopulating this state. Information on electromagnetic transition strengths were deduced for the gamma-ray transitions from the (9(-)), (10(-)), and (11(-)) states, and in the case of the (10(-)) and (11(-)) states limits on the B (M1) and B(E2) strengths were estimated. The results are compared with total Routhian surface predictions and semiclassical calculations. Tilted-axis cranking calculations based on a relativistic mean-field approach (TAC-RMF) have also been performed in order to test the possibility of magnetic rotation in the 166Re nucleus. While the TAC-RMF calculations predict a quadrupole-deformed nuclear shape with similar beta(2) deformation as obtained by using the TRS model, it was found that the experimental electromagnetic transition rates are in better agreement with a collective -rotational description., Swedish Research CouncilSwedish Research Council [621-2010-3694]; Academy of Finland under the Finnish Centre of Excellence ProgrammeAcademy of Finland; UK Science and Technology Facilities CouncilScience & Technology Facilities Council (STFC); European UnionEuropean Union (EU) [262010]; China Scholarship CouncilChina Scholarship Council [201306210205]; Academy of FinlandAcademy of Finland [131665]; Science and Technology Facilities CouncilScience & Technology Facilities Council (STFC) [ST/L005670/1, EP/E004385/1, ST/L005689/1, ST/G008671/1, ST/J000094/1, EP/C015266/1], The authors would like to thank the staff at the Accelerator Laboratory of the University of Jyvaskyla for their excellent technical support. This work was supported by the Swedish Research Council (Project No. 621-2010-3694), the Academy of Finland under the Finnish Centre of Excellence Programme 2012 - 2017, the UK Science and Technology Facilities Council, and the European Union Seventh Framework Programme Integrating Activities-Transnational Access, Project No. 262010 (ENSAR). Li is supported in part by the China Scholarship Council under Grant No. 201306210205. Additionally, we thank the GAMMAPOOL European Spectroscopy Resource for the loan of the detectors for JUROGAM II array. T.G. acknowledges the support from the Academy of Finland (Contract No. 131665).

A lifetime measurement has been made for the first excited 11/2(+) state in the proton-unbound nucleus (109)(53)I56 using the recoil-distance Doppler-shift method in conjunction with recoil-proton ...

The lifetime of an excited state above a weakly populated isomer in the proton-unbound odd-odd nucleus 144Ho has been measured using the recoil distance Doppler shift method. This measurement represents the first differential-plunger lifetime measurement to utilize recoil-isomer tagging. The first excited I[pi]=(10+) state above the two-quasiparticle [pi]h11/2[circle times operator][nu]h11/2(8+) isomer was determined to have a lifetime of [tau]=6(1)�ps. Potential energy surface calculations, based on the configuration-constrained blocking method, predict the isomeric state to have [gamma]-soft triaxial-nuclear shape with [gamma][approximate]24�. The lifetime of the (10+) state can be understood from these calculations if there is a degree of rotational alignment in this band, with the K value being lower than the bandhead spin. However, the validity of the K quantum number with large predicted triaxiality and gamma softness requires further theoretical study.

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 ...

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.

Submitted to European Physical Journal A - Expérience GANIL; The odd-Z isotope 255Lr, its daughter 251Md and grand-daughter 247Es were studied in two experiments performed at GANIL and the University of Jyväskylä. The 255Lr nuclei were produced using the cold fusion-evaporation reaction 209Bi(48Ca, 2n)255Lr at a bombarding energy of 217MeV. The single-particle structure and decay properties were investigated using α, γ and electron spectroscopy. The ground-state spin and parity could be assigned for 255Lr (1/2-) and 251Md (7/2-). States corresponding to the 7/2+[633], 7/2-[514] and 1/2-[521] Nilsson orbitals were observed. Results are compared to experimental data obtained in neighbouring isotopes and to Hartree-Fock-Bogoliubov calculations using the Skyrme interaction SLy4 and a density-dependent pairing interaction. The position of the 1/2-[521] orbital from the spherical 2f5/2 shell is discussed.

WOS: 000240847400007, The observation of the new nuclide Re-159(75)84 provides important insights into the evolution of single-particle structure and the mass surface in heavy nuclei beyond the proton drip line. This nuclide, 26 neutrons away from the nearest stable rhenium isotope, was synthesised in the reaction Cd-106(Ni-58, p4n) and identified via its proton radioactivity using the RITU gas-filled separator and the GREAT focal-plane spectrometer. Comparisons of the measured proton energy (E-p = 1805 +/- 20 keV) and decay half-life (t(1/2) = 21 +/- 4 mu s) with values calculated using the WKB method indicate that the proton is emitted from an h(11/2) state. The implications of these results for future experimental investigations into even more proton unbound nuclei using in-flight separation techniques are considered. (c) 2006 Elsevier B.V. All rights reserved., Science and Technology Facilities Council [EP/C543157/1, EP/C015371/1, EP/C015266/1, ST/G008671/1]

The stability of an atomic nucleus is determined by the outcome of a tug-of-war between the attractive strong nuclear force and the repulsive electrostatic force between the protons in the nucleus. If 100 protons and about 150 neutrons or more are assembled into a nucleus, the repulsion usually becomes dominant and causes the nucleus to fission. For certain 'magic numbers' of protons and neutrons this repulsion can be overcome and the nucleus stabilized. In particular an 'island of stability' is predicted beyond the actinides, where long-lived or even stable superheavy elements can exist, but its precise limits are unknown. Experiments can help determine where this island lies, however. Spectroscopy of the nobelium isotope, 254No reveals three excited structures, two of them metastable. This finding will help to constrain nuclear models of the superheavy elements, and provides more data for the search for the next magic numbers. Spectroscopic studies of the nobelium isotope 254No — the heaviest nucleus studied in this manner to date — details three excited structures, two of which are metastable, which should help to constrain nuclear models of the superheavy elements. A long-standing prediction of nuclear models is the emergence of a region of long-lived, or even stable, superheavy elements beyond the actinides. These nuclei owe their enhanced stability to closed shells in the structure of both protons and neutrons1,2,3. However, theoretical approaches to date do not yield consistent predictions of the precise limits of the ‘island of stability’; experimental studies are therefore crucial. The bulk of experimental effort so far has been focused on the direct creation of superheavy elements in heavy ion fusion reactions, leading to the production of elements up to proton number Z = 118 (refs 4, 5). Recently, it has become possible to make detailed spectroscopic studies6,7 of nuclei beyond fermium (Z = 100), with the aim of understanding the underlying single-particle structure of superheavy elements. Here we report such a study of the nobelium isotope 254No, with 102 protons and 152 neutrons—the heaviest nucleus studied in this manner to date. We find three excited structures, two of which are isomeric (metastable). One of these structures is firmly assigned to a two-proton excitation. These states are highly significant as their location is sensitive to single-particle levels above the gap in shell energies predicted at Z = 114, and thus provide a microscopic benchmark for nuclear models of the superheavy elements.

Gamma rays from excited states of 190Po have been observed using the Jurosphere Ge-detector array coupled to the RITU gas-filled separator. They were associated with a collective band which from spin 4 onwards resembles the prolate rotational bands known in the isotones 188Pb and 186Hg. This indicates that in 190Po the prolate configuration becomes yrast above I = 2. The experimental results are interpreted in a two-band mixing calculation and are in agreement with α-decay data and potential energy surface calculations.

The techniques of recoil-gating and recoil-decay tagging have been employed at Jyvaskyla to perform in-beam γ-ray and electron spectroscopy studies of heavy nuclei. The JUROSPHERE γ-ray array and the SACRED electron spectrometer have been placed at the target position of the JYFL gas-filled recoil separator recoil ion transport unit (RITU). The RITU separator has been used to collect the recoils of interest and separate them from beam particles and fission products. At the focal plane a detector system consisting of time-of-flight and implantation detectors has been used for further event identification. The method and some highlights from the results in the lead region close to the proton drip line and in the transuranium region will be presented and discussed.

The low-energy nuclear structure and decay properties of the neutron-deficient isotopes 195At and 191Bi have been studied. 195At was produced in the reaction 142Nd(56Fe,p2n)195At and 191Bi as the daughter activity of 195At. The activities were implanted in a position-sensitive silicon detector after being separated from the primary beam by a gas-filled recoil separator. The 1/2+ intruder state was determined to be the ground state in 195At with an alpha-decay energy of E α = 6953(3) keV and a half-life T 1/2 = 328(20) ms. Another state with an alpha-decay energy E α = 7075(4) keV and a half-life T 1/2 = 147(5) ms was found to decay to a 148.7(5) keV excited state in 191Bi for which a spin and parity of 7/2- were deduced. Consequently, the same 7/2- character was assigned to the initial state at 32(7) keV in 195At on the basis of unhindered alpha-decay. The 9/2- state, being the ground state in heavier odd-mass astatine isotopes, was not observed.

The $\ensuremath{\alpha}$-decay branch of the $\ensuremath{\pi}{h}_{11/2}$ isomer in $^{164}\mathrm{Ir}$ has been identified using the GREAT spectrometer. The $^{164}\mathrm{Ir}$ nuclei were produced using the ${}^{92}\text{Mo}({}^{78}\text{Kr},p5n){}^{164}\text{Ir}$ reaction and separated in flight using the recoil ion transport unit (RITU) gas-filled separator. The measured $\ensuremath{\alpha}$-decay energy of $6880\ifmmode\pm\else\textpm\fi{}10$ keV allowed the excitation of the $\ensuremath{\pi}{h}_{11/2}$ state in $^{160}\mathrm{Re}$ to be deduced as $166\ifmmode\pm\else\textpm\fi{}14$ keV. The half-life of $^{164}\mathrm{Ir}$ was measured with improved precision to be $70\ifmmode\pm\else\textpm\fi{}10\phantom{\rule{4pt}{0ex}}\ensuremath{\mu}$s and an $\ensuremath{\alpha}$-decay branching ratio of $4\ifmmode\pm\else\textpm\fi{}2$% was determined. Improved half-life and branching ratio measurements were also obtained for $^{165}\mathrm{Ir}$, but no evidence was found for the ground-state decays of either $^{164}\mathrm{Ir}$ or $^{165}\mathrm{Ir}$.

High-spin states of the neutron deficient (100)pd nucleus have been investigated via the Cr-50(Ni-58, 4p alpha) and Zn-70(S-36,6n) heavy-ion induced reactions. For the detection of evaporated particles and gamma rays the NORDBALL array equipped with ancillary detectors and the EUROGAM II detector system were utilized. By the use of in-beam spectroscopic methods 89 transitions belonging to (100)pd have been observed, 49 of which were identified for the first time. The level scheme has been extended up to E-X approximate to 16 MeV excitation energy and I approximate to 25h. The experimental results were compared with the predictions of cranked shell model calculations. Maximal spin alignments were found in the (pig(9/2))(12+)(-4) (vd(5/2),g(7/2)(3)h(11/2))(13-) and (pig(9/2)(-3)p(1/2))(11-)(vd(5/2)g(7/2)(3)h(11/2))(13-) configurations. Possible existence of octupole correlations is discussed on the basis of 6 (E 1)lB(E2) values deduced for the decays of high-spin levels in the yrast negative-parity band. (C) 2001 Elsevier Science B.V. All rights reserved.

Excited states in the nuclei 83 As and 84,86 Se have been studied via prompt -ray spectroscopy. The nuclei were produced by the proton-induced fission of a 238 U target, at the accelerator of the University of Jyvaskyla. The JUROGAM-II array was used to detect prompt -rays and a triple- coincidence analysis performed. A comparison of the N = 50 nuclei with shell-model calculations reproduces the low-lying states in 83 As and 84 Se well. The inclusion of particle-hole excitations is necessary to correctly describe the states above ∼ 3.5 MeV.

Excited states of the Z = 102 nuclide 254No have been studied in the reaction 208Pb(48Ca,2n) by means of in-beam γ -ray spectroscopy in combination with recoil gating and recoil decay tagging. A Ge detector array, consisting of four clover detectors, and a gas-filled separator were used. Six γ-ray lines were observed and associated with E2 transitions in the ground state band of 254No, the highest-lying of these being the 16+→ 14+ transition. Based on global systematics and the extrapolated 2+ 1 excitation energy, the value β2= 0.27 ± 0.03 was extracted for the quadrupole deformation. An improved value for the half-life of 254No, T1/2= (48 ± 3) s, was determined.

The high-spin structure of {sup 205}Rn has been investigated for the first time following the {sup 170}Er({sup 40}Ar,5n) and {sup 197}Au({sup 14}N,6n) reactions at beam energies of 183 MeV and 90{endash}110 MeV, respectively, using the Jurosphere and YRAST Ball arrays. Two new cascades have been identified which dominate the high-spin decay. One of these, consisting of ten stretched M1 transitions with unobserved E2 crossover transitions, is interpreted as a shears structure based on the {nu}i{sub 13/2}{sup {minus}1}{circle_times}{pi}i{sub 13/2}{sup 2} (or {nu}i{sub 13/2}{sup {minus}1}{circle_times}{pi}h{sub 9/2}i{sub 13/2}) configuration. {copyright} {ital 1999} {ital The American Physical Society}

Candidates for three excited states in the 66^Se have been identified using the recoil-{\beta} tagging method together with a veto detector for charged-particle evaporation channels. These results allow a comparison of mirror and triplet energy differences between analogue states across the A = 66 triplet as a function of angular momentum. The extracted triplet energy differences follow the negative trend observed in the f_7/2 shell. Shell-model calculations indicate a continued need for an additional isospin non-conserving interaction in addition to the Coulomb isotensor part as a function of mass.

An in-beam study has been performed to further investigate the known isomeric decays and to identify $T=1$ excited states in the medium-heavy $N=Z=33$ nucleus ${}^{66}$As. The fusion-evaporation reaction ${}^{40}$Ca(${}^{28}$Si,$pn$)${}^{66}$As was employed at beam energies of 75 and 83 MeV. The half-lives and ordering of two known isomeric states in ${}^{66}$As have been determined with improved accuracy. In addition, several prompt $\ensuremath{\gamma}$-ray transitions from excited states, both bypassing and decaying to the isomeric states in ${}^{66}$As, have been observed. Most importantly, candidates for the ${4}^{+}\ensuremath{\rightarrow}{2}^{+}$ and ${6}^{+}\ensuremath{\rightarrow}{4}^{+}$ transitions in the $T=1$ band have been identified. The results are compared with shell-model calculations using the modern JUN45 interaction in the $p{f}_{5/2}{g}_{9/2}$ model space.