Search

High-spin states of 40K have been populated in the fusion-evaporation reaction 12C(30Si,np)40K and studied by means of γ-ray spectroscopy techniques using one triple-cluster detector of the Advanced Gamma Tracking Array at the Istituto Nazionale di Fisica Nucleare, Laboratori Nazionali di Legnaro. Several states with excitation energy up to 8 MeV and spin up to 10 have been discovered. These states are discussed in terms of J=3 and T=0 neutron-proton hole pairs. Shell-model calculations in a large model space have shown good agreement with the experimental data for most of the energy levels. The evolution of the structure of this nucleus is here studied as a function of excitation energy and angular momentum, This work was financed by EURONS AGATA (Contract No. 506065-R113), the Swedish Research Council under Contracts No. 621-2008- 4163, No. 621-2011-4522, No. 822-2005-3332, and No. 821- 2010-6024, the Japan Society for the Promotion of Science (JSPS) Kakenhi Grant No. 23·01752, Ankara University (BAP Project No. 05B4240002), the Polish Ministry of Science and Higher Education under Grants No. DPN/N190/AGATA/2009 and No. N N202 073935, the German BMBF under Grants No. 06K-167, No. 06KY205I, and No. 06KY9136I, the Knut and Alice Wallenberg Foundation Contract No. 2005.0184, and STFC (UK). A. Gadea and E. Farnea acknowledge the support of MICINN, Spain, and INFN, Italy, through the AIC-D-2011-0746 bilateral action. A. Gadea’s activity has been partially supported by the Generalitat Valenciana, Spain, under Grant PROMETEO/2010/101. A. Gadea, A. Jungclaus, A. Poves, and B. Quintana acknowledge support from the MICINN, Spain, under Grant FPA2011-29854. A. Poves is partially supported by the Comunidad de Madrid (Spain) (HEPHACOS S2009-ESP-1473). G. Jaworski acknowledges the support of the Center for Advanced Studies of Warsaw University of Technology. B. Cederwall acknowledges the support of the Goran Gustafsson Foundation.

A new superdeformed band is reported in 193Hg which has properties that are consistent with it being based on the unfavoured N = 7 (π, α) = (−, +12) intruder orbital. The signature splitting at hω = 200 keV of this intruder orbital and its favoured (−, −12) partner is estimated to be 160±30 keV, which is in agreement with cranked mean field calculations. This band completes the set of low-lying quasi-neutron orbitals predicted to be at the N = 113 superdeformed Fermi-surface. The previously known superdeformed bands in 193Hg have been extended to higher rotational frequencies, hω ⩾ 0.40 MeV.

Superdeformed (SD) states with a 2:1 axis ratio have been observed in nuclei in the A = 150, 190, and the actinide regions. These states depopulate into normally deformed (ND) states by gamma decay, but so far the linking transitions have not been observed and the depopulation mechanism is not fully understood. Nuclei in different mass regions decay out at states with different spin (I), excitation energy above the ND yrast line (U) and lifetime ({tau}). This variation is due to differences in the nuclear properties such as the barrier penetration probability, the level densities and the gamma transition strength of SD and ND states. One important factor is the competition between the collective E2 decay along the SD band and the statistical decay to the ND states. These transition rates, or the partial lifetimes, can be determined if the lifetime and the intensity of the gamma rays depopulating the SD states are known.

The competition between collective rotation and single-particle behaviour at high spin in 158Er has been investigated with the Eurogam spectrometer. Band terminating states have been observed in three structures at Iπ = 46+, 48− and 49− and specific single-particle configurations are assigned by comparison with cranked Nilsson-Strutinsky calculations. These special states are found to be related by very simple single particle excitations. These data indicate that an oblate mean field (ϵ ∼ −0.14) is established for a nuclear core plus 12 aligned valence nucleons which is stable against single-particle rearrangements. In the (π, α) = (+, 0) states the collective and weakly collective terminating structures are observed to coexist between 30+ and 46+.

The highest spin states in a T(z)=1/2 nucleus have been observed in 77Sr: I(pi)=(49/2+) and (29/2-). In addition, states up to I(pi)=(22+) have been seen in 78Sr. The alpha=1/2, g9/2 band and both signature partners of the negative parity band in 77Sr were found to be identical to the yrast band in 78Sr with relative alignments of 1.22(7)HBAR, 0.52(5)HBAR (alpha=1/2), and 0.42(4)HBAR (alpha=-1/2), respectively. In one of the negative parity bands, the identicality persists through the first proton band crossing. The odd spin decay sequence of the 4- band in 78Rb is identical to the ground band of 78Sr [3.02(3)HBAR] at low spin and to the alpha=1/2, g9/2 band in 77Rb [1.11(3)HBAR] at higher spins. These are the only known examples of identical bands in the neutron deficient A=80 region. The analysis indicates that the [301]3/2 Nilsson orbital is a very good spectator orbital. (Less)

Temporary immobilization creates bone loss. The purpose of this investigation was to use an agent to protect the skeleton from bone loss bone during temporary immobilization. Eighty-nine 6-month-old retired breeder Sprague—Dawley female rats were used. Animals were randomly divided into six groups of equal numbers. Four groups were given drinking water from day 0, containing naproxen (100 or 200 mg/l). At day 7, half the animals in all groups had their right hindlimb immobilized. At day 49, half the immobilized rats and non-immobilized controls were sacrificed. The remaining rats were remobilized and the drug was stopped. At day 91, all remaining rats were sacrificed. Gastrocnemius and soleus muscle weights were determined. Right tibiae were analyzed for cancellous bone mass, bone structural and bone dynamic variables. At the close of immobilization, bone mass was lower in the right (immobilized) hindlimb of the immobilized group than in the non-immobilized group. Immobilized rats drinking 100 mg/l naproxen water had significantly higher bone mass in their immobilized limbs than did untreated immobilized rats, but all rats drinking 200 mg/l naproxen water had lower bone mass than controls. After 6 weeks of recovery, bone mass in the immobilized limb of untreated formerly immobilized rats improved, but remained below untreated never-immobilized rats. Formerly immobilized rats that had been treated with 100 mg/1 naproxen water had normal bone mass after 6 weeks of recovery. Naproxen, an agent that mildly depresses activation frequency, prevents some of the transient bone mass and structural deterioration during temporary immobilization. Such treatment facilitates a more rapid return to normal bone mass, though not to normal structure. The more rapid recovery occurs because the difference from normal is less, not because of more rapid formation in recovering animals.

The lifetime of the first excited 2(+) state in the neutron deficient nuclide (108)Te has been measured for the first time, using a combined recoil decay tagging and recoil distance Doppler shift t ...

A lifetime experiment, using the Doppler-shift attenuation method, has been performed at Gammasphere to measure the transition quadrupole moments ${Q}_{t}$ of strongly deformed bands in $^{171}\mathrm{Hf}$ and $^{172}\mathrm{Hf}$. The measured value of ${Q}_{t}$ $~$ 9.5 $e$ b for the band labeled ED in $^{171}\mathrm{Hf}$ strongly supports the recent suggestion that this sequence and several structures with similar properties in neighboring Hf isotopes are associated with a near-prolate shape with a deformation enhanced relative to that of normal deformed structures. The measured values of ${Q}_{t}$ $~$ 14 $e$ b for the bands labeled SD1 and SD3 in $^{172}\mathrm{Hf}$ confirm that these sequences are associated with a prolate superdeformed shape, a property inferred in earlier work from other measured characteristics of the bands. Similar bands in $^{173\ensuremath{-}175}\mathrm{Hf}$ are also likely to be associated with superdeformed shapes. The observations are in contrast to predictions of cranking calculations performed with the ultimate cranker code.

States above the known ${K}^{\ensuremath{\pi}}={8}^{\ensuremath{-}}$ 6 $\ensuremath{\mu}$s isomer in $^{138}\mathrm{Gd}$ have been populated with the $^{106}\mathrm{Cd}$($^{36}\mathrm{Ar}$,$2p2n$) reaction at a beam energy of 180 MeV at the University of Jyv\"askyl\"a, Finland. The recoil-isomer tagging technique was utilized to correlate delayed $\ensuremath{\gamma}$-ray decays, detected in the GREAT focal plane spectrometer, with prompt decays measured in the JUROGAM II spectrometer at the target position. The lifetime of the ${K}^{\ensuremath{\pi}}={8}^{\ensuremath{-}}$ isomeric state has been remeasured as 6.2(2) $\ensuremath{\mu}$s. Two high-lying strongly coupled bands have been established with ${K}^{\ensuremath{\pi}}\ensuremath{\geqslant}{12}^{\ensuremath{-}}$. Potential-energy surface calculations, in conjunction with $g$ factor measurements, reveal that they are built upon four-quasiparticle structures comprising two-quasineutron plus two-quasiproton configurations. The short half-life or lack of hindrance for the decays from these four-quasiparticle band-head states is reasoned to be a consequence of increased triaxial deformation and mixing due to the high density of states relative to the lower two-quasiparticle 6-$\ensuremath{\mu}$s isomeric state.

Recoil-isomer tagging with the {sup 54}Fe+{sup 92}Mo reaction was used to establish a 10(2)-{mu}s isomeric state in {sup 139}Eu. Prompt versus delayed {gamma}-ray coincidence data have revealed the presence of a prompt rotational band built upon the isomer. The alignment properties of the states in this band show that the isomer is based upon a proton g{sub 7/2} configuration. The decay of the isomer takes place through a single 26-keV E1 transition. The {gamma}-ray transition strength for this decay is consistent with those established in the neighboring isomeric gamma-soft nuclei. In these nuclei, isomers are expected to form as a consequence of differences in nuclear shapes or configurations, and the natural hindrance associated with configuration-changing E1 transitions. The isomeric nature of the state in {sup 139}Eu is reasoned to be because of difference in shape of the proton g{sub 7/2} state and the proton h{sub 11/2} ground state to which it decays.

A new Differential Plunger device for measuring pico‐second lifetimes of Unbound Nuclear States (DPUNS) is being built at The University of Manchester. DPUNS has been designed to work with alpha‐, beta‐ and isomer‐tagging methods using the existing JUROGAM II—RITU—GREAT infrastructure at the University of Jyvaskyla, Finland. The importance of proton emission from nuclei is that it provides valuable nuclear‐structure information as direct input to nuclear models beyond the drip line. New experimental data beyond the drip line can provide new extensions to these models especially with the possible coupling of weakly bound and unbound states to the continuum. The results of the first experiments to measure lifetimes of unbound nuclear states with this method was discussed along with possible future experiments which can be addressed with DPUNS using proton‐, isomer‐ and alpha‐tagging.

The electronion scattering experiment ELISe is part of the installations envisaged at the new experimental storage ring at the International Facility for Antiproton and Ion Research (FAIR) in Darmstadt, Germany. It offers an unique opportunity to use electrons as probe in investigations of the structure of exotic nuclei. The conceptual design and the scientific challenges of ELISe are presented. © 2011 Elsevier B.V. All rights reserved., The authors acknowledge financial support from the EC via the INTAS pro- gramme, grants No. 03-54-6545 and 05-1000008-8272. This work was partially supported by the Hessian LOEWE initiative Helmholtz International Center for FAIR

The Recoil‐Distance Doppler‐shift method has been combined with Recoil‐Decay Tagging for the first time to measure a lifetime in the proton‐unbound nucleus 109I. The lifetime value was determined using the Differential Decay‐Curve method in singles mode. The result has been compared to theoretical shell‐model calculations in order to better understand the nature of unbound valence nucleons at the proton drip line.

The location of nuclear closed shells, as evidenced through discontinuities in binding energy and one- and two-particle separation energy systematics, remains one of the simplest tests of global nuclear models. How shell gaps evolve, whether with increasing mass, increasing neutron:proton ratio or increasing deformation, is still uncertain, and it has recently been suggested that one must go beyond a static meanfield picture to include the effects of dynamic fluctuations in the nuclear shape even in the ground state. The identification of key properties which may distinguish between competing approaches is thus vital. Comparison of the binding energies of superdeformed nuclei in the A ≈ 190 region shows that two-proton separation energies are higher in the superdeformed state than in the normal state, despite the probably lower Coulomb barrier and lower total binding energy. Possible reasons for this difference are discussed. This somewhat counterintuitive result provides a critical test for global nuclear models.

International audience; The lifetimes of low-lying transitions in 138Gd have been measured using the recoil-distance Doppler-shift technique. The resultant reduced transition probabilities have been compared to X(5) critical-point calculations to assess the potential 'phase-transitional' behaviour of 138Gd. The X(5) symmetry describes the first order 'phase transition' between sphericity, U(5) and an axially deformed nuclear shape, SU(3). Although a high degree of correspondence is observed between the experimental and theoretical excitation energies, the large uncertainties of the experimental B(E2) values cannot preclude contributions from either vibrational or rotational modes of excitation. In order to further examine the nature of low-lying states in 138Gd, ongoing work is aiming to derive solutions to the Bohr Hamiltonian using a more general potential that is not restricted to the X(5) critical point. These results, in parallel to more extensive IBM-1 calculations, will eventually be compared to the experimental results to more accurately locate 138Gd along the U(5) − SU(3) arm of the structure triangle.

Lifetime measurements have been made in the ground-state band of the transitional nucleus (138)Gd from coincidence recoil-distance Doppler-shift data. (138)Gdnuclei were produced using the (106)Cd ((36)Ar, 2p2n) reaction with a beam energy of 190 MeV. Reduced transition probabilities have been extracted from the lifetime data collected with the Koln plunger placed at the target position of the JUROGAM-II array. The B(E2) values have been compared with predictions from X(5) critical-point calculations, which describe the phase transition between vibrational and axially symmetric nuclear shapes, as well as with IBM-1 calculations at the critical point. While the excitation energies in (138)Gdare consistent with X(5) predictions, the large uncertainties associated with the measured B(E2) values cannot preclude vibrational and rotational contributions to the low-lying structure of (138)Gd. Although experimental knowledge for the low-lying gamma and beta-vibrational bands in (138)Gd is limited, potential-energy surface calculations suggest an increase in gamma softness in the ground-state band. In order to more fully account for the effects of gamma softness, the X(5) and IBM-1 calculations need to be extended to include the gamma degree of freedom for (138)Gd.

This contribution focused on research to measure the lifetimes of unbound nuclear states using a differential‐plunger technique combined with recoil‐proton decay tagging. The results of the first lifetime measurements of unbound states in the spherical proton emitter, 109I, were discussed along with the limits to the technique. In order to proceed further, a new differential‐plunger device, DPUNS, has been designed and is currently being built at the University of Manchester. DPUNS has been optimised to work with the GREAT/RITU/TDR setup at the University of Jyvaskyla and the status of the new device is discussed.

A decay sequence above the I= 47 2 , 5.4 MeV level in 193Hg has been established through discrete γ-ray spectroscopy. The new energy levels exhibit single-particle character implying the dominant role of individual particle angular momentum alignment at moderate spins in the neutron-deficient Hg isotopes.

Dipole transitions linking signature partner superdeformed bands in 193Hg have been observed. Measurements of the photon decay branching ratios, taken together with the average superdeformed quadrupole moment measured in neighboring nuclei, enable the absolute M1 strengths to be determined. From these data, using the strong coupling model, we find (gK-gR)K/Q0=-0.14±0.01 (e b)−1, gK=-0.65±0.14 with Ω=2.8±0.8. These data are consistent with the superdeformed neutron orbital being [512]5/2− as predicted by cranked Woods-Saxon calculations.

The [ital K][sub [alpha]]-x-ray yields associated with the superdeformed and normal-deformed bands in [sup 193]Hg have been measured. The results indicate an excess yield of [ital K][sub [alpha]]-x rays in coincidence with the superdeformed cascade relative to that in coincidence with the normal-deformed cascade. The internal conversion of known transitions along the superdeformed cascade cannot account for the observed [ital K][sub [alpha]]-x-ray yield. It is likely that this excess x-ray yield is associated with low-energy interband-[ital M]1 transitions competing with the low-spin superdeformed-[ital E]2 transitions.

The 196Pb nucleus was populated via the 184W(16O,4n)196Pb and 186W(16O,6n)196Pb reactions at beam energies of 98 MeV and 120 MeV, respectively. A new Delta I=1 magnetic dipole band has been observed. This band is believed to be built on a collective oblate configuration involving high-K proton orbitals coupled to two rotationally aligned i13/2 neutrons. The previously observed 196Pb superdeformed band was also populated in these reactions.

The structure and decay properties of high-K isomers in {sup 176}Hf have been studied using beam sweeping techniques and the Gammasphere multidetector array. A new {Delta}K = 8 decay branch, from a K{sup {pi}} = 22{sup -}, six-quasiparticle, isomeric (t{sub 1/2} = 43 {micro}s) state at 4864 keV to the 20{sup -} state of a K{sup {pi}} = 14{sup -} band, has been identified. The reduced hindrance factor per degree of K forbiddenness for this decay is measured to be unusually low (f{sub ?} = 3.2), which suggests K mixing in the states involved. The deduced interaction matrix elements are discussed within the context of relevant K-mixing scenarios. The 3266-keV state, previously interpreted as a K{sup {pi}} = 16{sup +} intrinsic state, is reassigned as the J{sup {pi}} = 16{sup +} member of the band based on the K{sup {pi}} = 15{sup +} state at 3080 keV. The systematics of f{sub ?} values as a function of the degree of forbiddenness is discussed in light of this change.

A study of cooled Au-197 projectile-fragmentation products has been performed with a storage ring. This has enabled metastable nuclear excitations with energies up to 3 MeV, and half-lives extending to minutes or longer, to be identified in the neutron-rich nuclides Hf-183,Hf-184,Hf-186 and Ta-186,Ta-187. The results support the prediction of a strongly favored isomer region near neutron number 116.

The known level scheme of {sup 144}Dy has been extended and lifetime measurements have been made with the recoil-distance Doppler-shift method. Reduced transition probabilities and deformations have been determined for four low-lying transitions. These states form part of the first observed band crossing, giving information on the change in nuclear deformation resulting from the rearrangement of h{sub 11/2} protons in the nucleus. Two bands built upon excited 10{sup +} states have been assigned pi(h{sub 11/2}){sup 2} prolate and nu(h{sub 11/2}){sup -2} oblate configurations with tau=12(2)ps and 0.01

Excited states in the proton-unbound odd-odd nucleus $^{144}\mathrm{Ho}$ have been populated using the $^{92}\mathrm{Mo}(^{54}\mathrm{Fe},\mathit{pn})^{144}\mathrm{Ho}$ reaction and studied using the recoil-isomer-tagging technique. The alignment properties and signature splitting of the rotational band above the ${I}^{\ensuremath{\pi}}=({8}^{+})^{144m}\mathrm{Ho}$ isomer have been analyzed and the isomer confirmed to have a $\ensuremath{\pi}{h}_{11/2}\ensuremath{\bigotimes}\ensuremath{\nu}{h}_{11/2}$ two-quasiparticle configuration. The configuration-constrained blocking method has been used to calculate the shapes of the ground and isomeric states, which are both predicted to have triaxial nuclear shapes with $|\ensuremath{\gamma}|\ensuremath{\approx}{24}^{\ifmmode^\circ\else\textdegree\fi{}}$.

A measurement of the energy and spin of superdeformed states in {sup 190}Hg, obtained through the observation of transitions directly linking superdeformed and normal states, expands the number of isotopes in which binding energies at superdeformation are known. Comparison with neighboring nuclei shows that two-proton separation energies are higher in the superdeformed state than in the normal state, despite the lower Coulomb barrier and lower total binding energy. This unexpected result provides a critical test for nuclear models.

High-spin states of 165W and 166W were studied using the 106Pd(63Cu, p3n) and 106Pd(63Cu, p2n) reactions, respectively. Gamma rays in 165W were identified for the first time using the gamma -ray detector array POLYTESSA and the Daresbury recoil separator. Level schemes for 165W and 166W were constructed from the gamma - gamma coincidence data and angular correlation data from the POLYTESSA and TESSA3 arrays. In 166W the yrast band is established up to 30+ (32+), as well as two side bands up to 22- (28-) and 23- (29-). In 165W the yrast band is established up to 45/2+ and two side bands up to 55/2- (59/2-) and 53/2-. The rotational structures and band crossings observed are interpreted within the framework of the cranked shell model in terms of quasiparticle excitations. The systematics of the second i13/2 neutron alignment in the N=91 and 92 isotones are discussed.

Competition between single-particle and collective modes of excitation is observed in 119I at high spin. Whereas rotational states, associated with a prolate pi h11/2 orbital, are yrast for spins I

The nucleus 198Pb was populated via the 186W(17O,5n)198Pb reaction at beam energies of 92 and 98 MeV. A highly regular rotational ΔI=1 band has been found. Angular correlation measurements confirm the transitions to be dipoles. Assuming M1 multipolarity for these transitions the experimental data are interpreted in terms of a π([505] 9 2 − ⊗[606] 13 2 + ) K π =11 − ⊗ν( i 13 2 ) 2 configuration of oblate shape. This is the first such collective oblate structure identified in the A∼200 mass region.

Recoil-isomer tagging at the Accelerator Laboratory of the University of Jyvaeskylae has been used to establish the isomeric nature of a known (7{sup -}) excited state in the doubly odd nucleus {sup 134}Pm. The isomeric state was determined to have a half-life of 20(1) {mu}s and was populated from the decay of a {pi}h{sub 11/2} x {nu}h{sub 11/2} band using the {sup 92}Mo({sup 54}Fe,2{alpha}3pn) reaction at 305 and 315 MeV. The isomer decays by a 71-keV transition that provides an intermediate step in linking the established {sup 134}Pm high-spin level scheme to the lower-spin states observed from the {beta} decay of {sup 134}Sm. Electron-conversion analysis for the 71-keV {gamma}-ray transition reveals that it is of E1 character and its small reduced-transition probability suggests that {sup 134}Pm may have a nuclear shape more rigid than that of the neighboring nuclei.

Excited states of the nucleus Os-167 have been populated by the reaction Mo-92(Kr-78,2pn). The JUROGAM gamma-ray detector array has been used in conjunction with the RITU gas-filled separator and the GREAT spectrometer to observe prompt gamma rays in coincidence with recoiling fusion-evaporation residues and their subsequent decay by alpha particle emission. By correlating prompt gamma radiation with the characteristic alpha radioactivity of Os-167, it has been possible to extend the level scheme for this nucleus significantly. In particular, an extension of the yrast band and four previously unobserved bands are reported. In addition, the recoil distance Doppler-shift method was used to determine a lifetime of tau=20(4) ps for The I-pi=17/2(+) state in Os-167. Hence, the level of collectivity and magnitude of deformation of the low spin yrast band of this nucleus is established. .

Time-resolved Schottky mass spectrometry has been applied to uranium projectile fragments which yielded the mass value for the Hg-208 (Z=80, N=128) isotope. The mass excess value of ME=-13 265(31) keV has been obtained, which has been used to determine the proton-neutron interaction strength in Pb-210, as a double difference of atomic masses. The results show a dramatic variation of the strength for lead isotopes when crossing the N=126 neutron shell closure, thus confirming the empirical predictions that this interaction strength is sensitive to the overlap of the wave functions of the last valence neutrons and protons.

Recoil-isomer tagging has been used to characterize the states built upon an I{sup {pi}}=8{sup +} isomer in {sup 142}Tb. High-spin states of the neutron-deficient nucleus {sup 142}Tb were populated using an {sup 54}Fe beam, accelerated onto a {sup 92}Mo target of thickness {approx}500 {mu}g/cm{sup 2} at energies of 245, 252, and 265 MeV using the K130 cyclotron at the University of Jyvaeskylae, Finland. Use of the JUROGAM target-position Ge-detector array coupled with the GREAT focal-plane spectrometer at the RITU gas-filled recoil separator has significantly increased the efficiency of the isomer-tagging technique. The rotational band built upon the I{sup {pi}}=8{sup +} isomeric state was established with isomer-tagged {gamma}-{gamma} coincidence data and angular distributions were measured for some of the more intensely populated states. Two previously unobserved bands that bypass the isomer were also established. The new data have been interpreted within the framework of the cranked-shell model. The data show good agreement with the calculated triaxial nuclear shape with {gamma}=-30 deg. for the {sup 142m2}Tb isomeric state. The B(M1)/B(E2) branching ratios, nuclear alignment, signature splitting, and reduced transition probability, B(E1), of the isomeric state have been systematically compared with those of the neighboring nuclei. These comparisons give further evidence for themore » {pi}h{sub 11/2} x {nu}h{sub 11/2} configuration of the isomer.« less

The quadrupole moment of the I = K =25 + , T 1 2 =150 ns isomer in 182 Os has been measured by observing the time-dependent quadrupole interaction pattern of the decay radiation from the isomer implanted in a single crystal of Os. The result of | Q |=4.2(2) e b is consistant with the predicted deformation of β 2 =0.2 for 182 Os at I =25 and K = I for this isomer.

Gamma-ray transitions have been identified for the first time in 164W. The yrast band has been established up to 28+(30+) and the alignment of the first pair of i13/2 neutrons is observed at a rotational frequency h(cross) omega =0.29 MeV. Above h(cross) omega approximately 0.30 MeV the first pair of h11/2 protons are observed to gradually align with a strong interaction strength. The systematics of the neutron alignment in nuclei ranging from Dy to W and with neutron numbers from 88 to 98 are discussed. The variations of alignment frequency with neutron and proton number are explained in terms of changes in quadrupole and hexadecapole deformation and the changing position of the Fermi surface in relation to the aligning neutron orbitals.

A Doppler shift attenuation measurement has been carried out to determine the collectivity of the superdeformed band in 150 Gd. The data was found to be consistent with a constant inband quadrupole moment of 17 ± 3 e b. This corresponds to a quadrupole deformation of s 2 ≈0.58. In addition the measurement has resolved important questions regarding the de-excitation of the band, confirming the rapid de-excitation of the superdeformed band in 150 Gd with more than 80% of the band intensity being lost over one transition.

A t1/2 > 1 ms, high-K isomeric state feeding a strongly coupled rotational band has been identified following the deep inelastic reaction 23892U +18674W at 1600 MeV. Examination of γ-ray and X-ray data combined with a g-factor analysis derived from in-band branching ratios suggests the assignment of the new states to the neutron-rich nucleus 18573Ta.

Time-resolved Schottky mass spectrometry has been applied to uranium projectile fragments which yielded the mass value for the 208Hg (Z=80, N=128) isotope. The mass excess value of ME=-13 265(31) keV has been obtained, which has been used to determine the proton-neutron interaction strength in 210Pb, as a double difference of atomic masses. The results show a dramatic variation of the strength for lead isotopes when crossing the N=126 neutron shell closure, thus confirming the empirical predictions that this interaction strength is sensitive to the overlap of the wave functions of the last valence neutrons and protons.

An experiment has been performed to populate several extremely neutron-deficient nuclei around the mass-140 region of the nuclear chart, using a beam of {sup 54}Fe on a {sup 92}Mo target at an energy of 315 MeV. Analysis of these data using recoil-isomer tagging has established that the yrast {pi}h{sub 11/2} x {nu}h{sub 11/2},J{sup {pi}}=(8{sup +}), bandhead state in {sup 136}Pm is isomeric with a half-life of 1.5(1) {mu}s. This isomeric state decays via a 43-keV, probable-E1 transition to a J{sup {pi}}=(7{sup -}) state. Consideration of the theoretical Nilsson orbitals near the Fermi surface suggests that the J{sup {pi}}=(8{sup +}) state has a {nu}h{sub 11/2}[505](11/2){sup -} x {pi}h{sub 11/2}[532](5/2){sup -} configuration, which decays to the J{sup {pi}}=(7{sup -}) state with a {nu}h{sub 11/2}[505](11/2){sup -} x {pi}d{sub 5/2}[411](3/2){sup +} configuration. Differences in the shape-driving effects for these two configurations is reasoned to be responsible for the long half-life of the J{sup {pi}}=(8{sup +}) isomeric state. The non-observation of other {gamma} rays in prompt or delayed coincidence with the 43-keV transition suggests that this transition may feed another, longer lived isomeric state with a half-life of the order of milliseconds or greater. However, the present experiment was not sensitive to the decay ofmore » this new J{sup {pi}}=(7{sup -}) state by internal conversion or even {beta} decay.« less

International audience

Over 25 million Americans suffer from osteoporosis. Bone size and strength depends both upon the level of adaptation due to physical activity (applied load), and genetics. We hypothesized that bone adaptation to loads differs among mice breeds and bone sites. Forty-five adult female mice from three inbred strains (C57BL/6 [B6], C3H/HeJ [C3], and DBA/2J [D2]) were loaded at the right tibia and ulna in vivo with non-invasive loading devices. Each loading session consisted of 99 cycles at a force range that induced approximately 2000 microstrain (microepsilon) at the mid-shaft of the tibia (2.5 to 3.5 N force) and ulna (1.5 to 2 N force). The right and left ulnae and tibiae were collected and processed using protocols for histological undecalcified cortical bone slides. Standard histomorphometry techniques were used to quantify new bone formation. The histomorphometric variables include percentage mineralizing surface (%MS), mineral apposition rate (MAR), and bone formation rate (BFR). Net loading response [right-left limb] was compared between different breeds at tibial and ulnar sites using two-way ANOVA with repeated measures (p0.05). Significant site differences in bone adaptation response were present within each breed (p0.005). In all the three breeds, the tibiae showed greater percentage MS, MAR and BFR than the ulna at similar in vivo load or mechanical stimulus (strain). These data suggest that the bone formation due to loading is greater in the tibiae than the ulnae. Although, no significant breed-related differences were found in response to loading, the data show greater trends in tibial bone response in B6 mice as compared to D2 and C3 mice. Our data indicate that there are site-specific skeletal differences in bone adaptation response to similar mechanical stimulus.

A detailed study of known and new SD bands in Tb isotopes has been performed with the use of the EUROBALL IV gamma-ray array. The high-statistics data set has allowed for the extension of known SD bands at low and high spins by new gamma-ray transitions. These transitions, as it turns out, correspond to the rotational frequencies where the principal superdeformed gaps (Z=66,N=86) close giving rise to up- or down-bending mechanisms. This enables to attribute the underlying theoretical configurations with much higher confidence as compared to the previous identifications. Five new SD bands have been discovered, three of them assigned to the Tb-152 and the two others to the Tb-151 nuclei. Nuclear mean-field calculations have been used to interpret the structure of known SD bands as well as of the new ones in terms of nucleonic configurations.

This paper summarises the programme of Recoil-isomer tagging that has been performed over the last ten years at the University of Jyvaskyla, Finland. The nuclei studied lie in the mass 130-140 region of the Segre chart very close to the proton drip line. The evolution of the isomer character is seen to change from K-isomers, at N=74, to shape-isomers in the gamma soft N=77 nuclei to seniority-isomers around N=82. The influence of the proton drip line on the N=74 isomers and possible critical-point symmetries in the N=77 nuclei are discussed and the latest results presented. Developments of the isomer-tagging technique, using large beam currents with a dual Mufti-Wire Proportional Counter setup, and an Isomer-tagged Differential-Plunger setup are discussed along with a future programme of work at Jyvaskyla.

This report details the status of an experimental research programme which has studied isomeric states in the mass 130–160 region of the nuclear chart. Several new isomers have been established and characterised near the proton drip line using a recoil isomer tagging technique at the University of Jyvaskyla, Finland. The latest experiments have been performed with a modified setup where the standard GREAT focal‐plane double‐sided silicon‐strip detector was changed to a dual multi‐wire proportional‐counter arrangement. This new setup has improved capability for short‐lived isomer studies where large focal‐plane rates can be tolerated. The results of key recent experiments for nuclei situated above (153Yb, 152Tm) and below (144Ho, 142Tb) the N = 82 shell gap were presented. These studies have charted the evolution of isomeric states across the neutron shell from K‐Isomers at N = 74, to shape isomers at N = 77 and shell‐model isomers at N = 82, 83. The excitation energies for some of the lowest‐lying excited states in these isomeric nuclei show behaviour which is characteristic of an X(5) symmetry falling midway between the limits expected for pure vibrational and rotational behaviour. The future prospects for studies of these nuclei were discussed using an isomer‐tagged differential‐plunger setup. This technique will be capable of establishing the deformation of the states above the isomers and will aid in determining whether their behaviour is indeed well described by the X(5) symmetry limit.

Three superdeformed (SD) bands have been observed in 194Hg and four (or five?) SD bands in 193Hg using the 150Nd + 48Ca reaction. All bands except for two in 193Hg show a steady increase in dynamical moment of inertia J (2) with rotational frequency. The two exceptional bands form a classical pair of strongly interacting bands. It is suggested that the strong interaction between the bands is caused by a softness to octupole deformation. Evidence is found for the existence of dipole transitions connecting bands of opposite signature in 193Hg. The strengths of these transitions suggest that they are probably E1 supporting the importance of the role of octupole vibrations. These data suggest the wider importance of octupole softness in enhancing E1 transitions in the SD feeding and decay mechanisms. The spectroscopy of the observed SD bands in 193,4Hg are discussed in detail and attention is drawn to the “identical” energies of γ-rays in these isotopes with those in lighter isotopes. The similarities in bands relate to the neutron sub-shell closure for SD nuclei at N=112.

High spin states in 161 Er and 162 Er have been populated using the 130 Te + 36 S reaction at a bombarding energy of 170 MeV. In 161 Er, three rotational bands were extended from I≈35ħ to I≈50ħ. In 162 Er the positive parity yrast band was observed to I=44ħ. These rotational sequences are compared to a simple unpaired model which was successful in predicting the behaviour of similar high spin data on 159,160 Er. These studies of the light Er isotopes constitute the highest spins observed in normal deformed nuclei and yield direct and specific information on the single-neutron spectrum of states.

Questions on the validity of the K-selection rule for the decay of high spin isomers in deformed nuclei has been raised and an alternative mode by barrier penetration has been proposed. The present paper reports on a sensitive study of a K = 14 isomer in 174Hf where 20 different branches decay from the same level and consistently show low hindrance factors. It is found that the hindrance factors depend on K but have smaller absolute values than expected. The question of a barrier penetration decay mode is still open.

Four, possibly five, superdeformed bands have been observed in $^{193}\mathrm{Hg}$. Two of these bands have strikingly different dynamical moments of inertia from all previously observed superdeformed bands in this region. This behavior can be understood in terms of a level or band crossing. Evidence for transitions between two superdeformed bands is observed for the first time. This, together with the reduced alignments observed and the strong interaction between the crossing bands, is the first experimental evidence supporting the prediction for strong octupole correlations in superdeformed nuclei.

Three superdeformed bands have been observed in 194Hg. The dynamical moment of inertia J (2) of all three bands is observed to increase by 30–40% over the frequency range ħω = 0.1–0.4 MeV. This phenomena can be understood in terms of the gradual alignment of pairs of high-j intruder orbitals within the framework of the cranked Woods-Saxon and Nilsson models including pairing. The calculations together with the observed J (2) behaviour of the three bands indicate that pairing correlations in the superdeformed minimum are rather weak.