Search

Rotational structures have been measured using the Jurogam II and GAMMASPHERE arrays at low spin following the Gd155(α,2n)Dy157 and Nd148(C12,5n)Dy155 reactions at 25 and 65 MeV, respectively. We report high-K bands, which are conjectured to be the first candidates of a Kπ=2+γ vibrational band, built on the [505]11/2− neutron orbital, in both odd-ADy155,157 isotopes. The coupling of the first excited K=0+ states or the so-called β vibrational bands at 661 and 676 keV in Dy154 and Dy156 to the [505]11/2− orbital, to produce a Kπ=11/2− band, was not observed in both Dy155 and Dy157, respectively. The implication of these findings on the interpretation of the first excited 0+ states in the core nuclei Dy154 and Dy156 are also discussed.

Hyperion is a new high-efficiency charged-particle γ -ray detector array which consists of a segmented silicon telescope for charged-particle detection and up to fourteen high-purity germanium clover detectors for the detection of coincident γ rays. The array will be used in nuclear physics measurements and Stockpile Stewardship studies and replaces the STARLiTeR array. This article discusses the features of the array and presents data collected with the array in the commissioning experiment.

The spin distribution populated in the $^{150}\mathrm{Sm}(p,t)$ reaction with 25 MeV protons has been investigated using the silicon telescope and high-purity germanium array Hyperion. Angular distributions of outgoing tritons and relative intensities of $\ensuremath{\gamma}$ rays from low-lying levels are used to deduce the initial spin distribution using statistical calculations and are compared with a semiclassical model of the $(p,t)$ reaction. Experimental and theoretical results suggest a peak strength near $4\ensuremath{\hbar}$ when gated on outgoing tritons detected in Hyperion, while the full $4\ensuremath{\pi}$ distribution may peak near $2\ensuremath{\hbar}$. Additionally, the average $\ensuremath{\gamma}$-neutron branching ratio is determined from the data with the aid of one of two new codes presented in this work. The analysis is extended to other recent studies of $^{152,154}\mathrm{Sm}(p,t)$ to form systematics of the spin-dependence of the surrogate method applied to heavy nuclei in the transitional to deformed region.

High spin states in the isotope 194Hg were populated using the 150Nd (48Ca,4n) reaction at a beam energy of 213 MeV. A sequence of dip ole transitions has been observed above 8 MeV excitation energy. Cross-over transitions have also been identified. An interpretation connecting this sequence to a nuclear shape change is attempted. A comparison with similar structures in the neighbouring Hg isotopes is also attempted.

International audience; A multi-step Coulomb excitation measurement with the GRETINA and CHICO2 detector arrays was carried out with a 430-MeV beam of the neutron-rich $^{110}$Ru (t$_{1/2}$= 12 s) isotope produced at the CARIBU facility. This represents the first successful measurement following the post-acceleration of an unstable isotope of a refractory element. The reduced transition probabilities obtained for levels near the ground state provide strong evidence for a triaxial shape; a conclusion confirmed by comparisons with the results of beyond-mean-field and triaxial rotor model calculations.

New levels and $\ensuremath{\gamma}$-ray transitions were identified in $^{150,152}\mathrm{Sm}$ utilizing the $(p,t)$ reaction and particle-$\ensuremath{\gamma}$ coincidence data. A large, peak-like structure observed between 2.3--3.0 MeV in excitation energy in the triton energy spectra was also investigated. The orbital angular-momentum transfer was probed by comparing the experimental angular distributions of the outgoing tritons to calculated distorted wave Born approximation curves. The angular distributions of the outgoing tritons populating the peak-like structure are remarkably similar in the two reactions and are significantly different from the angular distributions associated with the nearby continuum region. Relative partial cross sections for the observed levels, angle averaged between 34 and 58 degrees, were measured. In $^{150}\mathrm{Sm}$, 39(4)% of the strength of the peak-like structure could be accounted for by the observed discrete states. This compares with a value of 93(15)% for $^{152}\mathrm{Sm}$.

The Gamma-Ray Energy Tracking In-beam Nuclear Array (GRETINA) is a new generation high-resolution γ - ray spectrometer consisting of electrically segmented high-purity germanium crystals. GRETINA is capable of reconstructing the energy and position of each γ - ray interaction point inside the crystal with high resolution. This enables γ - ray energy tracking which in turn provides an array with large photopeak efficiency, high resolution and good peak-to-total ratio. GRETINA is used for nuclear structure studies with demanding γ - ray detection requirements and it is suitable for experiments with radioactive-ion beams with high recoil velocities. The GRETINA array has a 1 π solid angle coverage and constitutes the first stage towards the full 4 π array GRETA. We present in this paper the main parts and the performance of the GRETINA system.

J. T. Burke, ∗ J. J. Ressler, J. E. Escher, N. D. Scielzo, I. J. Thompson, R. Henderson, J. Gostic, L. Bernstein, D. Bluel, M. Weideking, V. Meot, O. Roig, L. W. Phair, R. Hatarik, J. Munson, 4 C. Angell, B. Goldblum, C. W. Beausang, T. Ross, R. Hughes, M. Aiche, G. Barreau, N. Cappelan, S. Czajkowski, B. Hass, B. Jurado, L. Mathieu and I. Companis 8 Physics Division, Lawrence Livermore National Laboratory, Livermore, California 94550, USA Service de Physique Nucleaire, Commissariat a l’Energie Atomique, Bruyeres-le-Chatel, Arpajon, France Nuclear Science Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA Department of Nuclear Engineering, University of California, Berkeley, California 94720, USA Nuclear Physics Department, University of Richmond, Richmond, Virginia 23173, USA Centre d’Etudes Nucleaires Bordeaux Gradignan, CNRS/IN2P3, Univ. Bordeaux 1, Chemin du Solarium, 33175 GRADIGNAN, France Centre d’Etudes Nuclaires Bordeaux Gradignan, CNRS/IN2P3, Univ. Bordeaux 1, Chemin du Solarium, 33175 GRADIGNAN, France Horia Hulubei National Institute for Physics and Nuclear Engineering, 077125 Bucharest-Magurele, Romania

We report results from an experiment on the decay of the high-K isomers in 254No. We have been able to establish the decay from the known high-lying four-quasiparticle isomer, which we assign as a K π = 16 + state at an excitation energy of E x = 2.928 ( 3 ) MeV . The decay of this state passes through a rotational band based on a previously unobserved state at E x = 2.012 ( 2 ) MeV , which we suggest is based on a two-quasineutron configuration with K π = 10 + . This state in turn decays to a rotational band based on the known K π = 8 − isomer, which we infer must also have a two quasineutron configuration. We are able to assign many new gamma-rays associated with the decay of the K π = 8 − isomer, including the identification of a highly K-forbidden Δ K = 8 E1 transition to the ground-state band. These results provide valuable new information on the orbitals close to the Fermi surface, pairing correlations, deformation and rotational response, and K-conservation in nuclei of the deformed trans-fermium region.

The surrogate reaction 238 U( 3 He, tf ) is used to determine the 237 Np( n , f ) cross section indirectly over an equivalent neutron energy range from 10 to 20 MeV. A self-supporting ∼761 μg/cm 2 metallic 238 U foil was bombarded with a 42 MeV 3 He 2+ beam from the 88-Inch Cyclotron at Lawrence Berkeley National Laboratory (LBNL). Outgoing charged particles and fission fragments were identified using the Silicon Telescope Array for Reaction Studies (STARS) consisted of two 140 μm and one 1000 μm Micron S2 type silicon detectors. The 237 Np( n , f ) cross sections, determined indirectly, were compared with the 237 Np( n , f ) cross section data from direct measurements, the Evaluated Nuclear Data File (ENDF/B-VII.0), and the Japanese Evaluated Nuclear Data Library (JENDL 3.3) and found to closely follow those datasets. Use of the ( 3 He, tf ) reaction as a surrogate to extract ( n , f ) cross sections in the 10–20 MeV equivalent neutron energy range is found to be suitable.

Author(s): Henry, TW; Bentley, MA; Clark, RM; Davies, PJ; Bader, VM; Baugher, T; Bazin, D; Beausang, CW; Berryman, JS; Bruce, AM; Campbell, CM; Crawford, HL; Cromaz, M; Fallon, P; Gade, A; Henderson, J; Iwasaki, H; Jenkins, DG; Lee, IY; Lemasson, A; Lenzi, SM; Macchiavelli, AO; Napoli, DR; Nichols, AJ; Paschalis, S; Petri, M; Recchia, F; Rissanen, J; Simpson, EC; Stroberg, SR; Wadsworth, R; Weisshaar, D; Wiens, A; Walz, C | Abstract: Background: Triplet energy differences (TED) can be studied to yield information on isospin-non-conserving interactions in nuclei. Purpose: The systematic behavior of triplet energy differences (TED) of T=1, Jπ=2+ states is examined. The A=62 isobar is identified as having a TED value that deviates significantly from an otherwise very consistent trend. This deviation can be attributed to the tentative assignments of the pertinent states in Ga62 and Ge62. Methods: An in-beam γ-ray spectroscopy experiment was performed to identify excited states in Ga62 using Gamma-Ray Energy Tracking In-Beam Nuclear Array with the S800 spectrometer at NSCL using a two-nucleon knockout approach. Cross-section calculations for the knockout process and shell-model calculations have been performed to interpret the population and decay properties observed. Results: Using the systematics as a guide, a candidate for the transition from the T=1, 2+ state is identified. However, previous work has identified similar states with different Jπ assignments. Cross-section calculations indicate that the relevant T=1, 2+ state should be one of the states directly populated in this reaction. Conclusions: As spins and parities were not measurable, it is concluded that an unambiguous identification of the first T=1, 2+ state is required to reconcile our understanding of TED systematics.

The exact nature of the lowest Kπ=2+ rotational bands in all deformed nuclei remains obscure. Traditionally they are assumed to be collective vibrations of the nuclear shape in the γ degree of freedom perpendicular to the nuclear symmetry axis. Very few such γ bands have been traced past the usual backbending rotational alignments of high-j nucleons. We have investigated the structure of positive-parity bands in the N=90 nucleus Dy156, using the Nd148(C12,4n)Dy156 reaction at 65 MeV, observing the resulting γ-ray transitions with the Gammasphere array. The even- and odd-spin members of the Kπ=2+γ band are observed up to 32+ and 31+, respectively. This rotational band faithfully tracks the ground-state configuration to the highest spins. The members of a possible γ vibration built on the aligned yrast S band are observed up to spins 28+ and 27+. An even-spin positive-parity band, observed up to spin 24+, is a candidate for an aligned S band built on the seniority-zero configuration of the 0+2 state at 676 keV. The crossing of this band with the 0+2 band is at ℏωc=0.28(1)MeV and is consistent with the configuration of the 0+2 band not producing any blocking of the monopole pairing.

The standard γ-ray energy calibration source 152Eu is well known based on the 13.5 y decay of its ground state. Nevertheless, in addition to this decay 152Eu also has two relatively long-lived isomeric states: a 9 h Jπ=0- state at E*=46 keV and a 96 min Jπ=8- state at E*=148 keV. Here we report a new measurement of the half-lives of both of these isomeric states. Excited states in 152Eu were populated following the 154Sm (p,3n) reaction using a 25 MeV proton beam from the K-150 cyclotron at the Cyclotron Institute of Texas A&M University. Post irradiation, γ rays from the de-excitation of the long lived isomeric states were measured using the six BGO shielded high-purity germanium (HPGe) clover detectors that are part of the STARLiTeR array. The half-life of the Jπ=8- isomer 152m2Eu was obtained by measuring the decrease in intensity of the 90 keV γ ray from the cascade to the ground state. The half-life of this state was measured to be 95.8(4) min which is in agreement with and significantly more precise than the previously measured value of 96(1) min. In a manner similar to the ground state the second long-lived isomer 151m1Eu, the Jπ=0- state atmore » 46 keV, β decays to excited states in 152Gd and 152Sm. Also, the half-life of this state was measured to be 9.39(7) h using five γ-ray transitions.« less

Low-spin single quasineutron levels in $^{153}\mathrm{Gd}$ and $^{157}\mathrm{Gd}$ have been studied following the $^{154}\mathrm{Gd}$($p,d\ensuremath{-}\ensuremath{\gamma}$)$^{153}\mathrm{Gd}$ and $^{158}\mathrm{Gd}$($p,d\ensuremath{-}\ensuremath{\gamma}$)$^{157}\mathrm{Gd}$ reactions. A combined Si telescope and high-purity germanium array was utilized, allowing $d\text{\ensuremath{-}}\ensuremath{\gamma}$ and $d\text{\ensuremath{-}}\ensuremath{\gamma}\text{\ensuremath{-}}\ensuremath{\gamma}$ coincidence measurements. Almost all of the established low-excitation-energy, low-spin structures were confirmed in both $^{153}\mathrm{Gd}$ and $^{157}\mathrm{Gd}$. Several new levels and numerous new $\ensuremath{\gamma}$ rays are observed in both nuclei, particularly for ${E}_{x}\ensuremath{\ge}1$ MeV. Residual effects of a neutron subshell closure at $N=64$ are observed in the form of a large excitation energy gap in the single quasineutron level schemes.

Measuring the neutron-induced fission cross-sections of short-lived nuclei represents an experimental challenge due to target activity and the low intensity of neutron beams. One way to alleviate the problems inherent in the direct measurement is to use the surrogate method, where one measures the decay probability of the same compound nucleus formed using a charged beam and a stable target. The decay probability of the compound nucleus is then used to estimate the neutron-induced cross-section. As an extension to the surrogate method, we introduce a new method of reporting the fission probabilities of two compound nuclei as a ratio, which has the advantage of removing most of the systematic uncertainties. The ratio method was checked in a known case, the 236U(n, f)/238U(n, f) cross-section ratio, which turned out to be the same as the probability ratio of P(236U(d, pf))/P(238U(d, pf)). As an application, the 237U(n, f)/235U(n, f) cross-section ratio was inferred, on the basis of the measured P(238U(d, d'f))/P(236U(d, d'f)) probability ratio.

The triaxial strongly deformed (TSD) bands in 167Lu were populated by the 123Sb(48Ca, 4n) reaction with a beam energy of 203 MeV. Gamma rays, requiring five fold or more in prompt coincidence, were detected with the Gammasphere spectrometer. Of particular interests are TSD bands 1 and 2 which have previously been interpreted as zero phonon and one phonon wobbling bands, respectively. Using the Doppler shift attenuation method (DSAM), a preliminary transition quadrupole moment of 6.9+0.3−0.3 eb was extracted for the TSD1 band. Data analysis continues for TSD2 which is considerably more weakly populated.

Low-energy excited states of 210 Ra and 208 Ra were investigated at the Wright Nuclear Structure Laboratory of Yale University. Fusion evaporation recoils were selected using the gas-filled spectrometer, SASSYER. Delayed γ-rays, following isomeric decays, were detected at the focal plane of SASSYER with a small array of HPGe detectors. Transitions following the proposed J π = 8 + isomers were observed, and the half-lives measured. The experiments are discussed and results compared to expectations from the seniority scheme.

Neutron-induced reaction cross sections are sometimes difficult to measure due to target or beam limitations. For two-step reactions proceeding through an equilibrated intermediate state, an alternate "surrogate reaction" technique [J.D. Cramer and H.C. Britt, Nucl. Sci. Eng. 41, 177 (1970), H.C. Britt and J.B. Wilhelmy, Nucl. Sci. Eng. 72, 222 (1979), W.Younes and H.C. Britt, Phys. Rev. C 67, 024610 (2003)] can be applicable, and is currently undergoing investigation at LLNL. Measured decay probabilities for the intermediate nucleus formed in a light-ion reaction can be combined with optical-model calculations for the formation of the same intermediate nucleus via the neutron-induced reaction. The result is an estimation for overall (n,γ/n/2n) cross sections. As a bench-mark, the reaction 92Zr(α, α ′ ), surrogate for n+91Zr, was studied at the A.W. Wright Nuclear Structure Laboratory at Yale. Particles were detected in the silicon telescope STARS (Silicon Telescope Array for Reaction Studies) and γ-ray energies measured with germanium clover detectors from the YRAST (Yale Rochester Array for SpecTroscopy) ball. The experiment and preliminary observations will be discussed.

The g factors of the 2 + 1 and 3 − 1 states in 96 Zr have been measured for the first time by Coulomb excitation of 96 Zr beams in inverse kinematics using transient magnetic fields. The resulting g factors are g (2 + 1 )=+0.03(7) and g (3 − 1 )=+0.98(15). The lifetime of the 2 + 1 state, τ =0.82(10) ps, was redetermined via the Doppler Shift Attenuation Method. The 2 + 1 →0 + 1 transition rate and the g -factor data are in fair agreement with shell-model calculations involving both proton and neutron excitations. The pronounced octupole strength of the 3 − 1 →0 + 1 transition is not seen in the g factor which exceeds significantly an expected Z / A value.

The g factor of the 2 1 + state in 44 Ca has been measured using the transient field technique and Coulomb excitation in inverse kinematics. A positive value of g(2 1 + , 44 Ca )=+0.12±0.05 was deduced. The result suggests the ( fp ) 4 ν configuration competes with excitations of the 40 Ca core. A simple model which considers that the wave function for the 2 1 + state consists of approximately equal admixtures of spherical four valence neutron configurations and a deformed core configuration accounts for the experimentally observed g factor as well as the previously measured quadrupole moment.

The Wright Nuclear Structure Laboratory has recently acquired a gas-filled recoil separator previously used at Berkeley National Laboratory for heavy-element synthesis. The separator will be used to separate reaction recoils from primary beam particles and fission products following target bombardment. Commissioning of the separator has recently been completed, and the structure of 203 Rn investigated.

A gamma-ray energy-tracking array (GRETA) consisting of a 4π array of highly segmented Ge detectors is a new concept for the detection of gamma radiation. In such an array, all of the individual interactions of each gamma-ray are identified by their energies and positions, the three-dimensional positions being determined by pulse-shape analysis of the signals from the segmented Ge detectors. Then, using tracking algorithms based on the properties of photoabsorption, Compton scattering and pair production, the gamma-ray scattering sequences can be reconstructed, even if many gamma-rays hit the array at the same time. Such a detector will have new and much improved capabilities compared to the current generation of gamma-ray spectrometers and will be vital to fully exploit the most exotic beams from future radioactive beam facilities. One implementation of the tracking array concept, called GRETA, is currently under development in the US. In this presentation the progress of the GRETA project will be reviewed and future plans and prospects will be discussed.

We report on four recent results concerning the population and the decay of superdeformed states, namely the structure of excited superdeformed states in 194Hg, the search for fine structure of the last superdeformed transitions in 194Pb, the primary decay-out strength analysis in 194Hg and, as a consequence of this, the possibility of using the decay-out as a tool to study order-to-chaos properties of normally deformed states.

B(E2;0+1→2+1) values for the unstable, neutron-rich nuclei 132,134Te were determined through Coulomb excitation, in inverse kinematics, of accelerated beams of these nuclei. The systematics of measured B(E2) values from the ground state to the first excited state have been extended to the N=82 shell closure in the Te nuclei and have been compared with the predictions of different theories. The measurements were performed at the Holifield Radioactive Ion Beam Facility (HRIBF) using the GRAFIK detector. The success of this approach, which couples a 5.7% efficient through-well NaI(Tl) γ-ray detector with thin foil microchannel plate beam detectors, also demonstrates the feasibility for Coulomb excitation studies of neutron-rich nuclei even further from the valley of beta stability, both at present-generation ISOL facilities and at the proposed Rare Isotope Accelerator.

High-spin states of 194 Pb have been populated by the reaction 184 W( 16 O, 6n) at 113 MeV beam energy and studied using the EUROGAM-1 array. The level scheme has been extended up to spin of 33 ℏ and excitation energy of 11.1 MeV. The high-spin part of the level scheme is dominated by bands of dipole transitions. New dipole bands have been observed and the configurations of their band heads are discussed. Besides the well-known coupling of the K π =11 − two-proton state to several νi 13/2 rotation-aligned neutron states, the K π =8 + two-proton state is also involved. Such a coupling is identified for the first time in a lead isotope. Moreover, the K π =11 − two-proton state is coupled to the rotation-aligned proton pair ( πh 11/2 ) 2 . Thus many multiparticle configurations involving all the high- j subshells located around the proton and neutron Fermi levels, πh 11/2 , πh 9/2 , πi 13/2 , and νi 13/2 have been identified in this nucleus.

The $^{236}\mathrm{Pu}(n,f)$, $^{237}\mathrm{Pu}(n,f)$ and $^{238}\mathrm{Pu}(n,f)$ cross sections have been inferred by utilizing the surrogate ratio method. Targets of $^{239}\mathrm{Pu}$ and $^{235}\mathrm{U}$ were bombarded with 28.5-MeV protons, and the light ion recoils, as well as fission fragments, were detected using the STARS detector array at the K150 Cyclotron at the Texas A cyclotron facility. The ($p$, $tf$) reaction on $^{239}\mathrm{Pu}$ and $^{235}\mathrm{U}$ targets was used to deduce the $\ensuremath{\sigma}$ $(^{236}\mathrm{Pu}(n,f))/\ensuremath{\sigma}$$(^{232}\mathrm{U}(n,f))$ ratio, and the $^{236}\mathrm{Pu}(n,f)$ cross section was subsequently determined for ${E}_{n}=0.5--7.5$ MeV. Similarly, the $(p,df$) reaction on the same two targets was used to deduce the $\ensuremath{\sigma}$$(^{237}\mathrm{Pu}(n,f))/\ensuremath{\sigma}$$(^{233}\mathrm{U}(n,f))$ ratio, and the $^{237}\mathrm{Pu}(n,f)$ cross section was extracted in the energy range ${E}_{n}=0.5--7$ MeV. The $^{238}\mathrm{Pu}(n,f)$ cross section was also deduced by utilizing the $(p,{p}^{\ensuremath{'}})$ reaction channel on the same targets. There is good agreement with the recent ENDF/B-VII.1 evaluated cross section data for $^{238}\mathrm{Pu}(n,f)$ in the range ${E}_{n}=0.5--10.5$ MeV and for $^{237}\mathrm{Pu}(n,f)$ in the range ${E}_{n}=0.5--7$ MeV; however, the $^{236}\mathrm{Pu}(n,f)$ cross section deduced in the present work is higher than the evaluation between 2 and 7 MeV.

New sideband partners of the yrast bands built on the $\ensuremath{\pi}{h}_{11/2}\ensuremath{\nu}{h}_{11/2}$ configuration were identified in ${}_{55}\mathrm{Cs}$, ${}_{57}\mathrm{La}$, and ${}_{61}\mathrm{Pm}$ $N\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}75$ isotones of ${}^{134}\mathrm{Pr}$. These bands form with ${}^{134}\mathrm{Pr}$ unique doublet-band systematics suggesting a common basis. Aplanar solutions of 3D tilted axis cranking calculations for triaxial shapes define left- and right-handed chiral systems out of the three angular momenta provided by the valence particles and the core rotation, which leads to spontaneous chiral symmetry breaking and the doublet bands. Small energy differences between the doublet bands suggest collective chiral vibrations.

The g factors of the 2 + 1 and 3 − 1 states in semi-magic 90 Zr have been measured for the first time with the technique of Coulomb excitation of 90 Zr beams in inverse kinematics in combination with transient magnetic fields. The resulting g factors, g (2 + 1 )=+1.25(21) and g (3 − 1 )=+0.986(56), are both consistent with a dominant g 9/2 proton configuration and a closed N =50 neutron shell. The lifetime of the 2 + 1 state was measured by the Doppler shift attenuation method, τ =0.126(3) ps.

The Yale Rochester Array for SpecTroscopy, YRAST Ball, is described. Containing up to 30 Compton suppressed Ge detectors YRAST Ball is a powerful new array for c-ray spectroscopy. Several of its auxiliary detectors, including a multi-element solar cell array for heavy charged fragment detection and a new state of the art plunger system for recoil distance measurements are also described. ( 2000 Elsevier Science B.V. All rights reserved.

g factors of the 2 + 1 and 4 + 1 states in 92,94 Zr have been measured via Coulomb excitation of isotopically pure 92,94 Zr beams in inverse kinematics in combination with the transient field technique. The high precision results, g ( 92 Zr; 2 + 1 ) = −0.180(10) and g ( 94 Zr; 2 + 1 ) = −0.329(15) as well as the new data on the 4 + 1 state, g ( 92 Zr; 4 + 1 ) = −0.50(11), provide, for the first time, clear evidence of the dominant role of d 5/2 neutrons in the wave functions of these nuclei just above the N =50 shell closure. Moreover, the data imply increased purity of the d 5/2 neutron component in the wave function with increasing spin.

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}

Lifetimes of the 0 2 + and 2 γ + states in 154 Sm were measured using the Doppler-shift Attenuation Method following Coulomb excitation. The experiment employed the gamma-ray detector array YRAST Ball at Yale University in conjunction with an array of photo-electric cells. 154 Sm was identified as one of the few deformed nuclei where the first excited 0 + state is the β -vibration of the ground state. The 0 3 + level has no collective decay to the ground state band and is interpreted as a spherical shape coexisting state based on its decay properties and calculations in the framework of the interacting boson model (IBM) and geometric collective model (GCM).

A high statistics experiment performed on Gd nuclei with the use of the EUROGAM II array resulted in the discovery of twelve new superdeformed (SD) bands. Three of them have been assigned to ${}^{148}\mathrm{Gd}$ and seven to ${}^{149}\mathrm{Gd}$ giving a total of thirteen SD bands now known in this last nucleus. The close relationship in transition energies between these bands and those in neighboring nuclei has been used to suggest configurations. Most of the new bands exhibit more or less pronounced irregularities in their dynamical moments of inertia with consequences on their identities with other bands.

The quadrupole moments and deformations have been measured for six superdeformed bands in Gd-150. The results indicate evidence for deformation driving properties of both the high-hi intruder and a ...

In a recent experiment performed with the EUROGAM II {gamma}-ray spectrometer three superdeformed (SD) bands have been established in {sup 153}Ho. The properties of these bands are discussed in terms of single-particle proton excitations and are compared with respect to the SD magic nucleus {sup 152}Dy. These results represent the first observation of SD structures in a holmium nucleus and provide further information on the proton orbitals lying above the Z=66 shell gap. {copyright} {ital 1997} {ital The American Physical Society}

Theπh9/2[541 1/2−] band in 167Tm has been studied through the 124Sn(48Ca, p4n)167Tm reaction at E beam = 210 MeV. The favoured signature of the πh9/2[541 1/2−] band is observed to spin 61/2h. A remarkable small gain in aligned angular momentum at the AB-band crossing has been found. The crossing frequency and the gain in aligned angular momentum for 167Tm are compared with data for the N = 98 isotones of Lu, Ta and Re, and contrasted with Cranked Shell Model predictions, based on frequency diabatic configurations. Large deviations are found for the gain in aligned angular momentum.

High — spin states in 122Xe have been investigated by γ − γ coincidence measurements using the EUROGAM array. The reaction 96Zr(30Si,4n)122Xe at a beam energy of 135 MeV was used to populate states of 122Xe. The level scheme has been extended up to ∼ 13.5 MeV and also enriched as compared to previous studies. New structures of competing dipole to quadrupole transitions have been observed. Experimental B(M1)/B(E2) ratios have been extracted for these structures and compared with theoretical estimates. They have also been compared with similar structures in Xe, Ba and Ce nuclei.

Odd-mass gadolinium isotopes around $N=90$ were populated by the ($p$,$d$) reaction, utilizing 25-MeV protons, resulting in population of low-spin quasineutron states at energies near and below the Fermi surface. Systematics of the single quasineutron levels populated are presented. A large excitation energy gap is observed between levels originating from the $2{d}_{3/2}$, $1{h}_{11/2}$, and $3{s}_{1/2}$ spherical parents (above the $N=64$ gap), and the $2{d}_{5/2}$ (below the gap), indicating that the spherical shell model level spacing is maintained at least to moderate deformations.

The near-yrast structure of the near-magic, odd-odd nucleus, ${}_{39}^{88}$Y${}_{49}$, has been studied into the high-spin regime. Investigations were performed at the Wright Nuclear Structure Laboratory, Yale University, using the ${}^{74}$Ge(${}^{18}$O,$p3n$) and ${}^{76}$Ge(${}^{18}$O,$p5n$) fusion-evaporation reactions at beam energies of 60 and 90 MeV, respectively. Gamma-ray energy coincidence analyses using both double (${\ensuremath{\gamma}}^{2}$) and triple (${\ensuremath{\gamma}}^{3}$) fold coincidences, together with angular correlation measurements, have been used to extend the previously reported level scheme to an excitation energy of 8.6 MeV and a spin and parity of 19${}^{(\ensuremath{-})}$. The presented level scheme is compared with predictions of a truncated valence space shell-model calculation, which assumes an inert ${}^{56}$Ni core with proton and neutron excitations allowed within the ${f}_{5/2}$, ${p}_{3/2}$, ${p}_{1/2}$, and ${g}_{9/2}$ single-particle states. The shell-model calculations show a reasonable comparison with the experimental data for the yrast, positive-parity states up to spin 18 $\ensuremath{\hbar}$, with larger variations evident for negative-parity states with spins greater than 16 $\ensuremath{\hbar}$. In spite of a significant increase in angular momentum input associated with the thin target ${}^{76}$Ge(${}^{18}$O,$p5n$) reaction channel, as compared to the backed target data using the ${}^{74}$Ge target, no additional discrete states were identified in the former data set, suggesting that the level scheme for this nucleus fragments significantly above the observed states, possibly indicating cross-shell excitations becoming dominant for $Ig$19 $\ensuremath{\hbar}$.

Intermediate-energy Coulomb excitation measurements are performed on the N≥40 neutron-rich nuclei Fe66,68 and Cr64. The reduced transition matrix elements providing a direct measure of the quadrupole collectivity B(E2;2+1→0+1) are determined for the first time in Fe4268 and Cr4064 and confirm a previous recoil distance method lifetime measurement in Fe4066. The results are compared to state-of-the-art large-scale shell-model calculations within the full fpgd neutron orbital model space using the Lenzi-Nowacki-Poves-Sieja effective interaction and confirm the results of the calculations that show these nuclei are well deformed, This work was supported by the National Science Foundation under Grant No. PHY11-02511 (NSCL), and by the U.S. Department of Energy under Awards No. DEAC02- 05CH11231 (LBNL), No. DE-FG02-08ER41556 (NSCL), No. DE-FG52-06NA26206, and No. DE-FG02- 05ER41379 (University of Richmond). Part of this work was performed under the auspices of the U.S. Department of Energy Lawrence Livermore National Laboratory (LLNL) under Award No. DE-AC52-07NA27344. A. P. recognizes MICINN (Spain) (Grant No. FPA2011-29854) and Comunidad de Madrid (Spain) (Project No. HEPHACOS S2009-ESP-147) for support. We would also like to thank the operations staff at NSCL for their outstanding work in beam delivery

High spin states in the isotope194Hg were populated using the150Nd (48Ca,4n) reaction at a beam energy of 213 MeV. The analysis ofγ-γ coincidences has revealed two new structures at excitation energies above 6 MeV and at moderate spin. The two structures are a manifestation of the deviation of nucleus from the collective rotation which dominates its lower excitation behaviour. A comparison with similar structures in the neighbouring Hg isotopes is also attempted.

The nucleus195Pb has been populated with the184W+16O reaction at 113 MeV. Two dipole γ-ray cascades have been observed using the EUROGAM spectrometer. A comprehensive level scheme related to these structures has been established. Multiparticle configurations are attributed to these high-spin structures from detailed comparison with the neighbouring nuclei,193Hg,194Pb and195Tl. Band crossings due to i13/2 neutron pair breaking are observed in195Pb at about the same frequencies as in the isotone193Hg.

The goal of this communication is to propose a model of interaction of the cultures based on the concept of radiation by analogy with the quantum model of the light. Just as the light can be considered in modern physics either a flow of particles or an undulation, in the same way, to the granular dimension of the information emitted by an organization in its data flows, we will add a wave-like dimension in the form of radiation. The socio technical device of radiation is a particular form of Distic

rays depopulating high-spin states in have been detected using the EUROGAM phase-1 array. A crossing which is possibly observed at a rotational frequency of MeV in a quasi-neutron band is interpreted as being due to the alignment of a pair of neutrons.

Intruder rotational bands have been investigated to high frequency in $_{51}^{109}\mathrm{Sb}$. Five decoupled (\ensuremath{\Delta}I=2) bands extending to rotational frequencies above 1.4 MeV/\ensuremath{\Elzxh} have been observed. At the highest frequencies, the ${\mathit{J}}^{(2)}$ dynamic moments of inertia for four of these bands are seen to decrease steadily to unexpectedly low values, ${\mathit{J}}^{(2)}$ \ensuremath{\sim} 10 ${\mathrm{\ensuremath{\Elzxh}}}^{2}$ ${\mathrm{MeV}}^{\mathrm{\ensuremath{-}}1}$. These four bands, which are interpreted as being based on deformed 2p-2h proton excitations across the Z=50 closed-shell gap, achieve the so-called ``smooth band termination'' following alignment of the valence nucleons outside of $^{100}\mathrm{Sn}$. In addition, two strongly coupled (\ensuremath{\Delta}I=1) bands have been observed, which are related to 1p-1h proton excitations across the gap. \textcopyright{} 1996 The American Physical Society.