Search

Low-spin states in the neutron-rich, N = 90 nuclide 146Ba were populated following β decay of 146Cs, with the goal of clarifying the development of deformation in barium isotopes through delineation of their nonyrast structures. Fission fragments of 146Cs were extracted from a 1.7-Ci 252Cf source and mass selected using the CAlifornium Rare Ion Breeder Upgrade (CARIBU) facility. Low-energy ions were deposited at the center of a box of thin β detectors, surrounded by a highly efficient high-purity Ge array. The new 146Ba decay scheme now contains 31 excited levels extending up to ∼2.5 MeV excitation energy, double what was previously known. These data are compared to predictions from the interacting boson approximation (IBA) model. It appears that the abrupt shape change found at N = 90 in Sm and Gd is much more gradual in Ba and Ce, due to an enhanced role of the γ degree of freedom. [ABSTRACT FROM AUTHOR]

Excited states in 74 Se were populated following thee ε/β+ decay of 74Br, mainly from the J = K = 4,13.8-keV β-decaying isomer. Off-beam y-ray spectroscopy was performed with the array of Clover HPGe detectors at WNSL Yale. Many new transitions were observed and rigorous spin assignments were made based on y-y angular correlations. The β-decay strength was found to proceed almost entirely to a few high-lying states near 4500 keV, which are consistent with deformed two-quasineutron high-AT configurations. These doorway states then provide an effective tool for populating and identifying the lower prolate structures. Once categorized, the low-lying states of 74Se can be described as a set of near-spherical vibrational levels mixing strongly with a spectrum of prolate states which have an unperturbed bandhead near 1350 keV. [ABSTRACT FROM AUTHOR]

Recent antisymmetrized molecular dynamics (AMD) calculations for 28Si suggest the presence of a superdeformed (SD) band with a dominant 24Mg + α clustering for its configuration, with firm predictions for its location and associated moment of inertia. This motivates a review of the experimental results reported in the literature with a particular focus on 24Mg(α,γ) studies, as well as on a-like heavy-ion transfer reactions such as 12C(20Ne,α)28Si. Combining this information for the first time leads to a set of candidate SD states whose properties point to their α-cluster structure and strong associated deformation. Analysis of data from Gammasphere allows the electromagnetic decay of these candidate states to be probed and reveals further supporting evidence for such a structure. This paper appraises this body of information and finds the evidence for an SD band is strong. [ABSTRACT FROM AUTHOR]

Precise electromagnetic transition matrix elements in 10Be and 10C have provided surprisingly stringent tests of modern ab initio calculations using realistic nuclear forces. The analog transition in 10B can further constrain these new calculations and probe the symmetry of the wave functions across the A = 10 multiplet. We report on a careful measurement of the β-ray intensities from states populated in the 10B(p,p') reaction at 10 MeV, including a determination of the key E2 branch from the J = 2 T = 1 state at 5164 keV to the J = 0 T = 1 state at 1740 keV of 0.16(4)%. [ABSTRACT FROM AUTHOR]

The lifetime of the Jπ = 21+ state in 10C was measured using the Doppler shift attenuation method following the inverse kinematics p(10B, n)10C reaction at 95 MeV. The 21+ state, at 3354 keV, has τ = 219 ± (7)stat ± (10)sys fs, corresponding to a B(E2) ↓ of 8.8(3) e² fm4. This measurement, combined with that recently determined for 10Be [9.2(3) e² fm4], provides a unique challenge to ab initio calculations, testing the structure of these states, including the isospin symmetry of the wave functions. Quantum Monte Carlo calculations using realistic two- and three-nucleon Hamiltonians that reproduce the 10Be B(E2) value generally predict a larger 10C B(E2) probability but with considerable sensitivity to the admixture of different spatial symmetry components in the wave functions and to the three-nucleon potential used. [ABSTRACT FROM AUTHOR]

The structure of 72Se was investigated following the ϵ/β+ decay of 72Br produced in the 58Ni(16O, pn) reaction at 50 MeV. Using a beam chopping system, off-beam γ-ray decay data was collected with an array of clover Ge detectors. γ-γ coincidence measurements provided a significant modification of the prior level scheme, and γ-γ angular correlation measurements allowed spin determinations and multipole mixing ratio extraction. The new information on the non-yrast states was combined with previous in-beam data to investigate the issue of shape coexistence by comparing to various configuration mixing approaches. Clear evidence for shape coexistence is found, with a ground state of modest, or slightly oblate, deformation and a well-deformed prolate shape that would lie at an unperturbed excitation of 875 keV. The shape mixing is near complete at low spin. [ABSTRACT FROM AUTHOR]

States in 209Tl were populated using a multinucleon transfer reaction with a 136Xe beam impinging on a thick 208Pb target at E=785 MeV. The beam was pulsed at 825-ns intervals in order to perform isomer decay spectroscopy. The known Jp=17/2+ isomer in 209Tl was located at 1228(4) keV and measured to have a half-life of T1/2=146(10) ns. A second isomer with Jp=13/2+ was found to have T1/2=14(5) ns. The previously suggested low-energy X and Y transitions were found to have energies 57(2) and 47(2) keV respectively, while the measurement of conversion coefficients and a new decay path make the spin assignments below the isomers experimentally firm. Correlating the delayed γ transitions with the prompt beam flash allowed the decay of states above the isomer to be found. The longer-lived isomer represents full alignment of the simplest two-particle, one-hole configuration and illuminates the remarkably weak coupling of the proton hole to the 210Pb core. [ABSTRACT FROM AUTHOR]

A new γ-decay branch has been found from the well-known 661.659(3)-keV Jπ =11/2-, T1/2=2.552(1) min isomer in 137Ba which is populated in the β decay of 137Cs. The new 377.9(3)-keV γ ray connects the isomer to the low-lying 283.5 keV, Jπ =1/2- state. It is of near-pure E5 character. The decay has a γ branching ratio (Brγ = Γγ/Γtot) of 1.12(9) × 10-7. The new decay has a B(E5) of 0.71(6) W.u. [B(E5) ↓ = 6.5(6) × 105e²fm10], a value consistent with other "single-particle" E5 decays in the region. The new decay branch is of topical interest, as it competes with the much-sought "two-photon" second-order electromagnetic decay from this state. [ABSTRACT FROM AUTHOR]

Particle decay of 69Br and 65As was observed through β-delayed proton emission of 69Kr and 65Se, respectively. Decay spectroscopy was performed through β-p correlations using a position-sensitive silicon-implantation detector surrounded by a γ-ray detector array. A β-decay half-life of 27(3) ms was measured for 69Kr and 33(4) ms for 65Se. The 69Kr ground state decays by a superallowed transition to its unbound isobaric analog state in 69Br which immediately decays by a 2.97(5)-MeV proton group to the first excited state in 68Se at 854.2 keV. This chain of decays constrains both the mass and spin of the 69Kr ground state. We observed no evidence of ground-state proton decay from 69Br. [ABSTRACT FROM AUTHOR]

The rate of the T=1, 2+ to T=1, 0+ transition in 10B (T=1, Tz=0) is compared to the analog transitions in 10Be (T=1, Tz=-1) and 10C (T=1, Tz=+1) to provide constraints on ab initio calculations using realistic nuclear forces. The relevant state in 10B, at Ex=5.164 MeV, is particle unbound. Therefore, a determination of the B(E2) electromagnetic transition rate requires a precise and accurate determination of the width of the state, as well as the α-particle and γ-ray branching ratios. Previous measurements of the α-particle branching ratio are just barely in agreement. We report on a new study of the α-particle branch by studying the 10B(p,p')10B* reaction in inverse kinematics with the HELIOS spectrometer. The α-particle branching ratio that we observe, 0.144±0.027, is in good agreement with the evaluated value and improves the associated uncertainty. The resulting experimental B(E2) value is 7.0±2.2 e²fm4 and is more consistent with a flat trend across the A=10 triplet than previously reported. This is inconsistent with Green's function Monte Carlo predictions using realistic three-nucleon Hamiltonians, which overpredict the B(E2) value in 10C and 10B. [ABSTRACT FROM AUTHOR]

An oblate rotational sequence, built on an aligned, two-quasineutron isomeric state has been established in 196Pt. The isomer has a half-life of 7.7(7) ns and is associated with the Iπ = 12+, (i13/2)² neutron configuration. Excited states, with angular momentum generated primarily through successive nucleon alignments, have been populated through 1p transfer from 197Au. The nucleus 196Pt is the most neutron-rich Pt isotope for which high-spin states, beyond the 12+ isomeric state, have been established thus far. Cranked shell model calculations have been performed to understand shape evolution with spin, and the role of nucleons occupying specific Nilsson orbitals in generating aligned angular momentum for both prolate and oblate deformations has been explored. [ABSTRACT FROM AUTHOR]

An extensive study of the level structure of 61Co has been performed following the complex 26Mg(48Ca,2α4np?)61Co reaction at beam energies of 275, 290, and 320 MeV using Gammasphere and the Fragment Mass Analyzer (FMA). The low-spin structure is discussed within the framework of shell-model calculations using the GXPF1A effective interaction. Two quasirotational bands consisting of stretched-E2 transitions have been established up to spins I=41/2 and (43/2), and excitation energies of ~17 and ~20 MeV, respectively. These are interpreted as signature partners built on a neutron ?(g9/2)² configuration coupled to a proton πp3/2 state, based on cranked shell model (CSM) calculations and comparisons with observations in neighboring nuclei. In addition, four ΔI=1 bands were populated to high spin, with the yrast dipole band interpreted as a possible candidate for the shears mechanism, a process seldom observed thus far in this mass region. [ABSTRACT FROM AUTHOR]

Background: Two-photon emission, while well known in atomic physics, is arare second-order process in nuclear physics with only three cases where a two-photon branch is measured. The limited knowledge stems from the experimental difficulty in resolving two-photon emission from dominant single-photon emission, restricting practical cases for study to 0+ ⊿ 0+ (E0) transitions, since single-photon emission is forbidden. In practical terms, this limits the range of easily accessible cases to even-even nuclei with the unusual property of a first excited state with spin/parity of 0+. Purpose: Two-photon branches are measured for the closed-shell nuclei, 160,40Ca, and 90Zr. The intention of the present work was to obtain data for a case which was not a closed-shell nucleus. Of the possible nuclei relevant to such a study, 98Mo was chosen as its first-excited state is 0+ and lies below 1 MeV, meaning that internal pair transitions are not allowed. Method: The first excited state ( J = 0+) in 98Mo was excited in resonant inelastic proton scattering using a 6.7-MeV proton beam. The population of the state was selected using an annular double-sided silicon strip detector (DSSD). The decay of the state by conversion electrons was observed using the same DSSD, while Gammasphere was used to detect possible two-photon events. Results: An upper limit on the two-photon branch obtained was 1 x 10-4 at the 95% confidence level (CL). Conclusions The upper limit obtained is smaller than any other previously obtained two-photon branch. Phase space considerations suggest that the actual value of the branching ratio in this case may be significantly smaller than the upper limit obtained. [ABSTRACT FROM AUTHOR]

A study of excited states in 63Ni up to an excitation energy of 28 MeV and a probable spin of 57/2 was carried out with the 26Mg(48Ca,2α3nγ )63Ni reaction at beam energies between 275 and 320 MeV. Three collective bands, built upon states of single-particle character, were identified. For two of the three bands, the transition quadrupole moments were extracted, herewith quantifying the deformation at high spin. The results have been compared with shell-model and cranked Nilsson-Strutinsky calculations. Despite the Z = 28 shell closure and the approach to the purported N = 40 subshell, the 63Ni isotope is able to sustain collective excitations at moderate and high spin. [ABSTRACT FROM AUTHOR]

An earlier measurement on the 4+ to 2+ radiative transition in 8Be provided the first electromagnetic signature of its dumbbell-like shape. However, the large uncertainty in the measured cross section does not allow a stringent test of nuclear structure models. This Letter reports a more elaborate and precise measurement for this transition, via the radiative capture in the 4He+4He reaction, improving the accuracy by about a factor of 3. Ab initio calculations of the radiative transition strength with improved three-nucleon forces are also presented. The experimental results are compared with the predictions of the alpha cluster model and ab initio calculations. [ABSTRACT FROM AUTHOR]

The article presents a comparison of mirror symmetry in the A = 23, T = 1/2 mirror nuclei 23Na and 23Mg both to high spin, and high excitation energy, including beyond the proton threshold. Excited states in the region above the proton threshold have been studied in both nuclei. It presents methods of obtaining reaction rates for nuclear astrophysics. It concludes that estimated data of shell model calculations can be used if real data is not available.

Excited states of 76Ge have been populated in above-barrier Coulomb excitation and inelastic scattering of a 530-MeV 76Ge beam on a 238U target and studied using in-beam γ-ray spectroscopy with the Gammasphere array. The γ band was extended considerably and one new band was identified. Comparisons of the γ band with collective- and shell-model calculations suggest that 76Ge may be a rare example of a nucleus exhibiting rigid triaxial deformation in the low-lying states. [ABSTRACT FROM AUTHOR]

Deep-inelastic reactions and γ-ray spectroscopy have been used to study excited states in 195Au. A three-quasiparticle isomer with a mean-life of 18.6(3) µs has been assigned at 2461 + Δ keV, with decays into newly identified structures. Possible configurations for the isomer are discussed including a Jπ = 31/2- intrinsic state produced by coupling the 11/2- [505] proton hole to the 10+ state obtained from the 9/2+ [624], 11/2+ [615] two-neutron holes, expected from configuration-constrained potential-energy-surface calculations. Residual interactions are evaluated within a semi-empirical shell model basis. New lifetime information is also obtained for the 21/2+ and 25/2+ states at 1813 and 1980 keV. The relationship between these and other newly identified states and the negative-parity states in the even-even neighbors is discussed. [ABSTRACT FROM AUTHOR]

New high-spin microsecond isomers, with Jπ = (31+) and Jπ = (28-), have been identified in 206Bi at 10 170 and 9233 keV, respectively, using γ-ray coincidence spectroscopy following deep-inelastic reactions with the 76Ge + 208Pb system. Yrast and near-yrast levels populated in the decay of these isomers have been located and interpreted with the help of shell-model calculations. The states identified at energies up to approximately 7 MeV can be described well in terms of one-proton-particle, three-neutron-hole couplings. [ABSTRACT FROM AUTHOR]

Low-lying collective states of 154Sm are studied via the 12C(154Sm,154Sm*) Coulomb excitation reaction at 85% of the Coulomb barrier (570 MeV) using the Gammasphere Ge-detector array. Absolute transition strengths are obtained from the Coulomb excitation cross sections deduced from the relative y-ray yields. The results include transition strengths for E2 decays of energy levels in the low-spin part of the first excited K= 0+ rotational band of 154Sm. The agreement of these results with the confined β-soft rotor model predictions establishes the assignment of this band as a β band. [ABSTRACT FROM AUTHOR]

The evolution of the one-quadrupole phonon mixed-symmetry state is important for understanding the role of the quadrupole proton-neutron interaction in the valence shell. To study the evolution of the 21,ms+ mixed-symmetry state in the N = 78 isotones above Z = 50, a Coulomb excitation measurement was performed to identify the 21,ms+ state in 136Ce by measuring absolute transition strengths. The 21,ms+ state was found to be predominantly concentrated in the 24+ state of this nucleus. The simple picture of shell stabilization given to account for the fragmentation of the strength observed in 138Ce does not seem to apply to 136Ce. [ABSTRACT FROM AUTHOR]

The structure of 58Fe was investigated at Gammasphere using 48Ca(13,14C,xn) fusion-evaporation reactions at a beam energy of 130 MeV. The level scheme has been revised and extended to J ∼ 17ħ and an excitation energy of 16.6 MeV. Regular band structures consisting of low-energy ΔJ = 1ħ transitions have been observed at moderate spin (J ∼ 8ħ-l5ħ) and are candidates for magnetic rotational bands. Self-consistent tilted-axis-cranking calculations within a relativistic mean-field theory were applied to investigate these bands and were found to reproduce the experimental results well. In other parts of the level scheme, quasirotational bands composed of stretched-£'2 transitions have been extended to high spin, and other new bands have been identified. Positive-parity experimental states were compared to predictions of the spherical shell model using the GXPF1 A, KB3G, and FPD6 effective interactions in the fp model space. The projected shell model, with a deformed quasiparticle basis including the neutron νg9/2 orbital, was applied to interpret regular ΔJ = 2ħ band structures that extend beyond the maximum spin available for π[(f7/2)-2] ⨷ ν[(p3/2f5/2P1/2)4] configurations and exhibit features characteristic of rotational alignment. It is clear that the νg9/2 intruder orbital plays a crucial role in describing the quasirotational structures in this nucleus, even starting as low as J ∼ 5h. [ABSTRACT FROM AUTHOR]

Gamma-ray transitions have been observed in the proton-emitting N = Z + 2 (Tz = 1) isotope 112Cs. The transitions have been unambiguously assigned to 112Cs by correlation with the characteristic proton decay, using the method of recoil-decay tagging with mass selection. The measured proton-decay energy and half-life are Ep = 810(5) keV and T1/2 = 470(50) μs, respectively, which are consistent with previous measurements. Five γ-ray transitions have been observed which appear to form a rotational sequence. The energy differences between excited states in the sequence are consistent with an assignment as the favored signature of the v(h1/2)⨷ π(h11/2) structure. Tentative evidence for fine structure in the 112Cs proton decay is also observed. [ABSTRACT FROM AUTHOR]

We describe the investigation of high-spin states in 24Mg populated with the 12C(160, α)24Mg reaction at 62- and 68-MeV beam energy. The excited states were established through the coincident detection of up to four α and γ particles in complete decay cascades toward a final state of angular momentum zero, the ground state of either 20Ne or 160. We describe a new analysis method for the angular correlations in such events and apply it with the goal to assign spin and parity to a-unbound states in 24Mg. We establish a number of high-spin, natural-parity states between spins 6 and 12, including the lowest known 10+ and 12+ levels. The energy systematics of positiveand negative-parity high-spin states are compared to the predictions of modern shell-model calculations. [ABSTRACT FROM AUTHOR]

Excited states in the N = Z - 2 nucleus 44V have been observed for the first time. The states have been identified through particle-γ-γ coincidence relationships and comparison with analog states in the mirror nucleus 44Sc. Mirror energy differences have been extracted and compared to state-of-the-art shell-model calculations which include charge-symmetry-breaking forces. Observed decay pattern asymmetries between the mirror pair are discussed in terms of core excitations, electromagnetic spin-orbit effects and isospin mixing. [ABSTRACT FROM AUTHOR]

The decay branchings of a resonance in the 12C(12C,γ)24Mg reaction at Ec.m = 8.0 MeV have been studied with high resolution using the Gammasphere array. Radiative capture residues were discriminated from scattered beam and the dominant evaporation channels using the fragment mass analyzer coupled to a multistage Parallel Grid Avalanche Counter (PGAC)/ion chamber system. The clean selection of residues has allowed the population of excited states up to 10 MeV in 24Mg to be examined in detail. Strong feeding of an excited Kπ = 0- band is observed. A Jπ = 4+ assignment to the resonance is strongly favored. [ABSTRACT FROM AUTHOR]

Gamma rays assigned to Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed. have been identified with Gammasphere in deep-inelastic reactions involving a 450-MeV 76Ge beam and a 198Pt target. Using a combination of spectra produced by double gates on the known 454-, 843-, and 1095-keV members of the ground-state cascade, a coincident line at 199 keV has been identified and is tentatively assigned as the 8+ → 6+ transition. These γ-ray coincidences have been observed only in prompt events, indicating an 8+ half-life below 20 ns and requiring a large B(E2) enhancement compared to that expected from a seniority scheme. This value is consistent with models showing decay to a seniority v = 4, 6+ level that is depressed by the same two-body interaction responsible for the rather low 1095-keV Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed. energy, as compared to the valence-symmetry counterpart Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed. [ABSTRACT FROM AUTHOR]

Excited states in 55V and 55Cr have been populated via pn and 2n evaporation channels, respectively, following the fusion of a 48Ca beam at 172 MeV with a 9Be target. Level schemes have been deduced for the two nuclides to excitation energies of 7467 (55V) and 12226 keV (55Cr), with spins of 27/2+ and 33/2+, respectively. Negative-parity states are compared with shell-model calculations using three different effective interactions in the full fp model space. Negative-parity levels of 55Cr are explained in terms of single-particle fp-shell configurations outside N = 28 and N = 32 cores. Positive-parity states in both isotopes show evidence for the involvement of neutron g9/2 configurations. In the case of 55Cr, a quasirotational structure based on the 1/2+[440] Nilsson orbital is observed up to the terminating state. In 55V, positive-parity states do not exhibit well-developed collective features, and the observation of octupole decays is an indication of their importance in transitions from neutron g9/2 configurations to the fp shell. Experimental results are compared with the predictions of a traditional shell model, the projected shell model, and total-Routhian-surface calculations. [ABSTRACT FROM AUTHOR]

Low-lying collective states in 126Xe have been investigated via the 12C(l26Xe,126Xe*) projectile Coulomb excitation reaction at 399 MeV. The y decays were detected with the Gammasphere array. Coulomb excitation cross sections relative to the 21+ state were obtained. Twenty-two absolute E2 transition strengths have been deduced. An sd-interacting boson model (IBM-1) fit agrees well with the new experimental data. This makes a quantitative test of O(6)-symmetry breaking in 126Xe possible. The measured absolute B(E2) values indicate a preservation of O(5) symmetry, while the O(6) symmetry is broken. The evolution of O(6)-symmetry breaking and of O(5)-symmetry conservation in the 124,126,128Xe isotopic chain is discussed. [ABSTRACT FROM AUTHOR]

The decay of K isomers in Cm (Z = 96) isotopes has been studied using inelastic and transfer reactions. The half-life of a previously identified 2-quasiparticle (qp) Kπ=8- isomer in 246Cm has been measured. A new 2-qp isomer is observed in 248Cm, its half-life measured and its decay scheme established. The reduced K hindrances extracted for the decay transitions from the isomers in 246,248Cm indicate K to be a robust quantum number and validate axial symmetry in these nuclei. The excitation energies of the 2-qp isomers in 246Cm (N = 150) and 248Cm (N = 152) support the persistence of a deformed subshell gap at N = 152 in the Z≈100 region down to Z = 96 nuclei. [ABSTRACT FROM AUTHOR]

A six-quasiparticle isomer with T1/2 = 57(2) ns has been established in the doubly-odd isotope 200Tl and its level scheme is significantly extended. Half-lives of previously reported isomers in 200Tl and 201,202Pb have been determined and revised values are reported in a few cases, with T1/2 = 397(17) ns and 7.0(5) ns for the Iπ = 5+ and 7- states in 200Tl, 52(2) ns for the 41/2+ level in 201Pb, and 93(4) ns for the 16+ state in 202Pb. Configurations for the isomers have been assigned and these predominantly involve intrinsic excitations of neutrons from the i13/2 subshell. The inferred transition rates for the decay of these isomers compare well with single-particle estimates attesting to their intrinsic character. [ABSTRACT FROM AUTHOR]

The structure of decoupled positive-parity and semidecoupled negative-parity bands up to high spin in 197,199Hg has been studied using multinucleon transfer reactions with the Gammasphere array. A positive-parity band in 199Hg with the (νi13/2)³ decoupled configuration that deexcites to levels in the negative-parity sequences is newly established. The semidecoupled sequences in both isotopes are extended to higher spin. Rotation-aligned angular momenta and crossing frequencies determined from experiment are in fair agreement with those from cranking calculations. A transition from oblate collective rotation at low spin to triaxial noncollective shapes at high spin is indicated. [ABSTRACT FROM AUTHOR]

The structure of the odd-A isotopes 193,195,197Pt, which lie along the line of stability, has been studied up to high spin through multinucleon transfer reactions. Positive- and negative-parity sequences in 193,195Pt have been considerably extended and multiple band crossings established. An isomer with T1/2=5.0(5) ns and Iπ=25/2- is present in 195Pt. The isotopes 193,195Pt are characterized by moderate oblate deformation, and angular momentum generation at high spin in the yrast, positive-parity sequences is attributed to the rotation alignment of i13/2 neutrons and h11/2 protons. A detailed understanding of the observed features is presented using calculations based on tilted axis cranking covariant density functional theory as well as others with the ultimate CRANKER code. [ABSTRACT FROM AUTHOR]

A number of fission products possess isomeric states which have a nuclear spin significantly different from that of the ground state. The yield ratio of these states following fission is influenced by the angular momentum present in the fissioning system. The 134m,134Sb yield ratio had not been previously measured in the spontaneous fission of 252Cf; however, it had previously been observed to favor the (7-) isomer over the (0-) ground state in 235U(nth,f) and 232Th(25 MeV p,f). Using a mass-separated beam of low-energy 134,134mSb ions produced by 252Cf spontaneous fission at the CARIBU facility, β particles and γ rays were detected using the SATURN/X-Array decay station to determine the fission-yield ratio and β-decay half-lives. The 134mSb to 134Sb fission yield was determined to be 2.03±0.05 and the half-lives of 134mSb and 134Sb were found to be 9.87±0.08 s and 0.674±0.004 s, respectively. These results represent the first isomeric yield ratio measurement for this nucleus, and improved measurements of the 134Sb ground state and the 134mSb isomer half-lives. [ABSTRACT FROM AUTHOR]

The energy levels and γ-ray decay scheme of the positive-parity states in the Tz=1/2 nucleus 67As have been studied by using the 40Ca(36Ar,2αp)67As reaction at a beam energy of 145 MeV. Two new band structures have been identified which can be connected to the previously known levels. The results for these bands are compared with configuration-dependent cranked Nilsson-Strutinsky calculations. The good level of agreement between theory and experiment suggests that these structures can be interpreted in terms of configurations that involve three g9/2 particles and that both possess noncollective terminating states. [ABSTRACT FROM AUTHOR]

A sequence of low-energy levels in 7832Ge46 has been identified with spins and parity of 2+, 3+, 4+, 5+, and 6+. Decays within this band proceed strictly through ΔJ=1 transitions, unlike similar sequences in neighboring Ge and Se nuclei. Above the 2+ level, members of this sequence do not decay into the ground-state band. Moreover, the energy staggering of this sequence has the phase that would be expected for a γ-rigid structure. The energies and branching ratios of many of the levels are described well by shell-model calculations. However, the calculated reduced transition probabilities for the ΔJ=2 in-band transitions imply that they should have been observed, in contradiction with the experiment. Within the calculations of Davydov, Filippov, and Rostovsky for rigid-triaxial rotors with γ=30°, there are sequences of higher-spin levels connected by strong ΔJ=1 transitions which decay in the same manner as those observed experimentally, yet are calculated at too high an excitation energy. [ABSTRACT FROM AUTHOR]

Multi-quasiparticle high-K states, several of which are isomeric, were observed in 180Hf with the Gammasphere array. Lifetimes in the ns-μs range were determined using centroid-shift and decay measurements within a μs coincidence time window. The configurations of high-K states involve two and four quasiparticles, with states up to Kπ=(18-) established. High-K excitations are found to be progressively more favored with increasing excitation energy. The K quantum number is quite robust up to the highest spins observed, as evidenced by the large values of the reduced hindrance for isomeric decays. Rotational bands built on three high-K states are identified, and the measured branching ratios in these sequences enable the assignment of underlying configurations. Multi-quasiparticle calculations using the Lipkin-Nogami approach for pairing, with blocking included, reproduce the observed high-K energies quite well. [ABSTRACT FROM AUTHOR]

Background: Level sequences of rotational character have been observed in several nuclei in the A=60 mass region. The importance of the deformation-driving πƒ7/2 and νg9/2 orbitals on the onset of nuclear deformation is stressed. Purpose: A measurement was performed in order to identify collective rotational structures in the relatively neutron-rich 62Ni isotope. Method: The 26Mg(48Ca,2α4nγ)62Ni complex reaction at beam energies between 275 and 320 MeV was utilized. Reaction products were identified in mass (A) and charge (Z) with the fragment mass analyzer (FMA) and γ rays were detected with the Gammasphere array. Results: Two collective bands, built upon states of single-particle character, were identified and sizable deformation was assigned to both sequences based on the measured transitional quadrupole moments, herewith quantifying the deformation at high spin. Conclusions: Based on cranked Nilsson-Strutinsky calculations and comparisons with deformed bands in the A=60 mass region, the two rotational bands are understood as being associated with configurations involving multiple ƒ7/2 protons and g9/2 neutrons, driving the nucleus to sizable prolate deformation. [ABSTRACT FROM AUTHOR]

The decay of a Kπ=8- isomer in 244Pu and the collective band structures populating the isomer were studied using deep inelastic excitations with 47Ti and 208Pb beams, respectively. Precise measurements of M1/E2 branching ratios in the band confirm a 9/2-[734]ν⊗7/2+[624]ν configuration assignment for the isomer, validating the systematics of Kπ=8-, two-quasineutron isomers observed in even-Z, N=150 isotones. These isomers around the deformed shell gap at N=152 provide critical benchmarks for theoretical predictions of single-particle energies in this gateway region to superheavy nuclei. [ABSTRACT FROM AUTHOR]