Search

Motivated by the recent theoretical discovery [S.-M. Mullins et al., Nat. Commun. 9, 3352 (2018)] of a surprisingly contracted 60-atom hollow shell of chiral-icosahedral symmetry (I-Au

The accelerator mass spectrometer was commissioned recently at the iThemba LABS 6 MV tandem accelerator. Improvements in the vacuum system, requiring procurement of cryo-pumps and the reducing the tank pressure of the N2 + CO2 insulation gas mixture below the level used for IBA measurements, were necessary. This resulted in the reduction of the nitrogen background and improved the resolution of 14C from 14N background in the ionisation chamber. The nitrogen was leaking to the stripping canal because of inadequate sealing. The analysing magnet was scaled to detect C3+ ions, at 3 MV terminal potential. The first sensible spectra allowed for the pin-pointing of many persistent issues. This resulted in measurements with a precision better than 1 pMC, and current blank levels correspond to 12 half-lives of 14C or ∼68000 years. The radiocarbon sample preparation laboratory has reached production status. A brief outlook of the work towards the implementation of the measurement and chemical preparation protocols for radionuclides 10Be and 26Al is also summarised in the conclusion

CITATION: Lawrie, J. J., et al. 2019. Rotational structures in 196Hg. Physical Review C, 100(6):064321, doi:10.1103/PhysRevC.100.064321.

CITATION: Majola, S. N. T. et al. 2019. β and γ bands in N=88, 90, and 92 isotones investigated with a five-dimensional collective Hamiltonian based on covariant density functional theory: Vibrations, shape coexistence, and superdeformation. Physical Review C, 100(4). doi:10.1103/PhysRevC.100.044324.

International audience; In the last years we carried out several experiments aimed to investigate properties of short-lived SF isotopes. The neutron-deficient isotopes of nobelium were produced in fusion-evaporation reactions using 206,208Pb targets and an intense 48Ca-beam. Fusionevaporation residues were separated by the SHELS separator and implanted into a largearea double-sided 48×48 strip silicon detector surrounded by 3He-based neutron counters. Half-lives and decay branching ratios for 252,254No isotopes were measured. The average number of neutrons per spontaneous fission of 254No determined for the first time.

series of experiments performed in 2014–2015 using the SHELS separator and a beam of multicharged ions from the U-400 accelerator at the Flerov Laboratory of Nuclear Reactions (Joint Institute for Nuclear Research) in Dubna is described. In preparation for a large program of experiments with a beam of highly charged ions of 50Ti, an experiment is performed to study the spontaneous fissioning (SF) of short-lived neutron-deficient isotope 256Rf formed in complete fusion reaction50Ti + 208Pb = 256Rf + 2n. The half-life of 256Rf is measured along with the probability of its SF decay. The average number of neutrons per one event of 256Rf SF ( $$\bar v$$ = 4.47 ± 0.09) is obtained for the first time. The results from experiments to study the SF of short-lived neutron-deficient isotopes synthesized in complete fusion reaction 48Ca + 204Pb → 252No* are presented as well. Two short-lived activities attributed to the SF of the ground and isomeric states of 250No are revealed. The half-life, total kinetic energies of fission fragments, and neutron multiplicities are measured for the obtained short-lived nuclei. The average numbers of neutrons per one SF event are $$\bar v$$ = 4.38 ± 0.13 and $$\bar v$$ = 3.90 ± 0.20, respectively, for SF activity with t1/2 = 5.1 ± 0.3 and t1/2 = 36 ± 3 μs.

The problem of studying the spontaneous fission of nuclei from the exotic region of short-lived neutron-deficient isotopes with Z ≥ 100 is considered. A combined detecting system is created in the focal plane of the VASSILISSA separator. The main part of this system is a neutron detector that allows us to measure the yields of spontaneous fission neutrons from nuclei produced in a total fusion reaction with heavy ion beams in the on-line mode. This procedure is used for the first time to acquire data on the emission of spontaneous fission neutrons from short-lived 244,246Fm isotopes. Data gathered earlier for 252No isotopes are refined in the scope of this work.

This study describes an experiment on investigating the properties of spontaneous fission of shortlived neutron-deficient nuclei synthesized in the reaction of complete fusion 48Ca + 204Pb = 252No*. The experiment is performed using the SHELS separator and the beam of multicharged ions at U-400 accelerator (LNR, JINR). Two activities undergoing spontaneous fission, which can be related to the ground and isomeric states of 250No nucleus, are registered. The half-lives, total kinetic energies of fission fragments, and neutron multiplicities are measured for the short-lived nuclei. The average number of neutrons per fission for the activity with t 1/2 = 5.1 ± 0.3 μs is = 4.38 ± 0.13 μs, and for nuclei with the half-life t 1/2 = 36 ± 3 μs it is xxxxx.

High spin states in 195Hg, populated using the 150Nd(48 Ca,3n) reaction, were investigated by γ-ray spectroscopic techniques. Two backbendings are observed in the yrast band considered to be caused by the alignment of a pair of i13/2 and p3/2 neutrons respectively. The strong backbending behaviour observed in the negative parity side band is consistent with the alignment of a pair of i13/2 neutrons. The similarity with the corresponding backbendings in the neighbouring isotopes is impressive.

A pair of rotational bands associated with the pi h(9/2) circle times nu i(13/2)(-1) configuration at lower spins and with the pi h(9/2) circle times nu i(13/2)(-3) configuration at higher spins is found in Tl-194. The two 4-quasiparticle bands show exceptionally close near-degeneracy in the excitation energies. Furthermore close similarity is also found in their alignments and B(M1)/B(E2) reduced transition probability ratios. Such close near-degeneracy probably indicates chiral geometry in the angular momentum space. (c) 2013 Elsevier B.V. All rights reserved.

International audience; Spontaneous fission properties of the short-lived neutron-deficient 256Rf nucleus produced in thecomplete fusion reaction with a beam of multiply charged heavy 50Ti ions from the U-400 cyclotron (FLNR,JINR) are experimentally investigated. Its half-life and decay branching ratio are measured. The averagenumber of neutrons per spontaneous fission of 256Rf ( = 4.47 ± 0.09) is determined for the first time.

Two pairs of positive-and negative-parity doublet bands together with eight strong electric dipole transitions linking their yrast positive- and negative-parity bands have been identified in ^{78}Br. They are interpreted as multiple chiral doublet bands with octupole correlations, which is supported by the microscopic multidimensionally-constrained covariant density functional theory and triaxial particle rotor model calculations. This observation reports the first example of chiral geometry in octupole soft nuclei.

A complete kinematics measurement was performed using the 6 Li (3 He ,t) charge exchange reaction to populate 6 Be at Elab = 50 MeV . Decay mode of the ground and first excited states were studied through the analysis of the energy and angular distributions of the break-up particles in the 6 Be center of mass frame. Two-body decay is observed above the first excited state but not firmly assigned to a 6 Be resonant state. Experimental challenges regarding the identification of true 6 Be events in the excitation energy region 5 < Ex < 20 MeV are discussed.

We have used the AFRODITE γ-ray spectrometer to measure yrare structures in 152,154,155Gd using (α,xn) reactions. The measurements on 152,154Gd have shown that there is no convincing evidence that the lowest excited 0 2 + states are β-vibrations based on the 0 1 + ground state. Rather these levels may be regarded as a “second vacuum” each with its own γ and octupole vibrations. This is confirmed by the blocking of the coupling of this core 0 2 + state in 154Gd to the [ 505 ] 11 / 2 − single-particle quasi-neutron orbital in 155Gd. The coupling of this orbital to the 2 + γ-vibration is observed since this coupling is not Pauli-blocked.

The low-lying, odd-spin negative parity bands in the mass 160 region have been identified as candidates for the rotation of a tetrahedral shape, as they have very weak in-band E2 transitions. We report the observation of such bands in 160 Yb and 154 Gd. They are crossed by 2 quasiparticle bands which allow band mixing calculations to be carried out to derive relative quadrupole moments. However, those studied are not consistent with zero, as required for tetrahedral shape. The aligned angular momenta of the bands suggest an octupole vibrational assignment.

A semi-thick target has been used to measure the stopping power for recoils, produced in heavy ion induced reactions, by γ-ray lineshape analysis. The target thickness has been chosen such that the recoils are partially slowed down in the target and subsequently escape into vacuum. For transitions deexciting long-lived states the Doppler lineshape then depends only on the stopping power. Stopping-power parameters have been determined for Pm, Sm and Nd nuclei in Cd. The results for the electronic stopping power agree within uncertainties with the predictions of the Lindhard, Scharff and Schiott theory. The nuclear stopping power can be well described in the framework of the Ziegler, Biersack and Littmark parameterization using the software package Stopping and Range of Ions in Matter (SRIM)2006.

The spectroscopy of $^{76}\mathrm{Se}$ has been studied using the $^{70}\mathrm{Zn}(^{12}\mathrm{C}, \ensuremath{\alpha}2{\mathrm{n})}^{76}\mathrm{Se}$ fusion evaporation reaction. The yrast band of $^{76}\mathrm{Se}$ has been extended to substantially higher spin, allowing observation of the second band crossing. The much-delayed ${g}_{9/2}$ proton-pair alignment is discussed in terms of the cranked shell model and most likely is caused by a shape transition from prolate to oblate along the yrast line occurring in $^{76}\mathrm{Se}$. Based on the systematic investigation of the band crossings associated with the ${g}_{9/2}$ quasiparticle alignments and their relationships with the shape evolutions in the even-$A$ Se and Kr isotopes, a comprehensive picture of shape evolution along with spin and isospin in these nuclei is obtained.

Excited states in 175Yb, 176Yb and 177Yb were populated via the bombardment of a 176Yb target with a 750 MeV 136Xe beam. Gamma-ray decays from these states were measured with the AFRODITE multi-detector spectrometer. The rotational band previously assigned to the ground state of 177Yb has been reassigned to the first-excited state of 175Yb. A new rotational band based on the ground state of 177Yb is presented, and the band based on the Kπ = 4- two-quasiparticle state in 176Yb has been identified. Also a candidate for the rotational band based on the Kπ = 8-, T1/2 = 11.4(3) s two-quasiparticle state in 176Yb has been found. Comparisons of gK values derived from in-band branching ratios are consistent with the ν9/2+[624] assignment to the ground state of 177Yb, the ν2{9/2+[624] ⊗ 1/2-[510]} assignment to the Kπ = 4- state and with the ν2{9/2+[624] ⊗ 7/2-[514]} assignment to the Kπ = 8- metastable excited state in 176Yb.

High-spin states in 197Bi were studied with the AFRODITE γ-ray array at iThemba LABS using the 181Ta( 22Ne, 6n) reaction at a beam energy of 125 MeV. A new shears band was found and linked to the low-lying states in 197Bi. Its dynamic moment of inertia, \( \Im^{{(2)}}_{}\), is considerably larger than the \( \Im^{{(2)}}_{}\) of the shears bands in the neighbouring Pb isotopes. This is probably a result of the involvement of an additional high-Kh9/2 proton orbital.

The average g factors of high-spin states in 180,182,184 Pt were measured by the transient-field technique. In all three isotopes the quasicontinuum g factor at an angular momentum of ∼20ℏ is 〈 g 〉∼0.37. This contrasts with similar measurements on other nuclei that have 70⩽ Z ⩽80, where typical values of 〈 g 〉∼0.22 have been attributed to the influence of quasineutron alignments. Evidently proton and neutron configurations are about equally important at high spin in the Pt isotopes near mid-shell. This inference is consistent with the discrete spectroscopy, including the contention, supported by g K − g R values, that h 9/2 proton pairs align along with the i 13/2 neutrons at rotational frequencies of ℏ ω ≈0.3 MeV in 184 Pt. Links between the quasicontinuum g factors and features in the discrete spectroscopy are explored by comparing and contrasting the behavior of 184 Pt and 166 Hf.

The nuclear structure of the stable nucleus 184 76 Os has been studied including five newly identified rotational bands built on 2-quasiparticle K π =0 + , 6 − , 8 − couplings. The excitation energies of the proposed multi-quasiparticle excitations are in good agreement with predictions of blocked BCS calculations. The interaction responsible for the first band crossing, caused by a high- K tilted 2-neutron configuration, is calculated and a new interpretation presented for the yrast states after the interaction. A second crossing with an aligned s– β band is also reported. The yrast behaviour at high spins is dominated by a wealth of short-lived (nanoseconds and shorter) high- K levels. The low reduced hindrances for intrinsic state decays are discussed, and attributed to the triaxial shapes and fluctuations predicted by configuration-constrained potential-energy-surface calculations. Comparisons with neighbouring nuclei are made.

A brief survey of results of studies of nuclear chirality in the mass 80 and 190 region at iThemba LABS is given, before looking at the case of 106 Ag in detail. Here, the crossing of a pair of candidate chiral bands is re-interpreted as the crossing of a prolate band by an aligned four-quasiparticle band.

The high-spin states in 194Tl were studied using the 181Ta(18O, 5n) reaction and the AFRODITE $ \gamma$ -ray spectrometer at iThemba LABS. The level scheme of 194Tl was considerably extended with several new bands. Three negative-parity 4-quasiparticle bands were observed and associated with $ \pi h_{9/2}\otimes\nu i_{13/2}^{-3}$ configurations. Two of these form a candidate chiral pair with excellent near-degeneracy. In addition two new positive-parity bands were found.

The nature of the chiral candidate bands in $^{106}\mathrm{Ag}$, one of only two known examples of candidates which actually cross, is investigated experimentally and theoretically. Lifetimes have been determined for these bands in $^{106}\mathrm{Ag}$ using the Doppler-shift attenuation method with the $\ensuremath{\gamma}$-detector array AFRODITE. The level scheme of $^{106}\mathrm{Ag}$ has been extended, and three negative-parity bands have been observed to high spins. Configurations were assigned to the negative-parity bands based on a quasiparticle alignment analysis and on configuration-fixed constrained relativistic mean field calculations. The excitation energies, $B(M1)$ and $B(E2)$ values, as well as $B(M1)/B(E2)$ ratios have been compared with results of particle-rotor model calculations. From the investigations, it is concluded that the three close-lying negative-parity bands are a two-quasiparticle high-$K$ band and a pair of four-quasiparticle bands. The proposal that the two lowest-lying bands are chiral partners has not been confirmed.

The nucleus 134 La has been produced using the 124 Sn( 15 N, 5n) reaction. High-spin states have been observed to a maximum spin of 24 + using the CAESAR HPGe array. Bands have been observed that are suggested to be based on the πh 11/2 ⊗νh 11/2 , πh 11/2 ⊗νh 11/2 3 , πh 11/2 ⊗ νg 7/2 h 11/2 2 , and πg 7/2 ⊗νg 7/2 h 11/2 2 configurations. A band fragment, with features similar to the chiral band of 134 Pr, is proposed as the chiral partner of the πh 11/2 ⊗νh 11/2 band.

A study was made to determine whether the population of superdeformed states in 193Hg and 195Hg can be enhanced by using reactions in which alpha particles are emitted. The search utilized a 184W(18O,αXn) reaction at 115 and 120 MeV for the 193Hg study and a 186W(18O,αXn) reaction at 105 and 110 MeV for the 195Hg study. Two known superdeformed states of 193Hg were observed. The intensities of the superdeformed states in 193Hg populated by a reaction involving the emission of an alpha particle were found to be reduced by at least a factor of four relative to the intensities of these states produced in reactions involving only the emission of neutrons and γ-rays. No rotational bands built on superdeformed states in 195Hg with transition intensities >0.8% of the total 195Hg yield were found. Evidence is shown that the energy of the alpha particle that is associated with superdeformed states may be lower than that of alpha particles associated with normally deformed states.

High spin states in 198{Bi} were populated using a 184W(19F, 5n) reaction at 107 MeV. Three 198Bi γ-ray cascades resulting from a series of magnetic dipole transitions were observed. Measurements of the B(M1)/B(E2) ratio, angular correlation ratios and second moment of inertia are presented.

Lifetime measurements of states in nuclei with A=187 and 188 have been performed, using reactions between 155Gd and 36Ar and following the transport of evaporation residues to the focal plane of a gas-filled recoil separator. In a separate experiment using the 159Tb(32S, 4n) reaction the γ-decay of isomeric levels in 187Tl has been studied using delayed γ-γ coincidence measurements. From observation of their subsequent γ decay, the mean lifetimes were measured to be 1000 ± 55 ns and 1600 ± 100 ns. Although it was not possible to characterize the isomers completely, they are proposed as candidates for one-proton, two-neutron excitations. In the course of this study, the decay of an isomer in 188Pb was also observed and its lifetime was measured as 1150 ± 30 ns, and limits of 20–600 ns were placed on the meanlife of an isomer conjectured in 187Pb.

Gyromagnetic ratios were measured in the 1 2 + [411] ground-state band of 169 Tm by the transient field technique in such a manner that the extracted g -factors are independent of assumptions concerning the strength and velocity dependence of the transient field. Precise γ-ray branching intensities and multipolarity mixing ratios were determined from measured particle-γ-ray angular correlations. The electromagnetic properties of the low-lying natural parity states in 169 Tm are compared with particle-rotor calculations based on the Woods-Saxon potential and the implications of the measured magnetic moments for the calibration of the transient field strength are discussed.

We observe for the first time rotational bands of enhanced deformation (ED) in 127 Pr and 128 Pr, and suggest that these bands are built upon πg9/2 ( [404] 9 2 ) in 127 Pr and on the πg9/2νh11/2 orbitals in 128 Pr. These are the lightest isotopes of Pr for which ED bands have been observed. A contrasting trend in the dynamical moments of inertia ( J (2) ) versus N is observed at low frequencies for the “normal-deformed” πh11/2 and “enhanced-deformed” πg9/2 bands of 127 – 131 Pr both experimentally and in self-consistent Woods-Saxon calculations. The trends in J (2) and β2 are correlated with a decreasing probability for pair scattering into the deformation-driving νh9/2/f7/2 ( [541] 1 2 ) orbital.

Results are presented of a systematic survey of {Delta}I=4 bifurcation in 19 superdeformed bands in A{approximately}150 Eu and Gd nuclei. The majority of bands show no sign of this regular oscillation in energy levels. The statistical significance of the few examples that exhibit the effect is examined. {copyright} {ital 1998} {ital The American Physical Society}

Excited states in Ta-180 have been identified using the Yb-176(B-11,alpha 3n)Ta-180 and Yb-176(Li-7,3n)Ta-180 reactions and associated time-correlated gamma-ray spectroscopy, including particle-gamma coincidences for channel selection. As well as identifying the rotational band based on the 9(-) two-quasiparticle state at 75 keV, at least eight other low-lying two-quasiparticle states and associated rotational bands have been established. Lifetimes in the few nanosecond region were isolated using gamma-gamma-time techniques. Most of the observed two-quasiparticle states and some of the band members can be identified with states known from particle transfer studies. The properties of the observed Omega(n)+/-Omega(p) partners of 1(+) and 8(+) bands from the nu 9/2(+)[624]circle times pi 7/2(+)[404] configuration and the 0(-) and 9(-) pair from the nu 9/2(+)[624]circle times pi 9/2(-)[514] configuration are discussed. High-K structures identified include the band based on the four-quasiparticle 45 mu s, 15(-) isomer, a 32 ns, four-quasiparticle 18((+)) isomer, and a six-quasiparticle 19((-)) intrinsic state and its band. Configuration assignments are aided by analysis of the in-band decay properties, which confirm, for example, a predominantly nu pi(3) configuration for the 15- isomer. The results are compared with multiquasiparticle calculations. A number of yrast high-K six- and eight-quasiparticle states which could be accessible in future studies are predicted.

Excited states in Ta-181 have been identified using time-correlated gamma-ray spectroscopy and particle-gamma techniques following the incomplete fusion reaction Yb-176(B-11,alpha 2n) Ta-181. As well as observing the rotational band based on the 11 ns isomer at 482 keV from the 5/2(+)[402] proton configuration, which is found to be essentially identical to that associated with its 7/2(+)[404] pseudospin partner, several multi-quasiparticle isomers are observed including a 33 mu s state, of probable spin and parity 21/2(-), at 1483 keV. Experimental states are compared with multi-quasiparticle calculations.

The stable nucleus ${}^{177}$Hf was studied with time-correlated particle-$\ensuremath{\gamma}$-$\ensuremath{\gamma}$ techniques following the reaction ${}^{176}\mathrm{Yb}{(}^{9}\mathrm{Be},\ensuremath{\alpha}{4n)}^{177}$Hf at a beam energy of 70 MeV. New high-spin states include extensions to three-quasiparticle bands based on the ${K}^{\ensuremath{\pi}}{=23/2}^{+}$ and ${25/2}^{\ensuremath{-}}$ configurations, together with a new band associated with the ${K}^{\ensuremath{\pi}}{=19/2}^{\ensuremath{-}}$, ${T}_{1/2}=56$ \ensuremath{\mu}s isomer. Moreover, the band based on the five-quasiparticle ${T}_{1/2}$=51 minute, ${K}^{\ensuremath{\pi}}{=37/2}^{\ensuremath{-}}$ state has been found, and a band assigned to a new ${K}^{\ensuremath{\pi}}{=39/2}^{+}$, five-quasiparticle state. Values of ${(g}_{K}\ensuremath{-}{g}_{R}{)/Q}_{0}$ agree well with the configuration assignments made to new and previously known bands. Comparison with multiquasiparticle calculations that incorporate a Lipkin-Nogami treatment of pairing correlations with blocking, suggests that all of the most favored three- and five-quasiparticle states have been observed. The dependence of the $\ensuremath{\gamma}$-ray intensities on the angular yields of the $\ensuremath{\alpha}$ particles suggests that the population arises from two entry distributions: one associated with complete fusion of the beam with the target, the other with incomplete fusion.

Eight superdeformed bands have been observed in the nuclei {sup 147,148}Eu. Some of these are identical to bands in the Z+1 nuclei {sup 148,149}Gd, and are interpreted as having the same single-particle configurations with the exception of a hole in one of the [301]1/2 proton orbitals. Some of the bands in {sup 147}Eu exhibit either upbends or downbends in their moments of inertia which are related to the crossing of {pi}6{sup 1} and {pi}6{sup 3} proton intruder configurations. These results constitute the first evidence of this crossing. {copyright} {ital 1998} {ital The American Physical Society}

The odd-proton nuclei 127Pr and 131Pm have been investigated using the 96Ru(35Cl,2p2n) and 96Ru(40Ca,αp)/96Ru(39K,2p2n) reactions, respectively, at beam energies of 164, 180, and 186 MeV. States belonging to the yrast bands of 127Pr and 131Pm, which are interpreted as being based upon the h11/2 [541]3/2- proton configuration, have been observed from the 11/2- band head to spin 47/2-. The properties of these two new structures are observed to be different to those of similar configurations in the heavier odd mass isotopes. The systematics of the band crossings in the πh11/2 bands of the odd mass Pr and Pm isotopes are discussed and compared with extended total Routhian surface calculations.

The high-spin structure of ${}^{111}$In has been investigated with $\ensuremath{\gamma}$-ray spectroscopic methods using the ${}^{96}$Zr${(}^{19}$F,4$n)$ reaction with thin and backed targets. A comprehensive level scheme has been constructed which exhibits interesting collective as well as novel single-particle excitations. Unambiguous evidence of proton particle-hole excitations is found for the first time in a $Zl$50 nucleus in the form of decoupled bands involving proton ${g}_{7/2}{(d}_{5/2})$ and ${h}_{11/2}$ orbitals above the $Z$=50 spherical shell gap. The high-spin structure of ${}^{111}$In also involves the recently discovered magnetic rotation mechanism which is manifest as high-spin $\ensuremath{\Delta}I$=1 bands with no signature splitting and large $B(M1)$ strengths, but only a small associated deformation.

The nuclear structures of 165Ho and 167Er have been investigated by means of Coulomb excitation. These nuclei excited at moderate spins exhibit γ-vibrational bands with K π = 11 2 − , 3 2 − in 165Ho and K π = 11 2 + in 167Er. The γ-vibrational bands in 165Ho are found to be isospectral; heaving very nearly identical in-band γ-ray energies. Gamma-ray branching ratios are analysed to extract information on collectivity and Coriolis mixing. Experimental results are compared with calculations performed with the Cranked Shell Moedl + RPA + particle-vibration coupling and by invoking the generalized intensity relations (GIR) in the unified model scheme. Although this model explains many features of the data, puzzling aspects such as identical transition energies for the bands in 165Ho remain unexplained. The role of the K quantum number in identical bands is discussed.

Particle- coincidence studies have been a promising but not well exploited means of using incomplete fusion reactions to gain access to states in heavy nuclei near stability. At beam energies near the Coulomb barrier, fusion of the heavy fragment from break-up of the projectile with emission of non-equilibrated particles or other charged particles can be used to study relatively neutron-rich nuclei which cannot be reached by fusion, evaporation reactions with stable beams. Qualitative features which make the reactions attractive as a spectroscopic tool include a spin input which is higher than that achievable if fusion reactions were carried out with beams equivalent to the massive fragment and a correlation between the angle of emission of the light fragment and the number of evaporated neutrons which assists channel identification.

{Delta}I=4 bifurcation has been observed in two superdeformed bands, the newly discovered yrast superdeformed band of {sup 148}Eu, and a previously known excited band in {sup 148}Gd. Both of these bands have moments of inertia that are identical to the yrast band of {sup 149}Gd, the first superdeformed band in which this bifurcation was observed. This first observation of {Delta}I=4 bifurcation in identical superdeformed bands provides a crucial test of recent models. {copyright} {ital 1997} {ital The American Physical Society}

High-spin states in the nucleus {sup 116}Te have been studied with the reaction {sup 64}Ni({sup 56}Fe,2p2n) at 236 MeV using an early implementation of the Gammasphere array. Three rotational bands extending to spins I{approximately}(25{minus}42){h_bar} and excitation energies E{sub ex}{approximately}(11{minus}24) MeV have been identified and connected to known low-lying states. In the most extended band, a gradual decrease in the dynamic moment of inertia J{sup (2)} with increasing rotational frequency has been observed and interpreted as evidence for smooth band termination. Several energetically favored states based on aligned single-particle configurations also have been found to coexist with weakly deformed collective structures at low spins. {copyright} {ital 1997} {ital The American Physical Society}

Three superdeformed bands have been observed in the nucleus ${}^{144}$Eu with the GAMMASPHERE spectrometer in its early implementation phase. The reaction used was ${}^{122}$Sn${(}^{27}$Al,5${n)}^{144}$Eu at a beam energy of 142 MeV. All three bands are identified as single-neutron excitations with respect to ${}^{143}$Eu. One band is a confirmation of a previously suggested candidate. It is assigned as the yrast sequence based on the $\ensuremath{\pi}{6}^{1}\ensuremath{\nu}{7}^{1}$ configuration, and is believed to undergo an interaction with the $\ensuremath{\nu}$[514]9/2${}^{\ensuremath{-}}$ orbital. The other two bands are assigned as signature partners based on the $\ensuremath{\pi}{6}^{1}\ensuremath{\nu}{6\mathrm{\ifmmode \tilde{}\else \~{}\fi{}}}^{1}$ configuration, where $6\mathrm{\ifmmode \tilde{}\else \~{}\fi{}}$ corresponds to a mixed [651]1/2${}^{+}$/ [642]5/2${}^{+}$ state. The partner that contains the $\ensuremath{\alpha}$=-1/2 signature component of the $6\mathrm{\ifmmode \tilde{}\else \~{}\fi{}}$ orbital is identified from a band crossing that occurs in related bands in ${}^{145}$Gd and ${}^{146}$Gd. Alignment plots suggest that the interaction strength becomes stronger as the mass number increases.

High-spin states in 178Hf have been identified using particle-γ-γ-time techniques and the incomplete fusion reaction, 176Yb(9Be,α3n)178Hf. The rotational band associated with the four-quasiparticle T 1 2 = 31 year, Kπ = 16+ isomer in 178Hf has been established. The gK−gR values obtained from the in-band decay properties confirm the configuration of the isomer as does its alignment which matches the sum of the alignments of the two Kπ = 8− two-quasiparticle bands that contain the components of the 16+ configuration. New information has also been obtained on the four-quasiparticle 14− band and on the two-quasiparticle 6+ and 8− bands.

For experiments aimed at the study of spontaneous fission of transfermium nuclei improvements in the focal plane detector system of recoil separator VASSILISSA have been made. A neutron detector consisting of 54 3He-filled counters has been mounted around the focal-plane detector chamber. The reaction 48Ca + 206Pb = 2n + 252No is used for tuning the separator settings and calibrating the detector system with the spontaneous fission of the 252No. The average neutron number per 252No spontaneous fission event is as large as ν̅ = 4.06 ± 0.12. The short-lived heavy isotopes 244,246Fm, produced in the complete fusion reactions 40Ar + 206,208Pb, are investigated. The average number of neutrons per spontaneous fission of 244,246Fm from the experimental data were (ν̅ = 3.3 ± 0.3) and (ν̅ = 3.55 ± 0.50), respectively. Both values are determined for the first time.