A six-quasiparticle isomer with $K^{\pi }={21}^{-}$, a half-life of 290(12) ms, and the ${\pi }^3{\nu }^3$ configuration has been identified in the odd-odd nucleus ${}_{}{}^{178}{}_{}{}^{}\mathrm{Ta}$, at an excitation energy of 2902 keV. The rotational bands built on the known $K^{\pi }={15}^{-}$ isomer and on the newly found ${16}^{+}$ four-quasiparticle and ${22}^{+}$ six-quasiparticle states, have also been identified, allowing characterization of the configurations. The ${15}^{-}$ band is predominantly of $\pi {\nu }^3$ character with a ${\pi }^3\nu$ admixture. When the mixing is taken into account the excitation energies of the main yrast multi-quasiparticle states can be reproduced. The multi-quasiparticle states observed are related essentially through the addition of the two-quasiparticle component ${\nu }^2\left[6^{+}\right]$ or ${\pi }^2\left[6^{+}\right]$. Depending on whether the transition between the states involves the change ${\nu }^2\left[6^{+}\right]\to \mathrm{}\left[0\right]\mathrm{}$ or ${\pi }^2\left[6^{+}\right]\to \mathrm{}\left[0\right]\mathrm{}$, the $E2\mathrm{}$ hindrance factors for decays between the six- and four-quasiparticle states are relatively large or small. This dependence mimics the pattern observed in the two-quasiparticle core transitions and, because the ${15}^{-}$ isomer is mainly $\pi {\nu }^3$, the magnitude sequence is inverted compared to that observed in ${}_{}{}^{176}{}_{}{}^{}\mathrm{Ta}$.

A model of an expanding hot nuclear matter is discussed. A Fokker-Planck equation is used to describe the conversion of the gaseous phase into the liquid phase. It is shown that the apparent exponent ${\tau }_{\mathrm{eff}}$ entering the power-law fit to charge fragment distribution $\sigma \mathrm{}\left(Z\right)\mathrm{}\propto Z^{-{\tau }_{\mathrm{eff}}}$ differs considerably from the critical exponent $\tau$. If the nuclear matter is strongly supercooled, ${\tau }_{\mathrm{eff}}$ should be small both for small and for large systems. This fact may serve as a possible explanation of the low values of ${\tau }_{\mathrm{eff}}$, obtained recently at Michigan State University.

We studied the magnetic dipole moments $\mu$ of even-odd C isotopes, ranging from proton-rich to neutron-rich nuclei, with antisymmetrized molecular dynamics (AMD). The results are in good agreement with the experimental data. In the ${}_{}{}^9{}_{}{}^{}\mathrm{C}$ ground state the total intrinsic spin of the protons is found to be nonzero ($S_p\ne 0$), which is unusual in even-odd nuclei. The interesting point is that the spin-orbit force breaks slightly the coupling off of intrinsic spins of the even nucleon group in isospin $T=\frac{3}{2}$ nuclei. This result is consistent with the newly measured $\mu$ data that, when combined with ${}_{}{}^9{}_{}{}^{}\mathrm{Li}$ data, indicate an unusual $〈\sigma 〉$ value larger than unity. A $\mu$ moment $-1.05\mathrm{}{\mu }_N$ of ${}_{}{}^{17}{}_{}{}^{}\mathrm{C}$ is theoretically predicted. We also show a good reproduction of $E2\mathrm{}$ transition data.

We modify the method of Albergo et al. for determining the temperature of an excited nucleus from double ratios of isotope yields and present a statistical model which accounts for the population and decay of excited states of the emitted fragments. Nuclear temperatures are extracted using experimental ratios of isotopic yields of fragments from helium through carbon for the reactions ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$ + ${}_{}{}^{58}{}_{}{}^{}\mathrm{Ni}$, ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ar}$ + ${}_{}{}^{58}{}_{}{}^{}\mathrm{Ni}$, ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$ + ${}_{}{}^{58}{}_{}{}^{}\mathrm{Fe}$, and ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ar}$ + ${}_{}{}^{58}{}_{}{}^{}\mathrm{Fe}$ at 33 MeV/nucleon projectile energy. Using the model we obtain consistent values for the temperature from various isotope combinations within the experimental error when accounting for the population and decay of the excited fragments.

High-spin states in ${}_{}{}^{86}{}_{}{}^{}\mathrm{Mo}$ were studied by means of the fusion evaporation reaction ${}_{}{}^{58}{}_{}{}^{}\mathrm{Ni}$${(}^{32}$S,2p2n${)}^{86}$Mo at 135 MeV beam energy. Charged-particle-γγ and -γγγ coincidences recorded with the early implementation of the GAMMASPHERE array and the MICROBALL charged-particle detection system were used to largely extend the level scheme of the ${\mathit{T}}_{\mathit{z}}$=1 nucleus ${}_{}{}^{86}{}_{}{}^{}\mathrm{Mo}$ to a possible spin of I=24ħ at 13 MeV excitation energy. The excitation scheme is compared to neighboring nuclei. There is evidence for enhanced shell-model influence in the 4 quasiparticle region (I=12–16 ħ). The observed (π=+,α=0) sequence at spin I≥16ħ appears to be associated with a triaxial collective rotational band. This interpretation is supported by calculations within the configuration-dependent shell-correction approach with the cranked Nilsson potential. © 1996 The American Physical Society.

The ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$${(}^7$Li,${\mathrm{}}^7$Beγ) reaction at E${(}^7$Li)/A = 70 MeV has been used to investigate isovector giant resonances and to measure the ratio of ΔS=1 to ΔS=0 spin strength in ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$ at high excitation energy. In the singles spectrum, the analogue of the giant dipole resonance is observed. Another resonance is observed at ${\mathit{E}}_{\mathit{x}}$≊15 MeV in the residual nucleus, which we suggest is a collective $2^{\mathrm{-}}$ state. The isovector spin transfer strength at high excitation for the calcium target is compared to that measured with a carbon target under the same experimental conditions. Although more spin transfer strength at high excitation is observed for the calcium target than for the carbon target, this only accounts in part for an apparent discrepancy between previous ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$(p→,p${\to }^{\prime }$) and ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$${(}^7$Li,${\mathrm{}}^7$Be) experiments. The general utility of the ${(}^7$Li, ${}_{}{}^7{}_{}{}^{}\gamma$) reaction is discussed. © 1996 The American Physical Society.

The structure of the mirror nuclei ${}_{}{}^9{}_{}{}^{}\mathrm{Be}$ and ${}_{}{}^9{}_{}{}^{}\mathrm{B}$ is studied in a microscopic α+α+n and α+α+p three-cluster model using a fully antisymmetrized nine-nucleon wave function. The two-nucleon interaction includes central and spin-orbit components together with the Coulomb potential. The ground state of ${}_{}{}^9{}_{}{}^{}\mathrm{Be}$ is obtained accurately with the stochastic variational method, while several particle-unbound states of both ${}_{}{}^9{}_{}{}^{}\mathrm{Be}$ and ${}_{}{}^9{}_{}{}^{}\mathrm{B}$ are investigated with the complex scaling method. The calculation for ${}_{}{}^9{}_{}{}^{}\mathrm{Be}$ supports the recent identification for the existence of two broad states around 6.5 MeV, and predicts the 3/$2_2^{\mathrm{-}}$ and 5/$2_2^{\mathrm{-}}$ states at about 4.5 MeV and 8 MeV, respectively. The similarity of the calculated spectra of ${}_{}{}^9{}_{}{}^{}\mathrm{Be}$ and ${}_{}{}^9{}_{}{}^{}\mathrm{B}$ enables one to identify unknown spins and parities of the ${}_{}{}^9{}_{}{}^{}\mathrm{B}$ states. Available data on electromagnetic moments and elastic electron scatterings are reproduced very well. The enhancement of the E1 transition of the first excited state in ${}_{}{}^9{}_{}{}^{}\mathrm{Be}$ is well accounted for. The calculated density of ${}_{}{}^9{}_{}{}^{}\mathrm{Be}$ is found to reproduce the reaction cross section on a carbon target. The analysis of the beta decay of ${}_{}{}^9{}_{}{}^{}\mathrm{Li}$ to ${}_{}{}^9{}_{}{}^{}\mathrm{Be}$ clearly shows that the wave function of ${}_{}{}^9{}_{}{}^{}\mathrm{Be}$ must contain a small component that cannot be described by the simple α+α+n model. This small component can be well accounted for by extending a configuration space to include the distortion of the α particle to t+p and h+n partitions. © 1996 The American Physical Society.

We explore statistical correlations of collective nuclear excitations under a multiparameter deformation of the Hamiltonian, in the framework of the interacting boson model. The distribution of Hamiltonian matrix elements is found to behave as P(|${\mathit{H}}_{\mathit{ij}}$|)∝1/√|${\mathit{H}}_{\mathit{ij}}$|exp(-|${\mathit{H}}_{\mathit{ij}}$|/V), with a parametric correlation of the type ln〈H(x)H(y)〉∝-|x-y|. The studies are done in both the regular and chaotic regimes of the Hamiltonian. Model-independent predictions for a wide variety of correlation functions and distributions, which depend on wave functions and energies, are made from parametric random matrix theory and found to agree with the IBM results. Being a multiparameter theory, we consider general paths in parameter space and find that universality can be effected by the topology of the parameter space. Specifically, Berry’s phase can modify short distance correlations, breaking certain universal predictions. © 1996 The American Physical Society.

It is shown that the self-consistent angular-momentum cranking technique can be used to generate certain types of collective vibrational solutions of time-dependent mean-field equations. The method is suitable for systems having an equilibrium mean field with an axis of symmetry and is founded on a theorem (cranking bifurcation theorem) proposed in this paper, according to which cranking about an equilibrium axis of symmetry leads to new symmetry-breaking solutions that bifurcate from the axially symmetric solution at the critical cranking frequencies given by Ω=${\mathrm{\omega }}_{\mathrm{\mu }}$/${\mathit{K}}_{\mathrm{\mu }}$, where ${\mathrm{\omega }}_{\mathrm{\mu }}$ is a random-phase-approximation (RPA) frequency for any mode carrying ${\mathit{K}}_{\mathrm{\mu }}$≠0 units of angular momentum along the symmetry axis. The bifurcating solutions correspond to aligned multiphonon excitations including possible large-amplitude anharmonicities. A general heuristic proof of the method is provided, as well as a perturbative demonstration within the framework of the cranked Hartree-Fock (CHF) approximation, which includes a derivation of the RPA. The static CHF approach is then compared to a perturbative treatment of the time-dependent Hartree-Fock equations using the Lindstedt method. It is also shown that the cranking approach may be applied to phenomenological mean-field models to obtain anharmonic corrections to the vibrating potential model. Finally, the calculation of transition matrix elements is briefly discussed. © 1996 The American Physical Society.

A method for setting ${\mathrm{\epsilon }}_{\mathit{f}}$, one of the parameters in the interacting boson approximation-1 (IBA-1) with one f boson, by using the systematic behavior of the centroids of observed E3 strength is proposed and applied to obtaining fits for octupole bands in the deformed rare earth region. The ordering of bands with different K values, B(E3) strengths and B(E1) values are well reproduced. The calculations are in good agreement with the data in nearly all the K=0, 1, and 2 octupole bands examined here. The least satisfactory fits were obtained for the ${\mathit{K}}^{\mathrm{\pi }}$=$0^{\mathrm{-}}$ bands in ${}_{}{}^{160,162}{}_{}{}^{}\mathrm{Dy}$. It is predicted that in ${}_{}{}^{160,162,164}{}_{}{}^{}\mathrm{Dy}$, ${}_{}{}^{168}{}_{}{}^{}\mathrm{Er}$, and ${}_{}{}^{172}{}_{}{}^{}\mathrm{Yb}$ the K=3 octupole states based on the ground state and having significant E3 strength are above 6 MeV and are strongly fragmented. These results are quite different from predictions made previously. © 1996 The American Physical Society.

The γ vibrational states in odd-mass deformed nuclei are studied within the multiphonon method. Special attention is paid to low-energy multiphonon states in order to see if the anharmonicities observed in even-even nuclei, in which the first vibrational state ${\mathit{K}}^{\mathrm{\pi }}$=$2^{+}$ appears well below the energy gap, are also found in the odd-A neighboring nuclei. © 1996 The American Physical Society.

Angular and Q-value distributions for a large variety of charge and mass partitions populated in the reaction ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$ + ${}_{}{}^{124}{}_{}{}^{}\mathrm{Sn}$ have been measured at 170 MeV with a new time-of-flight magnetic spectrometer. Reaction channels involving the net transfer of up to six protons and six neutrons have been detected. Population patterns, cross sections, and energy-loss distributions are compared with results of theoretical calculations based on independent single-nucleon transfer modes. The overall agreement is good, but more complex mechanisms may be needed to account for the larger drift towards neutron stripping revealed by the experimental data. © 1996 The American Physical Society.

Coincidence γ-ray data from the spontaneous fission of ${}_{}{}^{242}{}_{}{}^{}\mathrm{Pu}$ were collected at the Lawrence Berkeley Laboratory high purity Ge (HPGe) array, GAMMASPHERE. Data from several cold-fission (0 neutron emission) isotopic pairs were observed and are presented. An interesting trend in the fractional population of cold-fission events was observed and is discussed. Relative yields of Zr-Xe, Sr-Ba, and Mo-Te pairs were measured. The Zr-Xe system has the most complete data set. Some speculations on the trend in the number of neutrons emitted as a function of the mass of the Xe isotope populated are presented. Comparisons between the yields from the spontaneous fission of ${}_{}{}^{242}{}_{}{}^{}\mathrm{Pu}$ and the yields from thermal-neutron-induced fission of ${}_{}{}^{241}{}_{}{}^{}\mathrm{Pu}$ are also presented. © 1996 The American Physical Society.

Differential and total cross sections for ${\mathrm{\pi }}^{+}$ absorption on ${}_{}{}^6{}_{}{}^{}\mathrm{Li}$, leading to the pp${+}^4$${\mathrm{He}}_{\mathrm{g}.\mathrm{s}.\mathrm{}}$, pp${+}^4$${\mathrm{He}}^{\mathrm{*}}$, and pp+X final states, are presented at incident pion energies of 100 and 165 MeV. We conclude that most of the cross section is confined to the level of coplanarity expected from quasideuteron absorption in the nuclear environment and that the contributions of nonquasideuteron absorption mechanisms are small. © 1996 The American Physical Society.

The ${}_{}{}^{103}{}_{}{}^{}\mathrm{Rh}$(n,${\mathit{n}}^{\prime }$${)}^{103}$${\mathrm{Rh}}^{\mathit{m}}$ cross section was measured by the activation method in the neutron energy range 5.7–12 MeV with an uncertainty of ≊5%. Monoenergetic neutrons produced by the D(d,n${)}^3$He reaction were used to irradiate metallic Rh samples at 0° relative to the deuteron beam. The K x rays from ${}_{}{}^{103}{}_{}{}^{}\mathrm{Rh}_{}^{\mathit{m}}{}_{}{}^{}$ were measured with a calibrated Si detector, and the neutron fluence was determined by means of a ${}_{}{}^{238}{}_{}{}^{}\mathrm{U}$ fission chamber. The measured cross sections resolve the discrepancies in previous data and agree with the results of recent statistical model calculations of the fast-neutron cross sections of rhodium. © 1996 The American Physical Society.

The fully energy-damped yields from the ${}_{}{}^{35}{}_{}{}^{}\mathrm{Cl}$${+}^{12}$C reaction have been systematically investigated using particle-particle coincidence techniques at a ${}_{}{}^{35}{}_{}{}^{}\mathrm{Cl}$ bombarding energy of ∼8 MeV/nucleon. The fragment-fragment correlation data show that the majority of events arises from a binary-decay process with rather large numbers of secondary light-charged particles emitted from the two excited exit fragments. No evidence is observed for ternary break-up events. The binary-process results of the present measurement, along with those of earlier, inclusive experimental data obtained at several lower bombarding energies are compared with predictions of two different kinds of statistical model calculations. These calculations are performed using the transition-state formalism and the extended Hauser-Feshbach method and are based on the available phase space at the saddle point and scission point of the compound nucleus, respectively. The methods give comparable predictions and are both in good agreement with the experimental results thus confirming the fusion-fission origin of the fully damped yields. The similarity of the predictions for the two models supports the claim that the scission point configuration is very close to that of the saddle point for the light ${}_{}{}^{47}{}_{}{}^{}\mathrm{V}$ compound system. The results also give further support for the specific mass-asymmetry-dependent fission barriers needed in the transition-state calculation. © 1996 The American Physical Society.

We report observations from the (p,n) reaction on ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ at 135 MeV. The experiment was performed with the beam-swinger neutron time-of-flight system at the Indiana University Cyclotron Facility. Neutrons were detected in large-volume plastic scintillation detectors located in three detector stations at 0°, 24°, and 45° with respect to the undeflected beam line; the flight paths were 91 m, 91 m, and 74 m, respectively. Overall time resolutions of about 825 ps provided energy resolutions of about 350 keV in the first two stations and about 425 keV in the third station. The angular distributions for states with excitation energies up to 10 MeV are presented and comparisons are made with DWIA calculations that use one-body density matrices from 0ħω and 1ħω shell-model calculations. New information is deduced on the excitation energies, widths, and spin-parity assignments for several energy levels of ${}_{}{}^{12}{}_{}{}^{}\mathrm{N}$. © 1996 The American Physical Society.

The relative yield of decay modes of a projectile remnant as a function of 〈${\mathit{Z}}_{\mathrm{bound}}$〉 has been analyzed from the ALADIN data of (600 MeV/nucleon) Au + Cu, and it is consistent with the corresponding theoretical results of the incomplete-fusion-fragmentation model. The experimental and theoretical results of the relative yield of decay modes and of the Campi plot and the theoretical results of the thermodynamical temperature plot show nicely the competition and transformation processes of the decay modes of the projectile remnant with the decreasing of 〈${\mathit{Z}}_{\mathrm{}\mathrm{bound}}$〉. © 1996 The American Physical Society.

The isotopic yields for the spontaneous cold fission of ${}_{}{}^{252}{}_{}{}^{}\mathrm{Cf}$ are predicted by using a double-folding potential and the M3Y nucleon-nucleon forces. The penetrabilities through this barrier are obtained within the one-dimensional WKB approximation. Realistic fragment ground-state deformations are used for the calculations. The results are in good agreement with zero neutron channel yields extracted from γ-γ-γ coincidence studies in the spontaneous fission of ${}_{}{}^{252}{}_{}{}^{}\mathrm{Cf}$ recorded with the early implementation Gammasphere. The double fine structure in such cold fragmentations has been experimentally observed for the first time. © 1996 The American Physical Society.

In order to study effects of clustering of colliding nuclei in the fragmentation process, the fragmentation of the ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}$${+}^{12}$C reaction at 35 MeV/nucleon is analyzed by antisymmetrized molecular dynamics. It is found that ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ fragments from ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ fragmentation are much more abundant than those from ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}$ fragmentation. Characters of ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ fragments from ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ fragmentation are investigated and it is found that this abundance in ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ fragmentation results from the three-alpha breakup in a short time scale where the excited states with excitation energy 7–15 MeV play an important role. © 1996 The American Physical Society.