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Several new high-spin states are observed in the prompt $\ensuremath{\gamma}$-rays emitted from the neutron-rich, odd-$Z$ ${}^{145,147}\mathrm{La}$ fragments produced in the spontaneous fission of ${}^{252}\mathrm{Cf}.$ Alternating parity bands are extended up to spins 41/2 and 43/2 in ${}^{145,147}\mathrm{La},$ respectively. A new band completes the evidence for two sets of parity doublets expected for octupole correlations. Eight $B(E1)/B(E2)$ ratios (four new) between two bands in ${}^{145}\mathrm{La}$ are all essentially constant and somewhat larger than similar ratios in ${}^{143,144}\mathrm{Ba},$ where stable octupole deformation and/or correlations are reported. The new ratios out of the ${31/2}^{\ensuremath{-}}$ levels in both nuclei show a sharp spike compared to other states, presumably from a strong reduction in $E2$ strengths in this backbending region. In ${}^{145}\mathrm{La},$ collective bands show competition and coexistence between symmetric and asymmetric shapes. Band crossings occur in both nuclei around $\ensuremath{\Elzxh}\ensuremath{\omega}\ensuremath{\approx}0.26--0.30 \mathrm{MeV}.$ Their backbends are associated with the alignment of two ${i}_{13/2}$ neutrons according to cranked shell model calculations.

Several $\ensuremath{\gamma}$ transitions in ${}^{101--103}\mathrm{Nb},{ }^{98,100}\mathrm{Y},{ }^{146}\mathrm{La},$ and ${}^{149}\mathrm{Pr}$ are identified from spontaneous fission studies employing a ${}^{252}\mathrm{Cf}$ source and the Gammasphere detector array. In particular, the pairing-free bands in ${}^{100}\mathrm{Y}$ and ${}^{102}\mathrm{Nb}$ are extended, two rather highly deformed negative-parity bands feeding the 4.3-s $\ensuremath{\beta}$-decaying isomer of ${}^{102}\mathrm{Nb}$ are identified, and their possible bandhead configurations are discussed. In the case of ${}^{101,103}\mathrm{Nb},$ we have extended previously reported level schemes by over 20 transitions in each nuclide. For the fission partners ${}^{146}\mathrm{La}$ and ${}^{149}\mathrm{Pr}$ we have elucidated their previously unreported yrast level schemes.

The phenomenon of cold (neutronless) alpha ternary fission in spontaneous fission of {sup 252}Cf was experimentally observed by triple gamma coincidence technique with Gammasphere with 72 gamma-ray detectors. Correlated pairs of {sub 36}Kr-{sub 60}Nd, {sub 38}Sr-{sub 58}Ce, {sub 40}Zr-{sub 56}Ba, {sub 42}Mo-{sub 54}Xe, {sub 44}Ru-{sub 52}Te, and {sub 46}Pd-{sub 50}Sn were observed to be associated with {alpha} ternary fission of {sup 252}Cf. Yields of cold {alpha} ternary fission were extracted. {copyright} {ital 1998} {ital The American Physical Society}

Ten new transitions in {sup 107}Mo have been observed and levels in {sup 109}Mo are identified for the first time in a {gamma}-{gamma}-{gamma} coincidence study from the spontaneous fission of {sup 252}Cf with 72 Compton suppressed Ge detectors in Gammasphere. Two sets of bands, each set intertwined by E1 transitions are observed in {sup 107}Mo and one such set in {sup 109}Mo. The observed level schemes are interpreted in terms of possible octupole deformation originating from the strong interaction of the h{sub 11/2} and d{sub 5/2} neutron shells. {copyright} {ital 1997} {ital The American Physical Society}

The {gamma} transitions in {sup 147}Ba, {sup 149}Ce, and {sup 151,153}Nd have been identified from {gamma}-{gamma}-{gamma}, {gamma}-{gamma}, {ital x}-{gamma}, and {ital x}-{gamma}-{gamma} coincidence studies of spontaneous fission of {sup 252}Cf. The yrast positive parity band in {sup 149}Ce is assigned to an {ital i}{sub 13/2}, neutron favored signature. The yrast negative parity band in {sup 149}Ce is assigned a {ital h}{sub 9/2} proton favored signature. The positive parity band in {sup 151}Nd corresponds to the positive parity band in {sup 149}Ce. The negative parity band in {sup 153}Nd corresponds to the negative parity bands of {sup 149}Ce and {sup 161}Er. The band observed in {sup 147}Ba is built on the {ital h}{sub 9/2} orbital. The plots for {ital J}{sub 1} in these isotopes are remarkably similar, supporting our assignments. {copyright} {ital 1996 The American Physical Society.}

The levels in{sup 108,110,112}Ru have been investigated in the spontaneous fission of {sup 252}Cf using {gamma}-{gamma}-{gamma}-, {gamma}-{gamma}-, x-x-, x-{gamma}-, and x-{gamma}-{gamma}-coincidence techniques. The levels up to 16{sup +} and 9{sup +} in the yrast bands and {gamma}-vibrational bands have been identified with very little energy staggering in {sup 108,110,112}Ru. The ground bands in {sup 108,110}Ru have identical {gamma}-ray transition energies up to 8{sup +}. These are the lightest observed even-even nuclei with extended identical ground bands. Calculations in a collective model which includes rotations and vibrations reproduce the level energies and {gamma} band branching ratios above the 3{sup +} state rather well, while rigid triaxial rotor model calculations reproduce the branching ratios for the 2{sup +} and 3{sup +} states.

From an experiment with Gammasphere and a ${}^{252}\mathrm{Cf}$ spontaneous fission source, a new negative-parity band in ${}^{154}\mathrm{Nd}$ and new negative-parity levels in ${}^{152}\mathrm{Nd}$ were identified and the yrast bands were extended to ${18}^{+}$ in ${}^{154}\mathrm{Nd}$ and ${20}^{+}$ in ${}^{152}\mathrm{Nd}$ in a triple gamma coincidence study. These new negative-parity bands are consistent with octupole vibrational mode. There is a constant difference as a function of spin between the ${J}_{1}$ values for the negative-parity band in ${}^{152}\mathrm{Nd}$ and ${J}_{1}$ for the similar negative-parity band in ${}^{154}\mathrm{Nd},$ however, their ${J}_{2}$ values are essentially identical. These bands indicate a new kind of identical band.

Neutron-rich {sup 147,149,151}Pr nuclei, produced in the spontaneous fission of {sup 252}Cf, were studied using the Gammasphere array. Possible parity doublets in {sup 147}Pr with N=88 and {pi}h{sub 11/2} bands in {sup 149,151}Pr are proposed. These new data on the level structures of odd Pr isotopes suggest that octupole correlations may also be present in the neutron-rich {sub 59}{sup 147}Pr{sub 88} nucleus such as those observed in {sub 58}{sup 146}Ce{sub 88}, and also that the h{sub 11/2} bands in the {sup 149,151}Pr track in energy the yrast bands in {sup 148,150}Ce. The backbending related to the breaking of the neutron i{sub 13/2} pair is observed at {Dirac_h}{omega}{approx}0.27 (MeV) for the proton h{sub 11/2} band of {sup 149}Pr.

High spin states in neutron-rich odd-{ital Z} {sup 143,145}Ba nuclei have been investigated from the study of prompt {gamma} rays in the spontaneous fission of {sup 252}Cf by using {gamma}-{gamma}- and {gamma}-{gamma}-{gamma}- coincidence techniques. Alternating parity bands are identified for the first time in {sup 145}Ba and extended in {sup 143}Ba. A new side band, with equal, constant dynamic, and kinetic moments of inertia equal to the rigid body value, as found in superdeformed bands, is discovered in {sup 145}Ba. Enhanced E1 transitions between the negative- and positive-parity bands in these nuclei give evidence for strong octupole deformation in {sup 143}Ba and in {sup 145}Ba. These collective bands show competition and coexistence between symmetric and asymmetric shapes in {sup 145}Ba. Evidence is found for crossing M1 and E1 transitions between the s=+i and s={minus}i doublets in {sup 143}Ba. {copyright} {ital 1999} {ital The American Physical Society}

Low- and high-spin states of /sup 68/Ge are investigated through in-beam ..gamma..-ray spectroscopy via the /sup 58/Ni(/sup 12/C,2p), /sup 63/Cu(/sup 7/Li,2n), and /sup 52/Cr(/sup 19/F,p2n) reactions. A surprising richness of collective bands is observed in /sup 68/Ge including three even parity bands built on 8/sup +/ levels, the lower two of which are assigned as rotational aligned bands built on both proton and neutron (g/sub 9/2/)/sup 2/ configurations, and three odd parity bands built on ..pi.. and ..nu.. configurations that include the g/sub 9/2/ orbit. Details of the multiple bands and other levels observed in /sup 68/Ge are presented. Rotation-aligned model calculations and interacting boson model calculations for /sup 68/Ge are also described.

A new radioactivity of Np was discovered by chemical separations from targets of /sup 244/Pu and /sup 242/Pu irradiated with 30--160 MeV neutrons. Five ..gamma.. rays were identified with E/sub ..gamma../, I/sub ..gamma../: 159.1 keV, 32; 265.1 keV, 24; 785.7 keV, (100); 944.8 keV, 63; and 1104 keV, 0.6. The half-life is 5.5 +- 0.1 min and various cross bombardments established that the mass number is 242. I/sup r/ was assigned 6/sup +/ with the configuration 5/2/sup +/(642)/sub p/, 7/2/sup +/(624)/sub n/ and a decay scheme is proposed.

Sources of /sup 235/Th and /sup 235/Pa were prepared by medium energy neutron and proton irradiations of uranium followed by radiochemical separations. Gamma-ray spectroscopy showed 13 new ..gamma.. rays in the decay of /sup 235/Th. Its half-life is 7.3 +- 0.1 min, and that of /sup 235/Pa is 24.6 +- 0.2 min. A partial decay scheme is proposed for /sup 235/Th, and a large anomalous retardation is reported in one branch of the /sup 235/Pa ..beta../sup -/ decay.

The interactions between a K/sup ..pi../ = 5/sup -/ aligned two-quasineutron band and two octupole bands have been observed in /sup 164/Er. Band crossings occur in both even- and odd-spin sequences. The members of all three bands are observed from the bandheads (L/sup ..pi../ = 1/sup -/, 2/sup -/, and 5/sup -/) to about 12/sup -/.

Decay schemes, based on $\ensuremath{\gamma}$-ray and $\ensuremath{\beta}$-ray spectroscopy, are proposed for 93-min $^{230}\mathrm{Ra}$ and 122-sec $^{230}\mathrm{Ac}$. Of 48 observed $\ensuremath{\gamma}$ transitions following decay of $^{230}\mathrm{Ra}$, 39 are accommodated among 19 levels in $^{230}\mathrm{Ac}$. For decay of the $^{230}\mathrm{Ac}$, 135 $\ensuremath{\gamma}$ transitions were observed and 98 are accounted for among 46 levels (22 known previously) in $^{230}\mathrm{Th}$. The ground state of $_{89}^{230}\mathrm{Ac}_{141}$ is assigned ${I}^{\ensuremath{\pi}}={K}^{\ensuremath{\pi}}={1}^{+}$. A number of levels are discussed in terms of Nilsson orbital assignments. ${Q}_{{\ensuremath{\beta}}^{\ensuremath{-}}}\ensuremath{\approx}0.71$ MeV for $^{230}\mathrm{Ra}$ and ${Q}_{{\ensuremath{\beta}}^{\ensuremath{-}}}=2.70$ MeV for $^{230}\mathrm{Ac}$.RADIOACTIVITY $^{230}\mathrm{Ra}$, $^{230}\mathrm{Ac}$ from $^{232}\mathrm{Th}$($n$,$2pn$)$^{230}\mathrm{Ra}\stackrel{{\ensuremath{\beta}}^{\ensuremath{-}}}{\ensuremath{\rightarrow}}^{230}\mathrm{Ac}$; radiochemistry, Ge(Li) and plastic detectors. Measured ${T}_{\frac{1}{2}}$, ${E}_{\ensuremath{\gamma}}$, ${I}_{\ensuremath{\gamma}}$, ${I}_{{\ensuremath{\beta}}^{\ensuremath{-}}}$; deduced ${I}_{{\ensuremath{\beta}}^{\ensuremath{-}}}$, $log\mathrm{ft}$, decay schemes, $J$, $\ensuremath{\pi}$, Nilsson assignments.

Evidences for the existence of triaxial shapes in the ground states of even-even nuclei are considered. Most if not all previous reports that support the existence are not definite. The observed decreasing of the energies of the ${2}_{1}^{+}$ and ${4}_{1}^{+}$ states for $^{198,200}\mathrm{Hg}$ compared to the lighter Hg nuclei is opposite to the expected when $N$ increases and deformation decreases. We show that a triaxial model with a phase transition between $N=116 \mathrm{and} 118$ qualitatively can explain the regularities in $B(E2)$ ratios and ${E}_{I}$ for the collective levels with ${I}^{\ensuremath{\pi}}={2}_{1}^{+}, {4}_{1}^{+}, {6}^{+}, \mathrm{and} {2}_{2}^{+}$ in $^{192\ensuremath{-}200}\mathrm{Hg}$.NUCLEAR STRUCTURE Analysis of levels in $^{192\ensuremath{-}200}\mathrm{Hg}$ in triaxial rotor model.

From an analysis of the experimental data, we assign I/sup ..pi../ = 3/sup -/ (and I = 4/sup +/) levels in even /sub 86/Rn nuclei. These levels, together with known levels with I/sup ..pi../ = 1/sup -/ in /sub 86/Rn and negative parity levels K/sup ..pi../ = 0/sup -/; I = 1/sup -/, 3/sup -/, and 5/sup -/ in /sub 88/Rn, /sub 90/Th, and /sub 92/U, demonstrate features of strong Coriolis coupling. The existence of strong Coriolis coupling effects is typical only for rotational bands based on one-phonon octupole vibrational states which include particles with large j ( j/sub 15/2/, i/sub 13/2/, etc.), but not for bands based on states K/sup ..pi../ = 0/sup -/; I = 1/sup -/ with stable octupole deformation.

Analysis of aligned angular momenta i/sub ..cap alpha../(..omega..) in different rotational bands extracted from experimental data with a linear spin term approx.BI in the formulas for E/sub rot/(I) reveal that, in actinide nuclei in the levels with modest spin I< or =23, i/sub ..cap alpha../(..omega..) usually is very small (< or approx. =0.7), i.e., is much smaller than in rare earth nuclei.

The $\ensuremath{\gamma}$-ray spectrum of 14.1-h $^{240}\mathrm{U}$ was obtained almost free of interference by the much more intense $\ensuremath{\gamma}$ radiation from its $^{240}\mathrm{Np}^{m}$ daughter by means of continuous radiochemical separations. Thus 16 new transitions (49.1-299.8 keV) were revealed in addition to the single one at 44.1 keV previously identified, and a tentative decay scheme for $^{240}\mathrm{U}$ is proposed. A detailed study of separated $^{240}\mathrm{Np}^{m}$ showed $70\ensuremath{\gamma}$ transitions whose ${E}_{\ensuremath{\gamma}}$ and ${I}_{\ensuremath{\gamma}}$ values agree well with previous data, and in addition 29 new transitions were found. The absolute intensity of the 554.6-keV $\ensuremath{\gamma}$-ray transition is (20.6\ifmmode\pm\else\textpm\fi{}0.5)%, the $^{240}\mathrm{Np}^{m}$ half-life is 7.22\ifmmode\pm\else\textpm\fi{}0.02 min, and the fraction decaying by isomeric transition is (0.12\ifmmode\pm\else\textpm\fi{}0.01)%. A decay scheme of $^{240}\mathrm{Np}^{m}$ is proposed which shows several new levels in $^{240}\mathrm{Pu}$ and some changes in previous ${I}^{\ensuremath{\pi}}$ and ${K}^{\ensuremath{\pi}}$ assignments. The isomeric state is assigned ${I}^{\ensuremath{\pi}}={1}^{(+)}$, ${K}^{\ensuremath{\pi}}={0}^{(+)}$ with the probable configuration ${\frac{7}{2}}^{+}{[633]}_{p}$, ${\frac{7}{2}}^{+}{[624]}_{n}$.RADIOACTIVITY $^{240}\mathrm{U}$, $^{240}\mathrm{Np}^{m}$ from $^{244}\mathrm{Pu}\stackrel{\ensuremath{\alpha}}{\ensuremath{\rightarrow}}^{240}\mathrm{U}\stackrel{{\ensuremath{\beta}}^{\ensuremath{-}}}{\ensuremath{\rightarrow}}^{240}\mathrm{Np}^{m}$; radiochemistry, Ge(Li) and $4\ensuremath{\pi}$ gas proportional detectors. Measured ${T}_{\frac{1}{2}}$, ${E}_{\ensuremath{\gamma}}$, ${I}_{\ensuremath{\gamma}}$; deduced ${I}_{\ensuremath{\beta}}$, $log\mathrm{ft}$, decay schemes, $I$, $\ensuremath{\pi}$, Nilsson assignments.

Decay of /sup 241/Np (T/sub 1/2/ = 13.9 +- 0.2 min) was studied by ..gamma..-ray spectroscopy. The Np sources, prepared by the /sup 238/U(..cap alpha..,p) and /sup 244//sup( /n,p3n) reactions, were chemically separated and purified. Eleven ..gamma.. rays, mostly new, were observed between 42.0 and 929.7 keV, and their intensities per disintegration were determined. A decay scheme for /sup 241/Np is proposed which helps to elucidate the level structure of /sup 241//sup ./ Comparison with nuclear reaction data is used to identify a 5/2/sup -/ octupole vibrational state and to characterize some of the other levels.

The decays of $^{236}\mathrm{Th}$ and its $^{236}\mathrm{Pa}$ daughter were studied by $\ensuremath{\gamma}$-ray spectroscopy. By means of radiochemical methods and a continuous separation technique pure sources of parent and daughter were prepared so that each was free (or almost free) of the other. For $^{236}\mathrm{Th}$, 14 of the 17 observed $\ensuremath{\gamma}$ rays are new; for $^{236}\mathrm{Pa}$ 16 new $\ensuremath{\gamma}$ rays were found. Absolute intensities of all the $\ensuremath{\gamma}$ rays were determined with the aid of $4\ensuremath{\pi}$ beta measurements on $^{236}\mathrm{Pa}$. A new decay scheme is proposed for $^{236}\mathrm{Th}$ and a considerably expanded one is given for $^{236}\mathrm{Pa}$. The half-lives determined are 37.5\ifmmode\pm\else\textpm\fi{}0.2 min for $^{236}\mathrm{Th}$ and 9.1\ifmmode\pm\else\textpm\fi{}0.1 min for $^{236}\mathrm{Pa}$.

A nuclear spectroscopic study of the high-spin ground state of /sup 240/Np (I/sup ..pi../ = 5/sup +/) showed substantial differences from earlier work. The sources, prepared by the /sup 238/U(..cap alpha..,pn) and /sup 244/Pu(n,p4n) reactions, were chemically separated and purified. A total of 34 ..gamma.. rays (139.9--1167.1 keV) were observed of which 13 are new; nine others which were reported previously are not confirmed. Absolute intensities of the ..gamma.. rays were determined with the aid of 4..pi.. beta measurements. A modified decay scheme is proposed and discussed; six levels in /sup 240/Pu with I/sup ..pi../ = 1/sup -/, 2/sup -/, 3/sup -/,..., 6/sup -/ are assigned to a K/sup ..pi../ = 1/sup -/ octupole vibrational band. The half-life measured with high purity sources is 61.9 +- 0.2 min.