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A new interpretation for the two new rotational bands in the 102Nb nucleus is presented. These two bands in 102Nb are proposed to be semi-decoupled bands where the odd proton with Ωp = ½ is coupled to the rotation axis and odd neutron with Ωn≠½ is strongly coupled to the deformation axis of the 100Zr deformed core. The likely orbitals are π½[431] and ν3/2[532].

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}

The phenomenon of cold (neutronless) binary and ternary fission in spontaneous fission of252 Cf was experimentally observed by triple gamma coincidence technique with Gammasphere with 72 gamma-ray detectors. Many correlated pairs for both binary and ternary (4He,10Be) fission were observed in the spontaneous fission of252 Cf. Yields of cold ternary and cold binary fission were extracted. These results are compared with the theoretical calculations using M3Y nucleon-nucleon potential and WKB approximation for barrier penetration.

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}

From an experiment with Gammasphere and a 252 C spontaneous fission source, two bands with signatures -i and +i are identified in 153 Nd Also several new transitions in 149 Nd are observed for the first time. The band with signature -i in 153 Nd shows no back bending, similar to the one observed in 161 Er . The signature splitting observed in the ground band of 153 Nd is similar to the ones observed in N=93 isotones in this mass region. In 149 Nd the new transitions are placed into a band with a proposed configuration of [Formula: see text].

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.}

New insights into the fission process and the structure of neutron-rich nuclei have been gained by measuring γ-γ and γ-γ-γ coincidences of the prompt γ-rays following the spontaneous fission of 252Cf. The data were taken with the Compton Suppression Spectrometer System at HHIRF. New high spin levels were observed in 143,145,147Ba Only in 143Ba are intertwined bands observed with the characteristics of the octupole structure found only in 144Ba. New high spin states observed in the N = 84 136 Te, 138 Xe, 140 Ba nuclei exhibit a symmetry pattern suggestive of a pseudospin f - shell . For the first time in fission, the relative yields and neutron multiplicities were measured directly. Yields and multiplicities were measured directly for the ZrCe and MoBa correlated fragment pairs by observing the coincidences between the γ-rays in each fragment. Zero-neutron to ten-neutron emission yields were determined; the latter for the first time. The zero-neutron emission can be understood as a new example of cluster radioactivity. These results demonstrate that the use of the high resolution γ-γ-γ coincidence technique employed here for the first time opens up a new approach to the study of the fission process that will provide previously inaccessible details of the process.

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.

New, high spin band structures are established for the neutron-rich nuclei 142,143,145,147Ba, and 144Ce, and levels of 144,146Ba extended to higher spins from the study of γ-γ and γ-γ-γ coincidence studies in spontaneous fission. Alternating parity sequences connected by strong electric dipole transitions are identified in 142,143Ba and 144Ce but not in 145,147Ba to confirm theoretical predictions of stable octupole deformation for N = 86.

It is shown that in the crossing of two bands withK≠0 in deformed nuclei, two new effects are observed that are not seen in the crossing ofK=0 bands; namely, a)Icritical at which the bands cross is lowered and b) Band crossing occurs at different values ofIcrit for oddI (orI+1/2 in oddA) and evenI (orI+1/2). These predictions are shown to be observed in the odd-A rare-earth nuclei where data are available to high spin.

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.

A new region of stable octupole deformation was predicted to occur with its center around the reinforcing shell gaps for β3∼0.15 at Z=56, N=88, and with 56145Ba89 was predicted to be a prime candidate for stable octupole deformation. Evidence for stable octupole deformation was found in 144Ba, 146Ce and expanded to include odd-A 143Ba and other neighboring isotopes but was not observed in 145Ba. Recently we found evidence for the rotational enhancement of stable octupole deformation in 145,147La. In a reinvestigation of 145Ba, two new bands were discovered that are connected by enhanced, intertwined E1 transitions to two different previously known bands in 145Ba. These new data support the predicted presence of octupole deformation in 145Ba, which is rotation-enhanced above about spin 19/2. In both 145La and 145Ba, the low spin ground bands are built on a symmetric rotor shape and at intermediate spins there are shifts to the yrast bands having asymmetric octupole shape. These are the first examples of th...

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}

Evidence for stable octupole deformation in neutron-rich nuclei bounded by Z=54–58 and N=85–92 is described. More vibrational type octupole modes are observed to either side of this region in 140Ba and 152,154Nd. The largest stable octupole deformation (β3∼0.1) is reported in 144Bagg. The theoretically predicted quenching (β3→0) of stable octupole deformation with increased rotation is observed in 146Ba. There is good agreement between theory and experiment for the strongly varying electric dipole moments as a function of mass for 142–148Ba. In odd-A 143Ba and odd-Z, 145La, two pairs of positive and negative parity bands with opposite spins, parity doublets are observed. In 145La the ground band with symmetric shape coexists with the asymmetric octupole shape which stabilizes above about spin 19/2+. The isotope 109Mo was identified and a new region of stable octupole deformation is identified in 107,109Mo centered around N=64–66 as earlier predicted. This is the first case of stable octupole deformation i...

Level energies of negative parity yrast bands (NPB) have been studied with a recently proposed, sensitive method. The irregular behaviour of the NPB's in theN=88 nuclei around spin 9–11 and the smooth behaviour in156Dy (up toI=13) and in238U (up to I=19) support calculations by Vogel, where NPB's are described as aligned octupole bands up to a critical spin where intersection with two-quasiparticle bands takes place. Considering the NPB levels (I≦13) in156Dy as members of an aligned octupole band, we obtain a remarkably good reproduction of their decay properties and energies using the VMI model.

The energies of the yrast levels extending up to I = 28 in even-even actinide nuclei were analyzed in terms of an angular velocity expansion E rot ( I ) = ∑ i =1 n α i ω I 2 i with n = 2−7 to test the application of this expansion to high spin. A strong ω 2 -dependence is observed for the Variable Moment of Inertia model (VMI) with two parameters α i ( ω 2 ), particularly at the higher spins. There is a marked difference in the ω 2 -dependence, of these parameters between the N = 142 and other nuclei studied in this region to indicate structure effects are present at the higher spin.

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.

Rotational bands with K π = 1 + in the odd-odd nuclei 100,102 39 Y and 102,104 41 Nb are postulated from β − decay of t heir even-even parents. Each two-quasiparticle band has a moment of inertia very close to that of a rigid spheroidal nucleus with deformation β ∼ 0.3, hence these bands are nearly “pairing free”.

Rotational side-bands in 162Dy have been studied using the 160Gd(α, 2nγ)162Dy reaction. Seven side-bands are observed, with Kπ = 2+, 2−, (0)−, 0+, 5−, 4+ and (6−). Four of these bands have collective structure at low spin: the Kπ = 2+ γ-vibrational band, the Kπ = 0+ β-vibrational band, and the Kπ = 2− and (0)− octupole vibrational bands. Of the remaining bands, the 4+ band is deformation coupled while the 5− and (6−) bands are rotation-aligned. Several bandcrossings are observed in this nucleus. The β and γ-bands are crossed at I = 6 h and 12 h , respectively, by a highly aligned ( i 13 2 )2 S-band; extrapolation of this S-band to higher spin suggests that it crosses the g.s.b. between I = 18 h and 20 h . The 2− octupole band is crossed by the 5− band at I = 9 h and again by the (6−) band at I = 12 h . The latter bandcrossings are discussed in terms of two-quasiparticle plus rotor calculations.

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 -/.

The backbending or irregularities of band spacings of states near the yrast line were fit using simple rotational energy expressions which include band mixing of the yrast and yrare states. In our model the sharp backbending requires two large mixing terms, a spin-independent term arising from the pairing interaction and a Coriolis coupling term. Least-squares fitting of backbenders in the deformed even-even nuclei indicate a near cancellation of the mixing matrix elements near the virtual band crossing. Although the idealized and simplified expressions for the backbending spin in terms of the pairing gap Δ, high- j orbital spacing, high- j Coriolis matrix element J tT , and moment of inertia I may not be quantitatively correct, they do indicate the general conditions required for backbending.

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.

The expansions Erot(I)= Sigma i=1n1Ai(I(I+1))i and Erot(I)= Sigma i=1n2 alpha i omega I2i that describe the energies of the levels in the ground-state rotational bands with Kpi =0+ are generally not equivalent unless n1=n2=1 or infinity . A method is proposed to characterise this non-equivalency quantitatively. It was found that in some nuclei, like 248Cm and 176Er, the I(I+1) expansion is better than the omega 2 expansion, whereas in the majority of nuclei the omega 2 expansion is better. The data demonstrate that the rates of convergence of the I(I+1) and omega 2 expansions for Erot depend on the individual properties of the nuclei.

Ground-state potential energy surfaces for 176,178,180Pt have been calculated by using the Woods-Saxon single-particle potential and the Strutinsky renormalisation procedure. These potential energy surfaces predict a ground-state shape change from a large prolate deformation for 178,180Pt ( beta 2 approximately=0.24) to a smaller triaxial deformation for 176Pt with a second minimum developing at large prolate deformation ( beta approximately=0.23) above the 4+ state. There is excellent agreement between these independent calculations and recent measurements of the yrast bands in 176,178Pt.

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.

Simultaneous analysis of the effective moment of inertia as a function of (h(cross) omega )2 and of i( omega )=INPB( omega )-IGRB( omega ) indicates that the yrast negative-parity band (NPB) in 232Th experiences an unexpected band crossing between Ipi =9- and 13-. These spins are significantly lower than those predicted before at I=21-25. In the NPB of 236,238U such band crossing is not observed at these low spins.

Systematic examinations of the angular momentum generated by particle alignment were made for Dy and Er isotopes. Marked deviations are observed from the aligned spin values expected for full alignment of i 13 2 ( odd A) and ( i 13 2 ) 2 ( even A) particles. Suggested origins of these differences are presented.

The possible manifestations of an oblate-shape region at high spin in A = 160--180 nuclei are considered. We focus attention on the fact that rotational band phenomena indeed can exist in nuclei with oblate shapes. From estimates of transition energies, the yrast cascade there could consist largely of low-energy, alternating M1 transitions within bands and E2 transitions between bands. If the recently found stretched-dipole transitions are confirmed as M1, these results may be an indication for the existence of oblate shapes at high spin.

Analysis of the anomalous behaviour of the gamma band in156Dy demonstrates the interference of the effect of ‘internal’ Coriolis coupling and quadrupole (ΔK=2) coupling.

It is shown that in the crossing of two bands withK≠0 in deformed nuclei, two new effects are observed that are not seen in the crossing ofK=0 bands; namely, a)Icritical at which the bands cross is lowered and b) Band crossing occurs at different values ofIcrit for oddI (orI+1/2 in oddA) and evenI (orI+1/2). These predictions are shown to be observed in the odd-A rare-earth nuclei where data are available to high spin.

Superbands, responsible for the backbending in156Dy and other N=90 and N=88 nuclei, are proposed to be alignedn(i13/2)2 bands, whereas it is argued that the recently discovered positive parity band in156Dy withIπ= (2+) up to 10+ members does not constitute the low spin extension of the superband.

An approximate I(I+1) behaviour of the yrast level energies in transitional nuclei corresponding to rotation along the axis of symmetry is expected when angular momentum is generated by aligning that of the individual nucleons along the symmetry axis. From an analysis of the yrast energies for states with I=14 to 37 in 152Dy, an I(I+1) behaviour was reported (T.L. Khoo et al. 1978) and interpreted as the first experimental demonstration of rotation along the axis of symmetry. The present authors show that such a significance for the experimental data is not possible.

Analysis of level energies in aligned octupole bands in even-even deformed nuclei using the VMI-model expressed in terms of the rotational angular momentumR, show that almost complete alignment is reached at low spin values. It is shown that the alignment is almost spin independant. Using the ground-state band VMI-parameters only a renormalization of the alignment parameter 〈J⊥〉 is enough to reproduce the level energies of the NPB's.