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Minor changes in the assignments of gamma rays following the alpha decay of228Pa in two previous studies make possible a reinterpretation of224Ac into two alternative level schemes. The resulting level structures arise from the reflection asymmetric configurations π3/2±(0.0 −0.3)−ν3/2±(−0.1 0.6), π5/2±(0.0 −0.2)±ν3/2±(−0.1 0.6) and π5/2±(0.0 −0.2)±ν1/2±(0.2 −0.1 3) which give rise to eitherK=0± or 1±,K=4±,K=2± andK=3± parity doublet bands. The bands with appreciable band structure, namelyK=0± or 1± andK=3±, have average parity doublet splittings of 11.0 and 5.8 keV respectively. These are extremely small values and suggest that224Ac is the most octupole deformed nucleus studied thus far. A method of calculating the parity doublet splitting in odd-odd nuclei is suggested and tested for224Ac. It seems to work remarkably well. The systematics of the hindrance factors for the bands with extended band structures confirm their interpretations as band structures. Finally, the two alternative level schemes are analyzed in the framework of the axially-symmetric rigid rotor model including the Coriolis interaction.

Alpha recoil sources of221Rn were used to study the level structure of217Po and the ground state of213Pb. The half-life of217Po was measured to be (1.6±0.2) s. When combined with unpublished data, an alpha-decay hindrance factor (HF) of 1.3 was obtained for the alpha-decay, strongly suggesting a g9/2 → g9/2 transition between217Po and213Pb ground states. Alpha-gamma coincidence studies confirm the previously observed 11/2+ band head in217Po. It is suggested that an unobserved 9/2+ ground state lies below the 11/2+ state in217Po and an attempt is made to observe connecting links between these two parts of the217Po level scheme.

The level structures populated in alpha decay of all odd-Z-even-N nuclei withZ=(83–93) andN=(126–142) up to 500 keV are presented. More data on the 4n+3 nuclear sequences are given from215Bi to235Np. Particular emphasis is placed on the hindrance factors to alpha decay in interpreting the level structures in term of the shell model, the octupole-quadrupole model and the Nilsson model. The level structures and the hindrance factors go through transition region in which mixtures of the properties of two different nuclear models are appropriate. These transition regions represent a challenge to nuclear theorists to develop more all-encompassing nuclear models.

The interchange of two sets of spins in the level structure of219Ra observed following the alpha decay of223Th and the suggestion that the ground state of219Ra was not observed in the heavy ion reaction spectroscopy208Pb(14C, 3n), allow the correlation of these levels which were previously unconnected. The resulting level structure is interpreted in terms of $$K = \tfrac{1}{2}^ \pm $$ and $$K = \tfrac{5}{2}^ \pm $$ parity doublet bands which evolve from anomalous rotational structures into vibrational-like structures with alternating spins and parities. The level structure of219Ra is successfully interpreted both in terms of octupole deformed (e 3=0.08) Nilsson levels and in terms of intermediate coupling using normal Nilsson levels with very strong octupole correlations. The levels in219Ra are then compared to the corresponding levels in a series of isotopic and isotonic nuclei to trace the collapse of octupole-quadrupole deformed nuclear structure into the more degenerate shell-model spectroscopy.

The remarkable features of the spectra of the odd-A Fr isotopes from213Fr (with 126 neutrons) through225Fr (with 138 neutrons) serve as a sequence of examples for the application of a variety of nuclear models. As the shapes vary from spherical to spherical with strong octupole correlations to octupole-deformed, the corresponding symmetry breaking leads to increasingly complex spectra. Of considerable interest is the fact that the219Fr 9/2− ground state has the character of an h9/2 shell model state while still having the rotational properties appropriate as a legitimate member of a reflection asymmetric K=1/2− band. It is also possible to follow the expansion of the more degenerate shell model states into the less degenerate reflection asymmetric states. This results from dramatic decreasing in decoupling parameters with increasing mass number.

A total of 74 levels from 21 multiplets of the nuclei 206 Tl , 208 Tl , 208 Bi , and 210 Bi have been calculated with a Generalized Intermediate Coupling Model, with Gaussian and delta potentials with and without an interaction between octupole phonon and odd nucleons. The goodness of fit is compared with that of other calculations of Molinari et al. and Schiffer and True. It is quite clear that the calculations work well in spite of the fact that they are required to fit simultaneously odd-odd nuclei with neutron and proton shells which differ by principal harmonic oscillator quantum numbers Δ N = +1.

The quadrupole moments of three decoupled bands in the odd-odd nuclei {sup 130}Pr and {sup 132}Pr were measured using the Doppler shift attenuation method in the bombardment of {sup 105}Pd with {sup 35}Cl at 173 MeV. The {pi}h{sub 11/2}{circle_times}{nu}(f{sub 7/2},h{sub 9/2}) configuration was assigned to these structures on the basis of the observed in-band properties and relative deformations. New information is presented on the shape-driving behavior of the 1/2{sup {minus}}[541] (f{sub 7/2},h{sub 9/2}) intruder neutron orbital, whose involvement in a particular configuration leads to quadrupole deformation values which are intermediate between those known for normally deformed and so-called superdeformed bands in this mass region. {copyright} {ital 1999} {ital The American Physical Society}

Energies of the first 2+, 3− and 4+ states of even-even nuclei are plotted against proton and neutron number. Using this systematics, shell effects and the corresponding quadrupole and hexadecapole collectivity and deformation effects are compared and contrasted. Also, the correspondingB(E2),B(E3) andB(E4) values are plotted against neutron number and their very different systematics compared. Among the new results are the presence of hexadecapole collectivity at the 82 proton and neutron closed shells and the presence of the maximum values ofB(E4) at neutron numbers 10, 90–92 and 140–146. Finally, the systematics of the hexadecapole (K=4+) vibrations is compared with that of the quadrupole (K=2+) gamma vibrations in the quadrupole deformed rare earth region.

A comprehensive review of the present understanding, both theoretical and experimental, of intrinsic and rotational level structures in medium-heavy deformed odd-odd nuclei is presented. A discussion of the various experimental methods is presented, emphasizing the need for a variety of experimental approaches. The odd-odd nuclei that are immediately amenable to fruitful additional study are pointed out. A discussion of the intrinsic level structures, Gallagher-Moszkowski (GM) splittings, Newby (N) shifts, and role of the residual p-n interaction is presented. Currently available data in the rare-earth region allow the empirical determination of 137 GM splittings and 36 N shifts for 25 odd-odd nuclei in the mass region 152{le}A{le}188. A new parametrization of the residual p-n interaction is presented which also takes into account the 27 GM splittings and 12 N shifts from the actinide region. Newly discovered features of rotational bands, such as odd-even staggering, and other high-spin phenomena, such as signature inversion and delay in bandcrossing frequency, are discussed. The role of higher-order Coriolis coupling is pointed out. Systematics of the two-quasiparticle excitations, shape coexistence, isomers, and four-quasiparticle states are presented. Calculated results of the two-quasiparticle intrinsic excitations using two methods, the intrinsic level spacings for odd-{ital A} neighboring nuclei andmore » the quasiparticle-plus-phonon coupling model, are compared with experiment. {copyright} {ital 1998} {ital The American Physical Society}« less

High-spin states of {sup 157}Tb were populated via the reactions {sup 154}Sm({sup 7}Li,4n) at 35 MeV and {sup 150}Nd({sup 11}B,4n) at 55 MeV. Previously known bands have been extended and one new structure has been identified. The rotational alignment behavior of the bands and band crossing systematics have been analyzed. Experimental B(M1)/B(E2) ratios for the strongly coupled bands have been extracted and compared with theoretical predictions. New results were also obtained for the N=92 isotone {sup 155}Eu. The [411]3/2 and [413]5/2 pseudo-spin partner bands were observed in both nuclei. Experimental B(E1)/B(E2) ratios have been determined in both {sup 155}Eu and {sup 157}Tb. However, the estimated large B(E1) strengths can be explained without static octupole deformation. The [411]3/2 bands in {sup 155}Eu and {sup 157}Tb have been found identical up to spin I=(23)/(2), which might be explained by changes in deformation. {copyright} {ital 1998} {ital The American Physical Society}

The level structure of {sup 219}Rn has been studied using the alpha decay of {sup 223}Ra and coincident gamma rays. While only modest changes are required in the level structure, and only above 342.8 keV, severe changes are required throughout the level scheme in the spin assigments. These changes allow the assignment of two sets of anomalous bands with K=5/2{sup {plus_minus}} and K=3/2{sup {plus_minus}}. The K=5/2{sup {plus_minus}} bands have configurations intermediate between the reflection asymmetric configuration and the g{sub 9/2} shell model configuration, while the K=3/2{sup {plus_minus}} bands have configurations intermediate between the mixed reflection asymmetric configuration and the i{sub 11/2} shell model configuration. Comparison of the systematics of {sup 219}Rn with neighboring isotones, isobars, and isotopes shows clearly the collapse of the quadrupole-octupole-type configurations into the less degenerate shell model configurations. {copyright} {ital 1998} {ital The American Physical Society}

Two strongly coupled bands with large dynamic moment of inertia values have been observed for the first time in the neutron-deficient odd-odd nucleus ${}^{130}$Pr using Gammasphere and the Microball charged-particle detector array. These bands involve the important ${g}_{9/2}$[404]9/2 proton orbital. This new information on ${}^{130}$Pr coupled with Projected Shell Model calculations provide valuable insight on rotational alignment processes taking place in this mass region, the size of the $N$=72 deformed shell gap, and the position of the ${i}_{13/2}$[660]1/2 neutron intruder orbital at the boundary of the $A$=135 superdeformed region.

The well known experimental levels of {sup 208}Bi have been calculated with a generalized intermediate coupling model with Gaussian potential with and without an octupole phonon interaction parameter. The neutron-proton interaction parameters are taken from those obtained in the calculation of 34 experimental levels in {sup 210}Bi. The goodness of fit of the calculated energies to the energies of the 36 experimentally assigned states in {sup 208}Bi is quite remarkable in spite of the fact that the neutron-proton interaction parameters have been transferred from fitting in {sup 210}Bi, a neutron shell away. Finally, the calculated levels of {sup 208}Bi are compared with those calculated by a delta force. {copyright} {ital 1997} {ital The American Physical Society}

Second minimum structures have been observed for the first time in the doubly odd nucleus ${}_{59}^{132}$Pr. Two new bands are interpreted as based on the $\ensuremath{\pi}{g}_{9/2}[404]9/2\ensuremath{\bigotimes}\ensuremath{\nu}{i}_{13/2}[660]1/2$ configuration and a third as the $\ensuremath{\pi}{h}_{11/2}[532]5/2\ensuremath{\bigotimes}\ensuremath{\nu}{i}_{13/2}[660]1/2$ configuration. Signature splitting effects observed in the $\ensuremath{\pi}{(g}_{9/2}{)}^{\ensuremath{-}1}$ bands provide new information regarding the positive parity proton orbitals at large deformation. Results from the extracted $B(M1)/B(E2)$ ratios are consistent with a large deformation for the $\ensuremath{\pi}{(g}_{9/2}{)}^{\ensuremath{-}1}$ bands.

Sources of ${}^{220}$Ac in secular equilibrium with ${}^{221}$Pa were produced using the reaction ${}^{209}$Bi${(}^{18}$O,$3n)$${}^{224}$Pa. The alpha decay of ${}^{220}$Ac and coincident gamma and electron spectra were used to study the level structure of ${}^{216}$Fr. The levels in ${}^{216}$Fr can be interpreted in terms of the $\ensuremath{\pi}{(h}_{9/2})$${}_{9/2}^{5}\ensuremath{\nu}{(g}_{9/2})$${}_{9/2}^{3},$ $\ensuremath{\pi}{(h}_{9/2})$${}_{0}^{4}{(f}_{7/2}{)}_{7/2}\ensuremath{\nu}{(g}_{9/2})$${}_{9/2}^{3},$ and $\ensuremath{\pi}{(h}_{9/2}{)}_{9/2}^{5}\ensuremath{\nu}{(g}_{9/2}{)}_{0}^{2}{(i}_{11/2}{)}_{11/2}$ shell model configurations. The alpha decay hindrance factors of the ground state to ground state transitions in the sequence ${}^{224}\mathrm{Pa}{\ensuremath{\rightarrow}}^{220}\mathrm{Ac}{\ensuremath{\rightarrow}}^{216}\mathrm{Fr}{\ensuremath{\rightarrow}}^{212}$At suggest the collapse of quadrupole-octupole Nilsson orbitals into the more degenerate shell model orbitals. The sequence of hindrance factors in this odd chain are mirrored in the corresponding odd proton and odd neutron sequences beginning with ${}^{223}$Pa and ${}^{223}$Th, respectively.

A total of 34 experimental levels of {sup 210}Bi have been fitted with a generalized intermediate coupling model involving a n-p interaction with a Gaussian radial dependence with and without coupling to an octupole phonon. {chi}{sup 2} values are somewhat lower with the octupole parameter. Comparison of {chi}{sup 2} values with those obtained by fitting the same 34 experimental levels using the delta force radial dependence indicate the Gaussian radial dependence is 8{endash}10 times lower. The n-p interaction parameters are then used to calculate other {sup 210}Bi levels. {copyright} {ital 1997} {ital The American Physical Society}

The alpha and coincident gamma decays of $^{216}\mathrm{Fr}$ and $^{212}\mathrm{At}$ in secular equilibrium with 0.8 s $^{224}\mathrm{Pa}$ and 26.1 ms $^{220}\mathrm{Ac}$ have been studied with emphasis on the level scheme of $^{212}\mathrm{At}$. The level structure has been interpreted in terms of the shell model configurations \ensuremath{\pi}(${\mathit{h}}_{9/2}$${)}_{9/2}^{3}$\ensuremath{\nu}(${\mathit{g}}_{9/2}$), \ensuremath{\pi}(${\mathit{h}}_{9/2}$${)}_{0+}^{2}$(${\mathit{f}}_{7/2}$)\ensuremath{\nu}(${\mathit{g}}_{9/2}$), and \ensuremath{\pi}(${\mathit{h}}_{9/2}$${)}_{9/2}^{3}$\ensuremath{\nu}(${\mathit{i}}_{11/2}$). These configurations are then compared with the calculated configurations in $^{212}\mathrm{At}$ and with the corresponding experimental configurations in $^{210}\mathrm{Bi}$ and $^{212}\mathrm{Bi}$. In all three cases plots of the experimental energies vs the spin show the expected inverted parabola shape, but as we move farther away from the $^{208}\mathrm{Pb}$ closed shells, the inverted parabolas become more compressed. \textcopyright{} 1996 The American Physical Society.

High-spin states have been studied in neutron-deficient {sup 132}Nd, produced in the {sup 105}Pd({sup 35}Cl,{alpha}{ital p}3{ital n}{gamma}) reaction, using the Gammasphere {gamma}-ray spectrometer in conjunction with the Microball charged-particle detector array. Three new, weakly populated rotational bands have been found, which are believed to be associated with a superdeformed (second minimum) prolate shape. Comparison of the properties of these bands with Woods-Saxon cranking calculations suggests that they are built upon negative-parity neutron configurations that involve only one intruder orbital ({nu}{ital i}{sub 13/2}) from the {ital N}=6 shell. One of the bands has been linked into the normally deformed states allowing an estimation of the spin, parity, and excitation energy of the band. {copyright} {ital 1996 The American Physical Society.}

The octupole-octupole interaction has been added to the old pairing-plus-quadrupole model. Symmetries of the HF mean field are discussed. It is shown that under the assumption of the S-symmetry of the HF mean field, only two quadrupole and two octupole parameters have non-zero expectation values in HFB ground state. A detailed analysis of two possible approaches to the HFB treatment of the model Hamiltonian is presented.

An iron-free beta spectrometer with pre- and post-acceleration of electrons was used to study \ensuremath{\beta} branches and conversion electrons at very low energies in the \ensuremath{\beta} decay of $^{228}\mathrm{Ra}$. Results of conversion-electron and \ensuremath{\gamma}-ray spectroscopy are analyzed using \ensuremath{\beta} selection rules and two-quasiparticle-rotor model considerations. A tentative $^{228}\mathrm{Ac}$ level scheme, including model-dependent spin-parity and configuration assignments consistent with the available data, is presented.

The symmetry properties of reflection-asymmetric nuclei are discussed in the framework of the Hartree-Fock-Bogoliubov method. A comparison of reflection-symmetric and reflection-asymmetric approaches is made.

The experimental level structure of $^{223}\mathrm{Fr}$ has been studied using the 1.4% alpha decay of 21.8 yr $^{227}\mathrm{Ac}$ and subsequent gamma rays to extend the level scheme recently observed following the ${\mathrm{\ensuremath{\beta}}}^{\mathrm{\ensuremath{-}}}$ decay of $^{223}\mathrm{Rn}$. The level structure of $^{223}\mathrm{Fr}$ was also studied theoretically by using the quasiparticle model of Soloviev with octupole degrees of freedom. Both experimentally and theoretically there is strong evidence that $^{223}\mathrm{Fr}$ is reflection asymmetric. The theoretical study of microscopic structure of several of the positive-parity bands also indicates the presence of important Nilsson configurations arising from the shell below. The comparison of the level structures of $^{223}\mathrm{Fr}$, $^{221}\mathrm{Fr}$, and $^{219}\mathrm{Fr}$ tends to elaborate the mechanism by which the octupole-modified Nilsson orbitals collapse into the more degenerate shell model states as the mass number decreases.

The level structure of $^{227}\mathrm{Th}$ has been studied using the electron capture decay of $^{227}\mathrm{Pa}$ and the ${\mathrm{\ensuremath{\beta}}}^{\mathrm{\ensuremath{-}}}$ decay of $^{227}\mathrm{Ac}$ to give a total of 20 levels where only four were previously known. This level structure then makes possible a more complete interpretation of the recently studied $^{231}\mathrm{U}$ alpha decay into $^{227}\mathrm{Th}$. The level structure can be interpreted using both strong coupling and intermediate coupling models in terms of K=1/${2}^{\ifmmode\pm\else\textpm\fi{}}$,K=3/${2}^{\ifmmode\pm\else\textpm\fi{}}$, and more tentative K=5/${2}^{\ifmmode\pm\else\textpm\fi{}}$ parity double bands which implies that $^{227}\mathrm{Th}$ has reflection asymmetry. Futhermore, the detailed interpretation of the level structure of $^{227}\mathrm{Th}$ solves the long standing problem of the ground state spin-parity of $^{227}\mathrm{Th}$ which is shown to be 1/${2}^{+}$.

The remarkable features of the spectra of the odd-A Ac isotopes from 215Ac (with 126 neutrons) through 231Ac (with 142 neutrons) serve as a sequence of examples for the application of a variety of nuclear models. As the shapes vary from spherical to spherical with strong octupole correlations to octupole-deformed, the corresponding symmetry breaking leads to increasingly complex spectra. The spectrum of 215Ac can be described in terms of the shell model configurations π(h9/2)4f7/2 and π(h9/2)4i13/2. However, even in this 126-neutron nucleus there is already a strongly enhanced E3 transition. The spectra of 217Ac and 219Ac can be interpreted in terms of the weak coupling of the h9/2 proton to the 216Ra and 218Ra cores, respectively. However, the existence of parity doublet bands (same spins but opposite parities) in 219At and the interleaving of positive and negative states in 218Ra clearly demonstrate the increasing importance of octupole deformation. Parity doublet bands are also present in the spectra of 221Ac. However, in both 219Ac and 221Ac the positive parity members of the parity doublets appear to cut off before reaching the low spin values expected from the negative parity bands. In 223Ac, 225Ac, and 227Ac the experimental spectra clearly show the existence of parity doublet bands built on the parity mixed configurations 5/2±(0.0; −0.2) and 3/2±(0.0; −0.3). The fact that the ordering of these two configurations changes for 223Ac results from decreasing quadrupole deformation. Other spectroscopic properties also confirm octupole deformation in these three isotopes. In 229Ac and 231Ac the only detailed but limited spectroscopic information comes from the (t, α) reaction on 230Th and 232Th. While it is consistent with the presence of parity doublets, much more detailed spectroscopic studies could give information about the possible coexistence of reflection asymmetry and reflection symmetry in these nuclei.

Experimental data on energy levels of the odd-odd deformed nucleus180Re obtained from radioactive-decay and heavy-ion reaction studies are analysed to deduce spin-parity and configuration assignments for the six observed rotational bands based on the selection rules for fast beta transitions, criteria for the relative-energy ordering of the triplet and singlet bandheads, two-particle-plus-rotor model calculations including Coriolis mixing, rotational energy systematics involving staggering features, and considerations of gyromagnetic ratios, signature splittings and rotational band alignments.

The residual p-n interaction in doubly odd deformed nuclei is examined in the framework of the unified model. Extensive experimental information about the Gallagher-Moszkowski splitting energies and Newby shifts in the rare-earth and actinide regions is used to deduce empirical parameters of the residual p-n interaction. Delta interaction and Gaussian-shape radial potential are assumed, Empirical p-n parameters are discussed and compared with previously deduced parameters. For the first time, errors in the parameters are estimated and special attention is paid to parameter significance.

The level structure of $^{212}\mathrm{Bi}$ has been studied by observing the alpha decay of $^{216}\mathrm{At}$ which is in secular equilibrium with $^{220}\mathrm{Fr}$ and $^{224}\mathrm{Ac}$. Eight states are observed and tentatively assigned to the configuration \ensuremath{\pi}${\mathit{h}}_{9/2}$\ensuremath{\nu}(${\mathit{g}}_{9/2}$${)}^{3}$ and three to the configuration \ensuremath{\pi}${\mathit{h}}_{9/2}$\ensuremath{\nu}(${\mathit{g}}_{9/2}$${)}^{2}$${\mathit{i}}_{11/2}$. These two lowest configurations in $^{212}\mathrm{Bi}$ are compared with the corresponding configurations in $^{210}\mathrm{Bi}$ and the calculations of Warburton.

The level structure of [sup 215]Rn has been studied by observing the alpha decay of [sup 219]Ra ([ital t][sub 1/2]=10 ms) in secular equilibrium with [sup 232]Th ([ital t][sub 1/2]=0.66 s) produced by the reaction [sup 208]Pb ([sup 18]O,3[ital n]). Guidance in the interpretation of the five levels is available from the more comprehensive level structure of the isotone [sup 217]Ra. Both of these level structures are interpreted in terms of the shell model and the reflection asymmetric model.

Previously proposed high spin states in [sup 22,23]Na are compared with calculations from the cranked Nilsson model including Strutinsky renormalization. High [ital K] rotational isomers are proposed for [ital I][sup [pi]]=6[sup [minus]] in [sup 22]Na and 11/2[sup +], 13/2[sup +], and possibly 15/2[sup +] in [sup 23]Na. The positive parity yrast sequences in these two nuclei are analyzed in terms of the change from collective to single particle behavior at [ital I]=9 ([sup 22]Na) and 17/2 ([sup 23]Na). The systematics of band terminations in eight nuclei between [sup 20]Ne and [sup 26]Mg shows that [ital I][sup max] or [ital I][sup max][minus]1 has tentatively been reached in six of these eight nuclei, where [ital I][sup max] is the maximum possible [ital sd] shell spin for the given nucleus.

The spectroscopy of the odd-A Ra isotopes from 215 Ra through 227 Ra is analyzed to see the effects of octupole deformation on the transition from spherical nuclei (where the more degenerate shell model applies) to quadrupole deformed nuclei (where the less degenerate Nilsson model is operative). 215 Ra with 127 neutrons can be interpreted qualitatively in terms of the weak coupling of the levels in 214 Ra with the shell model states g9/2 and j15/2. 217 Ra and 219 Ra can be understood in terms of both shell model spectroscopy with octupole correlations and increasingly with 219Ra in terms of octupole deformed Nilsson levels. 221,223,225 Ra are all relatively good examples of the octupole deformed model with, however, some differences in the Coriolis coupling between low lying K=3/2± and K=1/2± parity doublet bands. The spectrum of 227 Ra shows the coexistence of both parity doublets and an octupole vibration expected for an octupole-quadrupole deformed system and a coexisting normal deformed system.

The level structure of178Hf is interpreted on the basis of the population of the states following178Hf (d, d′),177Hf (d, p) and179Hf (d, t) reactions. Evidence for quadrupole and octupole vibrational bands and unmixed and intermixed two-quasiparticle configurations is presented.

Using a selective fluorination method, mass-separated sources of 228Pa (separated as PaF4+ ions) were used to study the level structure of 224Ac following 2% alpha decay. The levels in 224Ac are interpreted as K=0+or- and K=3+or- parity doublet bands which are explained naturally in reflection asymmetric models. The average energy splittings between the parity doublet bands are 12.7 keV for the K=0+or- bands and 7.3 keV for the K=3+or- bands. These very small splittings are expected because of the additional polarization effects of the two odd particles in 224Ac. It is shown theoretically that the Newby shifts in all odd-odd reflection asymmetric nuclei with K=0+or- bands must have the same absolute magnitude but opposite sign in the strong coupling limit. The experimental Newby shifts in 224Ac approach this theoretical expectation.

The structures of the low-lying intrinsic states in 152 Eu and 154 Eu are calculated using a microscopic quasiparticle phonon model similar to that of Soloviev. Experimental data with specific emphasis on stripping and pick-up cross-sections on 153 Eu are in agreement with the calculations. Octupole correlations between these calculated intrinsic states are analyzed. The opposite parities and appropriate octupole correlations of several of the states provide a theoretical basis for the previous interpretation of parity doublets in 152 Eu and 154 Eu . The E1 enhancements of the ΔK=0 transitions in both nuclei are also discussed.

The $^{179}\mathrm{Hf}$(t,\ensuremath{\alpha}${)}^{178}$Lu reaction has been studied using beams of 17 MeV tritons from the McMaster University tandem Van de Graaff accelerator. Reaction products were analyzed with a magnetic spectrograph, and the resolution achieved for the alpha spectra was \ensuremath{\sim}20 keV (FWHM). Two-quasiparticle states in $^{178}\mathrm{Lu}$ involving the 9/${2}^{+}$[624] target neutron coupled with the 7/${2}^{+}$[404], 9/${2}^{\mathrm{\ensuremath{-}}}$[514], and 1/${2}^{+}$[411] proton orbitals were identified. The difference in ground-state (t,\ensuremath{\alpha}) Q values for $^{178}\mathrm{Hf}$ and $^{179}\mathrm{Hf}$ components of the target, combined with the known masses of $^{177}\mathrm{Lu}$, $^{178}\mathrm{Hf}$, and $^{179}\mathrm{Hf}$, yields an improved value of -50 351\ifmmode\pm\else\textpm\fi{}5 keV for the mass excess of $^{178}\mathrm{Lu}$. This result, combined with the two-quasiparticle assignments from the present work, has resolved the long-standing puzzle concerning the character and excitation energy of the well-known 23 min high-spin beta-decaying isomer in $^{178}\mathrm{Lu}$.

Microscopic structures of the low-lying nonrotational (intrinsic) states in the odd-odd nucleus $_{63}^{156}\mathrm{Eu}_{93}$ are investigated using the quasiparticle-phonon nuclear model Hamiltonian including the pairing, quadrupole-quadrupole, octupole-octupole, and residual p-n interactions. The extent of vibrational admixtures to the two-quasiparticle configurations and the intrinsic matrix elements of electric octupole operator for the ``same K opposite parity'' bands are examined to conclude that, contrary to some recent suggestions, the low-energy $^{156}\mathrm{Eu}$ spectrum does not contain ``parity doublets'' characteristic of reflection asymmetric shapes, in contrast with the structures seen in $^{152}\mathrm{Eu}$ and $^{154}\mathrm{Eu}$.

The219Ra levels, fed by the α-decay of223Th, have been studied by anα−γ coincidence experiment. AK=1/2+ band, based on the 7/2+ ground state, with a large decoupling parameter a=−5.5 is proposed. Three levels with spins 5/2, 9/2, 7/2 and lowα-hindrance factors around 140 keV, can be considered as members of aK=5/2+ band, perturbed by the Coriolis coupling of configurations arising from theg9/2 shell. TheseK =1/2+ and 5/2+ orbitals are expected forN=131 in the reflection asymmetry model with ɛ2≃ɛ3−0.1. How-ever no evidence was found for the corresponding negative parity bands in this transitional nucleus.

Microscopic structures of the low-lying intrinsic bands in the odd-neutron N = 91 153 Sm , 155 Gd and N = 93 155 Sm nuclei near the onset of the quadrupole deformation region are investigated with special attention being paid to the formation of octupole collectivity. Octupole correlations between nonrotational states are analyzed using a model Hamiltonian containing an axially symmetric mean field, pairing, quadrupole-quadrupole and octupole-octupole interactions. In addition, the strong ΔK = 0 E1 transitions in the N = 91 nuclei are examined. These calculations provide a theoretical basis for the previous parity doublet assignments in 153 Sm in the low energy region, and less conclusively for 155 Gd . They suggest a more complex spectroscopy for 155 Sm , intermediate between octupole vibration and deformation.

Microscopic structures of the proposed parity doublet bands in the odd-proton Z=61151Pm and Z=63153, 155Eu nuclei are examined using the quasiparticle phonon nuclear model Hamiltonian including the residual pairing and multipole-multipole interactions. Octupole correlations between intrinsic nonrotational states are studied to check the suggested assignments of parity doublet partners in these nuclei. We conclude significant octupole correlations between a pair ofK π = 1/2± doublets in each of these nuclei, with somewhat weaker correlations betweenK π = 3/2± bands in both the Eu isotopes. No octupole connection between the lowestK π = 5/2± bands is found; however, significant octupole collectivity, built on the low-lying 5/2− bands, is predicted in the higher-lying 5/2+ bands which contain the 5/2+ [402] fragmented strength.

Experimentally observed energy levels of deformed even-even nuclei with Z ≥ 88 and N ≥ 134 are classified in terms of their intrinsic structures and associated rotational bands. Interleaving of the ground-state K π = 0 + band and the first excited K π = 0 − band levels in the beginning of the region is presented as possible evidence for spin evolution of reflection-asymmetric (stable octupole) shapes. Rotational alignment and possible backbending in the ground-state band levels is discussed. Structures connected with one-phonon quadrupole (β and γ) and octupole and two-phonon vibrations are described. Other modes of excitation for 0 + structures, for example, pairing vibrations and α clustering, are pointed out. Available information on the occurrence of collective dipole excitations connected with the “scissors” or “twisting” mode is also included. Bands connected with two-quasiparticle excitations are listed. Evidence for superdeformations and hyperdeformations connected with fission isomers, and related spectroscopies in the second and third well, is presented. Our literature cutoff date is March 1991.

Using a selective fluorination method, mass separated sources of 224 Ac (separated as [Formula: see text]) were used to study the level structure of 220 Fr following alpha decay. Parity doublet bands with K = 1± were observed and three other bands with K = 2± and K = 0− were proposed. All five bands can be explained in terms of low lying n − p configurations predicted in reflection asymmetric models. Evidence is presented that 220 Fr is a transitional nucleus with spectroscopy intermediate between shell model and octupole-quadrupole spectroscopies.

The microscopic approach for the description of low-lying intrinsic states in deformed odd-odd nuclei is formulated as a generalization of the quasiparticle-phonon model. In comparison with other models used for deformed odd-odd nuclei, the approach proposed in this paper involves vibrational degrees of freedom of the doubly-even core, their coupling to quasiparticle degrees of freedom and then-p interaction between the odd particles. Our model treats all of these modes of nuclear motion on the same microscopic footing. This proposed model is applied to calculate the energies and phonon-quasiparticle structure of the intrinsic states of the odd-odd Ho isotopes withA=160, 162, 164, 166 and 168. It is found that the low-lying intrinsic states in the odd-odd Ho isotopes have only small vibrational components. In general the vibrational states are fragmented over many intrinsic states.

Comparison of the six states recently observed in $^{168}\mathrm{Ho}$ with the states in $^{166}\mathrm{Ho}$ suggests configurational assignments for all six states. The validity of these assignments is strengthened by the allowed unhindered beta decay of $^{168}\mathrm{Dy}$ to the two ${1}^{+}$ states in $^{168}\mathrm{Ho}$ and by microscopic theoretical calculations of the quasiparticle structure of the corresponding states in $^{166}\mathrm{Ho}$ and $^{168}\mathrm{Ho}$.

The systematics of superdeformation (∈≈0.6) is studied throughout the mass regions from A~8 to the fission isomers with A~242, including the recently observed superdeformed nuclei with A~152 and ~192. Strong shell effects are calculated which are described in a shell energy landscape in terms of valleys of stability which proceed from oblate through spherical to normal-deformed (∈≈0.25–0.3) and on to superdeformed and hyperdeformed (∈≈0.86) shapes with increasing nucleon number. Local minima in these valleys are calculated for prolate nuclei with 4, 10, 16, 28–32, 40–44, 60–66, 80–86, 110–116 and 140–150 neutrons and/or protons when the ratio of the major to minor axes is ≈ 2:1 and the deformation ∈≈0.6. Although the local minima represent the regions of greatest stability, the shell energy valleys should be viewed as more or less continuous structures in which a variety of different deformations can occur. Other local minima in the valleys of the shell energy landscape are observed for oblate (∈≈−0.75) and hyperdeformed nuclei. When shell effects are added to the liquid-drop potential in the Nilsson-Strutinsky formalism, spherical and normal deformation shapes tend to predominate. However, superdeformed, oblate and hyperdeformed shapes are also predicted. In the case of superdeformed nuclei, shell effects predominate over the liquid-drop potential for the light nuclei creating superdeformed ground states. In intermediate-mass nuclei, the liquid-drop potential predominates and superdeformation is only observed at fairly high energy and at high spins where the superdeformation is stabilized. In the heaviest nuclei, the combined effect of the Coulomb potential and the fissionability of the liquid drop causes the potential to reach a maximum at ∈≈0.6. The shell effect then produces a second minimum 2–3 MeV above the ground state with its coexisting spectroscopy. Existing experimental data throughout the nuclear periodic table are shown to be in remarkable agreement with theoretical expectations. Predictions of new regions of superdeformation are presented.

Mass-separated sources of {sup 223}Ac (separated as AcF{sub 2}{sup +}) were used to study the level structure of {sup 219}Fr following alpha decay. The levels in {sup 219}Fr are interpreted in terms of {ital K}=1/2{sup {plus minus}}, 3/2{sup {plus minus}}, and 5/2{sup {plus minus}} parity doublet bands which have a natural theoretical explanation in terms of reflection asymmetric models. The 9/2{sup {minus}} ground-state member of the {ital K}=1/2{sup {minus}} band in {sup 219}Fr can be understood in terms of both reflection asymmetry and the collapse of the quadrupole-octupole Nilsson orbitals towards the {ital h}{sub 9/2} orbitals of spherical symmetry. Comparison of the {ital K}=1/2{sup {minus}} ground-state bands in {sup 219}Fr and {sup 221}Fr reveals the details of this transformation. Theoretical analysis of the microscopic structure of several of the positive-parity bands indicates the presence of important Nilsson configurations arising from the shell below.

The experimental hindrance factors determined from the fine structure in the $^{14}\mathrm{C}$ decay of $^{223}\mathrm{Ra}$ are strikingly similar to the hindrance factors observed in the alpha decay of odd-A reflection-asymmetric deformed nuclei in spite of the deformed to spherical shape which occurs in the $^{14}\mathrm{C}$ decay. Calculations of the overlap between the reflection-asymmetric ground state of $^{223}\mathrm{Ra}$ and the spherical shell-model orbitals of $^{209}\mathrm{Pb}$ involved in the $^{14}\mathrm{C}$ decay are consistent with the experimental hindrance factors from the $^{14}\mathrm{C}$ fine structure except that the ${\mathit{j}}_{15/2}$ orbital is more strongly populated experimentally than the calculations suggest.

A data set of 29 experimentally determined Newby shifts in rare-earth nuclei is examined for the reliability of each values. Using this data set, Newby shifts are obtained which are free from the Coriolis and the particle-particle coupling effects. These new empirical values help resolve the failure of a recently proposed rule for the sign of the Newby shift in the {5/2[413]p − 5/2[642]n} configuration of160Tb and the {5/2[402]p − 5/2[512]n} configuration of174Lu. Also the Newby shifts are significantly modified in two other cases namely the {1/2[411]p − 1/2[521]n} configuration in168Tm and the {1/2[541]p − 1/2[521]n} configuration in172Lu. Only marginal changes are seen in the rest of the cases in the rare-earth nuclei.