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The level structure of 190 Os has been investigated by the techniques of radioactive decay and neutron transfer reaction spectroscopy. The existence of 3.3 h 190m Re has been confirmed; it decays ≈ 49% by isomeric transitions and ≈ 51% by β − decay to levels in 190 Os with spins $ = 5 . In a re-investigation of the 12 d 190 Ir decay, a virtually complete decay scheme has been established and discrepancies between the I π values assigned to several 190 Os levels by earlier workers have been resolved. The reaction 189 Os(d, p) 190 Os has been studied and information about the locations of two-quasiparticle states involving the 3 2 [512]ν orbital and about the microscopic compositions of collective excitations has been derived. Various aspects of the 190 Os level structure are discussed in the light of the combined radioactivity and transfer reaction results.

The Nilsson model of high-spin states is developed to include particle-hole excitations for rotation around an arbitrary axis. Potential-energy surfaces are calculated with constraints not only on the total spin but also on parity and signature. The method is applied to very light nuclei with A ~ 10. Good agreement for the ground-state bands of 8Be and 12C is obtained and predictions are made for the excitation energy of higher-spin states ( I ⪆ 4 ) of positive and negative parity. It is pointed out how the “positive-parity yrast levels” of 11B and 11C form a rotational band with a very small rotational parameter. When taken in conjunction with the much larger rotational constants of the negative-parity bands, this can be interpreted in terms of a super backbend. We discuss the possible association of these positive-parity bands with a calculated potential-energy minimum at a large prolate deformation which for positive parity develops already at low spins. Special attention is paid to the question of signature splitting.

A broad discussion of the ground-state potential-energy surfaces of doubly even deformed and transitional nuclei with Z = 50–82 is presented. The surfaces are calculated microscopically as functions of the quadrupole axial e and non-axial γ and the axial hexadecapole e4 deformations. A correlation between the form of the surfaces and the experimental spectroscopic trends is extensively discussed. Comparisons are made with the experimental data including the ground-state band 2+, 4+ and 6+ energy levels, the quasi-gamma band heads, 2'+ and the quasi-beta band heads, 0'+. Some general correlation is found although for more detailed comparisons a need of dynamics becomes evident. In addition, the electric quadrupole moments and moments of inertia of the nuclei are discussed.

The level structure of 165Ho has been studied by means of the 166Er(t, α)165Ho, 164Dy(α, t)165Ho, and 164Dy(3He, d)165Ho reactions using magnetic spectrographs and photographic emulsions. The results were interpreted on the basis of the Nilsson model with pairing and Coriolis mixing effects included. Experimental nuclear structure factors were obtained and compared with calculated results. Previously identified bands based on the 7 2 [523], 3 2 [411], 1 2 [411], 7 2 [404], and 5 2 [413] Nilsson orbitals were observed. The previously suggested 1 2 [541] band was confirmed and levels up to spin 9 2 were assigned. The 11 2 member of the 9 2 [514] band was also identified. States assigned earlier as the spin 5 2 and 7 2 members of the 5 2 [532] band were reassigned to the 5 2 [402] orbital. New evidence is presented which indicates that the previously assigned 5 2 [413] band is actually the (K0+2) γ-vibration based on the 1 2 [411] state, with a large admixture (≈ 50%) of the 5 2 [413] single-particle configuration.

The 0 level structure of 188Os has been investigated by the 189Os(d, t)188Os reaction using a broad range magnetic spectrograph, and the properties of the 188Os levels populated in the decay of 188Ir have been re-examined. The (d, t) results yield new information about the location of two-neutron excitations in 188Os involving the 3 2 [512] orbital. Since the 188Os ground state contains admixtures of both K = 3 2 and K = 1 2 character, cross-section formulae for single-neutron transfer from a target state which is not pure in K are considered, and it is found that rather small K = 1 2 admixtures in the 189Os ground state give rise to striking interference effects, which are manifested in the experimental (d, t) cross sections into the members of the 188Os ground state band. The consequences of the mixed character of the target state on the (d, t) population of members of the Kπ = 2+ γ-vibration and of higher-lying two-quasiparticle bands are also discussed.

The level structure of 225 Ra has been studied using the (d, t) reaction with both unpolarised and polarised deuterons and the β − decay of 225 Fr. Cross sections and excitation energies have been measured for 41 levels below 1800 keV in the (d, t) reaction, and levels up to 724 keV have been established from the β − decay measurements. The level structure is interpreted in terms of the Nilsson model.

The band structure and formation mechanism of odd-A rotational bands based on intruder orbitals are studied using the particle-core coupling model of de-Shalit. Since quadrupole interaction is assumed between the particle and the core, the E2 static and transition moments of the core excited states determine the odd-A band structure. The relationship between the E2 moments of the core states and the odd-A energy spectrum is used to discuss about the core shape. Shapes considered are γ-stable, γ-vibrational, axially symmetric or spherically vibrational. This approach is found to work fairly well for the transitional nuclei with A = 187–199. The γ-stable model of Davydov and Fillippov is also shown to be almost equivalent to the γ-vibrational model of Bohr and Mottelson.

The level structure of 227Ra has been studied using the (n, γ), (d, p) and ( t , d) reactions and the β− decay of 227Fr. A model-independent level scheme was established including 28 levels below 1500 keV. Cross sections and excitation energies have been measured for 72 levels below 2.5 MeV and analysing powers have been measured for 25 levels below 1.4 MeV. The level structure is interpreted in terms of the Nilsson model. The ground-state configuration is 3 2 + [631↑] and the first excited band [633↓] starts at 1.7 keV. Several octupole vibrations coupled to single-particle configurations are tentatively assigned above 280 keV. The neutron binding energy was determined to be 4561.41 ± 0.27 keV. The half-life of 227Fr was measured to be 148 ± 2 s.

A theoretical description is formulated for odd-A nuclei whose intrinsic shape is axially elongated and statically or dynamically reflection asymmetric. It is used to evaluate data in the Ra-Ac-Th-Pa region on energy levels, decoupling factors, α-transitions and electromagnetic M1, E1 and E3 matrix elements. The results provide firm empirical evidence for a predicted transition from octupole vibrations above A ∼ 229 to more or less stable octupole deformation in lighter isotopes. Some parity-mixed Nilsson orbitals resulting from strong coupling to the intrinsic reflection asymmetry can be identified.

The 210mBi(t, α)209Pb reaction has been measured using an 8 μg/cm2 target of 210mBi in the 9− isomeric state at 0.271 MeV. Thirty-four levels up to about 5 MeV excitation were observed with the bulk of the transition strength comprising two-particle one-hole configurations of the form [ππ−1ν]. The 2 g 9 2 and 1 i 11 2 single neutron states were excited and their relative spectroscopic strengths provide information about the πν configurations in the 9− target state. Transitions to the 15 2 − states at 1.423 and 3.059 MeV are used to estimate admixtures of the [ 208 Pb (3 − ) ⊗ g 9 2 ] particle-plus-core configuration. The gross features of the 210mBi(t, α) spectrum are compared with (t, α) spectra measured from 208Pb and 209Bi. The level densities, summed cross sections and average Q-values are discussed.

The cranked Nilsson-Strutinsky formalism is applied to the many-faceted spectrum of 16 O. The deformation parameters ϵ, γ and e 4 are varied independently and many-particle-many-hole excitations are considered in the rotating system. Potential-energy surfaces are presented at different values of spin, parity and signature. Surprisingly good agreement is obtained when the different minima are compared with the measured states. Generally, it is observed that the more particles that are excited to higher shells, the larger becomes the intrinsic deformation. Rotational bands as well as pure p-h excitations, the latter sometimes constituting the termination of a rotational band, are identified. Additional high-spin states ( I ⩽ 12) are suggested. A microscopic analysis is performed of the rotational bands which emerge when 16 O in its triaxial 4p-4h configuration rotates around each of its three principal axes.

Negative-parity excited states of doubly even nuclei have earlier been attributed to vibrational excitations. This paper shows that an interpretation starting from a reflection asymmetric intrinsic state is more appropriate for certain nuclei in the radium region. Theoretical evidence for stable octupole deformation comes from a deformed shell-model calculation in which we use a single-particle potential with a realistic radial shape and a finite-range interaction for the surface energy. The octupole effect systematically improves the agreement between theoretical and experimental masses. The low-lying O + excitations observed in experiment are compatible with the calculated collective octupole potentials. The possibility of obtaining further evidence from the spectroscopy of odd-mass nuclei is considered in an exactly solvable model, which shows that the smaller energy splitting observed in odd- A parity doublets mainly reflects single-particle fragmentation of the collective mode. The systematics of theoretical shell structure and experimental spectroscopy suggests the presence of other regions of octupole collectivity near the limits of stability.

The level structure of 223 Ra is reinterpreted in terms of 3 2 ± , 5 2 ± , and 1 2 ± parity-doub The non-adiabatic rigid reflection-asymmetric rotor model reproduces the main features of the experimental data assuming the presence of octupole deformation β 3 ∼- 0.1. In particular, the experimental E1 transition rates are accounted for by the calculated permanent collective electricdipole moment.

The tetrahedrally deformed model is applied to the excited states in the 16 O nucleus. Single-particle spectra and wave functions are calculated using a tetrahedrally deformed potential. The intrinsic energy for 16 O is determined as a function of the depth of the tetrahedrally deformed potential assuming the nuclear force has a soft core. Vibration and deformation which break the tetrahedral symmetry are discussed.

The spectroscopic factors for (d, p) excitation of gamma vibrational states in even deformed nuclei of the rare-earth region are calculated using the current microscopic description. The cross sections for populating these bands and also some two-quasi-particle bands are calculated and compared with experiment. Agreement is found to be fairly good.

Characteristic features of the excitation spectra of K = 0 + intrinsic states are discussed for even deformed nuclei in the rare-earth region within the framework of the random phase approximation, using the pairing-plus-quadrupole force model. The distributions in collectiveness of both pairing and quadrupole β-vibrations of the ten lowest K = 0 + states are numerically analysed. The β-vibrational character is more dominant in the spectra of nuclei in the beginning of the deformed region, whereas the pairing modes are relatively more important in the middle of the deformed region. An interaction Hamiltonian that describes the non-adiabatic coupling between the K = 0 + intrinsic excitation and the rotation is derived, using the cranking model. The effects of rotational disturbances on both pairing and quadrupole fields are taken into account simultaneously. Then, the Hamiltonian is used to investigate band mixings between the ground and the K = 0 + excited rotational states. Detailed numerical analyses are performed on the deviations of the rotational energies of the ground band from the I ( I +1 ) law. The relative contributions of various excited states to these deviations are investigated.

Ground state moments of inertia and collective gyromagnetic ratios of deformed even nuclei with 50

Using the equation Download : Download full-size image it is possible to estimate the A-dependence of Icrit resulting from Coriolis anti-pairing. This estimate gives I c r i t ( I c r i t + 1 ) ∝ ˜ A 5 2 . The A-dependence of Icrit can be compared with experiment by making plots of 2I/ℏ2versus (ℏω)2 for the observed ground state rotational bands of a number of deformed even nuclei in the A-regions ≈ 22, ≈ 102 and ≈ 126. These plots suggest that the values of Icrit, defined as the spin for which the maximum change in moment of inertia is occurring, are ≈ 3, 8–10 and 10–12 for the A-regions ≈ 22, ≈ 102 and ≈ 126 respectively, in agreement with the Coriolis anti-pairing estimates. The alternative explanation of Stephens and Simon gives I c r i t ( ( I c r i t + 1 ) ∝ ˜ A 7 6 . It is suggested that the two explanations may compete in the region 100 ≦ A ≦ 190 with the Stephens and Simon explanation relatively more important in the aetinide region and less important in the A ≈ 22 region.

The nuclear levels of 153Sm have been investigated by Ge(Li) and Si(Li) detector measurements of both high- and low-energy γ-rays following thermal neutron capture in 152Sm, and by magnetic spectrograph measurements of the tritons from the 154Sm(d, t) reaction. The observed states are classified within the Nilsson scheme as follows: the mixed 3 2 + [651] + [402] ground state band up to the 13 2 + member, the 3 2 − [521] band to the 7 2 − member, the 3 2 − [532] band to the 11 2 − member, the 11 2 − [505] band head, the 3 2 + [402]+ [651] configuration up to 7 2 + , and the members up to 7 2 − of a K π = 1 2 − band that is partly 1 2 − [521] and partly vibrational. Also, tentative assignments have been made of the 5 2 + [642] , 1 2 − [530] and 1 2 + [400] bands, as well as a K π = 3 2 − beta-vibrational band. The K π = 3 2 + rotational bands are severely distorted, presumably due to Coriolis coupling. An estimate is made of the amount of mixing between the 3 2 + [651] and 3 2 + [402] orbitals. Comparisons are made with the level structure of other 91-neutron nuclei and with theoretical calculations.

Thirty-one levels in 164 Ho have been observed up to an excitation energy of 994 keV utilizing 12 MeV deuterons and the reaction 165 Ho(d, t) 164 Ho. The ground state Q -value was determined to be −1730±15 keV. The spectrum has been interpreted in terms of the coupling of the [523↑] Nilsson proton orbital with the neutron orbitals prominent in the (d, t) spectrum of 163 Dy. Based on this interpretation, the singlet-triplet splitting energies for the [523↓], [642↑], [521↑], [402↓] and [400↑] neutron orbitals coupled to the [523↑] proton orbital were determined to be −144, +67, +171, −85 and +102 keV, respectively. Theoretical calculations of these energies made for a zero-range spin-dependent central potential gave values of −248, +74, +160, −82 and +73 keV, respectively.