High-spin states in 155Ho

High-spin states in ¹⁵⁵Ho have been populated in the ¹⁴⁵Nd(¹⁴N, 4n)¹⁵⁵Ho reaction. Excitation functions, lifetimes, angular distributions and γ-γ coincidences were measured. An $\text{11}\text{2}{}^{\mathrm{?}}$ isomeric state with $\text{T}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 0.88}\text{ms}$ has been found at very low energy. The rotational band built on this state is developed up to spin $\text{35}\text{2}$. The behaviour of its moment of inertia is compared with that of the doubly even neighbouring nuclei.     

High-spin states in the N = 84 nucleus 152Er

High-spin states in ¹⁵²Er have been populated through the ¹⁴⁴Sm(¹²C, 4n)¹⁵²Er reaction. Excitation functions, angular distributions, prompt and delayed coincidences against the beam burst were measured. Three isomeric states at 2183 keV (τ = 1.8 ns), 4519 keV (τ = 1.2 ns) and 4915 keV (τ = 6.6 ns) have been observed. The decay scheme is developed up to 7 MeV and is discussed and compared with that of ¹⁵⁰Dy.     

High-spin states and two-quasiparticle structure in 172Hf

Five rotational bands in ¹⁷²Hf have been observed to high spin following the ¹⁶⁰Gd(¹⁶O, 4n)¹⁷²Hf reaction, using γ-γ coincidence techniques. The ground-state band is extended to spin 20⁺ without backbending, in contrast to the neighbouring even-even isotones. The most strongly populated side-band, consisting of separated odd-spin and even-spin sequences, appears to result from the partial decoupling of an i_{$\text{13}\text{2}$} neutron. Three other bands are identified with the following band-heads: an 8^? state at 2006 keV with 163 ns half-life; a 6⁺ state at 1685 keV with a half-life < 16 ns; and a level at 1857 keV with spin 4, 5, 6 or 7 and a half-life < 16 ns. The differences between the bands are discussed in terms of the influence of Coriolis forces and the two-quasiparticle level structure.     

High-spin yrast levels of 38Ar

High-spin states of ³⁸Ar have been studied with the ³⁵Cl(α, pγ)³⁸Ar reaction at E_α = 18 MeV and with the ²⁴Mg(¹⁶O, 2pγ)³⁸Ar reaction at $\text{E(}{}^{16}\text{O}\text{) = 38}\text{and}\text{45}\text{MeV}$. The ³⁸Ar level scheme is obtained with the former reaction from a proton-γ coincidence measurement. Gamma-gamma coincidence, γ-ray angular distribution and linear polarization experiments have been performed with a Ge(Li)-Na(Tl) Compton suppression spectrometer and a three-crystal Ge(Li) Compton polarimeter. Unambiguous spin-parity assignments of $\text{J}{}^{\mathrm{\pi }}\text{= 7}{}^{\mathrm{?}}\text{, 7}{}^{\mathrm{+}}\text{, 8}{}^{\mathrm{+}}\text{, 7}{}^{\mathrm{?}}\text{, 9}{}^{\mathrm{?}}\text{and}\text{11}{}^{\mathrm{?}}$to the ³⁸Ar levels at E_x = 7.51, 8.08, 8.57, 8.97, 10.17 and 11.61 MeV, respectively, are obtained. The 8.57 MeV, 8⁺ level has a mean life below 0.8 ps. Excitation energies, branching ratios, multipole mixing ratios and transition strengths are reported. The experimental results are compared with shell-model calculations.     

Lifetimes of high-spin yrast states in 154Er

Lifetimes for high-spin levels (between about 10 and 30 ?) in ¹⁵⁴Er have been measured by the recoil-distance method. Non-collective, moderately collective and collective E2 transitions from states with lifetimes between at most 10 and 400 ps have been found. All available data on this nucleus are discussed within the framework of the oblate coupling scheme with the addition of collective degrees of freedom.     

High-spin states in 58Ni

High-spin states of ⁵⁸Ni were investigated via the study of in-beam γ-ray induced by the compound reaction ⁴⁸Ti(¹²C, 2n)⁵⁸Ni between 26 and 48 MeV. The energies and decay modes of these levels were determined from the analysis of γ-γ coincidence measurements at 35 MeV. The most intense lines in the ⁵⁸Ni γ-ray spectrum correspond to a cascade to the ground state, through levels at 1.454, 2.459, 3.619 and 4.381 MeV, also fed in other reactions, and by two previously unknown levels at 5.125 and 5.662 MeV; the spin assignments based on the present study are (apart from the ground state) 2, 4, 4, 5, 6 and 7 respectively for these levels. The first three were already known and the last three are new. The mixing ratios for the transitions between these levels are also determined. We observe also the same cascade in the reaction ⁵⁶Fe(α, 2n)⁵⁸Ni at an incident energy 18–24 MeV. Comparisons with other reactions, previous studies and recent shell-model calculations are presented.     

High-spin states in 38K

High-spin states in ³⁸K are investigated with the ²⁴Mg(¹⁶O, pnγ)³⁸K reaction at $\text{E(}{}^{16}\text{O}\text{) = 36–44}\text{MeV}$. A recently developed Compton-suppression spectrometer with 120 msr solid angle and a pulsed beam are employed to study their γ-decay. For the E4 transition from the isomeric level at E_x = 3458 keV to the ground state a branching ratio of (0.15 ± 0.02)% is found. On the basis of angular distribution and polarization measurements, in which the delayed feeding component is eliminated, spin-parity assignments are obtained of J^π(2646 keV) = (2, 4)^?, J^π(3420 keV) = (4, 6)^? and J^π(3458 keV) = (5, 7)⁺. Prompt-delayed and prompt γγ coincidence experiments are performed to locate high-spin levels above the isomer. Hitherto unobserved levels of high spin are found at E_x = 5254, 7397, 8693, 8747 and 10980 keV and assignments of J^π = (9⁺), (10^?), (12^?), (11^?) and (13^?) respectively, are suggested by weak-coupling considerations. The experimental results are compared with a large-scale shell-model calculation performed in a configuration space with a ²⁸Si core and ten active particles distributed over the ($\text{2}\text{s}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{, 1}\text{d}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}\text{, 1}\text{f}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}\text{, 2}\text{p}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}\text{)}$ shells. The high-spin states appear to have a rather simple shell-model structure.     

High-spin states in 208Rn

The yrast decay scheme of ²⁰⁸Rn has been investigated up to spin $\text{≈ 20}\text{h}\text{?}$ and an excitation energy of ≈ 6 MeV. Several different γ-ray spectroscopic techniques were used to determine the properties of excited states and transitions in the nucleus. Significant changes to the previously established level scheme are proposed, based on the existence of an unobserved 3.1 keV transition. Simple empirical shell-model calculations of level energies aided in the assignment of shell-model configurations to excited states and the decay scheme is discussed in terms of these configurations. The energy level systematics for the even radon isotopes, from A = 206 to 212 are discussed, as are core polarization effects in the even radon isotopes (A = 204 to 210) and polonium isotopes (A = 202–208).     

High-spin states in 90Nb

The high-spin states in ⁹⁰Nb have been studied by in-beam γ-ray spectroscopy using the 35 MeV ⁸⁹Y(α, 3nγ)⁹⁰Nb and 33 MeV ⁹⁰Zr(³He, p2nγ)⁹⁰Nb reactions. A new isomeric state with half-life 0.44±0.02 σs and J^π = 11^? has been located in this nucleus. The level scheme derived from these measurements is compared with shell-model calculations.     

High-spin states in 59Ni

High-spin states in ⁵⁹Ni have been investigated via the study of in-beam γ-rays following the reactions ⁵⁰Cr(¹²C, 2pn)⁵⁹Ni (26–58 MeV) and ⁵⁶Fe(α, n)⁵⁹Ni (10, 15, 22.5 MeV). The spins of previously known levels have been confirmed or determined for the first time, in particular for those at $\text{3376.8}\text{keV}\text{(J =}\text{11}\text{2}\text{)}\text{and}\text{4141.3}\text{keV}\text{(J =}\text{13}\text{2}\text{or}\text{15}\text{2}\text{)}$. New states have been established and their spin determined, at $\text{1739.2}\text{keV}\text{(J =}\text{9}\text{2}\text{), 2349.2}\text{keV}\text{(J =}\text{11}\text{2}\text{), 2535.5}\text{keV}\text{(J =}\text{13}\text{2}\text{), 4455.4}\text{keV}\text{(J =}\text{13}\text{2}\text{), 4947.5}\text{keV}\text{(J =}\text{15}\text{2}\text{)}\text{and}\text{5251.7}\text{keV}\text{(J =}\text{13}\text{2}\text{or}\text{15}\text{2}\text{)}$. The resulting ⁵⁹Ni decay scheme is discussed in the framework of nuclear models.     

High-spin states in 218Ra

Yrast states in ²¹⁸Ra up to spin and parity I^π = 17^? were identifíed by means of the ²⁰⁸Pb(¹³C, 3n) reaction and standard γ-ray spectroscopic techniques. The level scheme is characterized by two bands of opposite parity with nearly constant level spacing. A cascade of strong E1 interband transitions connects both bands.The results are discussed within the systematics of the even Ra isotopes. The negative-parity band which is observed from the I^π = 5^? to the I^π = 17^? state, is interpreted as an octupole vibrational band. The level scheme can be well reproduced in the vibrational limit of the interacting boson approximation (IBA1) which fails, however, to explain the strong E1 feeding of the negative-parity band from the ground-state band     

High-spin states in 222Th

Levels to spin 16⁺ in the ground band and 17^? in the octupole band in ²²²Th have been identified using the reaction ²⁰⁸Pb(¹⁸O, 4n)²²²Th at 93 MeV. To suppress intense γ-ray background from fission a residue detector was built and operated in coincidence with the Ge(Li) and NaI(Tl) detectors. The apparent moment of inertia in the ground-state rotational band rises very rapidly with increasing spin, however, no indications of backbending were observed. The octupole band at low spin has an aligned angular momentum $\text{J ≈ 3}\text{h}\text{?}$ relative to the ground-state band. Strong cross-band E1 transitions competed with collective E2 transitions within each band. Analysis showed that the ratios $\text{B(}\text{E}\text{1)}\text{B(}\text{E}\text{2)}$ were within experimental uncertainty independent of both the spin and parity of the parent state.The average γ-ray multiplicity per cascade was measured for ²²²Th. The results were in reasonable agreement with the computer code ORNL-ALICE.     

High-spin states in 34CI

High-spin yrast states in ³⁴Cl have been studied with the reactions ³¹P(α, nγ)³⁴Cl at E_α = 11.7?16.3 MeV and ²⁴Mg(¹²C, pnγ)³⁴Cl at E(¹²C) = 32–35 MeV. Ambiguities in the ³⁴Cl level scheme for levels at E_x = 4.82 and 5.32 MeV have been resolved through combination of threshold measurements with the ³¹P + α reaction and gamma-gamma coincidence and E_γ-measurements with the ²⁴Mg + ¹²C reaction. Gamma-gamma coincidence and in-beam γ-γ angular correlation experiments have been performed employing a Compton-suppression spectrometer with a solid angle of 120 msr.Unambiguous spin-parity assignments of J^π = 6^?, 5⁺ and 7⁺ to the ³⁴Cl levels at E_x = 4.74, 4.82 and 5.32 MeV, respectively, are obtained.Previously unreported levels of high spin are found at E_x = 7.25 and 7.80 MeV with J^π = (9⁺) and (8⁺); τ_m = 200 ± 70 fs and 100 ± 70 fs, respectively. Excitation energies, mean lives, branching ratios and multipole mixing ratios are reported. The experimental results are compared with large-scale shell-model calculations. The high-spin yrast levels can be characterized by a rather simple shell-model structure.     

High-spin states in 92Tc

High-spin states in ⁹²Tc have been studied using the 33 MeV ⁹²Mo(³He, p2nγ)⁹²Tc reaction. Levels up to J = (13) are identified. The results are compared with various shell-model calculations.     

High-spin states of 39K and 42Ca

High-spin states of ³⁹K and ⁴²Ca have been investigated with the ²⁸Si(¹⁶O, αpγ)³⁹K and ²⁸Si(¹⁶O, 2pγ)⁴²Ca reactions at a beam energy of 45 MeV. Gamma-gamma coincidence, γ-ray angular distribution and linear polarization measurements were performed with a Ge(Li)-NaI(Tl) Compton suppression spectrometer and a three-crystal Ge(Li) Compton polarimeter. High-spin states of ³⁹K at E_x = 7.14,7.78and8.03 and of ⁴²Ca at E_x = 7.75MeV are established. Unambiguous spin-parity assignments of $\text{J}{}^{\mathrm{\pi }}\text{=}\text{11}\text{2}{}^{\mathrm{?}}\text{,}\text{13}\text{2}{}^{\mathrm{?}}\text{,}\text{15}\text{2}{}^{\mathrm{+}}\text{,}\text{15}\text{2}{}^{\mathrm{?}}\text{,}\text{17}\text{2}{}^{\mathrm{+}}\text{and}\text{19}\text{2}{}^{\mathrm{?}}$ to the ³⁹K levels at E_x = 5.35, 5.72, 6.48, 7.14, 7.78 and 8.03 MeV and of 6^?, 7^?, 8^?, 9^? and(8, 10)^? to the ⁴²Ca levels at E_x = 5.49, 6.15, 6.41, 6.55 and 7.37 MeV, respectively, have been obtained. Further spin-parity restrictions, lifetime limits, excitation energies, branching ratios and multipole mixing ratios are reported. Discrepancies with previous J^π assignments are discussed in detail.     

High-spin states in 107Sn and 107In isotopes

The isotopes ¹⁰⁷Sn and ¹⁰⁷In were produced through the ¹⁰⁶Cd(³He, 2n)¹⁰⁷Sn and ¹⁰⁶Cd(³He, pn)¹⁰⁷In reactions. They were studied by means of γ-spectroscopy, excitation functions, γγ coincidences and angular distributions of γ-rays. A level scheme is proposed for the newly discovered ¹⁰⁷Sn, and new states belonging to ¹⁰⁷In are given. Microscopic calculations have been performed in a three-quasiparticle approximation for a large number of tin isotopes in order to get a wide view of the systematic evolution of the various states.     

High-spin states and rotation-particle coupling in 179W

The ¹⁷⁸Hf(α, 3n)¹⁷⁹W and ¹⁸¹Ta(p, 3n)¹⁷⁹W reactions are used to populate rotational states in ¹⁷⁹W. Particular attention is paid to the strongly perturbed positive-parity bands. The rotational energies within these bands are successfully explained within the unified model with pairing and Coriolis interactions included if the theoretical Coriolis matrix elements are reduced. The wave functions are calculated from a fit to the experimental energies and the theoretical and experimental transition probabilities are compared. Rotational bands built on the $\text{7}\text{2}$^?[514], $\text{1}\text{2}$^?[521] and $\text{5}\text{2}$^?[512] intrinsic states are also observed.     

High spin rotational states in 154Dy, 164Er And 162Yb

High spin rotational states in ¹⁵⁴Dy, ¹⁶⁴Er and ¹⁶²Yb have been investigated with (α, 4nγ) and (α, 6nγ) reactions. The ground state rotational bands have been identified up to spin 14 for ¹⁵⁴Dy and ¹⁶²Yb and spin 16 for ¹⁶⁴Er. Anomalous behaviour of the moment of inertia has been observed in ¹⁶⁴Er.     

High-spin states in 201Bi populated in the (α, 6n) reaction

High-spin States in ²⁰¹Bi are investigated by observing γ-rays in the reaction ²⁰³Tl(α, 6n)²⁰¹Bi. Three isomers are observed with suggested spins of $\text{17}\text{2}{}^{\mathrm{+}}\text{,}\text{21}\text{2}{}^{\mathrm{+}}$ or $\text{25}\text{2}{}^{\mathrm{+}}$ and $\text{29}\text{2}{}^{\mathrm{?}}$ and half-lives of 9.5 ns, 210 ns, and 160 ns. The level systematic of odd Bi isotopes with 201 ? A ? 207 is presented.     

The g-boson and the collective states of 168Er

Comparison between the IBM-I, IBM-II and the U(15) theories of the ¹⁶⁸Er spectrum, together with an analysis of the boson weights, supports the incorporation of the g-boson.