Rotational bands in the doubly odd 130Cs nucleus

The band structures built on the 5^- isomeric state ( T _1/2 = 3.46 m) in the doubly odd ¹³⁰Cs nucleus have been established up to I = 24? via the ¹²⁴Sn(¹¹B, 5n)¹³⁰Cs reaction. The previously observed bands based on the πh _11/2⊗νh _11/2, πg _7/2⊗νh _11/2 and πd _5/2⊗νh _11/2 configurations and a positive-parity side band with multiple connections to the α = 0 signature partner of the yrast πh _11/2⊗νh _11/2 band have been extended to higher spins. A new band based on the πh _11/2⊗νg _7/2 configuration is observed. The yrast πh _11/2⊗νh _11/2 band exhibits anomalous signature splitting whose magnitude decreases up to spin 15 and then increases without restoring the normal signature splitting. Received: 20 February 2001 / Accepted: 9 May 2001     

A simple model for doublet bands in doubly odd nuclei

Nuclear structure of doublet bands in doubly odd nuclei with mass A ∼ 130 is investigated within the framework of a simple model where the even-even core couples with a neutron and a proton in intruder orbitals through a quadrupole-quadrupole interaction. The model reproduces quite well the energy levels of doublet bands and electromagnetic transitions. The staggering of the ratios B(M1;I → I - 1)/B(E2;I → I - 2) of the yrast bands turns out to be described by the chopsticks-like motion of two angular momenta of the unpaired neutron and the unpaired proton when they are weakly coupled with the core.-1 An erratum to this article is available at .     

The doubly odd nucleus 144Pm: (II). Interpretation

Results from the proton transfer reactions, ¹⁴³Nd(³He, d) and ¹⁴³Nd(α, t), and γ-ray studies have been used to characterize the levels in ¹⁴⁴Pm. The spins, $\text{(}{}^3\text{He, d)}\text{(α, t)}$ cross section ratios and γ-ray branching ratios for the states below 600 keV can be interpreted consistently in terms of the mixed $\text{π2}\text{d}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}\text{ν2}\text{f}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}$ and $\text{π1}\text{g}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}\text{ν2}\text{f}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}$ shell-model configurations. The γ-ray intensity ratios measured in the ¹⁴¹Pr(α, nγ) and ¹⁴⁴Nd(p, nγ) reactions exhibit a strong and smooth dependence on level spin. Theoretical calculations employing a residual surface delta interaction are in reasonable agreement with the twelve observed low-lying negative parity states. The eight positive parity states between 841 and 1451 keV are presumed to arise from the $\text{π1}\text{h}{}_{\mathrm{<mtext>11</mtext><mtext>2</mtext>}}\text{ν2}\text{f}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}$ configuration.     

A 45 ns 8+ isomer in the doubly odd150Eu nucleus

In the doubly odd ₆₃ ¹⁵⁰ Eu⁸⁷ nucleus a 45 ns 8⁺ isomer at 589 keV excitation has been identified through (p, 3n) in beamγ ande ^? measurements. The low lying negative parity levels populated in its decay show great similarity to analogous states in the lighter odd-odd Eu neighbours suggesting a spherical shape for¹⁵⁰Eu. A spherical shape is also proposed for the isomer which is assigned as (πh _11/2 vf ₇ ^2/?3 )8⁺ state analogous to the 9⁺ isomers known in¹⁴⁸Eu and¹⁴⁶Eu. The spin change is attributed to the crossing of the half-filledf _7/2 neutron shell atN=86.     

First observation of the excited states in the doubly odd nucleus118Cs identified throughγ-recoil coincidences

The previously unknown nucleus¹¹⁸Cs has been identified through γ-γ and γ-recoil coincidences using the GASP γ-spectrometer and Recoil Mass Spectrometer. The level scheme constructed on the base of triple γ coincidences shows a collective structure based on the π^?1g_9/2?νh_11/2 configuration.     

Low-spin states of doubly odd 182Au

Low-lying states in the odd-odd light gold isotope ¹⁸²Au have been populated by the β⁺/EC decay of the ¹⁸²Hg nuclei. Level energies, spin and parity values were determined using on-line γ-ray and e^- spectroscopy measurements. No isomeric state with a long half-life was found in the ¹⁸²Au nucleus. Spin and parity I ^π = 2⁺ can be very likely assigned to the ¹⁸²Au ground state. Received: 19 December 2000 / Accepted: 28 February 2001     

Level structure of doubly odd154Ho

¹⁵⁴Ho was studied via¹⁴¹Pr(¹⁶O,3n) reaction at beam energy of 75 MeV. We found two new rotationally aligned bands made of neutron h_9/2 and f_7/2 orbitals coupled to a proton h_11/2 orbital. As with several new high-spin states, up to I=20, the ground state band with odd parity starts to show anomalous signature splitting at I=13 in this doubly odd¹⁵⁴Ho. The observed rotational bands in¹⁵⁴Ho are quite consistent with the onset of collectivity which appears in general at neutron number of 87 in neutron-deficient rare-earth nuclei.     

Low-spin states of doubly odd 184Au

Low-spin states of ¹⁸⁴Au have been studied using the β⁺/EC decay of ¹⁸⁴Hg. γ-ray and conversion-electron singles spectra were recorded with ¹⁸⁴Hg mass-separated sources. For γ-γ-t and X-γ-t coincidence measurements, mercury nuclei were produced in the ¹⁴⁸Sm + ⁴⁰Ar reaction and transported by a He-jet system. The electron spectra were recorded from ¹⁸⁴Hg sources produced at ISOLDE. A level scheme of ¹⁸⁴Au including 48 transitions is proposed. The experimental results are interpreted in the frame of a semi-microscopic axial-rotor-plus-two-quasiparticle model developed in the context of the HF+BCS approximation.     

First observation of low lying states in the doubly odd nucleus132Pr from beta decay of132Nd

Excited states of ¹⁰⁸ Te were populated in the ⁵⁴ Fe + ⁵⁸ Ni (270 MeV) reaction using the NORDBALL detector array equipped with charged-particle and neutron detector systems for reaction channel separation. Gamma rays belonging to the neutron deficient nucleus ¹⁰⁸ Te were identified for the first time. On the basis of γγ-coincidence and angular correlation relations a level scheme was constructed with tentative spin and parity assignments. The structure of the nucleus is discussed in the framework of systematics of heavier Te nuclei.     

Particle-rotor model for doubly odd transitional nuclei of the Tl-region

A model has been investigated describing a situation in which two noninteracting high-j Nilsson-BCS quasiparticles move in the deformed field of an axially and reflection symmetric rotor. According to the positions of thej-shells with respect to the proton and neutron Fermi surfaces structures of different character emerge referred to as semi- and doubly-decoupled. In particular, strongly Coriolis-distorted bands recently reported in doubly odd Tl nuclei are discussed. Also \(\tilde \pi h_{9/2} \) bands in neighbouring odd mass Tl isotopes are analysed on the same footing. It is shown that the pronounced odd even staggering of the transition energies can be understood as a specific quantal feature associated with the Coriolis interaction.     

Investigation of the two-quasiparticle bands in the doubly-odd nucleus 166Ta using a particle-number conserving cranked shell model

The high-spin rotational properties of two-quasiparticle bands in the doubly-odd ~(166)Ta are analyzed using the cranked shell model with pairing correlations treated by a particle-number conserving method, in which the blocking effects are taken into account exactly. The experimental moments of inertia and alignments and their variations with the rotational frequency ω are reproduced very well by the particle-number conserving calculations, which provides a reliable support to the configuration assignments in previous works for these bands. The backbendings in these two-quasiparticle bands are analyzed by the calculated occupation probabilities and the contributions of each orbital to the total angular momentum alignments. The moments of inertia and alignments for the Gallagher-Moszkowski partners of these observed two-quasiparticle rotational bands are also predicted.     

Gamma deexcitation of the 180m Ta isomer

Vibrational states built on the K ^π = 9^? isomer and on the ground state (K ^π = 1⁺) in ¹⁸⁰Ta are calculated within the quasiparticle-phonon nuclear model using the ¹⁷⁸Hf nucleus as a core. A procedure for calculating the rates of K-allowed γ-ray transitions from vibrational states built on the isomer to those built on the ground state is presented. The probabilities of two-step processes consisting of a dipole excitation of the isomer and successive E1 and E2 transitions from them to vibrational states built on the ground state of the ¹⁸⁰Ta nucleus are calculated. Two-step transitions from the isomer to vibrational states below 2.7 MeV and to the vibrational states built on the ground state appear to be very weak. There are many E1 transitions from the vibrational states built on the isomer to the vibrational states built on the ground state. They are weak and cannot be responsible for the strong deexcitation of ^180m Ta in the relevant (γ, γ′) reaction. A decisive role is played by collective E2 transitions from dipole excitations in several excitation energy intervals ranging between 2.7 and 4.0 MeV. These highly intense K-allowed two-step γ-ray transitions can be responsible for the strong deexcitation of the ^180m Ta state in the (γ, γ′) reactions.     

Study of the yrast band in the doubly odd156Tm

The yrast band in the doubly odd¹⁵⁶Tm nucleus was studied through¹⁴⁴Sm(¹⁹F,2p5n)¹⁵⁶Tm reaction at beam energy of 105MeV. Several high-spin states of¹⁵⁶Tm were identified and the highest spin of the band with configuration7/2^–[523] v1/2⁺[660] could be built up to spin 25. The level structure shows the onset of a non- or weak collectivity which generally appears at neutron number of 87 in neutron-deficient rare-earth nuclei.This work was supported in part by the Fok Ying Tung Education Foundation and the Natural Science Fund of China.     

High-spin states and band structures in the doubly odd <Superscript>136</Superscript>La nucleus

High-spin states of ¹³⁶La have been investigated with the reaction ¹³⁰Te( ¹¹B, 5n) at a beam energy of 60 MeV. The level scheme with three collective bands has been updated with spin up to 20 . The observed h_11/2 h_11/2 band shows -instability with increasing spin according to the TRS calculations. The band crossing and the signature splitting and inversion have been discussed. Other two collective bands based on 12^-and 16⁺ levels were proposed as oblate deformation with -60^°. They most probably originate from four- and six-quasiparticle configurations, that is, h_11/2 g_7/2h_11/2² and g_7/2 g_7/2²d_5/2h_11/2² respectively.     

On the interpretation of rotational bands in odd actinide nuclei

While the cranked quasiparticle model gives too large alignment of angular momentum for the ground state bands of ²³⁵U and ²³⁷Np, the empirical alignments are well reproduced in a quasiparticle plus rotor model with a rotation dependent interaction between core and quasiparticle. This model also gives better agreement with the data than a cranked quasiparticle model with Coriolis attenuation.