K.-H. Kaun

High-spin rotational states in 177, 173Lu and evidence for ΔK = 2 and ΔK = 4 mixings

Abstract The level schemes of the deformed odd-proton nuclei 171 Lu and 173 Lu have been studied by in-beam spectroscopy. Measurements of singles γ-ray spectra, angular distributions and γ-γ coincidences were performed in the 169 Tm(α, 2nγ) 171 Lu reaction at 27 MeV α-particle energy. In the reaction 173 Yb(d, 2nγ) 173 Lu singles spectra and γ-γ coincidences were measured. Additional γ-ray spectra were taken for the reactions 169 Tm(α, 2nγ) 171 Lu at E α = 23 MeV and 173 Yb(p, nγ) 173 Lu. The proposed level schemes of 171 Lu and 173 Lu involve rotational bands of the intrinsic states 7 2 + [404] , 1 2 + [411] , 5 2 + [402] , 1 2 − [541] and 9 2 − [514] up to spin 25 2 , 23 2 , 23 2 , 29 2 and 21 2 , respectively, in 171 Lu and up to spin 23 2 , 17 2 , 19 2 , 25 2 , and 23 2 , respectively, in 173 Lu. Transitions between some states of the 1 2 + [411] and 5 2 + [402] bands in 171 Lu indicate a strong mixing of states with ΔK = 2. Similarly, a ΔK = 4 mixing between states of the 1 2 − [541] and 9 2 − [514] bands in 171 Lu is indicated by interband transitions. These mixings are described in terms of the rotation-particle coupling, considering only the interaction between states with K and K ±1. The dependence of the side feeding to the 1 2 − [541] and 7 2 + [404] bands on the level spins and energies was investigated.

Levels in 167Tm excited in the reaction 165Ho(α, 2nγ)167Tm

Abstract Using in-beam techniques the γ-radiation following the reaction 165 Ho(α, 2nγ) 167 Tm has been studied with germanium detectors. Measurements of energies and intensities, angular distributions and γγ-coincidences were performed at a bombarding energy of 27 MeV. Furthermore the relative intensities of the γ-transitions have been measured at α-particle energies of 21, 23 and 25 MeV. A level scheme of 167 Tm has been established containing rotational levels of the single-particle states 1 2[411] , 7 2[404] and 7 2[523] up to spin values 23 2 , 23 2 and 23 2 , respectively. An additional rotational band with the members 9 2 − , 13 2 − , 17 2 − , 21 2 − and 25 2 − was found and interpreted as due to the 1 2[541] Nilsson orbital. In order to describe the rotational energies we used in the energy formula one or two terms with alternating sign for the 7 2 and 1 2 bands, respectively. The quantities ( g K − g R) 2 / Q 2 and [( g K − g R)/ Q ] 2 (1 ± b 0 ) 2 were evaluated.

Rotational states and rotation-particle coupling in 155Tb and 157Tb

Abstract For the investigation of excited states of the odd-proton nuclei 155 Tb and 157 Tb, studies have been made of the γ-radiation emitted in the reactions 153 Eu(α, 2n), 155 Gd(d, 2n) and 155 Gd(p, n) as well as 157 Gd(d, 2n) and 157 Gd(p, n), respectively. Measurements of coincidence relations were performed in the reactions with α-partieles and deuterons. Furthermore, in the reaction with α-partieles excitation functions and angular distributions γ-rays were measured. The level schemes proposed for 155 Tb and 157 Tb are very similar. They contain the band heads (energies are given in keV for 155 Tb and 157 Tb, respectively) 3 2 + [411] (ground state), 5 2 + [413] (271.3; 327.6), 7 2 + [404] (466.9; 658.6), 5 2 − [532] (227.0; 326.4) and 7 2 − [523] (545.3; 571.7), as well as several rotational states. In both nuclei the distorted rotational band built on the 5 2 − [532] band head has been analyzed in terms of the Coriolis coupling between the Nilsson orbitals based on the H 11 2 . shell-model state. In 155 Tb the Coriolis coupling (mainly with the 7 2 + [404] orbital) gives rise to an energy difference of only 63.7 keV between the 7 2 and 5 2 members of the 5 2 + [413] band.

Levels in 171Lu from the reactions 169Tn(α, 2nγ)171Lu and 171Yb(d, 2nγ)171Lu

Abstract Gamma radiation following the reactions 169 Tm(α, 2nγ) 171 Lu and 171 Yb(d,2nγ) 171 Lu has been studied using Ge(Li) detectors. Measurements of energies and intensities, γγ coincidences and angular distributions have been performed with α-particle and deuteron energies of 27 MeV and 13.5 MeV, respectively. Excitation data were derived from γ-ray intensity measurements at α-particle energies of 21, 23, 25 and 27 MeV. A level scheme is proposed involving Nilsson states 7 2 + [404], 1 2 + [411], 1 2 − [541], 5 2 + [402] and 9 2 − [514] and rotational bands up to spin values 23 2 , 19 2 , 25 2 , 17 2 and 11 2 , respectively. In the band 1 2 − [541] ( a ≈ 3) not only the low-lying sequence I+ 1 2 = odd was found but also 4 levels of the disfavoured sequence I+ 1 2 = even . Energies of rotational states were analysed in terms of a formula with four rotational parameters including one or two alternating sign terms for bands with K ≠ 1 2 or K = 1 2 , respectively. The perturbation of the 1 2 − [541] band caused by Coriolis mixing with the 3 2 − [532] band has been evaluated. The quantities (g K −g R ) 2 Q 2 0 , b 0 or (1−b 0 ) 2 (g K −g R ) 2 Q 2 0 have been deduced.

Rotational bands in 185Os and 187Os

Abstract The excited states of the odd-neutron nuclei 185 Os and 187 Os were investigated by in-beam γ-ray measurements using the reactions 183 W(α, 2n), 187 Re(d, 2n) and 187 Re(p, n). High-resolution singles γ-ray spectra and γ-γ coincidence spectra were measured. In addition, excitation functions and angular distributions of the γ-rays were determined for 185 Os. From the measurement of the delayed γ-radiation and the results of the γ-γ coincidence experiments, two isomers were found in 185 Os at energies of 102.3 and 275.7 keV. They were interpreted, quite similar to the known isomers in 187 Os, as being the Nilsson states 7 2 − [503] and 11 2 + [615] , respectively. Furthermore, in 185 Os the rotational states built on the ground state 1 2 − [510] up to spin 25 2 as well as the rotational bands built on the two isomeric states and on the 9 2 + [624] configuration were found. Interband transitions between some members of the bands based on the configurations 1 2 − [510] and 7 2 − [503] in 185 Os indicated a strong mixing of the two I = 13 2 rotational members which are very close in energy. This mixing of states with a difference of 3 units in the K quantum number was described by a Coriolis coupling calculation including only first-order matrix elements. Further calculations were performed to describe the 1 2 − [510] ground state band and the strongly perturbed 11 2 + [615] band. In 187 Os, the rotational bands belonging to the Nilsson states 7 2 − [503] and 11 2 + [615] were followed up to spin values of 17 2 and 19 2 , respectively.

Der Zerfall von 162Tb und 163Tb

Abstract The decay of 162 Tb and 163 Tb has been investigated with a Ge(Li) detector and a two-dimensional scintillation coincidence spectrometer. The half-lives of these isotopes are 8.0±0.5 min and 19.5±0.5 min, respectively. The activities were produced by (γ, p) reactions using the bremsstrahlung of a betatron. A decay scheme of 162 Tb is proposed which contains a 2 − level in 162 Dy at 1148 keV interpreted as a two-quasi-particle state K , K +11 of the proton system with the quantum numbers [411↑+523↑]. The ground state of 162 Tb has the spin and parity J π = 1 − . In the decay of 163 Tb about 30 gamma lines were observed. A proposal for the decay scheme is given and the characteristics of the levels in 163 Dy are discussed in the framework of the unified model.

Rotational bands and fast el transitions in 163Ho

Abstract The level scheme of the deformed odd-proton nucleus 163Ho has been investigated by in-beam and decay spectroscopic methods. Single γ-ray spectra, conversion electron spectra, γ-γ coincidences and angular distributions of the γ-rays were measured in the reaction 163Dy(d, 2nγ) at a deuteron energy of about 13.5 MeV. Single γ-ray spectra were also taken in the 163Dy(p, nγ) reaction with 6.7 MeV protons. Additional information on the 163Ho level scheme was obtained by re-investigating the γ-radiation in the electron capture decay of 163Er. The proposed level scheme of 163Ho contains in addition to the ground state band 7 2 − [523] the rotational bands built on the intrinsic states 7 2 + [404], 3 2 + [411], 1 2 + [411] and 7 2 − [541] (band heads at 439.94, 360.36, 297.88 and 471.25 keV, respectively). Further levels at 1113.5, 876.0 and 614.3 keV are interpreted as being mainly the quasiparticle excitations 5 2 − [532], 5 2 + [413] and possibly the ground state γ-vibration, respectively. A comparison of the quasiparticle excitations in the Ho isotopes is performed on the basis of the Nilsson model including pairing corrections. Discontinuities in the rotational bands are described by Coriolis coupling effects. Several fast E1 interband transitions were observed in 163Ho. Some of them connect levels of the 1 2 + [411] band with the ground state band 7 2 − [523]. The appearance of these K-forbidden transitions is explained by a weak mixing between states of the bands 7 2 + [411] and 7 2 + [404] caused by Coriolis interaction.

Rotational bands in 161Ho

Abstract The excited states of the deformed odd-proton nucleus 161 Ho have been studied in the reactions 159 Tb(α, 2n), 161 Dy(d, 2n) and 161 Dy(p, n). Gamma-ray spectra in single and coincidence modes as well as angular distributions and excitation functions of the transitions were measured. The proposed level scheme of 161 Ho contains besides of the ground state band 7 2 − [523] the bands 7 2 + [404], 3 2 + [411], 1 2 + [411] and 1 2 − [541] (band heads at 252.7, 298.7, 211.2 and 423.9 keV, respectively). An attempt was made to estimate the influence of Coriolis coupling between the bands 1 2 + [411] and 3 2 + [411], which are very close in energy. The 7 2 + [404] band was found to de-excite by very fast E1 transitions to the ground state band 7 2 − [523]. Nilsson retardation factors of about 0.03 for these transitions were deduced using the E2 E1 branching ratios. An investigation has also been made of the independent feeding of the levels from high-lying states.

Zum Elektroneneinfang-Zerfall des Hf175

By measurements of the KX-γ-coincidence spectra of Hf175 the K electron capture probability of the transition to the 433 keV level in Lu175 was found to be PK = 0.68±0.04. From this one obtains a decay energy Q433 = 157±2030 keV for the transition to this level. The log ft values of the electron capture transitions determined with the total decay energy Q = 590keV are in good agreement with data of corresponding transitions in neighbouring nuclei. In the γγ-coincidence spectra the 319 keV γ-transition was observed, the intensity relative to the 343 keV transition being I319I343 = 2.0 · 10−3.

Der elektroneneinfang-zerfall des 140 d Lu174i

Abstract In the decay of Lu sources produced by the reactions Yb(d, 2n) and Lu(n, 2n) we found two new cascades 995-280-175-76.5 keV and 630-365-280-175-76.5 keV. The intensity ratio of the cascades 995-280 keV and 630-365 keV is I995−280/I630−365=41±5. The measurement of the half life time permits the attribution of the transitions to the electron capture decay of the isomeric state of Lu 174 (T 1 2 = 140 d ) . A level scheme is proposed which contains a level at 1526 keV with Iπ = 7− interpreted as a two quasiparticle state K, K+2 of the neutron system with the characteristic [624↑+512↑]. Coming from this state the 995 keV and 630 keV transitions populate a 532 keV level (6+) and a 897 keV level (8+), belonging to the ground state rotational band.