Identification of a new isotope154Pr

The heaviest isotope of praseodymium,¹⁵⁴Pr, has been identified for the first time by γ-ray measurements of mass-separated activities obtained from a He-jet type on-line isotope separator for fission products of²³⁵U. The Nd-K X-rays and 10 γ-rays have been assigned to be generated by the β-decay of¹⁵⁴Pr. The half-life has been determined to be 2.3(1) s, which is not far from the theoretical predictions of 1.5 s and 4.0 s.     

Studies on the level structure of154Gd via the β-decay of154Eu nucleus

The excited states of¹⁵⁴Gd populated by theβ-decay of¹⁵⁴Eu (T _1/2=8.5y) have been studied. With a HPGe-NaI (T1) Compton suppression spectrometer and a HPGe-NaI(T1) coincidence circuitυ-ray singles spectra, coincidence spectra and theγ-γ directional correlational functions have been obtained. The deduced mixing ratios of multipolarities are presented. The energy levels and the relativeB(E2) values of the variousγ-transitions in¹⁵⁴Gd nucleus have been calculated both in the IBA model and it's extended version with boson surface delta interaction (BSDI).     

Levels in154Eu populated by thermal neutron capture

The level scheme of¹⁵⁴Eu has been investigated by means of thermal neutron captureγ-rays and conversion electrons. The high energyγ-ray spectrum from thermal neutron capture in enriched¹⁵³Eu has been studied in the energy range of 5700 to 6500 keV. Low energyγ radiation has been observed with Ge(Li) and Si(Li) detectors from 5 to 300 keV and conversion electrons have been measured from 15 to 300 keV. Low energy (n, γγ) coincidences and half lives of transitions have been measured. The data, combined with three very recent studies of the 8^? isomer decay in¹⁵⁴Eu has led to the construction of a level scheme with 12 excited levels. Nuclear Reaction¹⁵³Eu(n, γ),E _n =thermal, measuredE _γ ,I _γ ,E _ce ,I _ce ,γγ-coincidence, halflives,¹⁵⁴Eu deduced levels.     

High-spin structure in154Er

High spin states in the nucleus¹⁵⁴Er have been reinvestigated using the¹²³Sb(³⁵Cl, 4n) reaction and a variety of spectroscopic techniques including excitation functions,γ-γ coincidences,γ angular distribution and linear polarization measurements. From the measured energies, relative intensities and transition multipolarities a new level scheme has been deduced up to an excitation energy of ～12 MeV and spin 36. An interpretation of the experimental results is given in terms of the deformed Woods-Saxon orbitals. Gigantic backbending (superdeformation) effect is studied theoretically within the cranking model.     

Angular correlation measurements in154Gd

γ-γ angular correlation measurements were performed to determine the mixing parameters δ of some γ-transitions in¹⁵⁴Gd. High energy compton background could easily be eliminated using a two dimensional data aquisition system. The relativeB (E2)-values of (K=2→K=0) interband transitions were determined and compared with collective model predictions. Radioactivity:¹⁵⁴Eu[from¹⁵³Eu(n, γ)], enriched target. \(^{154} Eu\xrightarrow{{\beta ^{ --} }}^{154} Gd.\)      

High-spin states in154Er

High-spin states in¹⁵⁴Er have been populated by bombarding¹⁴⁷Sm and¹⁴⁸Sm with¹²C particles. Excitation functions, lifetimes, angular distributions andγ-γ coincidences were measured. AT _1/2=35ns isomeric state atE _x～3 MeV has been found and is interpreted as a two-quasi-particle state with aligned angular momenta. A cascade of intense individual lines from states with spin up to at least 26 (excitation energy up to 8.543 MeV) was found to feed the isomeric state. The level sequence above this yrast trap exhibits an irregular pattern which cannot be easily interpreted in terms of collective modes.     

High-spin states in the single-closed-shell nucleus 142Nd

The excited states of ¹⁴²₆₀Nd₈₂ have been studied using the ¹⁴⁰Ce(α, 2nγ)¹⁴²Nd and ¹⁴²Ce(α, 4γ)¹⁴²Nd reactions. Singles γ-ray, γ-γ coincidence spectra and angular distributions of γ-rays with respect to the beam direction have been measured. Excited states up to 6.7 MeV with spin values up to 14 are populated. The energy spacings between the lower excited states with spin values up to 8 are similar to those found in the lighter N = 82, even-Z isotones. The majority of the observed states with spin values up to 10 can be explained as two-quasiparticle states. Several of the highest-spin states can be explained qualitatively as fourquasiparticle states. Strong population of the highest excited states (at about 5.7 MeV) is noted, like in other N = 82 isotones. The observed levels in ¹⁴²Nd are compared with the shell model predictions using a simple δ-force interaction between two nucleons.     

Level structure of149Nd. The decay of149Pr

The decay of¹⁴⁹Pr (T _1/2=2.2 min) has been studied using the two fission product separators JOSEF and LOHENGRIN to produce the¹⁴⁹Pr nucleus. A level scheme for¹⁴⁹Nd has been established. Theβ-branching and logft values for the excited levels were deduced from the analysis ofγ-intensity balances. Furthermore, the spins and parities for most of the excited states observed were obtained from the comparison between the present work, the neutron capture results and the pick-up reactions. The positive parity levels have been described with the Nilsson model with Coriolis andΔN=2 interactions included. The properties of the negative parity states cannot be explained as easily; however, it has been attempted to extract the structure of the ground state \((I^\pi = \tfrac{5}{2}^ - )\) and the first excited states \((I^\pi = \tfrac{7}{2}^ - and\tfrac{3}{2}^ - )\) .     

Gamma-gamma directional correlations and coincidence studies in154Gd

The intensities, placements andE2/M1 mixing ratios of transitions in the decay of¹⁵⁴Eu have been carefully studied to provide accurate data for microscopic calculations. Coincidence relationships in the decay of¹⁵⁴Eu have been studied extensively with a multiparameterγ-γ coincidence system with two large volume Ge(Li) detectors. Spectra in coincidence with twenty energy gates were analyzed. Twenty-nine new coincidence relationships were established and confirmed most, but not all, of several levels previously assigned by energy fits only. From an analysis of coincidence spectra and singles spectra with a 18% efficiency Ge(Li) detector new information on the gamma-ray intensities were obtained. Precise values of theE2/M1 mixing ratios of transitions from the gamma- and beta-vibrational bands to the g.s. band have been determined fromγ-γ directional correlation measurements with a NaI(Tl)-Ge(Li) detector coincidence system. Mixing ratios were obtained for a number of other transitions including those fromK ^π =0^? and 2⁺ bands from direct and skipped cascade correlations.     

A muonic X-ray study of the charge distribution of 144, 148, 150, 152, 154Sm

We report the measurement of the energies of the 4f → 3d, 3d → 2p and 2p → Is muonic atomic transitions in separated isotopes of ^{144, 148, 150, 152, 154}Sm, and that of the 2s → 2p transitions of ¹⁵²Sm as well. Using these transition energies as well as the hyperfine splittings of the 2p levels, we have interpreted our data in terms of a deformed Fermi distribution for the charge density and obtained good fits. A model independent analysis of the isotope shifts in terms of generalized R_h moments has been made and is in good agreement with electronic X-ray and optical isotope shifts. The static quadrupole moments and the isomer shifts of the first excited state of ^{152, 154}Sm have been determined from the 2p hyperfine structure.     

The γ-decay of two-particle states in 210Bi

The γ-decay of excited states in ²¹⁰Bi up to 3330 keV excitation energy has been studied using the ²⁰⁹Bi(d, pγ)²¹⁰Bi reaction. From the observed decay scheme, tentative J^π values are made for 25 states. The excitation energies, (d, p) strengths and decay branching ratios of these states are compared with those calculated using the two-particle shell-model wave functions of Kim and Rasmussen and Kuo and Herling.     

Excited states of154Nd studied through the decay of154Pr

Excited states in the neutron-rich doubly-odd nucleus⁷⁸As have been identified for the first time by proton-γ and γ-γ coincidence measurements via the⁷⁶Ge(α, pn) reaction at 32, 36, and 40 MeV beam energy. Four levels have been found to decay with lifetimes in the nanosecond region. The 5⁽⁺⁾ to (10⁺) states are ascribed to the (πg _9/2?νg _9/2) intruder two-quasiparticle configuration with some collective components in the 9⁽⁺⁾ and (10⁺) states.     

High spin states in107Ag

¹⁰⁷Ag hasbeen investigated by the reactions¹⁰⁴Ru(⁶Li, 3nγ) and¹⁰⁴Ru(⁷Li, 4ny). γ-singles spectra,γ-γ-Δt-coincidences,γ-angular distributions and polarization measurements were taken. A level scheme has been established, spins and parities have been assigned.     

Decay of 129Ce to low-lying positive-parity states in 129La

Low-lying levels of the ¹²⁹La isotope have been investigated through the β⁺/EC decay of ¹²⁹Ce. The radioactive nuclei were produced in the ⁹⁴Mo+⁴⁰Ca reaction at a bombarding energy of 255 MeV and transported with a He-jet system. On-line mass separation was used to select the ¹²⁹Ce beta-decay γ-γ-t, X- γ- t, e^?-γ -t coincidence measurements as well as time multi-analysis were performed. Internal conversion electrons were recorded with a magnetic selector and multipolarities deduced. The level scheme of ¹²⁹La is discussed and compared with the calculations made in the frame of the neutron-proton Interacting Boson-Fermion Model (IBFM-2).     

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.     

A comparative study of the electric giant dipole resonance of 24−26Mg

The electric giant dipole resonance of ^24?26Mg has been explored up to 30 MeV excitation energy with bremsstrahlung. ΔE, E spectra of charged photo-particles and spectra of prompt deexcitation γ-rays from excited residual nuclear states were obtained at various bremsstrahlung endpoint energies. The ²⁵Mg(γ, p₀), (γ, d), ^24,25Mg(γ, α) differential cross sections as well as ^24?26Mg(γ, xγ′) integrated cross sections are presented. The results are discussed in terms of one-particle, one-hole excitations and isospin composition of giant resonance states. A comparison with calculations for ²⁴Mg gives poor agreement. Excitations from deeper shells were found in the giant dipole resonance of ²⁴Mg, but do not seem to be concentrated at higher energies. In ²⁵Mg, only weak excitations of this kind were found, and they are completely absent in ²⁶Mg.     

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.     

The decay scheme of the 3-s Isomer of100Nb and the properties of levels in100Mo

Theβ ^? decay of the longer-lived isomer in¹⁰⁰Nb has been studied at the fission-product separator JOSEF. Measurements ofγ-ray singles spectra, ofγ-γ coincidences and ofγ-γ angular correlations have been performed. A value oft _1/2=2.99(11)s has been determined for the isomer which probably hasI ^π=4⁺ or 5⁺. A scheme of the levels of¹⁰⁰Mo which are populated in the decay of this isomer has been established. Information on the spins of several states of¹⁰⁰Mo has been obtained. Thus,I=0 levels have been identified at 1,505, 2,038 and 2,087 keV. The mixing ratios have been determined for the 2₂ ⁺→2₁ ⁺ and 2₃ ⁺→2₁ ⁺ transitions. The results provide evidence for a vibrational structure of¹⁰⁰Mo with separate bands based on the ground state and on the first excited 0⁺ level.     

Level structure and lifetimes of excited states in 48Ti

The properties of excited states in ₂₂⁴⁸Ti₂₆ populated by means of the ⁴⁵Sc(α, pγ)⁴⁸Ti reaction were investigated. The Doppler-shift attenuation method was employed to determine the mean lives of 16 levels up to an excitation energy of 4073 keV. Proton-γ coincidence techniques were used to record simultaneously the Doppler-shifted de-excitation γ-rays emitted at 26 and 154 degrees to the incident beam direction. A comprehensive level and decay scheme is proposed. Detailed shell-model calculations have been made of M1 and E2 transition matrix elements for depopulation of states whose lifetimes have been measured. Salient nuclear structure aspects of this “self-cross-conjugate” nucleus are examined in light of critical comparisons of measured and calculated Ml and E2 reduced transition probabilities.     

New multi-phonon gamma vibrational bands in A∼110 neutron-rich nuclei

The high spin states of neutron-rich ¹⁰³Nb, ¹⁰⁷Tc and ¹⁰⁹Tc nuclei in A～110 region have been investigated by measuring prompt γ-γ-γ coincident measurements populated with the spontaneous fission of ²⁵²Cf with the Gammasphere detector array. In ¹⁰³Nb, one-phonon K = 9/2 and two-phonon K = 13/2 γ-vibrational bands have been identified. In ¹⁰⁷Tc and ¹⁰⁹Tc, one-phonon K = 11/2 and two-phonon K = 15/2 γ-vibrational bands, in which the zero-phonon bands are based on K=7/2 excited states, have also been identified. The two-phonon bands are first observed in odd-Z nuclei. The characteristics for these band structures have been discussed.