On the newly proposed levels in152Gd and152Sm

It is shown that there is no evidence for the existence of levels at 1312.41, 1485.67 and 1698.34 keV in¹⁵²Gd and at 1436.65 and 1681.56 keV in¹⁵²Sm, which were recently claimed to be observed in the decay of¹⁵²Eu(3^–, 15 y).Work supported in part by the Natural Science Fund of China and in part by the Department of Science and Technology of China Nuclear Energy Industry Corporation     

The decay of143Sm to levels in143Pm

The beta decay of¹⁴³Sm was reinvestigated with the aid of a Ge(Li) detector. Levels of¹⁴³Pm at 271.8, 1,056.5, 1,173.4, 1,342.1, 1,403.2, 1,514.9, 1,752.8, 1,816.3, 1,853.6, (2,000), 2,009.0, 2,080.5, 2,344, 2,443, 2,463, 2,906 and (3,054) keV were established. Logft values for all observed beta transitions have been calculated. Spin and parity assignments have been made from electron capture and positon disintegration considerations and gamma branches. The experimental level scheme of¹⁴³Pm is compared with the results of 1 and 3 q.p. calculations forN=82 nuclei.     

Energy levels of136Pm and136Nd via beta decay of136Sm and136Pm

¹³⁶Pm and¹³⁶Nd were studied using theβ decay of¹³⁶Sm and¹³⁶Pm. The radioactive nuclei were produced by the⁹²Mo (⁴⁸Ti,xpyn) and¹¹²Sn (²⁸Si,xpyn) reactions. The UNISOR isotope separator enabled mass identification. The previously unknown level scheme of¹³⁶Pm was constructed and the half-life of¹³⁶Sm was determined to be 47±2 s. Six new levels and thirteen newγ-ray transitions have been added to the level scheme of¹³⁶Nd.     

Decay of 143Sm

The decay of ¹⁴³Sm has been investigated by means of a Ge(Li) spectrometer. Levels of ¹⁴³Pm at 272.9, 1056.6, 1173.3, 1341.0, 1403.5, 1515.7, 1751.3, 1816.8, 2009.6, 2081.2 and 2172.5 keV have been established. Gamma-gamma coincidences confirmed the existence of the 272.9 keV level. Spin and parity assignments for all observed levels have been suggested from electron capture and positon disintegration considerations and gamma branches. The level is compared with an extreme one-quasi-particle model and an extended one-plus-three-quasi-particle Tamm-Dancoff approximation.     

Decay of the very neutron-deficient isotope 131Pm

The decay of ¹³¹Pm has been investigated by means of γ-ray spectroscopy. The ¹³¹Pm nuclei were produced by fusion-evaporation reaction of ¹⁰⁶Cd(³²S,3p4n) at the beam energy of 170 MeV. A helium-jet technique and a tape transport system were used to collect the activities and transfer them to a detecting position for X and γ rays measurement. Two γ rays of 185.0 and 220.0 keV were unambiguously identified to follow the β⁺ decay of ¹³¹Pm by results of X-γ and γ–γ coincidence. A growth-decay feature of the decay curve for 87.8 keV γ-ray of ¹³¹Nd confirmed the production of ¹³¹Pm nuclei. The half-life of ¹³¹Pm was measured to be 6.3 ± 0.8 s. A partial decay scheme of ¹³¹Pm is proposed on the basis of X-γ and γ–γ coincidence data in this experiment and the known structure information deduced from in-beam experiments of the daughter nucleus ¹³¹Nd. Received: 11 January 1999 / Revised version: 20 May 1999     

Levels in152Gd and152Sm populated by the decay of152Eu

The energy level schemes of¹⁵²Gd and¹⁵²Sm have been established on the basis of singlesγ-spectra, andγ- γ coincidence measurements. Ge(Li) detectors were used to study the gamma spectra produced in the EC/β⁺ and β^? decays of¹⁵²Eu to¹⁵²Sm and¹⁵²Gd, respectively. Thirteen new transitions are reported and data from eleven coincidence gates enabled five new levels to be suggested. Relative intensities and logf t values were calculated and spin/parities deduced. Comparisons are made with new predictions of the Interacting Boson Model.     

Detailed Ge(Li)-Ge(Li) coincidence studies of levels in152Sm and152Gd

The decay of 12.4 y¹⁵²Eu to¹⁵²Sm and¹⁵²Gd was studied in a high resolution singles measurement and two 4096×2048 Ge(Li)-Ge(Li) coincidence studies. Forty-five gates were analyzed in order to confirm or establish the placement of the γ rays as well as to accurately determine the intensities of the 12 doublets, which included several not previously reported. A new γ-β interband transition, 4 _γ ⁺ →2 _β ⁺ (561.4 keV), a possible 3 _γ ⁺ →2 _β ⁺ (423.7 keV) transition, and a new 330.9 keV transition between the 4 _γ ⁺ level and theI ^π K=3^?0 octupole level were established from coincidence data. Levels at 1757.0 keV in¹⁵²Sm and 1282.5, 1318.7, and 1692.2 keV in¹⁵²Gd are now established on the basis of coincidence data. These data also establish for the first time the population in the¹⁵²Eu decay levels at 1680.0 and 1047.9 keV in¹⁵²Sm and¹⁵²Gd, respectively, as well as a new level at 1700.8 keV in¹⁵²Sm.     

Structure of140Pm from beta decay of140Sm

The structure of¹⁴⁰Pm is investigated through the beta decay of¹⁴⁰Sm, whose half-life is measured to be (14.7 ± 0.2) m. A level structure comprising 41 transitions among 17 excited states is constructed. Using the deduced ft values and measured internal conversion coefficients, spin-parity assignments to several states in¹⁴⁰Pm were made. From beta end-point measurement, the total decay energy is deduced to beQ _EC =3.4±0.3 MeV, which is compared with the predictions of several mass formulae. The systematics of the odd-Z, N=79 isotones are discussed.     

TheK-shell particle parameter of the 122 keV transition in152Sm

TheK-shell particle parameter of the 122 keV transition in¹⁵²Sm has been investigated using different sources and different experimental arrangements. From our measurements we obtain the mean valueb ₂=1.77±0.03. This result deviates from the theoretical value by (6.5±1.5)%. We do not observe hygroscopic effects as reported in Ref.     

Structure of the145Sm states from the145Eu Decay

The -radiation from¹⁴⁵Eu has been studied by means of an anti-Compton spectrometer, the construction and operation of which are described. Altogether 91 -transitions have been observed, 20 of them for the first time. A decay scheme of¹⁴⁵Eu has been constructed incorporating 85 -transitions. Low-lying excited states in¹⁴⁵Sm have been analysed within the quasiparticle-phonon nuclear model as well as within the interacting boson-fermion model. Some systematic features in the positions of low-lying positive parity levels inN=83 nuclei have been revealed.     

On-line nuclear orientation of the deformed neutron-deficient Eu,Sm and Pm isotopes

Low-temperature nuclear orientation measurements made on-line at the SERC Daresbury Laboratory on^142m Eu,^141m Sm, and¹⁴¹Pm, with known magnetic dipole moments, have yielded the magnitude of the hyperfine fields of these isotopes in an iron host lattice. Thus measurements for the isotopes^{139, 138}Eu,^139m Sm, and¹³⁸Pm yielded values for the respective magnetic moments. Limits on the thermal relaxation times of Eu and Sm isotopes in Fe were also deduced. The results for¹³⁸Eu appear to contradict the earlier πh_11/2⊗νh_11/2 ground-state configuration assignment.     

Direct mass measurements of neutron-deficient 152Sm projectile fragments at the FRS-ESR facility

The FRS-ESR facility at GSI provides one of the most efficient methods for direct mass measurements. In the present experiment, exotic nuclei were produced via fragmentation of ¹⁵²Sm projectiles in a thick beryllium target at 500-600 MeV/u, separated in-flight with the fragment separator FRS, and injected into the storage-cooler ring ESR. Time-resolved Schottky Mass Spectrometry was applied for mass measurements of stored and electron-cooled bare and few-electron ions. 373 different nuclides were identified by means of the spectra of their revolution frequencies. Masses for 18 nuclides (⁸⁴Zr, ⁹²Ru, ⁹⁴Rh, ^107,108,110Sb, ^111,112,114I, ¹¹⁸Ba, ^122,123La, ¹²⁴Ce, ¹²⁷Pr, ¹²⁹Nd, ¹³²Pm, ¹³⁴Sm, ¹³⁷Eu) have been determined for the first time. Masses for ^111,112I and ¹¹³Xe have been obtained via known α-decay energies. The experiment and first results will be presented.     

Critical Point of the 152Sm, 154Gd,and 156Dy Isotones

Physics of Atomic Nuclei - The even—even rare-earth nuclei in U(5)—SU(3) region at neutron number (N) = 90, have been systematically studied using the Bohr—Mottelson Model (BM),...     

Decay of Cd and levels of Ag

The γ-ray spectrum following the decay of ¹⁰⁴Cd has been investigated with Ge(Li) spectrometers. Two unreported γ-rays with energies of 625.2 and 709.2 keV were observed and placed in the proposed decay scheme.     

Atomic masses of rare earth isotopes145Pm,145Sm and151Gd,derived from decay measurements of145Sm and151Gd

The comparison of experimental with calculated K-capture probabilities yielded the decay energies of¹⁴⁵Sm and¹⁵¹Gd,Q _EC=622(5) and 463(3) keV, respectively. Earlier discrepancies in the mass adjustment of these isotopes were removed and adjusted masses for¹⁴⁵Sm,¹⁴⁵Pm and¹⁵¹Gd derived. In the decay of¹⁵¹Gd five newγ-rays were found and the half-life remeasured to be 129(4) d.     

The multi-configuration Dirac-Fock calculation of the low-lying levels of Sm

The excitation energies and hyper-fine structure constants of the low-lying levels of Sm atom are calculated using the multi-configuration Dirac-Fock (MCDF) method. The results show that the excitation energies of the ground state multiplets can be calculated accurately using a small orbital set but the higher levels need larger orbital sets. Similar inference can also be drawn from the discrepancy between the calculated values of the hyper-fine constants and the experimental data. A sequence of MCDF calculation demonstrates the effect of the MCDF potential on the orbitals. Among the rare earth atoms Sm is a promising candidate for discrete symmetry violation experiments in atoms. This makes accurate theoretical calculations necessary since parameters in particle physics can be derived by combining the experimental results with the theoretical results. And these could be a probe for the physics beyond the standard model. Received 10 October 2000 and Received in final form 23 January 2001