Spectroscopy of Proton-Odd Transfermium Nuclei

GANIL-EXP, GANIL E375International audienceSpectroscopy of the proton-odd transfermium isotopes 247Es, 251Md and 255Lr has been performed using decay and in-beam techniques. Single particle states have been studied at GANIL and the University of Jyväskylä using spectroscopy after $\alpha$ decay of 255Lr. Prompt gamma-ray spectroscopy of 251Md and 255Lr was performed at Jyväskylä using the Jurogam array coupled to the RITU separator. These experimental results are compared to new Hartree--Fock--Bogoliubov calculations. Future prospects for the study of the heaviest elements at GANIL with the existing facility and the future SPIRAL2 and LINAG beams are presented

Internal conversion and summing effects in heavy-nuclei spectroscopy

Expérience GANIL, spectrometre LISEInternal conversion of low-energy nuclear transitions occurs with a high probability in heavy nuclei. After the emission of the conversion electron, a cascade of X-rays, Auger or Coster–Krönig electrons takes place. In $\alpha$-decay experiments in which the nuclei of interest are implanted into a silicon detector, these atomic processes contribute to the detected energy. To understand the distortions of $\alpha$-particle energy spectra, knowledge of the various atomic yields is required. Using state-of-the-art calculations, new atomic yields are computed in $_99$Es and compared to those available in the literature. Detailed simulations of the $^{251}_{101}$Md $\alpha$ decay are performed and compared to experimental data. Possible ways to discriminate between the available atomic yields are also discussed

Fission half-lives of super-heavy nuclei in a microscopic approach

A systematic study of 160 heavy and super-heavy nuclei is performed in the Hartree-Fock-Bogoliubov approach with the finite range and density dependent Gogny force with the D1S parameter set. We show calculations in several approximations: with axially symmetric and reflexion symmetric wave functions, with axially symmetric and non-reflexion symmetric wave functions and finally some representative examples with triaxial wave functions are also discussed. Relevant properties of the ground state and along the fission path are thoroughly analyzed. Fission barriers, Q$_\alpha$-factors and lifetimes with respect to fission and $\alpha$-decay as well as other observables are discussed. Larger configuration spaces and more general HFB wave functions as compared to previous studies provide a very good agreement with the experimental data.Comment: 26 pages, 15 figure

High-spin structures of 136Cs

Odd-odd 136Cs nuclei have been produced in the 18O + 208Pb and 12C + 238U fusion-fission reactions and their gamma rays studied with the Euroball array. The high-spin level scheme has been built up to ~ 4.7 MeV excitation energy and spin I ~ 16 hbar from the triple gamma-ray coincidence data. The configurations of the three structures observed above ~ 2 MeV excitation energy are first discussed by analogy with the proton excitations identified in the semi-magic 137Cs nucleus, which involve the three high-j orbits lying above the Z=50 gap, pi g_{7/2}, pi d_{5/2} and pi h_{11/2}. This is confirmed by the results of shell-model calculations performed in this work.Comment: 6 pages, 4 figures, 3 table

Isomeric states in 253^{253}No

6 pagesInternational audienceIsomeric states in 253No have been investigated by conversion-electron and gamma-ray spectroscopy with the GABRIELA detection system. The 31 micro second isomer reported more than 30 years ago is found to decay to the ground state of 253No by the emission of a 167 keV M2 transition. The spin and parity of this low-lying isomeric state are established to be 5/2+. The presence of another longer-lived isomeric state is also discussed

Analysis of the superdefomed rotational bands

All available experimental data for the $\Delta I=2$ transition energies in superdeformed bands are analyzed by using a new one-point formula. The existence of deviations from the smooth behavior is confirmed in many bands. However, we stress that one cannot necessarily speak about staggering patterns as they are mostly irregular. Simulations of the experimental data suggest that the irregularities may stem from the presence of irregular kinks in the rotational spectra. This could be a clue but, at the moment, where such kinks come from is an open question.Comment: 6 pages, RevTex, 7 p.s. figures, submitted to P.R.

High-spin states with seniority v=4,4,6 in 119-126Sn

The 119-126Sn nuclei have been produced as fission fragments in two reactions induced by heavy ions: 12C+238U at 90 MeV bombarding energy, 18O+208Pb at 85 MeV. Their level schemes have been built from gamma rays detected using the Euroball array. High-spin states located above the long-lived isomeric states of the even- and odd-A 120-126Sn nuclei have been identified. Moreover isomeric states lying around 4.5 MeV have been established in 120,122,124,126Sn from the delayed coincidences between the fission fragment detector SAPhIR and the Euroball array. The states located above 3-MeV excitation energy are ascribed to several broken pairs of neutrons occupying the nu h11/2 orbit. The maximum value of angular momentum available in such a high-j shell, i.e. for mid-occupation and the breaking of the three neutron pairs, has been identified. This process is observed for the first time in spherical nuclei.Comment: 20 pages, 22 figures, 12 tables, accepted for publication in Physical Review

Spectroscopy of the neutron-rich actinide nucleus U-240 following multinucleon-transfer reactions

B. Birkenbach et al.; 9 pags.; 9 figs.; 2 tabs.; PACS number(s): 23.20.Lv, 25.70.Hi, 27.90.+b, 29.40.GxBackground: Nuclear structure information for the neutron-rich actinide nuclei is important since it is the benchmark for theoretical models that provide predictions for the heaviest nuclei. Purpose: gamma-ray spectroscopy of neutron-rich heavy nuclei in the actinide region. Method: Multinucleon-transfer reactions in Zn-70 + U-238 and Xe-136 + U-238 have been measured in two experiments performed at the INFN Legnaro, Italy. In the Zn-70 experiment the high-resolution HPGe Clover Array (CLARA) coupled to the magnetic spectrometer PRISMA was employed. In the Xe-136 experiment the high-resolution Advanced Gamma Tracking Array (AGATA) was used in combination with PRISMA and the Detector Array for Multinucleon Transfer Ejectiles (DANTE). Results: The ground-state band (g.s. band) of U-240 was measured up to the 20(+) level and a tentative assignment was made up to the (24(+)) level. Results from gamma gamma coincidence and from particle coincidence analyses are shown. Moments of inertia (MoI) show a clear upbend. Evidence for an extended first negative-parity band of U-240 is found. Conclusions: A detailed comparison with latest calculations shows best agreement with cranked relativistic Hartree-Bogoliubov (CRHB) calculations for the g.s. band properties. The negative-parity band shows the characteristics of a K-pi = 0 band based on an octupole vibration. ©2015 American Physical SocietyThe research leading to these results has received funding from the German Bundesministerium fur Bildung ¨ und Forschung (BMBF) under Contract No. 05P12PKFNE TP4, the European Union Seventh Framework Programme (FP7/2007-2013) under Grant No. 262010-ENSAR, and the Spanish Ministerio de Ciencia e Innovacion under Contract No. FPA2011-29854-C04. A.V. thanks the Bonn-Cologne Graduate School of Physics and Astronomy (BCGS) for financial support. One of the authors (A. Gadea) was supported by MINECO, Spain, under Grants No. FPA2011-29854-C04 759 and No. FPA2014-57196-C5; Generalitat Valenciana, Spain, under Grant No. PROMETEOII/2014/019; and EU under the FEDER program.Peer Reviewe

High-spin structures of five N=82 isotones: 136Xe, 137Cs, 138Ba, 139La, and 140Ce

Five N=82 isotones have been produced in two fusion-fission reactions and their gamma-rays studied with the Euroball array. The high-spin states of 139La have been identified for the first time, while the high-spin yrast and near-to-yrast structures of the four others have been greatly extended. From angular correlation analysis,spin values have been assigned to some states of 136Xe and 137Cs. Several cascades involving gamma-rays of 139La have been found to be delayed, they deexcite an isomeric state with T1/2= 315(35) ns located at 1800-keV excitation energy. The excited states of these five N=82 isotones are expected to be due to various proton excitations involving the three high-j subshells located above the Z=50 shell closure. This is confirmed by the results of shell-model calculations performed in this work. In addition, high-spin states corresponding to the excitation of the neutron core have been unambiguously identified in 136Xe, 137Cs, and 138Ba.Comment: 18 pages, 18 figures, 10 tables, accepted for publication in Phys. Rev.

New gas-filled mode of the large-acceptance spectrometer VAMOS

Spectromètre VAMOSA new gas-filled operation mode of the large-acceptance spectrometer VAMOS at GANIL is reported. A beam rejection factor greater than 1010 is obtained for the 40Ca+150Sm system at 196 MeV. The unprecedented transmission efficiency for the evaporation residues produced in this reaction is estimated to be around 80% for ®xn channels and above 95% for xnyp channels. A detailed study of the performance of the gasfilled VAMOS and future developments are discussed. This new operation mode opens avenues to explore the potential of fusion reactions in various kinematics