The investigation of properties of short-lived SF isotopes (Z > 100) at the focal plane of VASSILISSA separator

For experiments aimed at the study of spontaneous fission of transfermium nuclei improvements in the focal plane detector system of recoil separator VASSILISSA have been made. A neutron detector consisting of 54 3He-filled counters has been mounted around the focal-plane detector chamber. The reaction 48Ca + 206Pb = 2n + 252No is used for tuning the separator settings and calibrating the detector system with the spontaneous fission of the 252No. The average neutron number per 252No spontaneous fission event is as large as ν̅ = 4.06 ± 0.12. The short-lived heavy isotopes 244,246Fm, produced in the complete fusion reactions 40Ar + 206,208Pb, are investigated. The average number of neutrons per spontaneous fission of 244,246Fm from the experimental data were (ν̅ = 3.3 ± 0.3) and (ν̅ = 3.55 ± 0.50), respectively. Both values are determined for the first time

Study of complete and incomplete fusion for loosely bound projectiles 6He and 6Li on 165Ho and 166Er targets

Complete fusion (CF) and incomplete fusion (ICF) reactions were studied for the cases of the loosely bound 6He and 6Li projectiles bombarding 166Er and 165Ho targets at energy of about 10 MeV/nucleon. Experiments were carried out to test an approach exploiting the measured intensities of γ rays emitted at the transitions between the yrast-band levels of reaction products formed after the termination of neutron evaporation. Partial waves feeding the CF reactions 165Ho ( 6Li, 5n) 166Yb and 166Er( 6He, 6n) 166Yb as well as ICF 165Ho ( 6Li, α3n) 164Er and 166Er( 6He, α4n) 164Er reaction channels were revealed from the obtained γ-ray data. The method of exit channel identification via the triple coincidence (γ1-γ2-light charged particle) was employed for these reactions study. © 2012 Pleiades Publishing, Ltd.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Prompt neutrons accompanying the spontaneous fission of 250^{250}No

International audienceThis paper describes the experiment conducted on the SHELS (Separator for Heavy Element Spectroscopy) separator [1] aimed at studying the properties of spontaneous fission of 250No. A separator detection system consists of a time-of-flight system and SFiNx (Spontaneous Fission, Neutrons and x-rays) detection system [2] is described. The SFiNx detection system consists of an assembly of double-sided Si detectors, around which 116 proportional neutron counters filled with 3He are placed. During experiment, 1366 events of spontaneous fission of 250No were registered. The average number of neutrons per one fission (⁠v¯ = 4.24 ± 0.13) and the distribution of neutron multiplicities were obtained, and the half-lives of the 250No were measured for the ground T1/2 = (3.89 ± 0.17) µs and isomeric states T1/2 = (39.14 ± 3.34) µs

Gamma and electron spectroscopy of heavy nuclei at FLNR JINR

Detailed spectroscopic information of excited nuclear states in deformed transfermium nuclei is scarce. Most of the information available today has been obtained from investigations of fine structure α decay. Although α decay gives access to hindrance factors and lifetimes which are strongly correlated to shell/subshell closures and the presence of isomers, only the combined use of γ and conversion electron spectroscopy allows the precise determination of excitation energy, spin and parity of nuclear levels. In particular, the study of odd isotopes gives crucial information on the single particle states available at and around the Fermi surface. In the following, the preliminary results of decay studies using α - γ and α - beta coincidences at the focal plane of the VASSILISSA recoil separator are presented. © 2007 American Institute of Physics.SCOPUS: cp.pinfo:eu-repo/semantics/publishe

Detailed spectroscopy in 249^{249}Fm

Excited states in 249Fm were populated via the alpha decay of 253No and the subsequent decay was observed with the GABRIELA detection system installed at the focal plane of the VASSILISSA recoil separator. The energies, spins, and parities of these states could be established through combined alpha, gamma, and conversion-electron spectroscopy. The first members of the ground-state rotational band were identified. Their excitation energies as well as the observation of a cross-over E2 transition confirm the assignment of 7/2+[624] for the ground state of 249Fm. Two excited states were also observed and their decay properties suggest that they correspond to the particle excitation 9/2-[734] and hole excitation 5/2+[622]. The analysis suggests that the 279-keV transition de-exciting the 9/2- state has anomalous E1 conversion coefficients

High-K,t1/2=1.4(1) ms, isomeric state in Lr255

An isomeric state in Lr255 with a half-life of t1/2=1.4(1) ms and Ex>720-keV has been observed for the first time using the GABRIELA setup at the focal plane of the VASSILISSA separator. Based on its K-forbiddeness, the configuration of the state is most probably formed by coupling the valence proton to a two quasiparticle neutron excitation. Possible three quasiparticle configurations are discussed. © 2008 The American Physical Society.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Complete and Incomplete Fusion of6He and6Li Projectiles with Medium Mass Targets at Energy ∼10 AMeV

Complete fusion (CF) and incomplete fusion (ICF) reactions were studied with the beams of loosely bound 6He and 6Li bombarding 166Er and 165Ho targets. Experiments were carried out to test an approach exploiting the measured intensities of y rays emitted at the transitions between the yrast-band levels of reaction products formed after the termination of neutron evaporation. Partial waves feeding the CF [ 165Ho(6Li,5n)166Yb, 166Er( 6He,6n)166Yb] and ICF [165Ho( 6Li,α3n)164Er, and 166Er( 6He,α4n)164Er] reaction channels were revealed from the obtained γ-ray data. © 2009 American Institute of Physics.SCOPUS: cp.pinfo:eu-repo/semantics/publishe

Isomeric states in 253No

Isomeric states in 253No have been investigated by conversion electron and γ -ray spectroscopy with the GABRIELA detection system. The 31μs isomer reported more than 30 years ago is found to decay to the ground state of 253No by the emission of a 167keV 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. © Società Italiana di Fisica and Springer-Verlag 2007.SCOPUS: ar.jinfo:eu-repo/semantics/publishe