Second experiment at VASSILISSA separator on the synthesis of the element 112

The upgraded separator VASSILISSA was used to confirm results of previous experiments on the synthesis of the heavy isotopes of the element 112 obtained in complete-fusion reactions of ⁴⁸Ca and ²³⁸U. An additional reason was the non-observation of any events in the same reaction studied with the BGS separator at Berkeley. Limits of for the atomic mass number of the observed spontaneously fissioning isotope were measured. The obtained results on the decay mode, half-life and production cross-section are in agreement with those obtained in our first experiment.Received: 10 June 2003, Revised: 29 July 2003, Published online: 2 December 2003PACS: 23.60. + e decay - 25.70.-z Low and intermediate energy heavy-ion reactions - 25.85.Ca Spontaneous fission - 27.90. + b      

Interaction of elemental mercury with selenium surfaces: model experiments for investigations of superheavy elements copernicium and flerovium

The adsorption behavior of ¹⁹⁷Hg and ^183–185Hg on red amorphous selenium (red a-Se) and trigonal selenium (t-Se) was investigated experimentally by off-line and on-line gas chromatographic methods, in preparation of a sensitive chemical separation and characterization of the transactinides copernicium (Cn, Z = 112) and flerovium (Fl, Z = 114). Monte-Carlo simulations of a diffusion controlled deposition were in good agreement with the experimental results, assuming as interaction limits ?ΔH _ads ^red a-Se (Hg) > 85 kJ/mol, and ?ΔH _ads ^t-Se (Hg) < 60 kJ/mol. Both Se allotropes can be used as stationary surfaces in comparative gas-chromatographic chemical investigations of Cn and Fl.     

GABRIELA setup for nuclear spectroscopy of the transfermium element isotopes at the VASSILISSA separator

The JINR (Dubna)-IN2P3 (France) Collaboration project aimed at the α, β γ, spectroscopy of the transfermium element isotopes using heavy-ion beams of the U-400 cyclotron and the modernized recoil separator VASSILISSA was launched at Dubna. During the first full-scale experiment in September–October 2004, nobelium and lawrencium isotopes produced in the ⁴⁸Ca + ^207,208Pb → ^255,256No* and ⁴⁸Ca + ²⁰⁹Bi → ²⁵⁷Lr* reactions were studied. The text was submitted by the authors in English.     

Measurement of evaporation residue cross-sections of the reaction 30Si + 238U at subbarrier energies

The reaction ³⁰Si + ²³⁸U → ²⁶⁸Sg^* was studied at beam energies close to the Coulomb barrier. At a center-of-mass energy of E _c.m. = 144.0MeV for reactions at half thickness of the target we measured three decay chains of ²⁶³Sg produced by evaporation of five neutrons. The cross-section was ( 67⁺⁶⁷ _-37) pb. At E _c.m. = 133.0MeV we measured three spontaneously fissioning nuclei which we assigned to the isotope ²⁶⁴Sg. The production cross-section was ( 10⁺¹⁰ _-6) pb and a half-life of ( 120⁺¹²⁶ _-44) ms was determined. This half-life is a factor of twenty shorter than theoretical predictions. At E _c.m. = 128.0MeV an upper cross-section limit of 15pb was measured. The cross-section data reveal a strong influence of the orientation of the deformed target nucleus on the production yield. Compared to excitation functions measured for the lighter system ¹⁶O + ²³⁸U → ²⁵⁴Fm^*, a reduction of the fusion probability was observed at low beam energies indicating increasing competition from quasifission processes.     

The upgrade of the kinematic separator VASSILISSA—experimental results and plans

Within the past twelve years, the recoil separator VASSILISSA has been used for the investigations of evaporation residues produced in heavy-ion-induced complete fusion reactions. In the course of the experimental work, fourteen new isotopes have been identified by the parent-daughter correlations in the region of elements with 92≤Z≤94. The study of the decay properties and formation cross sections of the isotopes of elements 110, 112, and 114 was performed using high-intensity ⁴⁸Ca beams and ²³²Th, ²³⁸U, and ²⁴²Pu targets. At the beam energies corresponding to the calculated cross-section maxima of the 3n evaporation channels, the isotopes ²⁷⁷110, ²⁸³112, and ²⁸⁷114 were produced and identified. For further experiments aimed at the synthesis of the superheavy element isotopes (Z≥110) with the use of intensive ⁴⁸Ca extracted beams, improvements in the ion optical system of the separator and the focal plane detector system have been made.     

Spectral and luminescent properties of N,N'-bis(5-bromosalicylidene)-1,3-propylenediamine and its zinc complex

Zn(II) complex with N,N'-bis(5-bromosalicylidene)-1,3-propylenediamine, which efficiently luminesce in the blue region of the visible spectrum, is synthesized for the first time. It is found that, at 293 K, azomethine and zinc complex fluoresce in both solution and the polycrystalline state. Fluorescence quantum yields of the compounds in diluted dimethylformamide and dimethylsulfoxide solutions are determined.     

Characteristics of spontaneous fission of <Superscript>250</Superscript>No

This study describes an experiment on investigating the properties of spontaneous fission of shortlived neutron-deficient nuclei synthesized in the reaction of complete fusion ⁴⁸Ca + ²⁰⁴Pb = ²⁵²No*. The experiment is performed using the SHELS separator and the beam of multicharged ions at U-400 accelerator (LNR, JINR). Two activities undergoing spontaneous fission, which can be related to the ground and isomeric states of ²⁵⁰No nucleus, are registered. The half-lives, total kinetic energies of fission fragments, and neutron multiplicities are measured for the short-lived nuclei. The average number of neutrons per fission for the activity with t _1/2 = 5.1 ± 0.3 μs is = 4.38 ± 0.13 μs, and for nuclei with the half-life t _1/2 = 36 ± 3 μs it is xxxxx.     

Spontaneous fission of <Superscript>256</Superscript>Rf,new data

Spontaneous fission properties of the short-lived neutron-deficient ²⁵⁶Rf nucleus produced in the complete fusion reaction with a beam of multiply charged heavy ⁵⁰Ti ions from the U-400 cyclotron (FLNR, JINR) are experimentally investigated. Its half-life and decay branching ratio are measured. The average number of neutrons per spontaneous fission of ²⁵⁶Rf (\(\bar v = \;4.47 \pm \;0.09\)) is 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 ?? 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, ⁵ n) ¹⁶⁶Yb and ¹⁶⁶Er(⁶He, ⁶ n) ¹⁶⁶Yb as well as ICF ¹⁶⁵Ho (⁶Li, ??3n) ¹⁶⁴Er and ¹⁶⁶Er(⁶He, ??4n) ¹⁶⁴Er reaction channels were revealed from the obtained ??-ray data. The method of exit channel identification via the triple coincidence (??1-??2-light charged particle) was employed for these reactions study.     

Spectroscopy of No and its daughters

New high-statistics data have been obtained on the decay properties of ²⁵³No and its daughters using the reaction ²⁰⁷Pb(⁴⁸Ca, 2n)²⁵³No. This was made possible thanks to an improved transmission of fusion–evaporation residues through the VASSILISSA recoil separator and an increased efficiency of the GABRIELA detector setup. The decay schemes of ²⁵³No and ²⁴⁹Fm have been revisited. The known level scheme of ²⁴⁹Fm has been confirmed, including a new level at 669 keV excitation energy. The observation of L X-rays in coincidence with the α decay of ²⁴⁹Fm gives additional support to the ground-state configuration of 1/²⁺[631]$1/2^{+}[631]$ instead of 5/²⁺[622]$5/2^{+}[622]$ for ²⁴⁵Cf. In both ²⁴⁹Fm and ²⁴⁵Cf, the interpretation of the data has been checked by comparing experimental α-particle and γ-ray spectra with realistic simulations of the decay cascades and of the interaction of particles and photons in the detectors of GABRIELA. The population of a 0.7 ms isomeric state attributed to ²⁵³No is confirmed by an α-tagged calorimetric measurement and the corresponding γ and electron decay spectra are presented. Possible evidence for more than one isomer is given and a tentative partial decay scheme is discussed in the light of the available experimental data, systematics and theoretical expectations.