Synthesis and properties of even-even nuclei with Z=114−116 produced in 48Ca induced reactions

In the irradiation of targets made from enriched ²⁴⁴Pu and ²⁴⁸Cm isotopes with beam doses of 1.5×10¹⁹ and 2.3×10¹⁹, respectively, the detector array situated in the focal plane of the gas-filled separator registered heavy atoms of new elements undergoing sequential α decays terminated by spontaneous fission. The time of the decay chains is approximately 1 min. Decay properties of the synthesized nuclei are consistent with the consecutive α decays originating from the parent nuclides ²⁸⁸114 and ²⁹²116 produced with the cross section of about 0.5 picobarn. Comparison of T _SF and T _α values for the nuclei with Z=110 and 112 with those obtained earlier for more light isotopes of these elements points to an enhanced stability of heavy nuclei with an increase in the neutron number. The α-decay energies Q _α, measured experimentally in the chains $116 \underrightarrow {\alpha _1 } 114 \underrightarrow {\alpha _2 } 112 \underrightarrow {\alpha _3 } 110$ , are compared with-theoretical predictions of different nuclear models. From this it follows that the theoretical models predicting the decisive influence of the nuclear structure on the stability of superheavy elements are well-founded not only qualitatively but in some sense also quantitatively. Some preliminary data, obtained in the first experiment aimed at the synthesis of element 118 in the reaction ²⁴⁹Cf+⁴⁸Ca, are presented in the paper. The prospects of further investigations in the field of superheavy nuclei are discussed briefly.     

High-spin states in the neutron rich fission fragments138Xe and139Xe

High-spin structures in the neutron-rich nuclei^138Xe and¹³⁹Xe have been investigated by observing prompt γ -rays from the spontaneous fission of²⁴⁸Cm with the Eurogam spectrometer. The partial level schemes were constructed on the basis of double-, triple- and quadruple-γ coincidences. The ground state band in¹³⁸Xe has been extended up to 5 MeV excitation energy. The structure of the newly observed medium-spin states in¹³⁹Xe is similar to the one of heavier N=85 isotones where vf ₇ ^2/3 , vh_9/2f ₇ ^2/2 and vf ₇ ^2/3 ? 3^? multiplets have been observed.     

The reaction 48Ca + 248Cm → 296116* studied at the GSI-SHIP

The synthesis of element 116 in fusion-evaporation reactions of a ⁴⁸Ca beam with radioactive ²⁴⁸Cm targets was studied at the velocity filter SHIP of GSI in Darmstadt. At excitation energies of the compound nuclei of 40.9MeV, four decay chains were measured, which were assigned to the isotope ²⁹²116, and one chain, which was assigned to ²⁹³116. Measured cross-sections of (3.4 _?1.6 ^+2.7 ) pb and (0.9 _?0.7 ^+2.1 ), respectively, and decay data of the chains agree with data measured previously at the Flerov Laboratory of Nuclear Reactions in Dubna. As a new result, one ??-decay chain was measured, which terminates after four ?? decays by spontaneous fission. The ?? energies of the second-to-fourth decay are considerably higher than those measured for the ?? decays of ²⁸⁹114, ²⁸⁵Cn, and ²⁸¹Ds and the spontaneous fission half-life is significantly longer than that of ²⁷⁷Hs measured in previous experiments. A possible assignment is discussed in the frame of excited quasiparticle states of nuclei populated in the decay chain from ²⁹³116. Also other possible assignments were considered and are discussed. At an excitation energy of 45.0MeV no events were observed resulting in a one-event cross-section limit of 1.6 pb. The technical aspects related with the use of radioactive target material at SHIP are described in detail. The experience gained in this experiment will serve as a basis for future experiments aiming to study still heavier elements at the velocity filter SHIP.     

Studies of neutron-deficient mendelevium isotopes at SHIP

The radioactive decay of the isotopes ²⁴⁷Md , ²⁴⁶Md and their daughter products was investigated by means of $ \alpha$ - $ \alpha$ and $ \alpha$ - $ \gamma$ coincidence spectroscopy. The isotopes were produced using the fusion reaction ⁴⁰Ar$ + $²⁰⁹Bi. Decay schemes are suggested for ²⁴⁷Md and ²⁴³Es . A new isomeric state in ²⁴⁶Md with a half-life of ( 4.4±0.8 s was observed. Previous data of electron-capture delayed fission of ²⁴⁶Md and ²⁴²Es were confirmed. The probability for this decay branch in ²⁴⁶Md was measured to be P _ECDF > 0.10 . The probability for electron-capture delayed fission in the case of ²⁴²Es was determined to be P _ECDF = 0.013^+0.012 _-0.007 .     

Symmetric and asymmetric fission of charged sodium clusters

A deformed-jellium model is used to calculate the fission barrier height of Na ₂₄ ²⁺ → Na ₂₁ ⁺ +Na ₃ ⁺ and Na ₄₂ ²⁺ → 2Na ₂₁ ⁺ within the Kohn—Sham Density Functional Theory (i.e., including shell effects). Although the shape of the barrier obviously depends on the parametrization of the fission path, we have found that the barrier maximum corresponds to a configuration in which the emerging fragments are already formed and rather well apart. The two examples chosen serve to illustrate the influence of the electronic shell effects.     

Pion photoproduction on197Au to ground and isomeric states in197Hg

The lifetime of the 331.3 keV 0 ₂ ⁺ state in¹⁰⁰Zr has been measured at the gas-filled recoil separator for fission products JOSEF. By observing the delayed coincidences between theβ-particles populating the level and theE0 conversion electrons from its decay into the ground state, a half-life of 3.37±0.30 ns has been obtained. From the measured lifetime and the relative intensities of the 0 ₂ ⁺ →0 ₁ ⁺ and 0 ₂ ⁺ →2 ₁ ⁺ transitions, values of 0.493±0.015 for theE0 strength parameterρ, and of 16 single particle units forB(E2,2 ₁ ⁺ → 0 ₂ ⁺ ) have been deduced. The enhanced nature of theE0 transitions suggests mixing of the 0 ₁ ⁺ and 0 ₂ ⁺ states which may be estimated by comparing the experimentalB(E2) values for the 2 ₁ ⁺ →0 ₁ ⁺ and 2 ₁ ⁺ →0 ₂ ⁺ transitions with the predictions of the asymmetric VMI model.     

Phenomenology of composite colored weak bosons

In composite models of quarks, leptons and weak bosons whereW-constituents are colored objects, color octet partners ofW ^± andZ ⁰ are predicted. We study in detail the phenomenology of these particles. Independent of the specific model one expects a color octet isotriplet of vector bosons (W ₈ ^± ,Z ₈ ⁰ ) with mass in the range of 100–200 GeV, and a color octet isosinglet vector bosonV ₈ ⁰ with substantially larger mass, due to mixing with the gluon. Moreover, relatively light color octet excitations of the leptons appear, while the existence of “color exotic” partners of the quarks is model dependent. These particles decay mainly into a lepton (quark) and a gluon. We construct the couplings ofW ₈ ^± ,Z ₈ ⁰ andV ₈ ⁰ to ordinary and “color exotic” fermions. The signals of color octet weak bosons in low energy weak reactions are explored in detail. The production cross section ofW ₈ ^± (Z ₈ ⁰ ) in hadron-hadron collisions is calculated for \(0.54TeV \leqq \sqrt s \leqq 20TeV\) . Various decay modes of colored weak bosons are studied. The most prominent decay signatures ofW ₈ ^± andZ ₈ ⁰ are events of the type (l ^+-: charged lepton;j: hadronic jet; : missing transverse momentum). The present CERN \(p\bar p\) collider data on such events are discussed in the light ofW ₈ ^± andZ ₈ ⁰ decays. If colored weak bosons are not found with a mass less than ～250 GeV composite model building will be strongly restricted.     

Neutron-rich hypernuclei in the chiral soliton model

The binding energies of neutron-rich strangeness S = ?1 hypernuclei are estimated in the chiral soliton approach using the bound state rigid oscillator version of the SU(3) quantization model. Additional binding of strange hypernuclei in comparison with nonstrange neutron-rich nuclei takes place at not large values of atomic (baryon) numbers, A = B ?? ??10. This effect becomes stronger with increasing isospin of nuclides, and for the ??nuclear variant?? of the model with rescaled Skyrme constant e. Binding energies of _?? ⁸ He and recently discovered _?? ⁶ H satisfactorily agree with data. Hypernuclei _?? ⁷ H, _?? ⁹ He are predicted to be bound stronger in comparison with their nonstrange analogues ⁷H, ⁹He; hypernuclei _?? ¹⁰ Li, _?? ¹¹ LI, _?? ¹² Be, _?? ¹³ Be, etc. are bound stronger in the nuclear variant of the model.     

Luminescence of Sc3+ and La3+ isoelectronic impurities in Lu3Al5O12 single-crystal films

The time-resolved luminescence and luminescence excitation spectra, and luminescence decay kinetics at 8 and 300 K of Lu₃A₁₅O₁₂ (LuAG) single-crystal films doped with Sc³⁺ and La³⁺ isoelectronic impurities and excited by synchrotron radiation are investigated. It is established that the La³⁺ isoelectronic impurity in the ?ub;c?ub; positions of the garnet lattice forms La _Lu ³⁺ luminescence centers emitting in the band with λ_max = 280 nm and the decay time of the main component τ = 300 ns at 300 K. The Sc³⁺ isoelectronic impurity located in the ?ub;c?ub; and (a) positions of the LuAG lattice forms two luminescence centers, Sc _Lu ³⁺ and Sc _Al ³⁺ , emitting in the bands with λ_max = 290 nm and τ = 240 ns and λ_max = 335 nm and τ = 375 ns, respectively, at 300 K. It is shown that the luminescence excitation of the La³⁺ and Sc³⁺ isoelectronic impurities in LuAG single-crystal films occurs through radiative decay of excitons localized near La _Lu ³⁺ , Sc _Lu ³⁺ , and Sc _Al ³⁺ centers. The energies of formation of these excitons are determined to be 6.8, 6.88, and 7.3 eV, respectively. It was found that the excited state of the excitons genetically related to the La _Lu ³⁺ , Sc _Lu ³⁺ , and Sc _Al ³⁺ enters has two radiative levels with different transition probabilities. This configuration leads to the presence of fast (2.3–8.4 ns) and slow (150–375 ns) main components in the luminescence of the centers formed by isoelectronic impurities in garnets.     

Production and loss of N 2 + , Ne+ and Ne 2 + during the decay period of plasmas produced in neon-nitrogen mixtures

Studies of the time dependencies of the number density of N ₂ ⁺ , Ne⁺ and Ne ₂ ⁺ ions have been made during the decay period of plasmas produced in neon containing various concentrations of nitrogen molecules. Reaction rate constants were obtained for N ₂ ⁺ +N₂+Ne→N ₄ ⁺ +Ne((1.2±0.2)×10^?29 cm⁶ sec^?1) and Ne⁺+N₂→N ₂ ⁺ + Ne ((2.9±0.3) × 10^?12 cm³ sec^?1). The ambipolar diffusion coefficient of N ₂ ⁺ in neon was found to beD _a p _o =350±20 cm² sec^?1 Torr.     

Conversion electron measurements and determination of rotational parameters in 177Lu and 177Hf

We discuss the possibility whether superheavy elements can be produced in Nature by the astrophysical rapid neutron capture process. To this end we have performed fully dynamical network r-process calculations assuming an environment with neutron-to-seed ratio large enough to produce superheavy nuclei. Our calculations include two sets of nuclear masses and fission barriers and include all possible fission channels and the associated fission yield distributions. Our calculations produce superheavy nuclei with $\ensuremath A\approx 300$ that however decay on time scales of days.     

Xα-SW-calculation of the chemically induced decay constant variation of Tc-99m in the tetrahedral oxy-complex ion and the octahedral halogen-complex ions

The tetrahedral and octahedral complex ions TcO ₄ ^? , TcCl ₆ ^2? , TcBr ₆ ^2? , TcI ₆ ^2? , which exhibit experimentally determined decay constant variations of Tc-99m [1], meet the conditions for the application of the X_α-SW-method. The results of the calculations are given, including the case of TcF ₆ ^2? . The decay constant variations are evaluated using the one-electron functions in a partial-wave expansion. The results are compared with the measured values and a detailed discussion gives a comprehensive picture of the decay constant variation induced by the chemical surroundings considered.     

Search for the K L 0 → π0ν \tilde v decay at the INEP U-70 accelerator: The KLOD project

The rare decay K _L ⁰ → π⁰ν $ \tilde v $ branching ratio measurement is one of the clearest Standard Model test. Calculations based on the SM predict Br(K _L ⁰ → π⁰ν $ \tilde v $ ) ≈ 2.8 × 10^?11, but the most accurate experimental value Br(K _L ⁰ → π⁰ν $ \tilde v $ ) < 6.7 × 10^?8 (90% C.L.). We present design of a new experimental setup KLOD (U-70 accelerator, IHEP, Protvino) for K _L ⁰ → π⁰ν $ \tilde v $ branching ratio measurement. Sensitivity of the KLOD experiment will be enough for registration of 2.4 events K _L ⁰ → π⁰ν $ \tilde v $ for every 10 days of the data taking (according to SM predictions).     

The effect of air impurities on pure neon luminescence

The luminescence decay curves of the 2p ₁ level of the NeI atom (the transition 3p??[1/2]₀?3s??[1/2] ₁ ^° , ?? = 585.2 nm) and the B ²?? _u ⁺ level of the N ₂ ⁺ molecule (the transition B ²?? _u ⁺ (?? = 0)?X ²?? _g ⁺ (??? = 0), ?? = 391.4 nm) in pure and air-containing neon are measured. The gas was excited by electron beam pulses (E _e = 150 keV, ?? = 5 ns, I _max = 500 A). It is shown that the molecular gases contained in air strongly quench the long-lived component of neon luminescence exciting due to dissociative recombination of Ne ₂ ⁺ molecular ions. The relative light yield at a wavelength of 585.2 nm as a function of the partial pressure of air in neon is determined to be ?? = (1+ 2??p)^?1, where p is the air pressure in Torr.     

Evidence for a 10+ state in132Te

A new isomeric state witht _1/2=3.9±0.3μs has been observed in the nucleus ₅₂ ¹³² Te₈₀ which has two protons more and two neutrons less than the doubly magic isobar ₅₀ ¹³² Sn₈₂. The deexcitation pattern suggests spin and parity 10⁺ for this level near 2,700 keV which is populated in fission. The energy and the half-life of the isomer can be understood with the assumption that it is the 10⁺ level based on theh ₁₁ ^2/?2 neutron hole configuration.     

Kinetic energy and angular distributions of instantaneous fission fragments in a classical model

The process of instantaneous fission in deep inelastic collisions is investigated in a classical model. Kinetic energies and angular distributions of the fragments are calculated for the proposed reaction Pb+U atE _cm ^inc =750 MeV; an experimental setup for the separation of the fragments originating from instantaneous fission from the fragments of thermal fission is explained. We also discuss fusion following instantaneous fission as a mechanism for the production of superheavy elements and arrive at rather promising estimates.     

Nuclear bremsstrahlung and electron-positron pair creation in heavy-ion collisions

Nuclear bremsstrahlung is investigated as a background effect in the X-ray-spectroscopy of superheavy electronic molecules. The intensity ratio between electric dipole and quadrupole radiation as function of frequency is given. The total cross section for electron-positron pair creation due to conversion of bremsstrahlungs-photons was found to beσ=3.8·10^?8b for the ₅₄ ¹³² Xe- ₉₂ ²³⁸ U system andσ=5.8·10^?8b for the ₉₂ ²³⁸ U? ₉₂ ²³⁸ U system at the Coulomb barrier. This demonstrates that bremsstrahlung pair creation can be neglected compared with the induced positron production in overcritical quasimolecules.     

Collision-induced dissociation of H 3 + ions

For collision energies between 100 and 500 eV the collision induced dissociation of H ₃ ⁺ colliding with H₂, He and Kr gas targets was measured. We obtained total cross sections and angular distributions of the charged collision fragments for the main reaction channels. H ₃ ⁺ +H₂→H⁺+2H² and H ₃ ⁺ +H₂→H ₂ ⁺ +H₂+H. An analysis of the kinetics yields that the dissociation proceeds via vibrational-rotational excitation of H ₃ ⁺ by mutually induced dipolmoments.     

Gyromagnetic ratios of low-lying rotational states in156, 158, 160Gd

Transient-field precessions were measured simultaneously for levels in the ground-state bands of^{156, 158, 160}Gd as ions of these nuclei traversed a thin polarized Fe foil. Relative g-factors of levels up to 6 ₁ ⁺ were deduced, those of the 4 ₁ ⁺ levels being determined with greatest precision. In contrast with the conclusions of the recent report by Alzner et al. [1], our results are consistent with g(4 ₁ ⁺ ) having the same value in all three isotopes and imply g(2 ₁ ⁺ )=g(4 ₁ ⁺ ) in¹⁵⁶Gd, consistent with nuclear structure models.     

Strange hadron production in d+Au collisions at RHIC

We report the centrality dependence of transverse mass (m _t ) spectra at mid-rapidity for the identified strange hadrons K _S ⁰ , ? $\Lambda + \bar \Lambda $ and $\Xi ^ - + \bar \Xi ^ + $ in d+Au collisions at RHIC. The measured transverse momentum (p _T ) covers 0.4<p _T <6.0 GeV/c for K _S ⁰ , ø, $\Lambda + \bar \Lambda $ and 0.6<p _T <5.0 GeV/c for $\Xi ^ - + \bar \Xi ^ + $ . The binary collision normalized nuclear modification factors R _CP of these hadrons indicate that the Cronin effect in d+Au collisions has a distinct particle-type dependence. the R _CP ratios show a distinct baryons versus mesons dependence: the R _CP for $\Xi ^ - + \bar \Xi ^ + $ follows that for $\Lambda + \bar \Lambda $ while the R _CP for the ? is close to that for the K _S ⁰ . Similar features have also been observed in Au+Au collisions. Initial parton scattering alone is not sufficient to explain this particle-type dependence. Hadronization processes are likely to be important for determining hadron properties in high-energy collisions as suggested by coalescence and recombination models.