Search for new isotopes of element 112 by irradiation of 238U with 48Ca

The reaction ⁴⁸Ca+²³⁸U was investigated at the recoil separator VASSILISSA at the Flerov Laboratory of Nuclear Reactions, JINR Dubna, in attempts to synthesize new isotopes of element 112. The experiments were performed at two beam energies resulting in excitation energies of the compound nucleus of 33 and 39 MeV. The collected beam dose was 3.5 × 10¹⁸ and 2.2 × 10¹⁸, respectively. Two spontaneous fission events were observed at the lower beam energy, which tentatively were assigned to the new neutron rich isotope ²⁸³112 produced in the reaction ²³⁸U(⁴⁸Ca,3n)²⁸³112. The measured cross-section is (5.0^+6.3 _−3.2) pb and the half–life is (81⁺¹⁴⁷ ₋₃₂) s. No event was observed at the higher beam energy resulting in the upper cross–section limit of 7.3 pb. Received: 12 October 1998 / Revised version: 12 January 1999     

The Process of the Aging of Articles on Acoustics. The View from Akusticheskii Zhurnal

Acoustical Physics - By analyzing references, one can obtain interesting information about the kind of research that is being performed, what approaches exist, information about scientists working...     

Analysis and elimination of systematic errors originating from coulomb mutual interaction and image charge in Fourier transform ion cyclotron resonance precise mass difference measurements

The effect of mutual Coulomb-mediated interactions between ions of two different mass-to-charge ratios (but equal ion cyclotron orbital radii) on their Fourier transform ion cyclotron resonance (FT/ICR) mass spectral frequency difference is derived analytically and measured experimentally. For a cylindrical ion trap, ion packets are modeled theoretically as infinitely extended lines of charge, and contributions to cyclotron frequency difference due to direct Coulomb repulsion between the lime charges as well as the forces arising from image charge induced on the trap electrodes by each line charge are calculated. A striking theoretical prediction is that the effect on ICR frequency difference of mutual Coulomb repulsion between ions in a mass doublet may be compensated by the image-charge effect. As a result, there is an optimal (calculable) ion cyclotron orbital radius at which the measured cyclotron orbital frequency difference between ions of two different mass-to-charge ratios is independent of mutual Coulomb-mediated interactions between the two components of the mass doublet! Moreover, if the two mass-doublet component ions are present in equal numbers, then the measured ion cyclotron orbital frequency difference is also independent of all Coulomb-mediated interactions between the two types of ions! Thus, the single largest systematic error in measurement of mass difference in a mass doublet by FT/ICR mass spectrometry may be virtually eliminated by appropriate control of ICR orbital radius and/or by performing measurements at various relative abundance ratios and extrapolating to equal relative abundance of the two mass-doublet components. We report experimental tests and verification of these predictions for two different mass doublets: ³He⁺/³H⁺ (cylindrical trap at 4.7 Tesla) and ¹²C¹H ₂ ⁺ /¹⁴ N⁺ (cubic trap at 7.0 Tesla). From the latter measurement, we determine the mass of atomic nitrogen as m(¹⁴N)=14.003 074 014(19) u.     

Random pining of localized states and the birth of deterministic disorder within gradient models

The birth of spatial disorder from almost regular initial conditions within the Swift-Hohenberg model equation with subcritical bifurcation is considered. The complexity of the space series (measured by the spatialK ₂-entropy) grows with time and reaches a stationary value depending on the period of the initial regular disturbance. A qualitative model is suggested describing the process via the birth of localized structures and its subsequent disordering due to weak interaction.     

Crystallization kinetics of thin-film amorphous Cox(PZT)100 − x nanocomposites

Conductivity of thin-film heterogeneous Co_x(PZT)_{1 ? x} structures has been studied in a wide ranges of metallic phase concentrations and temperatures. The crystallization kinetics of amorphous samples of Co_x(PZT)_{100 ? x} nanocomposites has been investigated by analyzing the time dependences of their conductivity. The main parameters of the crystallization process have been determined.     

Chromatography at the critical condition as a method for polymer analysis

The potential of critical chromatography in investigating the macromolecule structure of synthetic polymers is considered, such as the determination of the type and number of terminal functional groups, chain topology, and character of group alternation in the chain. New possibilities arising in the combination of critical chromatography with the mass spectrometry of macromolecules were discussed.     

Resonance states of superheavy hydrogen nuclei obtained in transfer reactions with exotic beams

A resonance state situated at 1.8±0.1 and, most likely, another state positioned at 2.7±0.1 MeV above the t+n+n decay threshold were observed in the missing mass energy spectrum of the ⁵H nucleus produced in the reaction ³H(t,p)⁵H. The peak located close to $E_{^5 H} = 1.8$ MeV also was seen in the ⁵H spectrum obtained from the energy distributions of ³H nuclei emitted in the reaction ²H(⁶He,⁵H)³He. The width (Γ_obs ≤ 0.5 MeV) obtained for the two ⁵H resonance states is surprisingly small. A state of ⁴H with E _res = 3.3 MeV and γ² = 2.3 MeV was obtained in the reaction ²H(t,p)⁴H from the proton spectrum.     

Effect of coalescence and of the character of the initial oxide on the photoluminescence of ion-synthesized Si nanocrystals in SiO<Subscript>2</Subscript>

The photoluminescence intensity (PLI) related to Si nanocrystals in a SiO₂: nc-Si system synthesized by ion implantation is studied experimentally and theoretically as a function of the Si+ ion dose at various annealing temperatures T_ann (1000–1200°C). The dose corresponding to the maximum PLI is found to decrease with increasing T_ann. These data are explained in terms of a model taking into account the coalescence of neighboring nanocrystals and the dependence of the probability of radiative recombination of quantum dots on their size. It is found that, when silicon oxide is grown in a wet atmosphere, the photoluminescence spectrum contains an additional band (near 850 nm), which is related to shells around the nanocrystals. This band weakens abrupily after high-temperature annealing in an oxidizing atmosphere (air).     

Quest for the 10He nucleus

The spectrum of ¹⁰He was studied by means of the ³H(⁸He, p)¹⁰He reaction at a laboratory energy of 25 MeV/A and small center-of-mass angles. Missing mass spectrum of ¹⁰He was derived from the obtained p-⁸He coincidence. A resolution of 0.7 MeV was achieved in this spectrum for the measured ¹⁰He energy. Most likely, a well isolated group of 10 events detected between 2 and 5 MeV and showing a maximum at about 3 MeV in the spectrum of the present work exhibits the ¹⁰He g.s. resonance.     

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.