A. N. Polyakov

Industrial laser cladding: current state and future

A state-of-the-art and development tendency of the laser surfacing industrial application is reviewed. Laser energy sources, emission transport and focusing systems, coating materials, and laser equipment are considered.

Focal plane detector of the Dubna gas-filled recoil separator

The focal plane detector of the Dubna gass-filled recoil separator has been developed to study fusion reaction products from heavy-ion-induced nuclear reactions in the region of heavy nuclei with Z > 104. It consists of a 12 strip position-sensitive silicon detector to measure the energy/position of implanted nuclides and decay products and two low-pressure proportional chambers to generate a TOF signal. Additional information on ΔE from the STOP chamber is stored to provide an opportunity to discriminate alpha decays to the ground state of daughter product from the ones accompanied by conversion electron emission. The detector was successfully applied for the nuclear reactions which led to the discovery of new nuclides with Z = 108, 110 (A = 267, 273). An appropriate data acquisition system is described.

Targets of uranium, plutonium, and curium for heavy-element research

The heavy-element research program of the Dubna gas-filled recoil separator requires the use of rather exotic, strongly radioactive targets which can withstand long-term, high-intensity heavy-ion bombardments. A number of targets with thicknesses of 0.1–0.8 mg/cm2 deposited on various backings by different techniques such as electrospraying, mechanical painting with organic solutions, as well as molecular plating or electrodeposition from organic solutions were tested. The best results were obtained for electroplated targets deposited on 1.5 μm Ti backings. Isotopically enriched targets of 235,236,238U, 242,244Pu, and 248Cm mounted on rotating disks were irradiated by ions ranging from neon to argon with intensities up to 2 × 1013pps delivered by the U400 cyclotron. During two months of irradiation the total beam dose of the 34S ions applied to the target of 244Pu reached 2.5 × 1019. Collaborative Dubna-Livermore experiments were performed in 1993–1995 by employing the Dubna gas-filled recoil separator and resulted in the discovery of the new nuclides 262104, 265106, 266106, 267108, and 273110. The experiments aimed at the synthesis of element 114 are under preparation. Target fabrication methods and experimental results for nuclear physics studies at Coulomb energies are described.

Synthesis of superheavy nuclei in 48Ca+244Pu interactions

This article reports the results of experiments aimed at producing hypothetical long-lived superheavy elements located near the spherical-shell closures with Z≥114 and N≥72. For the synthesis of superheavy nuclei, we used a combination of neutron-rich reaction partners, with a 244Pu target and a 48Ca projectile. The sensitivity of the present experiment exceeded by more than two orders of magnitude previous attempts at synthesizing superheavy nuclides in reactions of 48Ca projectiles with actinide targets. We observed new decay sequences of genetically linked alpha decays terminated by spontaneous fission. The high measured alpha-particle energies, together with the long decay times and spontaneous fission terminating the chains, offer evidence for the decay of nuclei with high atomic numbers. The decay properties of the synthesized nuclei are consistent with the consecutive alpha decays originating from the parent nuclides 288,289114, produced in the 3n-and 4n-evaporation channels with cross sections of about a picobarn. The present observations can be considered experimental evidence for the existence of the “island of stability” of superheavy elements and are discussed in terms of modern theoretical approaches.

An approximate formula for the angular dependence of the residual defect in a silicon surface barrier detector

Abstract A new formula for the angular dependence of the amplitude residual defect based on the surface recombination model for charge losses is presented. Experimental results for Xe and Ni ions are compared with calculated ones. An attempt to apply this formula in a computer code to generate the energy distribution of spontaneous fission events of nuclei implanted into the detector was made.

Observation of enhanced nuclear stability near the 162 neutron shell

In bombardments of {sup 248}Cm with {sup 22}Ne the authors discovered two new isotopes, {sup 265}106 and {sup 266}106, by establishing genetic links between {alpha} decays of the 106 nuclides and SF or {alpha} decays of the daughter (grand-daughter) nuclides. For {sup 266}106 they measured E{sub {alpha}}=8.62{+-}0.06 MeV followed by the SF decay of {sup 262}104 for which they measured a half-life value of 1.2{sup +1.0}{sub {minus}0.5} s. For {sup 265}106 they measured E{sub {alpha}}=8.82{+-}0.06 MeV. They estimated {alpha} half-lives of 10-30 s for {sup 266}106 and 2-30 s for {sup 265}106 with SF branches of {approximately}50% or less. The decay properties of {sup 266}106 indicate a large enhancement in the SF stability of this N=160 nuclide and confirm the existence of the predicted neutron-deformed shell N=162.

Real-time mode detection of heavy ion-induced nuclear reaction products

Abstract Design of spectrometers of two nuclear research facilities, the Dubna Gas-filled Recoil Separator and KHIPTI is reviewed. The sources of backgrounds are discussed and techniques used to suppress these backgrounds in one-event detection experiments aimed at the synthesis of heavy elements are presented. The first system was used in 1998 in experiments on Z =114 superheavy element. We consider the possibility of detection of rare time and position correlated recoil-alpha and alpha–alpha sequences in real-time mode as basic techniques to suppress beam and target-like associated backgrounds. Fields of application of such a technique are discussed from the viewpoint of synthesis of heavy elements and by studying their chemical properties.

Application of laser welding methods in industrial production

The laser welding methods of corrosion-resistant steel, aluminium and magnesium alloys, titanium, cast iron, dissimilar and other materials are examined. These methods are used in automobile, medical, electronic, shipbuilding and other industries.

A look at the phenomenon of charge multiplication in silicon radiation detector within the concept of dynamic focusing of the electric field

The spectra of /sup 34/S and /sup 40/Ar ions measured with silicon detectors were analyzed within the concept of dynamic focusing of the electric field. The ionization constant b was obtained for different fields. An estimation of the hot electrons temperature was carried out. A reasonable scenario for the development of charge multiplication process is suggested, taking into account the influence of initial electron-hole concentration on the formation of the hot carriers subsystem.

Parameter monitoring and control system of Dubna Gas-Filled Recoil Separator

A modified integrated parameter-monitoring and control system for experiments on the synthesis of superheavy nuclei at the U-400 cyclotron of the Flerov Laboratory of Nuclear Reactions is considered. Experiments on the irradiation of heavy actinide targets were performed at the Dubna Gas-Filled Recoil Separator (DGFRS) [1]. This system consists of three components, namely, the detection module parameter control subsystem, the beam parameter monitoring subsystem, and the separator technical parameter control subsystem. The system is designed in CAMAC standard, the software is written under Windows XP using RAD Borland C++ Builder 6.0 and Kk009Pci interface (LNR) [2, 3].