Yu. P. Tretyakov

Experiments on the synthesis of neutron-deficient kurchatovium isotopes in reactions induced by 50Ti Ions

Abstract By bombarding Pb isotopes with 50 Ti ions, two new isotopes of element 104 (kurchatovium) with mass numbers 255 and 256 have been synthesized. The isotope 256 Ku has been formed in the reaction 208 Pb ( 50 Ti, 2n) and has a spontaneous fission half-life of about 5 msec. The odd isotope 255 Ku has been formed with a maximum cross section in the reaction 207 Pb( 50 Ti, 2n) and has a half-life of several seconds. The experimental results obtained, together with the available data on the properties of kurchatovium, substantially change the understanding of the stability of heavy nuclei with respect to spontaneous fission. In this connection the influence of the structure of the fission barrier on the properties of heavy nuclei is discussed. On the basis of the experimental data on the synthesis of Fm and Ku neutron-deficient isotopes in reactions induced by ions heavier than argon, the possibilitie s of synthesizing elements with Z≧106 are investigated.

Acceleration of 48Ca ions and new possibilities of synthesizing superheavy elements

Abstract At the JINR U-300 heavy-ion cyclotron, a 48Ca ion beam has been first produced. Compared with other ions, these ions have great advantages for the synthesis of transuranic and superheavy elements. The extreme neutron excess of the 48Ca nucleus enables one to approach the double magic nucleus 298114 in fusion reactions. In addition, the 48Ca nucleus itself being doubly magic, fusion reactions with it lead to the formation of compound nuclei with low excitation energies. This sharply increases the cross sections for reactions with a small number of neutrons emitted. The model experiments carried out to synthesize the isotope 252102 in reactions with different Pb isotopes have confirmed these advantages of 48Ca ions.

The efficiency of consuming rare isotopes in a PIG ion source

The efficiency of consuming a working substance in the cyclotron arc ion source during operation at the LNR JINR cyclotrons is analyzed in comparison with the results obtained for the ECR ion source of GANIL and the Berkeley cyclotrons. The experimental results described have been obtained during the acceleration of rare isotopes ion beams (Mg‐Ge) at the U‐400 and U‐300 cyclotrons. Some features of solid working substances fed into the cyclotron ion source are described. The optimal conditions for the efficient use of working substances in the arc discharge are discussed. The results of producing and accelerating rare gas isotopes ion beams, including the radioactive isotope carbon‐14, are presented. Prospects for the future development of efficient ion sources for the LNR cyclotron complex consisting of the U‐400 and the U‐400M are also discussed.

The production of ions of solids from the PIG source with an additional anode

In this paper we report the results of production of ions of solids from the PIG source with an additional anode and solid material feed by cathode sputtering. The investigations were performed at the test bench and at the U‐400 cyclotron. Two versions of the ion source with different dispositions of the sputtering electrode were studied. In the first version the sputtering electrode is introduced into the discharge chamber through the wall opposite to the emission slit, the second version has lateral disposition of the sputtering electrode. The influence of the potential of an additional anode on the total extracted current and charge state distribution was studied at the test bench for both versions. The results of the test of the ion source with lateral disposition of the sputtering electrode at the U‐400 cyclotron are reported.

Experiments on the synthesis of neutron-deficient isotopes of kurchatovium in reactions with accelerated50Ti ions

ConclusionsA number of conclusions can be drawn from the aggregate of experimental results.The method of synthesis of transfermium elements in the irradiation of lead isotopes with ions with mass AI≥40 atomic units, investigated earlier [12] for the example of the reaction Pb(40Ar, xn)Fm, is also extremely effective using50Ti ions. The reactions Pb(40Ar, 2n)Fm and Pb(50Ti, 2n)Ku have approximately equal cross sections, which might have been expected on the basis of theoretical estimates. This permits us to hope that this method can be used successfully for the synthesis of heavier elements in the reactions induced by54Cr,55Mn, and58Fe ions.In all probability, the substantial changes in the systematics of the half-lives for even-even isotopes of kurchatovium are associated with the structure of the barriers to fission of these nuclei. From this standpoint, it seems important to investigate the properties of more neutron-deficient isotopes of kurchatovium, using, in particular, the reactions with204Pb, and to attempt to advance into the region of elements with Z≥ 106. On the other hand, a detailed theoretical analysis must be made of the data obtained on the basis of the modern theory of nuclear fission, which, in our opinion, will aid in a more reliable prediction of the properties of heavy and ultraheavy elements.

Quasimolecular KX-ray excitation by bombarding La targets with La and Xe ions

Abstract The X-ray emission from 85 to 150 MeV Xe and 115 MeV La bombardments of thick natural La targets has been measured. The spectra and yields of X-ray emission are obtained. Continuous X-ray distributions have been found to lie beyond the target and projectile characteristic X-ray energies. The high-energy parts of these continua are interpreted as K-radiation of quasi-molecules with effective atomic numbers Z = 111 and Z = 114, respectively.

Quasimolecular KX-ray excitation by bombarding As, Zr, Nb, Mo and Rh target with Nb ions

Abstract By bombarding various targets with 65 MeV and 40 MeV Nb ions continuous X-ray distributions have been obtained, which range up to the KX-ray energies of quasiatoms woth Z = Z 1 + Z 2 . The hogh-energy parts of these continua are interpreted as KX-radiation of quasimolecules transiently formed during the adiabatic heavy-ion atomic collisions.

The Doppler shift and anisotropy of quasimolecular X-rays emitted in Nb+Nb collisions at 67 MeV

The quasimolecularKX-ray spectrum obtained by bombarding Nb with 67 MeV Nb ions has been found to undergo a Doppler shift with an effective Doppler velocity equal to the mean center-of-mass velocity of the intermediate Nb+Nb molecule, corresponding to the projectile velocity. By applying Doppler shift corrections the intrinsic anisotropy of the quasimolecularKX-radiation is found.

An investigation of quasimolecularKX-radiation emitted in Nb+Nb and Ni+Ni collisions

Natural Nb targets were bombarded with 67 MeV and 96 MeV Nb ions, and natural Ni targets with 67 MeV Ni ions. Continuous quasimolecularKX-ray spectra have been obtained. The absolute yield and directional anisotropy of the quasimolecularKX-radiation have been derived. An attempt has been made to determine the endpoint energy of the measured continua.

Automatic control system of the PIG ion source for the U‐400 cyclotron

An automatic control system is described for the multiply charged ion source of the U‐400 cyclotron based on CAMAC apparatus and microprocessor controllers. The system allows the automatic tuning of the ion source to the necessary regime, including the automatic start‐up of discharge, determination of the necessary parameters of sputtering, and the automatic search for a maximum beam current for given discharge parameters. The system performs the tuning of the ion source to the quasioptimal regime in 10–15 min with up to 5% deviation from the preset parameters. It is possible to stabilize the beam current within 3% using the automatic correction of the discharge regime.