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Fission fragment mass distributions were measured in heavy-ion induced fission of 238U. The mass distributions changed drastically with incident energy. The results are explained by a change of the ratio between fusion and quasifission with nuclear orientation. A calculation based on a fluctuation dissipation model reproduced the mass distributions and their incident energy dependence. Fusion probability was determined in the analysis. Evaporation residue cross sections were calculated with a statistical model for the reactions of 30Si+238U and 34S+238U using the obtained fusion probability in the entrance channel. The results agree with the measured cross sections of 263,264Sg and 267,268Hs, produced by 30Si+238U and 34S+238U, respectively. It is also suggested that sub-barrier energies can be used for heavy element synthesis.

Two excited J(pi)=0(+) states in Pb-186 populated in the a-decay of Po-190 have been identified through alpha -particle/conversion electron coincidences in an experiment at the velocity filter SHIP ...

The production cross sections were measured for the xn, pxn, and αxn de-excitation channels of the 212Rn compound nuclei formed at excitation energies of 80–160 MeV in the reaction 22Ne + 190Os. The maximum cross sections obtained for the xn (x = 8–12), pxn (x = 8–11) and αxn (x = 8–11) reaction channels were fitted satisfactorily with the computer code HIVAP using its standard parameter set except that the single scaling parameter C = 0.65 was implemented to adjust the values of the liquid-drop fission barriers predicted by the Cohen-Plasil-Swiatecki (CPS) model. Additionally, an analysis of a large set of data on the formation cross sections of neutron-deficient Z = 83–92 nuclei showed that the whole body of data obtained for the nuclear region notable for the large variations of both the liquid-drop barrier and the shell effects, can be described well with practically the same parameter C = 0.55–0.68. One may take this observation as an indication that, though the CPS model overestimates the liquid-drop fission barriers, it reproduces well the relative behaviour of these barriers in the whole range of neutron-deficient Z = 83–92 nuclei.

A possibility of using the Cherenkov technique to measure the average energy of collimated relativistic nuclear 79Au beams is investigated in the article for specific beam—radiator interaction (strong deceleration, fragmentation) produces a considerable effect of the spreading of the Cherenkov one. Two Cherenkov methods — achromatic (E, α) and combined (“combi”) — were employed for this purpose. At an energy about 1 GeV/u the accuracy of measurement by the “combi” method was ± 1.4 MeV/u. The accuracy of measurement by the (E, α) method was ±0.9 MeV/u at the energy EAu≈640 MeV/u. These results turned out to be in good agreement with initial EAu0 data from the SIS accelerator with allowances made for energy losses over the beam line (the maximum discrepancy was ≤0.4%). With all the set of these data, the direction condition was for the first time checked for VChR from heavy nuclei. It is shown to be fulfilled to an accuracy above ±5′ in the angle range 27°

The reduced probabilities of the delayed fission channels P s df for 188 Bi and 196 At are determined, from experimental data, to be 3.4 × 10 −4 and 8.8 × 10 −4 , respectively. The comparison of the obtained and calculated value of P β df allows to estimate the fission barriers for 188 Pb and 196 Po.

Construction and properties of a double ionization chamber (DIC) are described. Heavy ion fusion-evaporation reaction products obtained at the focal plane of the kinematic separator VASSILISSA enter the DIC volume through a thin plastic window. After their thermalization in the gas, they drift in the electric field to the DIC cathode. Their α-decay and/or spontaneous fission are detected in 4π-geometry in two ionization chambers, divided by the common cathode. Using DIC the α-decay of Bi and Pb isotopes produced in the fusion reactions 40 Ar + 159 Tb and 40 Ca + 153 Eu were detected. A new isomer, 189m Bi was observed.

Heavy-ion fusion reaction ER's were studied in a wide excitation energy range of the 199,193,191 Bi and 217 Ac compound nuclei produced with bombarding ions of 40 Ar , 40 Ca and 20 Nc . The problems of the shell effect fading with increasing nucleus excitation energy and the isospin dependence of the macroscopic component of the fission barrier are discussed.