D.D. Bogdanov

New neutron-deficient isotopes of barium and rare-earth elements

Abstract This paper deals with an investigation of the short-lived neutron-deficient isotopes of barium and rare-earth elements. By using the BEMS-2 isotope separator with a heavy-ion beam, we succeeded in producing 19 new isotopes with mass numbers ranging from 117 to 138. Five of these ( 117 Ba, 129, 131 Nd and 133, 135 Sm) turned out to be delayed proton emitters. Theβ-decay probabilities for the new isotopes have been analyzed in terms of the β-strength function. An analysis of the proton spectrum shape has been performed using the statistical model for delayed proton

The BEMS-2 on-line isotope separator at the JINR heavy-ion cyclotron

Abstract The BEMS-2 on-line isotope separator operated in a heavy-ion beam employs a high-temperature surface-ionization ion source. The design features of the ion source with an external target are described. The recoil effect occuring in heavy-ion reactions is used to transport the radioactive isotopes under investigation into the source cavity through a 1.4 μm tantalum entrance foil. The operational characteristics of the ion source for Cs and Ba isotopes are studied. The average hold-up time of the activity in the ion source, τ, which is determined by the diffusion of recoils from the catcher, is measured. The value of τ depends on the temperature and type of the catcher used. For a tantalum catcher τ ≈ 1.0s at T = 2500°C, and the value of τ increases with decreasing temperature. In the case of a tungsten catcher, the hold-up time is several times longer. The ion source efficiency for Ba is equal to 30–50%.

A study of the decay of the delayed proton emitters 117Ba, 119Ba and 121Ba

Abstract The delayed proton emitters 117, 119, 121 Ba have been investigated using the on-line BEMS-2 isotope separator. From measurements of positron-proton coincidences the ( Q 0 - B p ) values for these isotopes (where Q 0 is the K-capture energy and B p is the proton binding energy of the daughter nucleus) have been obtained to be 7.9±0.3, 6.2±0.2 and 4.3±0.3 MeV, respectively. The shapes of the proton spectra have been analysed within the framework of the statistical model. The analysis indicates the presence of a local resonance in the β-strength function at an excitation energy of the daughter nucleus of 5 MeV.

New neutron-deficient isotopes of lanthanum and cerium

The short-lived neutron-deficient isotopes of lanthanum and cerium were produced in the 32S+96, 98Ru reactions and separated according to their masses. Seven isotopes 123–125La and 124–127Ce have been first observed and their half-lives and low-energy γ-ray data are reported. In addition, low-energy γ-ray data are given for the 122–125Ba and 127La decays. The β-decay probabilities for Ce, La and Ba isotopes are discussed in terms of the average β-strength function.

Delayed particle emission in the β+ decay of 116Cs and 118Cs

Abstract It is found that the delayed particles observed following the β+ decay of 116Cs are due to the β+ decays of two metastable states with half-lives of 0.65 ± 0.10 s and 3.9 ± 0.3 s. The long-lived component dominates in the delayed proton spectrum, whereas the delayed α-particle emission is associated with the β+ decay of the short-lived state. The total decay energies of the isotopes 116,118Cs have been measured.

The spontaneous fission of 224Fm and 246Fm

Abstract The average total kinetic energies for the fission products of the neutron-deficient isotopes 244 Fm and 246 Fm have been measured as 196 ± 4 and 199 ± 4 MeV, respectively. The values agree well with those expected on the basis of systematics.

Shell effects and cross sections of formation of neutron-deficient isotopes of Ac, Ra and Fr in 20Ne + 197Au reaction

Abstract The cross sections of the formation of Ac-, Ra- and Fr-evaporation residues in the 20 Ne + 197 Au reaction have been measured by means of the VASSILISSA kinematic separator in the range of the compound-nuclei excitation energies from 40 to 120 MeV. The experimental data have been analyzed on the basis of the statistical model of excited nuclei decay. The influence of different assumptions about the parameters of fission barriers on calculation results was considered.

On the fine structure in delayed proton spectra.

Abstract The fine structure in delayed-proton spectra is interpreted on the basis of statistical fluctuations associated with the variation of β-decay matrix elements and the relative proton widths of the excited states. Formulae are derived which give the variance of relative proton intensity in terms of the average characteristics of the delayed proton emission and the level density. The experimental data on the variance of the relative proton intensity for 111Te and the calculations using these formulae are in satisfactory agreement. The fluctuations predicted for 109Te considerably exceed the measured ones.

A surface-ionization ion source designed for in-beam operation with the BEMS-2 isotope separator

Abstract A surface-ionization ion source designed to operate in combination with the BEMS-2 isotope separator in a heavy ion beam in described. The ion source is adjusted for the separation of rare-earth elements. The separation efficiency for 150 Dy is determined to be equal to about 20% at an ionizer temperature of 2600 K. The hold-up times for praseodymium, promethium and dysprosium in the ion source range from 5 to 10 s at ionizer temperatures of 2500–2700 K.

Studies of formation of fusion evaporation residues with Z≥83 in heavy ion reactions

By employing the kinematic separator VASSILISSA and the beams of 20,22Ne, 24,26Mg, 40Ar and 40Ca we studied 18 projectile‐target combinations leading to formation of compound nuclei with atomic numbers 83‐102 and obtained xn, pxn, and αxn evaporation residues in the range of the projectile energy extending from the Coulomb barrier to the values corresponding to the compound nucleus excitation of about 100 MeV. The systematics is presented of the maximum xn reaction cross‐sections which are governed by the fissility of the reaction products. As a result, the values of macroscopic fission barriers were extracted for the neutron‐deficient nuclides in the range of Z=83–92 and N=104–134. These values are discussed in terms of contrasting with predictions of the rotating droplet model. Three isotopes, 252,253,254102, were obtained as deexcitation products of the 258102 compound nucleus formed by 22Ne and 26Mg projectiles. Some conclusions are drawn from these results about the possible use of 22Ne and 26Mg beam...