V.E. Zhuchko

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.

Analysis of some modes of multibody decays of low excited actinide nuclei

At the previous ICPPA (2015) we presented the report [1] where we discussed the results of the solution of the problem of estimation of statistical reliability of linear point structures, obtained from the experiments at the FOBOS spectrometer [2] dedicated to study of the spontaneous fission of the 252Cf nucleus in the mass correlation distribution of fission fragments. These new unusual structures bounded by magic clusters were interpreted as a manifestation of a new exotic decay called collinear cluster tri-partition (CCT) [3]. The reliability of these structures was estimated on the basis of methods of morphological image analysis [1], [4], [5]. To improve the quality of revealing and further estimation of linear structures statistical reliability in the mass correlation distribution of fission fragments we used the formalism of oblique projecting [6] and subjective modeling [7], [8].

EXPERIMENTAL TESTING OF THE HI MASS RECONSTRUCTION PROCEDURE AT LIS SETUP

Reconstruction of the heavy ion masses in the time-of-flight spectrometry is known to be a complicated task due to distortions both in timing and measuring of the ions energy using PIN diodes. Original procedure which takes into account simultaneously pulse height defect (PHD) and plasma delay for unbiased mass reconstruction was tested in series of experiments at the LIS setup using degrader foils.

STATUS OF THE VEGA PROJECT

Motivation and status of the VEGA (Velocity-Energy Guide based Array) project is presented. One armed fission fragments spectrometer with an electrostatic guide system is proposed for installation at the vertical experimental channel of the IBR-2 reactor. Scientific program aimed at investigation of new multi-body decays of actinides, shapeisomeric states in fission fragments and fission modes is reported.

STUDY OF SHAPE ISOMERIC STATES IN FISSION FRAGMENTS

In one of our experiments aimed at studying of the new multi-body decay called collinear cluster tri-partition (CCT) [1–3] additional absorber (Ti foil) was introduced just after the source at the distance of approximately 1 mm. It was motivated by the peculiarity of the CCT manifestation in the experiments namely specific structures in the region of an essential missing mass in the fission fragments (FFs) mass correlation distribution were observed in the spectrometer arm faced to the Cf source backing only. The effect was traced back to some angular divergence between two CCT partners flying in the same direction after passing the scattering medium on the flight pass due to the multiple scattering. As a result one of them can be lost in the PIN diode frame what is observed as” missing mass” or both fragments will be detected independently in the neighboring diodes. We have observed significant mass deficit in the total mass of the fission fragments detected in coincidence with Ti ions knocked out from the foil (fig. 1) [4]. For the sake of convenience, the FFs from such events are labeled as M1, M2 and M3 in an order of decreasing masses in the ternary event. The total mass of the two heavier fragments Ms = M1 + M2 is plotted vs. the mass of the lighter fragment M3. Such effect could be expected if the scattered fragment looks like a di-nuclear system destroying due to inelastic scattering on the Ti nucleus. A mean flight time between the Cf source and the foil does not exceed 0.1 ns. It can be regarded as a low limit for the life time of the di-nuclear system (shape isomer).

COLLINEAR CLUSTER TRIPARTITION: FIRST STEPS IN PHYSICAL TREATING

Preliminary results of the analysis of the rectangular structures in the mass correlation distributions of the fission fragments from 252 Cf (sf) are presented. The structures lie in the region of big missing mass and are connected with the multi-body decay of the mother system. The ternary chain-like prescission configuration seems to be too compact and could decay due to tunneling only. More elongated four-body configuration leading to the quaternary decay let meet energy conservation law in the scission point.