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[en] The results of the experiment aimed at the synthesis of 108 isotopes in the 226Ra(48Ca,xn)274-xHs nuclear reaction are presented. The experiment was performed using the Dubna gas-filled recoil separator at the U400 cyclotron. We observed six genetically linked decay chains of the parent 270Hs nuclei. The properties of this isotope decaying by α-emission with Qα=9.02±0.08 MeV and T1/2=7.6 s to the 266Sg, which undergoes spontaneous fission (T1/2=0.28 s), are compared with the properties of the same isotope produced earlier in the reaction 248Cm(26Mg,3-5n)269-271Hs . The values of the measured cross-sections of the reactions with evaporation of 3 to 5 neutrons are discussed. The obtained experimental results allow us to estimate the probability of nuclear fusion for the heavier particle-projectile combinations, e.g., with the 50Ti projectiles. One could expect that production cross sections of the reactions of 243Am+50Ti and 249Cf+50Ti that lead to the new elements 117 and 120 could exceed 0.2 pb .(author)
[en] A summary of some recent level density research is presented. Although the subject is an old one, it is argued that a number of unanswered questions remain. These include uncertainties in related quantities such as the parity ratio and the spin cutoff parameter, which are needed to deduce level density parameters from resonance counting for low energy neutrons. Additional points of interest are the extent to which the low energy region shows constant temperature rather than Fermi gas energy dependence, whether the region below the neutron binding energy shows significant structure and whether the level density for fixed A shows a drop for neutron-rich and proton-rich nuclei compared to nuclei on the valley of stability.
[en] A survey of experiments at the Dubna gas-filled recoil separator (Laboratory of Nuclear Reactions, JINR, Dubna) aimed at the detection and study of the “island of stability” of superheavy nuclei produced in complete fusion reactions of "4"8Ca ions and "2"3"8U–"2"4"9Cf target nuclei is given. The problems of synthesis of superheavy nuclei, methods for their identification, and investigation of their decay properties, including the results of recent experiments at other separators (SHIP, BGS, TASCA) and chemical setups, are discussed. The studied properties of the new nuclei, the isotopes of elements 112–118, as well as the properties of their decay products, indicate substantial growth of stability of the heaviest nuclei with increasing number of neutrons in the nucleus as the magic number of neutrons N = 184 is approached.
[en] Level densities and radiative strength functions in 171Yb and 170Yb nuclei have been measured with the 171Yb(3He,3He(prime) γ)171Yb and 171Yb(3He, αγ)170Yb reactions. A simultaneous determination of the nuclear level density and the radiative strength function was made. The present data adds to and is consistent with previous results for several other rare earth nuclei. The method will be briefly reviewed and the result from the analysis will be presented. The radiative strength function for 171Yb is compared to previously published work.
[en] One of the fundamental outcomes of the nuclear shell model is prediction of existence of the island of stability in the domain of the super heavy elements. This hypothesis has been under developments for more than 35 years in various nuclear models. It is the Dubna gas filled recoil separator (DGFRS) that allows to perform a set of successful experiments aimed to synthesize super heavy nuclides with Z = 112-118 experiments
[en] We show that the combined analysis of quasicontinuous γ spectra from the (3He,α) and (nth,2γ) reactions gives the possibility to measure the electromagnetic character of soft dipole resonances. Two-step γ-cascade spectra have been calculated, using level densities and radiative strength functions from the (3He,αγ) reaction. The calculations show that the intensity of the two-step cascades depends on the electromagnetic character of the soft dipole resonance under study. The difference reaches 40-100% which can be measured experimentally
[en] Two-step-cascade spectra of the 171Yb(n, γγ)172Yb reaction have been measured using thermal neutrons. They are compared to calculations based on experimental values of the level density and radiative strength function obtained from the 173Yb(3He,αγ)172Yb reaction. The multipolarity of a 6.5(15) μN2 resonance at 3.3(1) MeV in the strength function is determined to be M1 by this comparison
[en] Nuclear level densities have been extensively studied on or near the valley of stability. Because the data base is so sparse away from the valley of stability, the systematics found for stable nuclei are assumed to apply off the line of stability as well. A model which predicts different systematics off of the stability line is examined. A pair of recent measurements provide tentative support for the new hypothesis, though it is clear additional data are needed
[en] The Prompt Fission Neutron Spectrum (PFNS) from 235U(n,f) is very important for various nuclear applications. It has been investigated in different experiments. In spite of ∼50 years of experimental efforts, a continuing conflict exists at thermal neutron energy. Microscopic experimental PFNS cannot describe macroscopic data. In this report we discuss the current status of this problem and suggest a new experiment, which could possibly resolve this problem. (authors)