Narrow Results

The position of the neutron and proton drip-lines as well as properties of the isotopes Fe, Ni and Zn with neutron excess and neutron deficit are studied within the Hartree–Fock approach with the Skyrme interaction (Ska, SkM*, Sly4). The pairing is taken into account on the basis of the BCS approach with the pairing constant G = (19.5/A)[1 ± 0.51(N-Z)/A]. Our calculations predict that for Ni isotopes around N = 62 there appears a sudden increase of the deformation parameter up to β = 0.4. The zone with such big deformation, where Ni isotopes are stable against one neutron emission stretches up to N = 78. The magic numbers effects for the isotopes ⁴⁸Ni, ⁵⁶Ni, ⁷⁸Ni, ¹¹⁰Ni are discussed. The universality of the reasons standing behind the enhancement of stability of the isotopes ⁴⁰O and ¹¹⁰Ni which are beyond the drip-line is demonstrated. Calculated values of the two-neutron separation energy, and proton and neutron root mean square radii for the chain of Ni isotopes show a good agreement with existing Hartree–Fock–Bogoliubov calculations of these values.

Neutron rich nuclei has been studied with a new phenomenological mass formula. Predictions of different mass formulas for the location of the neutron drip line are compared with those from the present calculation. The implications of the new mass formula for r-process nucleosynthesis are discussed. It is found that though the neutron drip line obtained from this formula differs substantially from other formulas, the r-process abundance upto mass 200 are unlikely to be significantly different. The errors inherent in the mass formula are found to play an insignificant role beyond mass A = 80.

To produce and investigate exotic heavy neutron rich nuclei located in the “north-east” region of nuclear map the new setup is under construction at Flerov Laboratory for Nuclear Reactions (FLNR) of JINR, Dubna. In this setup available U-400M cyclotron beams will be used in low energy multi-nucleon transfer reactions. Products of 4.5 to 9 MeV per nucleon heavy-ion collisions, such as ¹³⁶Xe beam on ²⁰⁸Pb target, are to be captured in a gas cell, selectively laser-ionized and then transported towards mass separator by a sextupole (or quadrupole) ion guide extraction system.

Low-frequency collective K^π = 0⁺ modes in deformed neutron-rich unstable nuclei are investigated by means of the quasiparticle-random-phase approximation (QRPA) based on the coordinate space Hartree-Fock-Bogoliubov (HFB) formalism. It is found that the spatially extended structure of neutron quasiparticle wave-functions brings about a striking enhancement of the transition strengths. It is also found that the quadrupole pairing correlation plays an important role in generating coherence among two-quasiparticle excitations of neutrons.

The study of nuclear structure far from stability, which mainly rely on the availability of radioactive nuclear beams, can complementary be addressed by means of high intensity beams of stable ions. Deep-inelastic and multi-nucleon transfer reactions are a powerful tool to populate yrast and non yrast states in neutron-rich nuclei. Particularly successful is here the combination of large acceptance spectrometers with highly segmented γ-detector arrays. Such devices, eventually complemented by large coverage particle detectors, can provide the necessary channel selectivity to identify very rare signals. An example is the CLARA γ-ray detector array coupled with the PRISMA spectrometer at the Legnaro National Laboratories (LNL). Large data sets have been recently collected for nuclei close to the N = 28, 40 and 50 shell closures. The obtained results complement studies performed with current radioactive beam (RIB) facilities. The data clearly show the evolution of the effective single particle energies in very good agreement with the predictions of the mean field model with tensor interaction. New experimental information has been obtained on a wide range of nuclei close to the N = 28, 40 and 50 shell closures allowing the population of medium and high-spin yrast states. The excited states of the N = 50 isotones, extended down to Z = 31, and of N = 51 isotones, extended down to Z = 34, have been used to test the predictions of the shell evolution based on the effects of the tensor interaction as well as of the different effective interactions. As future perspective the development of a γ-ray detection system capable of tracking the location of the energy deposited at every γ-ray interaction point will also provide an unparallel level of detection sensitivity, and will open new revenues for nuclear structure studies.

Applicability of different nuclear reactions (fusion of stable and radioactive nuclei, multi-nucleon transfers and neutron capture) for the production of new neutron enriched heavy nuclei is discussed in the paper. For the first time, a narrow pathway is found to the middle of the island of stability owing to possible β⁺-decay of SH isotopes which can be formed in ordinary fusion reactions of stable nuclei. Neutron capture reactions can be also used for the production of the long-living neutron rich SH nuclei. Strong neutron fluxes might be provided by pulsed nuclear reactors and by multiple nuclear explosions in laboratory conditions and by supernova explosions in nature. Low-energy multinucleon transfer reactions with actinide beams and targets are of special interest for synthesis of new neutron enriched transfermium nuclei and not-yet-known nuclei around the closed neutron shell N = 126 having largest impact on astrophysical r process. The estimated cross sections for the production of these nuclei look very promising to plan such experiments at available accelerators. Several new test experiments of such kind are proposed to perform including those in which a role of the shell effects in low-energy reaction dynamics could be clarify much better.

We propose to search for the ⁷H g.s. using the quasifree (α,2α) knockout reaction from ¹¹Li having a spatially extended halo. In the quasi-free scattering ⁴He(¹¹Li,2α)⁷H reaction an α-particle is knocked out from ¹¹Li by the alpha target nucleus and the detection of these two α-particles is sufficient to extract the missing mass of ⁷H. The use of telescopes composed of a set of micro-strip Si deterctors provides a reconstruction of the vertex position inside the target with an accuracy of about ±100 μm. This accuracy also allows a very thick target which is only limited by the energy loss of the outgoing α-particles.

The talk is focused on several most exciting problems of present-day nuclear physics. First of all these are the state of affairs in production and study properties of super-heavy elements (stability of these nuclei with increasing of Z number, methods of their production, nearest experiments and further progress, search of SHE in cosmic rays, etc.). Then the problems of neutron rich nuclei (their astrophysical significance, possible reaction mechanisms for the production of heavy neutron rich nuclei, studying neutron rich nuclei with closed neutron shells including those located at the neutron drip line and beyond it) are discussed. The next subject is strange nuclei and antimatter. Extension of the nuclear map into the two additional directions would broaden significantly our comprehension of the nuclear matter. The fundamental problem of vacuum decay (spontaneous formation of electron-positron pairs) in super-strong electric field appearing in collisions of very heavy (U-like) nuclei is also discussed. This problem attracts recently new and great interest owing to our deeper understanding of the process and new experimental possibilities.

It will be interesting to perform study of neutron rich nuclei, for example ^5,7H, ^9,10He, etc. There are several planned experiments on the ACCULINNA, ACCULINNA-2 facilities to make such study with using of the neutron detectors. The prototype of array of the neutron detectors based on stilbene crystals was designed and manufactured in Flerov Laboratory of Nuclear Reactions, JINR Dubna for this purpose.

New data on β-decay properties on neutron-rich ^82,83Ga measured at TETRA neutron detector are reported. Pure beams of ^82,83Ga were produced at ALTO-facility using laser ionization technique. While T_1/2 (⁸²Ga) = 0.604(11)s , P_1/2 (⁸²Ga) = 22(2)% and T_1/2 (⁸³Ga) = 0.312(1)s are in agreement with literature values, P_1/2 (⁸³Ga) = 85(4)% was found to be significantly higher as compared to other available data. Therefore, we came to the conclusion that ⁸³Ga is a much stronger neutron emitter as it was reported previously.