Rogov I.S.1,2
1 Joint Institute for Nuclear Research, Dubna, Russia; 2 National Research Tomsk Polytechnic University, Tomsk, Russia
E-mail: isrogov@theor.jinr.ru
The possibility of application of dinuclear system model to spontaneous fission (SF) process is discussed.
In the model the nucleus is represented as dinuclear system (DNS), which can be described with the distance R between the centers of mass of the clusters and charge asymmetry coordinate Kz = (Zh – Zl)/(Zh + Zl), where Zh,l are charge numbers of heavy and light cluster, respectively.
Motion in Kz corresponds to cluster configuration formation; motion in R coordinate describes the decay process.
The determination of the DNS state for given parent nucleus can be obtained by solving the stationary Schrödinger equation with the inertia coefficient B(Kz) [1] and potential energy U(Kz) [2].
The potential energy and inertia parameter are approximated with step functions, therefore the Schrödinger equation can be directly solve [3].
Using this solution, the spectroscopic factors (the preformation probabilities) are calculated.
To compare the model results with experimental ones, half-lives T1/2 are calculated in the one-dimensional WKB approximation [4].
The SF mainly occurs from the DNS configurations corresponding to the minima the driving potentials. These minima are below the potential energy of mother nucleus.
Verification of the model is made for even-even uranium isotopes 232–236U.
The same set of parameters is used for all nuclei considered.
The calculated and experimental [5] half-live times are presented in table below:
232U 234U 236U
Ttheor, s 7.43×1020 1.61×1022 1.10×1023 Texp, s 3.73×1021 4.73×1023 6.38×1023
In terms of half-lives, the model presented describes well the experimental values. So, the basic assumption of the model on the collective coordinate for the SF seems to be correct.
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SEARCH FOR β+
EC AND ECEC PROCESSES IN
74Se
Barabash A.S.1, Brudanin V.B.2, Klimenko A.A.2, Konovalov S.I.1, Rakhimov A.V.2, Rukhadze E.N.3, Rukhadze N.I.2, Shitov Yu.A.2, Štekl I.3,Umatov V.I.1, Warot G.4
1 NRC “Kurchatov institute” ITEP,Moscow, Russia; 2 Joint Institute for Nuclear Research, Dubna, Russia; 3 Institute of Experimental and Applied Physics, CTU in Prague, Prague,
Czech Republic; 4 Laboratoire Souterrain de Modane, Modane, France E-mail: rukhadze@jinr.ru
Search for double beta decay processes (β+EC, EC/EC) of 74Se was performed at the Modane underground laboratory (LSM, France, 4800 m w.e.) using an ultra-low-background HPGe detector OBELIX with sensitive volume of 600 cm3 [1] and a sample of natural selenium. The sample of natural selenium was powder with a total mass of 1.6 kg containing ~ 0.89% (~ 14.24 g) of 74Se.
Selenium was filled in a circular Teflon box and placed on the end cap of HPGe detector. The measurement of selenium sample was lasted during 3040 h. The efficiency of measurement was obtained by using Monte Carlo simulations performed on the base of GEANT 4 and GEANT 3 and then tested by measurement of low active samples placed on the end cap of Obelix detector.
Low active samples were prepared on the base of La2O3 powder containing
~ 0.09% of 138La (T1/2 ≈ 1.02×1011 yr) and had activities of −19.3 and 61.8 Bq.
The method of efficiency calibration for low background measurements with low active samples was described in details in [2].
The main goals of present investigation were searches for radiative 0νECEC decay of 74Se into the ground 0+ state of 74Ge, 2νECEC decay of 74Se into 2+1, 596 keV and 2+2,1204 keV exited states of 74Ge, and β+EC decay into 2+1, 596 keV excited state of 74Ge. Based on preliminary calculations of experimental data new limits on β+EC and ECEC decays of 74Se into ground 0+, 2+1, 596 keV and 2+2,1204 keV exited states of 74Ge was obtained. They are ranged from T1/2 ~ 1×1019 yr (90% CL) to T1/2 ~ 5×1019 yr (90% CL) and significantly improved previous experimental limits [3, 4].
1. N.I.Rukhadze et al. // Izvestia RAN. Ser. Phys. 2013. V.77. P.424.
2. V.B.Brudanin et al. // JINST. 2017. V.12. 02204.
3. A.S.Barabash et al. // Nucl. Phys. A. 2007. V.785. P.371.
4. B.Lehnert et al. // J.Phys.G.Nucl. Part.Phys. 2016. V.43. P085201.
QUARTET STRUCTURE OF SELF-CONJUGATE NUCLEI
Sambataro M.1, Sandulescu N.21 Istituto Nazionale di Fisica Nucleare, Sezione di Catania, Italy; 2 National Institute of Physics and Nuclear Engineering, Magurele, Bucharest, Romania
E-mail: michelangelo.sambataro@ct.infn.it
A distinctive feature of self-conjugate nuclei is that of carrying an equal number of protons and neutrons distributed over the same single particle levels.
In these nuclei, as a consequence of the isospin invariance of the nuclear forces, the isovector proton-neutron (pn) pairing is expected to coexist in an equal amount with the proton-proton and neutron-neutron pairing. In addition, pn pairing is also expected to manifest itself in an isoscalar form. The treatment of these types of pairing in terms of conventional BCS-type approaches has revealed to be problematic.
We have shown [1–4] that pn pairing in self-conjugate nuclei can be very well accounted for in a formalism of J = 0, T = 0 quartets, namely four-body correlated structures formed by two protons and two neutrons coupled to total angular momentum J = 0 and isospin T = 0. We have therefore extended the quartet formalism to the treatment of realistic interactions both in the case of even-even [5, 6] and odd-odd [7] self-conjugate nuclei. The role of quartets other than J = 0, T = 0 in the description of these systems has been investigated and it will be illustrated.
The difficulties associated with a microscopic treatment of N = Z nuclei in a formalism of quartets rapidly grow with increasing the number of active nucleons. To make this formalism accessible also to large systems, we have recently explored an approach where elementary bosons replace quartets with J = 0, T = 0 and J = 2, T = 0. This boson architecture, which is clearly analogous to that of the Interacting Boson Model in its simplest formulation (IBM-1), has been employed for an analysis of 28Si [8]. The boson Hamiltonian has been derived with the help of a mapping procedure and the resulting spectrum and E2 scheme have been compared with the experimental data. As a peculiarity, the potential energy surface of this nucleus turns out to be that expected at the critical point of the phase transition of the IBM structural diagram.
1. N.Sandulescu et al. // Phys. Rev. C. 2012. V.85. P.061303(R).
2. M.Sambataro and N.Sandulescu // Phys. Rev. C. 2013. V.88. P.061303(R).
3. M.Sambataro, N.Sandulescu, and C.W.Johnson // Phys. Lett. B. 2015. V.740. P.137.
4. M.Sambataro and N.Sandulescu // Phys. Rev. C. 2016. V.93. P.054320.
5. M.Sambataro and N.Sandulescu // Phys. Rev. Lett. 2015. V.115. P.112501.
6. M.Sambataro and N.Sandulescu // Eur. Phys. J. A. 2017. V.53. P.47.
7. M.Sambataro and N.Sandulescu // Phys. Lett. B. 2016. V.763. P.151.
8. M.Sambataro and N.Sandulescu // Phys. Lett. B. 2018. V.786. P.11.