Speaker: Prof. Igor Izosimov, JINR in Dubna
Time: 15:30, January 24
Venue: Room 305, Modern Physics Building, School of Nuclear and Science & Frontiers Science Center for Rare Isotopes
Abstract:
The probability of the β-transition to the nuclear level with excitation energy Е is proportional [to the product of the lepton part described by the Fermi function f(Qβ – E) and the nucleon part described by the β-decay strength function Sβ(E). Sβ(Е) governs the nuclear energy distribution of elementary charge-exchange excitations and their combinations like proton particle (πp)–neutron hole (νh) coupled into a momentum Iπ : [πp Ä νh]Iπ and neutron particle (νp)–proton hole (πh) coupled into a momentum Iπ : [νp Ä πh)]Iπ. The strength function for β-transitions of the Gamow-Teller (GT) type describes excitations [πp Ä νh]1+ or [νp Ä πh]1+. At excitation energies E smaller than Qβ (total β-decay energy), Sβ(E) determines the characters of the β-decay. For higher excitation energies that cannot be reached with the β-decay, Sβ(E) determines the charge exchange nuclear reaction cross sections, which depend on the nuclear matrix elements of the β-decay type.
Reliable experimental data on the structure of Sβ(Е) are necessary for predicting half-lives of nuclei far from the stability line, verifying completeness of decay schemes, calculating energy release from decay of fission products in nuclear reactors, calculating spectra of delayed particles, calculating the delayed fission probability and evaluating fission barriers for nuclei far from the β-stability line, calculating production of various elements in astrophysical processes, developing microscopic models for calculation of Sβ(Е), especially in deformed nuclei, and etc.
Development of experimental technique allows application of methods of nuclear spectroscopy with high energy resolution for Sβ(E) fine structure measurement. Methods for investigating the structure of the strength function for the β-decay of atomic nuclei are considered and the results of measuring Sβ(E) by the Total Absorption Gamma Spectroscopy and high-resolution nuclear spectroscopy techniques are presented and discussed. Emphasis is placed on investigation of the fine structure of Sβ(E). Criteria for verifying the completeness of nuclear decay schemes are considered.
It was shown that the high-resolution nuclear spectroscopy methods give conclusive evidence of the resonance structure of Sβ(E) both for GT and first-forbidden (FF) β-transitions in spherical, deformed, and transition nuclei. The splitting of the peaks in the Sβ(E) for the GT β+/EC-decay of the deformed nuclei into two components was demonstrated. Resonance structure of the Sβ(E) for β-decay of halo nuclei was analyzed in. It was shown that when the parent nucleus has nn Borromean halo structure, then after Gamow-Teller (GT) β– - decay of parent state or after M1 γ-decay of Isobar Analogue Resonance (IAR) the states with np tango halo structure or mixed np tango + nn Borromean halo structure can be populated.
In this report the fine structure of Sβ(E) is analysed. Resonance structure of Sβ(E) for GT and FF β-decays, structure of Sβ(E) for halo nuclei, quenching of the weak axial-vector constant gAeff, splitting of the peaks in Sβ(E) for deformed nuclei connected with the anisotropy of oscillations of proton holes against neutrons (peaks in Sβ(E) of GT β+/EC-decay) or of protons against neutron holes (peaks in Sβ(E) of GT β– – decay), and Sβ(E) for the high-spin isomers β-decays in heavy and superheavy nuclei are discussed.
Biography:
Izosimov majored in Nuclear Physics and Nuclear spectroscopy in Physics faculty in Leningrad State University (St.Petersburg State University) in 1977, and then Laser spectroscopy in 1983. He finished Cand. Sci. (Ph.D., physics) dissertation “Production of nuclei polarization and nuclear polarization coherence by tunable laser radiation” in LSU in 1984. After that, he finished Doctor of Science (physics) dissertation “Non statistical effects in nuclear reactions and nuclear decays” in V.G. Khlopin Radium Institute in 1997. In 2003, he obtained Projects and technologies expert in Russian Federal Agency for Atomic Energy. Izosimov is now the leading scientific researcher of JINR in Dubna from 2006. Before that, Izosimov was employed as researcher, senior researcher, professor, leading scientific researcher, and head of laboratory of KRI from 1978 to 2012, and became researcher assistant, researcher and docent in LSU from 1977 to 1989.
Source: School of Nuclear and Science & Frontiers Science Center for Rare Isotopes
