N.B. Shul'gina

Neutron beta decay and the right-handed currenr problem

Abstract The renormalization of the axial-vector coupling constant λ = g A / g V , extracted from the neutron lifetime ( λ τ ) and from the neutron beta decay asymmetry ( λ c ) is considered carefully In the standard model of the electroweak interaction λ τ should be equal to λ c . According to recent experimental data on neutron beta decay, λ τ and λ c seem to differ from each other. This fact is explained in the framework of the manifestly left-right symmetric model SU(2) L × SU(2) R × U(1). The possibility of the existence of the right-handed current in the neutron beta decay is pointed out. A joint analysis of neutron beta decay and muon decay is performed, the right-handed current parameters are estimated. The axial-vector constant renormalization ( λ N ) by right-handed currents is evaluated.

Wigner SU(4)-symmetry restoration in heavy nuclei and the many-body forces problem

Abstract The contributions of the highest SU(4) Casimir operators in SU(4) mass formula are investigated for the A ≧ 216 region based on a hypothesis of the restoration of Wigner symmetry with increasing N − Z and on experimental mass-difference data. The experimental estimates for three- and four-body force terms in the modified mass formula are found. The experimental differences of the isobar masses in this region are described with an accuracy near 200 keV.

Theoretical studies of 8He β-decay

Abstract According to selection rules the β-decay of 8He 0g.s.+ to the first excited 1+, 0.98 MeV state of 8Li is an allowed Gamow-Teller transition, but it is strongly suppressed by the different SU(4) spin-isospin structure of the 8He and 8Li states. We find that a three-body α + t + n model of 8Li strongly underestimates the probability for β-decay (to the 8Li (0.98) state, 7 Li + n continuum and α + t + n continuum). A qualitative explanation of total BGT values, extracted from experiment, to different 1+ states can be given supposing an admixture of a “democratic” α + 4N configuration in the 8Li wave functions. We show that the experimental β-delayed neutron spectrum provides some evidence for the existence of 1− and/or 2− states in the vicinity of the two-body 7 Li + n and 7 Li ∗ (0.47) + n thresholds. Using the phase volume approximation to the analysis of the triton spectrum, the position of the Gamow-Teller resonance (Halo Analogue state) is estimated between 8.5 and 8.8 MeV excitation energy in the 8Li spectrum. One of the possibilities to excite this state could be the 6Li(6He,α)8He∗ reaction.

Three-body structure of 8Li and the 7Li(n,γ)8Li reaction

Abstract A three-body cluster 4He+t+n model is developed for 8Li using the method of hyperspherical harmonics with realistic cluster-cluster interactions fitted to experimental data. The model is used to calculate wave functions, spatial and matter densities of the ground state and the low lying excited state of 8Li. The model reproduces experimentally known properties of 8Li. Contrary to two-body models, our prediction for the radiative neutron capture on 7Li at low energies supports a lower cross section value.

Charged- and neutral-current disintegration of the 6Li nucleus by solar neutrino and reactor antineutrino

Abstract Low-energy neutrino-induced reactions in 6 Li are investigated both in neutral and charged channels with special stress on 6 Li → α + 2N disintegration. Cross sections are calculated in the allowed approximation, with recoil effects being neglected. Wave functions in the continuum as well as in the discrete spectrum are exact solutions of the three-body Schrodinger equation. The possibility of 6 Li used as a low-energy (anti)neutrino detector is discussed.

Three-cluster states in the spectrum of 8Be: (1) Structure and β-decay of 8B to 16.6 MeV state

Abstract The structure and spectrum of the three-cluster states in 8 Be around 16–20 MeV was studied in the framework of the hyperspherical harmonic method. For that purpose we have developed a potential formalism for T– p and 3 He – n (3+1) scattering and mechanism for the three-body mixed isospin calculations. We have studied the mechanism of the isospin mixing for 1 + , 2 + doublets in 8 Be and found a sharp sensitivity of isospin mixing to the experimentally not well defined parameters of the 3+1 intercluster interaction. The matrix elements of the β -decay of 8 B to 2 + doublet 16.6, 16.9 MeV were calculated and estimates were made for the probability of electron capture to 17.64 MeV state. It is found that about 90% of the Gamow–Teller (GT) sum rule is concentrated in the three-cluster 2 + and 1 + states, situated below the three-body thresholds, within narrow boundaries (16.5–19.0 MeV).

Three-cluster states in the spectrum of 8Be. (II). Interaction of 2+ doublet with α–α continuum

Abstract The interaction of 2 + mixed isospin states at 16.6, 16.9 MeV in 8 Be with α – α continuum is studied. Qualitative coupled channel model is used. Estimates, as well as results of the three-cluster calculations are used to put constraints on the model. Two methods to treat isospin mixing in the system are discussed.

Analytical approach to electromagnetic processes in loosely bound nuclei: application to 8B

Abstract In this Letter we develop an analytical model in order to study electromagnetic processes involving loosely bound neutron-rich and proton-rich nuclei. We construct a model wave function, to describe loosely bound few-body systems, having the correct behaviour both at large and small distances. The continuum states are approximated by regular Coulomb functions. As a test case we consider the two-body Coulomb dissociation of 8 B and, the inverse, radiative capture reaction. The difference between using a pure two-body model and the results obtained when incorporating many-body effects, is investigated. We conclude that the interpretation of experimental data is highly model dependent and stress the importance of measuring few-body channels.

CNO cycle: ”Soft E1” mode of the 17Ne excitation in the 17Ne+γ → 15O+2p reaction

The O-15(2p, gamma) Ne-17 reaction is studied using the time-reversed reaction of the Ne-17 E1 Coulomb dissociation on lead target in the context of nuclear astrophysics. Looking for the relation between the data on the Coulomb excitation and the astrophysical 2p-capture rate, one faces problem to extract the Coulomb E1 strength function from the measured Coulex cross section. We use a number of phenomenological approaches to estimate influence of such processes as Coulomb-nuclear interference, populations of states with different J(pi), etc. We calculate the Ne-17+ 2p astrophysical capture rate and compare the results with different calculations.

Experimental study of the 15O(2p, γ)17Ne cross section by Coulomb Dissociation for the rp process

The time-reversed reaction O-15(2p, gamma) Ne-17 has been studied by the Coulomb dissociation technique. Secondary 17Ne ion beams at 500 AMeV have been produced by fragmentation reactions of Ne-20 in a beryllium production target and dissociated on a secondary Pb target. The incoming beam and the reaction products have been identified with the kinematically complete LAND-(RB)-B-3 experimental setup at GSI. The excitation energy prior to decay has been reconstructed by using the invariant-mass method. The preliminary differential and integral Coulomb Dissociation cross sections (sigma(Coul)) have been calculated, which provide a photoabsorption (sigma(photo)) and a radiative capture cross section (sigma(cap)). Additionally, important information about the nuclear structure of the Ne-17 nucleus will be obtained. The analysis is in progress.