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A short review of the plethysm technique aiming to its application in finding branching rules for the reduction of an irreducible representation of a group under the restriction to one of its subgroups is given. The algebraic structure of the interacting boson model and some of its extensions is given together with the branching rules needed to classify their basis states, obtained by the use of plethysms.

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Systematic calculations of the neutron-nucleus scattering parameters at several neutron energies Ei < 2 keV have been performed for 37 isotopes (6Li,... 59Co) in the mass region of 6 ≤ A ≤ 60, using the large compilation of experimental neutron-nucleus scattering data obtained in Garching. In the first stage of these calculations, the s-wave potential scattering radius R’, the scattering lengths bcoh, b±, and the bound state parameters (Eb, Γγ , gΓ0n) have been calculated for each isotope, employing the general least squares fit (GLSQF) for the experimental and the corresponding theoretical values of the total neutron-nucleus cross sections σexptot(Ei) at several energies Ei, absorption cross sections σabs(Eo) and of the coherent scattering lengths bcoh. The theoretical expressions for these parameters were deduced on the basis of the usual S-matrix formalism with no assumption about the particular shape of the optical model potential. In the second stage of our calculations, the spherical Fiedeldey- Frahn optical potential was employed for the pure theoretical description or the above mentioned neutron-nucleus scattering characteristics. The results obtained have been analyzed and compared with the values deduced from measurements.

The low-energy part of the radiation emitted after thermal neutron capture in "'Ta has been investigated by different experimental techniques: Gamma-ray measurements were performed with a diffraction spectrometer, The conversion electron spectrum was recorded with a P spectrograph and measurements of gamma-gamma coincidences were carried out. For ten rotational bands in '"Ta, which were already proposed in an earlier work, a large amount of new decay data has been obtained and for most of these bands higher rotational levels have been found. These ten bands have for their lowest level the following energies and I K values: 0 keV 3 3, 16 keV 5+5, 114 keV 4 4, 150 keV 4+4, 173 keV 5 5, 250 keV 3+3, 270 keV 2 2, 402 keV 2+2, 547 keV 3 3, and 558 keV 1 0. New rotational bands with the following band head energies and structure have been established: 443.6 keV [5/2+[402]r, 3/2 [512]"]a "593. 0 keV [7/2+[404], 9/2+[624]"]a "and 647.6 keV [5/2+[402]", 1/2 [510]"]a z. Tentative band heads have been proposed at 390, 740, and 749 keV with I K values 6+6, 2 2, and 3+3. For the sake of completeness, previously found levels with K values ranging from seven to ten are also discussed. NUCLEAR REACTIONS Ta(n, y), E= thermal; measured Ey s Iy s Igg p pp coincidences. Ta deduced levels J, m, K, cc, p multipolarities, J of Ta neutron resonances. Natural targets.