Intense effort to explore the atomic nucleus has persisted through the past century. Despite of the great efforts, there still remains many open questions regarding the properties of the nucleus.
In particular, the low energy region of excited nuclei is a poorly known area. In this thesis we have used two complimentary techniques to investigate nuclear structure in the low energy region. Through 3He induced reactions we apply the so-called Oslo method to extract nuclear properties at excitation energies below the neutron separation threshold. Beyond the neutron threshold we have used photo-neutron experiments and studied nuclei with energies up to 13 MeV.
The new experimental data reviles special excitation modes of the nucleus, also known as resonances, some of which cannot be explained by existing theoretical models.
Furthermore, radiative neutron capture cross sections, relevant for astrophysical calculations, are extracted by use of the reaction code TALYS. Astrophysical reaction rates are also calculated, and we find that resonance features in the low energy region of excited nuclei have a significant impact on the reaction rates.
List of papers. Papers IV-VII are removed from the thesis due to publisher restrictions.
Paper I: H. T. Nyhus, S. Siem, M. Guttormsen, A. C. Larsen, A. Bürger, N. U. H. Syed, G. M. Tveten, and A. Voinov. Radiative strength functions in 163,164Dy. Phys. Rev. C 81, 024325 – Published 25 February 2010 doi:10.1103/PhysRevC.81.024325
Erratum: Radiative strength functions in 163,164Dy. [Phys. Rev. C 81, 024325 (2010)] Phys. Rev. C 82, 029909 – Published 30 August 2010 doi:10.1103/PhysRevC.82.029909
Paper II: H. T. Nyhus, S. Siem, M. Guttormsen, A. C. Larsen, A. Bürger, N. U. H. Syed, H. K. Toft, G. M. Tveten, and A. Voinov. Level density and thermodynamic properties of dysprosium isotopes. Phys. Rev. C 85, 014323 – Published 25 January 2012 doi:10.1103/PhysRevC.85.014323
Paper III: Hiroaki Utsunomiya, Tatsushi Shima, Keiji Takahisa, Dan Mihai Filipescu, Ovidiu Tesileanu, Ioana Gheorghe, Hilde-Therese Nyhus, Therese Renstrøm, Yiu-Wing Lui, Yasuhisa Kitagawa, Sho Amano, Shuji Miyamoto. Energy Calibration of the NewSUBARU Storage Ring for Laser Compton-Scattering Gamma Rays and Applications. IEEE Transactions on Nuclear Science VOL. 61, NO. 3, JUNE 2014 doi:10.1109/TNS.2014.2312323 (c) 2014 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other users, including reprinting/ republishing this material for advertising or promotional purposes, creating new collective works for resale or redistribution to servers or lists, or reuse of any copyrighted components of this work in other works.
Paper IV: H.-T. Nyhus, T. Renstrøm, H. Utsunomiya, S. Goriely, D.M. Filipescu, I. Gheorghe, O. Tesileanu, T. Glodariu, T. Shima, K. Takahisa, Y.-W. Lui, S. Hilaire, S. Péru, M. Martini, and A.J. Koning. Photoneutron cross sections for neodymium isotopes: toward a unified understanding of (γ,n) and (n, γ) reactions in the rare earth region I. Manuscript.
Paper V: D.M. Filipescu, I. Gheorghe, H. Utsunomiya, S. Goriely, H.-T. Nyhus, T. Renstrøm, O. Tesileanu, T. Glodariu, T. Shima, K. Takahisa, Y.-W. Lui, S. Hilaire, S. Péru, M. Martini, and A.J. Koning. Photoneutron cross sections for samarium isotopes: toward a unified understanding of (γ, n) and (n, γ) reactions in the rare earth region II. Manuscript.
Paper VI: H.-T. Nyhus, T. Renstrøm, A.-C. Larsen, H. Utsunomiya, S. Goriely, D.-M. Filipescu, I. Gheorghe, M. Guttormsen, Y.W. Lui, T. Shima, S. Siem, K. Takahisa and O. Tesileanu. Photo-neutron cross sections, radiative strength functions and astrophysical reaction rates of dysprosium isotopes. Manuscript.
Paper VII: T. K. Eriksen, H. T. Nyhus, A. Bürger, M. Guttormsen, A. Görgen, A. C. Larsen, P. Mansouri, T. Renstrøm, S. J. Rose, I. E. Ruud, S. Siem, H. K. Toft, G. M. Tveten, and J. N. Wilson. Discovery of a weak pygmy resonance, and signs of a transitional region in Pd-isotopes. Manuscript.