Almost a century after the discovery of the atomic nucleus, all of its secrets are still not revealed. This dissertation presents experimental observations on statistical properties of medium-mass nuclei at high temperatures. This has long been the main research field of the nuclear physics group at the Oslo Cyclotron Laboratory, where the experiments were performed.
In the experiments, the nuclei were excited to high-energy quantum levels and the decay from these levels was studied by means of statistical methods. By impinging small helium particles on metallic vanadium and scandium foils, the temperature of these nuclei were increased up to about ten billion degrees Celsius. When the nucleus cools down, it emits small particles and light. These were measured with nanosecond precision.
The most surprising observation is that the nucleus emits -rays with much lower energies than previously thought. The results are especially interesting from an astrophysical point of view, as the nuclear structure close to the particle separation energies influences strongly the nucleosynthesis processes that take place in extreme stellar environments such as supernovae.
List of papers.
1. M. Guttormsen, R. Chankova, U. Agvaanluvsan, E. Algin, L. A. Bernstein, F. Ingebretsen, T. Lönnroth, S. Messelt, G. E. Mitchell, J. Rekstad, A. Schiller, S. Siem, A. C. Sunde*, A. Voinov and S. Ødegård, Radiative strength functions in 93-98Mo, Phys. Rev. C 71, 044307 (2005).
2. R. Chankova, A. Schiller, U. Agvaanluvsan, E. Algin, L. A. Bernstein, M. Guttormsen, F. Ingebretsen, T. Lönnroth, S. Messelt, G. E. Mitchell, J. Rekstad, S. Siem, A. C. Larsen, A. Voinov, and S. W. Ødegård, Level densities and thermodynamical quantities of heated 93-98Mo isotopes, Phys. Rev. C 73, 034311 (2006).
3. A. C. Larsen, R. Chankova, M. Guttormsen, F. Ingebretsen, T. Lönnroth, S. Messelt, J. Rekstad, A. Schiller, S. Siem, N. U. H. Syed, A. Voinov, and S. W. Ødegård, Microcanonical entropies and radiative strength functions of 50,51V, Phys. Rev. C 73, 064301 (2006).
4. A. C. Larsen, M. Guttormsen, R. Chankova, F. Ingebretsen, T. Lönnroth, S. Messelt, J. Rekstad, A. Schiller, S. Siem, N. U. H. Syed, and A. Voinov, Nuclear level densities and -ray strength functions in 44,45Sc, Phys. Rev. C 76, 044303 (2007).
5. A. V. Voinov, S. M. Grimes, A. C. Larsen, C. R. Brune, M. Guttormsen, T. Massey, A. Schiller, S. Siem, and N. U. H. Syed, Level densities of 44Sc and 47Ti from different experimental techniques, Phys. Rev. C 77, 034613 (2008).
* In 2006 I changed my last name from 'Sunde' to 'Larsen'.