Detailed spectroscopic information of excited nuclear states in deformed transfermium nuclei is scarce. Most of the information available today has been obtained from investigations of fine structure α decay. Although α decay gives access to hindrance factors and lifetimes which are strongly correlated to shell/subshell closures and the presence of isomers, only the combined use of γ and conversion electron spectroscopy allows the precise determination of excitation energy, spin and parity of nuclear levels. In particular, the study of odd isotopes gives crucial information on the single particle states available at and around the Fermi surface. In the following, the preliminary results of decay studies using α ‐ γ and α ‐ beta coincidences at the focal plane of the VASSILISSA recoil separator are presented.

The thermal motion of single particles represents the largest contribution to level density (or entropy) in atomic nuclei. The concept of single particle entropy is presented and shown to be an approximate extensive (additive) quantity for mid‐shell nuclei. A few applications of single particle entropy are demonstrated.

In order to learn more about the different properties of the nuclei like, e.g., collective motion, thermo‐dynamical behaviour and temperature, level density and γ‐ray strength function, it is important to study the effect of internal excitation energy. When approaching major shell gap, nuclear structure changes significantly. This makes an impact on the level densities and γ‐strength function. Around closed shells, effects from the increasing single particle energy spacing can be expected. These will also influence the entropy difference between odd‐mass and even‐even nuclei. Therefore, statistical description of the transition from closed shells to deformed nuclei is of great interest.

The nuclear level densities of 44,45Sc and 50,51V have been measured using the Oslo method. From the level density thermal properties such as entropy and temperature are deduced. Also the radiative strength functions (RSF) of 50,51V have been extracted. The gross properties of the RSF are generally described by the low‐energetic tail of the giant electric dipole resonance (GEDR). At γ energies below ∼ 3 MeV, the RSFs show an unexpected enhancement.

The nuclear level densities of (SC)-S-44,45 and V-50,V-51 have been measured using the Oslo method. From the level density thermal properties such as entropy and temperature are deduced. Also the radiative strength functions (RSF) of V-50,V-51 have been extracted. The gross properties of the RSF are generally described by the low-energetic tail of the giant electric dipole resonance (GEDR). At 7 energies below similar to 3 MeV, the RSFs show an unexpected enhancement.

The energy dependent nuclear level densities of 205–208Pb nuclei below the nuclear binding energies were determined by using the Oslo method. The experimental primary γ‐ray per excitation energy bin have been extracted for scattering and transfer reactions. The Axel‐Brink hypothesis was then used to separate out level density and γ‐strength function from the primary γ spectra. The influence of closed shells is quite obvious in the measured level densities.

Radiative strength functions (RSFs) in 93-98Mo have been extracted using the (3He,alpha gamma) and (3He,3He' gamma) reactions. The RSFs are U-shaped as function of gamma energy with a minimum at around E_gamma=3 MeV. The minimum values increase with neutron number due to the increase in the low-energy tail of the giant electric dipole resonance with nuclear deformation. The unexpected strong increase in strength below E_gamma=3 MeV, here called soft pole, is established for all 93-98Mo isotopes. The soft pole is present at all initial excitation energies in the 5-8 MeV region.

The level densities and radiative strength functions (RSFs) in V-50,V-51 have been experimentally measured using the (He-3, alpha gamma) and (He-3,He-3 'gamma) reactions, respectively. From the level density thermodynamic properties such as entropy and temperature can be extracted. The microcanonical heat capacity shows negative branches. The gross properties of the RSF are described by the giant electric dipole resonance. At gamma energies below 3 MeV. the RSFs show an unexpected enhancement.

From a starting point of experimentally measured nuclear level densities, we discuss thermodynamical properties of nuclei below the particle emission threshold. Since nuclei are essentially mesoscopic systems, a straightforward generalization of macroscopic ensemble theory often yields unphysical results. A careful critique of traditional thermodynamical concepts reveals problems commonly encountered in mesoscopic systems. One of which is the fact that microcanonical and canonical ensemble theory yield different results, another concerns the introduction of temperature for small, closed systems. Finally, the concept of phase transitions is investigated for mesoscopic systems.

The pygmy resonance at 3.3(1) MeV in Yb-172 has now been established with a strength of B(M1) = 6.5(15)mu(2)(N) and M1 multipolarity. In addition, a strong unexpected enhancement of the radiative strength function has been found at low gamma-ray energy in medium light Fe nuclei and also in the heavier Mo nuclei.

The level density and the γ‐strength function have been extracted experimentally. From the level densities thermodynamical quantities such as temperature and heat capacity can be found. Structures in the micro‐canonical temperature are interpreted as the onset of new degrees of freedom by the breaking of Cooper pairs. The S‐shape in the heat capacity curves, found within the canonical ensemble, indicates the pairing‐phase transition, and a critical temperature for the quenching of pair correlations is found. The pygmy resonance at 3.3(1) MeV in 172Yb has now been established with a strength of B(M1)=6.5(15)μN2 and M1 multipolarity, the so‐called scissors mode. In addition, a strong unexpected enhancement of the radiative strength function (RSF) has been found at low γ‐ray energy in medium light Fe nuclei and also in the heavier Mo nuclei.