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Isomeric states in $^{256}\mathrm{No}$ were investigated using internal conversion electron and $\ensuremath{\gamma}$-ray spectroscopy with the GABRIELA detection system at the focal plane of the SHELS recoil separator, at the Flerov Laboratory for Nuclear Research (FLNR, JINR, Dubna). The nuclei of interest were produced using the highly asymmetric fusion-evaporation reaction $^{238}\mathrm{U}(^{22}\mathrm{Ne},4n)^{256}\mathrm{No}$. The emission of internal conversion electrons and $\ensuremath{\gamma}$ rays occurring between a $^{256}\mathrm{No}$ implantation and a subsequent $\ensuremath{\alpha}$-decay event were studied, resulting in the observation of high-$K$ isomerism in this nobelium isotope. The nature of the isomeric states is discussed in terms of possible two- and four-quasiparticle structures.

Evaporation residue cross sections for the $^{16}\mathrm{O}+^{203,205}\mathrm{Tl}$ reactions were measured at laboratory beam energies in the range of 82--113 MeV using a gas-filled separator. Transmission efficiency of the separator was estimated using a calibration reaction $^{16}\mathrm{O}+^{197}\mathrm{Au}$ and by simulating the evaporation residues angular distributions. Statistical model calculations were performed for both the measured systems. These calculations overestimate the experimental evaporation residue cross sections. This could be attributed to the presence of noncompound nuclear fission. An estimation of noncompound nuclear fission contribution was carried out. Comparison with neighboring systems shows that a slight change in the entrance channel or the compound nucleus properties makes a large difference in evaporation residue cross sections.

The structure of low-lying excited states in $^{251}\mathrm{Fm}$, populated by the $\ensuremath{\alpha}$ decay of $^{255}\mathrm{No}$, has been investigated by means of combined $\ensuremath{\gamma}$ and internal conversion electron spectroscopy. The values for the internal conversion coefficients for the $1/{2}^{+}\ensuremath{\rightarrow}5/{2}^{+}$ and $5/{2}^{+}\ensuremath{\rightarrow}9/{2}^{\ensuremath{-}}$ transitions have been measured. The determined $M2/E3$ mixing ratio and lifetime for the $5/{2}^{+}$ decay to the ground state allowed to determine the corresponding reduced transitions strengths of $B(E3)=18(6)$ W.u. and $B(M2)=3.0(6)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$ W.u. These results, as well as the results of previous studies in $N=151$ isotopes, are compared to theoretical calculations beyond the mean-field approach, including the first QRPA calculations using the Gogny D1M parametrization for such heavy odd-$N$ nuclei. The comparison points to the importance of accounting for the octupole vibrations for a proper understanding of the low-lying nuclear structure of some of the heaviest elements.

The deformed doubly magic nucleus (270)Hs has so far only been observed as the four-neutron (4n) evaporation residue of the reaction Mg-26+Cm-248, where a maximum cross section of 3 pb was measured. Theoretical studies on the formation of (270)Hs in the 4n evaporation channel of fusion reactions with different entrance channel asymmetry in the framework of a two-parameter Smoluchowski equation predict that the reactions Ca-48+Ra-226 and S-36+U-238 result in higher cross sections due to lower reaction Q values, in contrast to simple arguments based on the reaction asymmetry, which predict opposite trends. Calculations using HIVAP predict cross sections for the reaction S-36+U-238 that are similar to those of the Mg-26+Cm-248 reaction. Here, we report on the first measurement of evaporation residues formed in the complete nuclear fusion reaction S-36+U-238 and the observation of (270)Hs, which is produced in the 4n evaporation channel, with a measured cross section of 0.8(-0.7)(+2.6) pb at 51-MeV excitation energy. The one-event cross-section limits (68% confidence level) for the 3n, 4n, and 5n evaporation channels at 39-MeV excitation energy are 2.9 pb, while the cross-section limits of the 3n and 5n channel at 51 MeV are 1.5 pb. This is significantly lower than the 5n cross section of the Mg-26+Cm-248 reaction at similar excitation energy.

An isomeric state in {sup 255}Lr with a half-life of t{sub 1/2} = 1.4(1) ms and E{sub x}>720-keV has been observed for the first time using the GABRIELA setup at the focal plane of the VASSILISSA separator. Based on its K-forbiddeness, the configuration of the state is most probably formed by coupling the valence proton to a two quasiparticle neutron excitation. Possible three quasiparticle configurations are discussed.

An isomeric state in {sup 209}Ra has been observed for the first time, using the GABRIELA setup at the focal plane of VASSILISSA, to decay to the ground state of {sup 209}Ra via a cascade of 238-keV (M2) and 644-keV transitions. The half-life of the isomer has been measured to be 117(5) {mu}s and from systematics is assigned as a neutron i{sub 13/2}{sup -1} excitation.

Excited states in {sup 249}Fm were populated via the {alpha} decay of {sup 253}No and the subsequent decay was observed with the GABRIELA detection system installed at the focal plane of the VASSILISSA recoil separator. The energies, spins, and parities of these states could be established through combined {alpha},{gamma}, and conversion-electron spectroscopy. The first members of the ground-state rotational band were identified. Their excitation energies as well as the observation of a cross-over E2 transition confirm the assignment of 7/2{sup +}624 for the ground state of {sup 249}Fm. Two excited states were also observed and their decay properties suggest that they correspond to the particle excitation 9/2{sup -}734 and hole excitation 5/2{sup +}622. The analysis suggests that the 279-keV transition de-exciting the 9/2{sup -} state has anomalous E1 conversion coefficients.