Search Results (5 total)

In-beam γ-ray spectroscopic measurements have been made on ₁₀₂²⁵³No. A single rotational band was identified up to a probable spin of 39/2ℏ, which is assigned to the 7/2⁺[624] Nilsson configuration. The bandhead energy and the moment of inertia provide discriminating tests of contemporary models of the heaviest nuclei. Novel methods were required to interprete the sparse data set associated with cross sections of around 50 nb. These methods included comparisons of experimental and simulated spectra, as well as testing for evidence of a rotational band in the γγ matrix.

An in-beam study of excited states in the transfermium nucleus ²⁵²No has been performed using the recoil separator RITU together with the JUROSPHERE II array at the University of Jyväskylä. This is the second transfermium nucleus studied in an in-beam experiment. Levels up to spin 20 were populated and compared to levels in ²⁵⁴No. An upbend is seen at a frequency of 200 keV/ħ corresponding to spin 16. We also use an improved systematics to connect the energy of the lowest 2⁺ state with its half-life and find that the deformation of both ^252,254No is slightly larger than previously assumed.

Excited states have been observed for the first time in the neutron deficient nuclei ¹⁶⁶Os and ¹⁶⁴Os. The nuclei were produced using the reactions ¹⁰⁶Cd(⁶³Cu,p2n)¹⁶⁶Os, ¹¹²Sn(⁵⁸Ni,2p2n)¹⁶⁶Os, and ¹⁰⁶Cd(⁶⁰Ni,2n)¹⁶⁴Os at beam energies of 292, 286, and 257 MeV, respectively. The γ rays emitted by ¹⁶⁶Os and ¹⁶⁴Os were identified by correlating the associated recoil evaporation residues with their subsequent characteristic α decays. The deduced level schemes indicate that ¹⁶⁶Os and ¹⁶⁴Os continue the trend of decreasing deformation moving away from the N=104 midshell. The level energy systematics of the low-spin states are presented.

The entry distribution in angular momentum and excitation energy for the formation of ²⁵⁴No has been measured after the ²⁰⁸Pb(⁴⁸Ca,2n) reaction at 215 and 219 MeV. This nucleus is populated up to spin 22ħ and excitation energy ≳6 MeV above the yrast line, with the half-maximum points of the energy distributions at ∼5 MeV for spins between 12ħ and 22ħ. This suggests that the fission barrier is ≳5 MeV and that the shell-correction energy persists to high spin.

The ground-state band of the Z  =  102 isotope ²⁵⁴No has been identified up to spin 14, indicating that the nucleus is deformed. The deduced quadrupole deformation, β  =  0.27, is in agreement with theoretical predictions. These observations confirm that the shell-correction energy responsible for the stability of transfermium nuclei is partly derived from deformation. The survival of ²⁵⁴No up to spin 14 means that its fission barrier persists at least up to that spin.