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The high spin state structure of the nucleus220Ac was investigated by means of the209Bi(14C, 3n) reaction. In beam? ray spectroscopy was carried out using the Château de Cristal multidetector array. Gamma ray multipolarities were established by extracting directional correlation ratios from the Ge—Ge coincidence data and by intensity balance considerations. The level scheme, established up to 18 h above the lowest observed state, consists of three alternating parity bands. The data are interpreted in terms of the reflection asymmetric shapes of the nucleus. The analysis of the parity doublet candidates does not show the decrease of the parity splitting predicted for an odd-odd nucleus.

The decay of57Ni was studied using both single and coincidence gamma-ray spectroscopy. Four new low-intensity transitions were observed in the single spectra. The energies and intensities of these transitions related to the 1378 keV transition were determined as 304.1 keV, 0.002%; 696.0 keV, 0.001%, 1350.5 keV, 0.002% and 1603.3 keV, 0.005%. Weak transitions at 541.9, 755.3 and 1279.9 keV were confirmed in agreement to earlier works, and their intensities related to 1378 keV were determined as 0.005%, 0.007% and 0.0012%, respectively.

The Internal Bremsstrahlung Electron Capture spectrum from55Fe was measured with a HPGe detector. The total spectrum was unfolded taking into account the secondary detection effects and agrees with Glauber and Martin calculations. The measured intensity relative to K capture in the range 35 to 231 keV is 3.24(6)·10-5 while the calculated one is 3.20·10-5. TheQ value for the electron capture was deduced as 230.7(19) keV.

Excited states of220Ac have been investigated by means of the209Bi(14C,3n) reaction and using the “Château de Cristal” gamma ray facility. The observation of bands with alternating parity states reveals the reflection asymmetric nuclear shape of220Ac. The extracted B(E1)/B(E2) ratios display a clear spin dependence.