0000000000139799
AUTHOR
D.j. Middleton
Isomeric state in the doubly odd196At nucleus
An excited isomeric state has been identified in the 196At nucleus using the recoil decay tagging technique. This is the first identification of an excited state in this neutron-deficient odd-odd nucleus. Several tentative prompt γ-rays have also been correlated with 196At α-decay, although it has not been possible to assign them to specific energy levels in 196At. The mean lifetime of the isomeric state has been measured as τ = 11±2 µs. The new level is compared with similar low-lying states in neighbouring nuclei and is de-excited by an E2 γ-ray transition, the large hindrance of which is not expected.
Gamma-spectroscopy of the 199At nucleus with the recoil filter detector
The neutron deficient 199At nucleus has been studied in the 175Lu+28Si reaction at Eb= 141 MeV. In order to select events of interest in the presence of the very strong background caused by fission, γ-rays have been detected in coincidence with recoiling evaporation residues. The excited states of 199At observed for the first time may indicate that this nucleus is deformed.
First observation of excited states in $^{197}$At: the onset of deformation in neutron-deficient astatine nuclei
Excited states in the Z= 85 nucleus 197At have been identified for the first time using the recoil-decay-tagging (RDT) technique. The excitation energy of these states is found to be consistent with the systematics of neutron-deficient astatine nuclei and with theoretical calculations indicating that the nucleus may be deformed in its ground state.