“Stretched” states are one of the simplest nuclear excitations in the continuum. Their structure is dominated by a single particle-hole component for which both the particle and the hole occupy orbitals with the highest angular momentum in their respective shells, and couple to the highest possible spin which such configuration offers. In light nuclei they appear as high-lying excitations resulting from the p3/2 → d5/2 stretched transitions. The direct measurement of stretched states decay paths, poorly known, thus far, should provide a very demanding test of state-of-the-art theory approaches, like for example, Gamow Shell Model (GSM).
The recent experiments at Cyclotron Centre Bronowice at IFJ PAN have highlighted the feasibility of populating stretched states in 13C, 14N, 16O, and 12C systems via proton inelastic scattering at 135 MeV and the possibility to extract the information on their decay channels via γ-proton and particle-proton coincidence measurements. The detection setup consisted of: i) the KRATTA telescope array for detection of scattered protons, ii) two clusters of the PARIS scintillator array and four LaBr3 detectors for γ-ray measurement, and iii) four thick DSSD detectors for light charged particles detection.
The results of the experimental studies on the decays of the stretched excitations lying around 20 MeV in 13C, 14N, 16O, and 12C isotopes will be presented. In particular, the preliminary results of the very recent experiment performed in autumn 2024 at CCB IFJ PAN, populating stretched states in the 12C nucleus, will be discussed.
Adam Maj