Speaker
Description
Stretched resonances are rather simple nuclear excitations, even though in light nuclei they appear in the continuum energy region. The structures of these states are dominated by a single particle-hole component for which the excited particle and the residual hole couple to the maximal possible spin value available on their respective shells. The simplicity of their configurations results from the expected low density of other one-particle-one-hole configurations of high angular momenta in this energy region. Therefore, their theoretical description could provide clean information about the role of continuum couplings in stretched states.
In p-shell nuclei, these excitations are realized through the p$_{3/2}$ → d$_{5/2}$ stretched transitions [1] and are observed in high-energy regions above the nucleon separation energies. Therefore, the decays of stretched resonances are expected to be dominated by the proton and neutron emission, however, the knowledge about their decay patterns is rather scarce. The direct measurement of stretched states decay paths should provide data which can be used as a very demanding test of state-of-the-art theory approaches – such as, for example, Gamow Shell Model (GSM) [2] - which is an adequate tool for describing these excitations. Recently, experimental findings on the proton and neutron decay branches from the 21.47-MeV stretched state in the $^{13}$C nucleus were compared with theoretical calculations from the GSM, extended to describe stretched resonances in p-shell nuclei [3]. A very good agreement obtained between the measured and predicted decay properties of the 21.47-MeV state in $^{13}$C demonstrated the high quality of the GSM calculations.
Preliminary results from an experiment performed at the Cyclotron Centre Bronowice (CCB) at IFJ PAN in Kraków (Poland), aiming at the first experimental investigation of the decay of the 19.6-MeV stretched resonance in $^{12}$C, will be presented. The state of interest in $^{12}$C was populated in the proton inelastic scattering reaction $^{12}$C(p,p’) at 135 MeV proton energy. 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 LaBr$_3$ detectors for γ-ray measurement, and iii) four thick DSSD units for light charged particles detection. Information on the decay paths from the 19.6-MeV stretched state in $^{12}$C was obtained by measuring the protons inelastically scattered off a $^{12}$C target in coincidence with γ rays from daughter nuclei and charged particles emitted in the decay of the resonance.
[1] J. Speth, Electric and Magnetic Giant Resonances in Nuclei, World Scientific Publ. Company (1991).
[2] N. Michel, W. Nazarewicz, M. Płoszajczak, T. Vertse, J. Phys. G: Nucl. Part. Phys. 36 (2009) 013101.
[3] N. Cieplicka-Oryńczak et al. Phys. Lett. B 834, 137398 (2022).
