Seminarium Fizyki Jądra Atomowego
sala 1.01, ul. Pasteura 5
2023-10-26 (10:15) 
dr Natalia Cieplicka-Oryńczak (IFJ PAN, Kraków)
“Stretched” states decays studied at CCB IFJ PAN by gamma-particle coincidences
The structure of the “stretched” nuclear excitations is dominated by a single particle-hole component for which both the excited particle (proton or neutron) and the residual 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 resonances resulting from the p3/2 → d5/2 stretched transitions [1]. Due to the expected low density of other one-particle-one-hole configurations of high angular momenta in this energy region, their structure should be relatively simple comparing to other nuclear excitations in the continuum. This feature makes them attractive as their theoretical analysis could provide clean information about the role of continuum couplings in stretched excitations.
The decays of stretched excitations in light nuclei are expected to be dominated by the proton and neutron emission, however, their decay patterns are poorly known experimentally, thus far. 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, like for example, Gamow Shell Model (GSM) [2] which is an adequate tool for the theoretical description of these excitations.
The results of the first experimental studies on the decay of the 21.47-MeV stretched resonance in 13C will be presented. It was investigated in a 13C(p, p′) experiment at 135 MeV proton energy, performed at the Cyclotron Centre Bronowice (CCB) at IFJ PAN in Krakow. The information on the proton and neutron decay branches from the 21.47-MeV state in 13C was obtained by measuring the protons inelastically scattered on a 13C target in coincidence with charged particles from the resonance decay and γ rays from daughter nuclei. In particular, emitted γ rays give a precise knowledge of the feeding to specific states. The detection setup consisting of: i) the KRATTA telescope array, ii) an array of LaBr3 detectors, iii) two clusters of the PARIS scintillator array, and iv) a thick position-sensitive Si detector, was used. The experimental results were compared with theoretical calculations from the GSM, extended to describe stretched resonances in p-shell nuclei. A very good agreement between the measured and predicted properties of the 21.47-MeV state in 13C was obtained.
In a similar measurement at CCB, the decays of stretched resonances in 16O nucleus were also investigated. A triplet of close lying states in 16O, namely at 17.79, 18.98, and 19.80 MeV, was populated. The decay channels via p and α emission were identified by studying the γ rays from daughter nuclei in coincidence with scattered protons. The quantitative information on the decay branching ratios could be extracted from a systematic analysis of the proton-γ matrix. The physical interpretation of the results would largely profit from theoretical calculations, which are not available at the moment. However, the obtained results support the extension of the investigation of the stretched states decays in other nuclei such as 14N, using the present method.
[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.
The decays of stretched excitations in light nuclei are expected to be dominated by the proton and neutron emission, however, their decay patterns are poorly known experimentally, thus far. 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, like for example, Gamow Shell Model (GSM) [2] which is an adequate tool for the theoretical description of these excitations.
The results of the first experimental studies on the decay of the 21.47-MeV stretched resonance in 13C will be presented. It was investigated in a 13C(p, p′) experiment at 135 MeV proton energy, performed at the Cyclotron Centre Bronowice (CCB) at IFJ PAN in Krakow. The information on the proton and neutron decay branches from the 21.47-MeV state in 13C was obtained by measuring the protons inelastically scattered on a 13C target in coincidence with charged particles from the resonance decay and γ rays from daughter nuclei. In particular, emitted γ rays give a precise knowledge of the feeding to specific states. The detection setup consisting of: i) the KRATTA telescope array, ii) an array of LaBr3 detectors, iii) two clusters of the PARIS scintillator array, and iv) a thick position-sensitive Si detector, was used. The experimental results were compared with theoretical calculations from the GSM, extended to describe stretched resonances in p-shell nuclei. A very good agreement between the measured and predicted properties of the 21.47-MeV state in 13C was obtained.
In a similar measurement at CCB, the decays of stretched resonances in 16O nucleus were also investigated. A triplet of close lying states in 16O, namely at 17.79, 18.98, and 19.80 MeV, was populated. The decay channels via p and α emission were identified by studying the γ rays from daughter nuclei in coincidence with scattered protons. The quantitative information on the decay branching ratios could be extracted from a systematic analysis of the proton-γ matrix. The physical interpretation of the results would largely profit from theoretical calculations, which are not available at the moment. However, the obtained results support the extension of the investigation of the stretched states decays in other nuclei such as 14N, using the present method.
[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.