The excess of the energy of the excited atomic nucleus above the neutron biding energy could be given to giant resonances. These excitations are described macroscopically as nucleon vibrations in the nucleus. By measuring their decay, can be obtained the information about the properties of the atomic nuclei, in which giant resonances are excited. The well-known are giant dipole resonance (GDR), studied in the process of their g decay, in many experiments carried out in the last decades. In contrast to the GDR, the properties of giant quadrupole resonance (GQR) have not been extensively investigated. The g decay of GQR has been measured so far only in the experiment carried out in the 1980s, using inelastic scattering of ¹⁷O on ²⁰⁸Pb. The outcome of this experiment are the only published results of the GQR g decay studies.

Thanks to the construction of the experimental setup for nuclear physics research at the Bronowice Cyclotron Center (CCB) of the Institute of Nuclear Physics, Polish Academy of Sciences, a newly established center for hadron therapy, it has been started the research on GQR g decay using a high-energy proton beam. The article published in Phys. Rev. C shows the results of the measurement of GQR g decay for the ²⁰⁸Pb nucleus performed as one of the first nuclear physics experiments at the CCB. To excite giant resonances the inelastic scattering of protons with an energy of 85 MeV on a ²⁰⁸Pb target was used. During the experiment, the energy of scattered protons, carrying information about the excitation energy of ²⁰⁸Pb nuclei, and the energy of grays emitted as a result of the decay of excited states, were measured simultaneously. The data corresponding to the decay to the ground state, for which the excitation energy was equal to the energy of the emitted g rays, were analyzed. Taking into account the observed g decay of GDR, the spectrum of g rays emitted from the GQR decay was obtained. As the result of the analysis, the probability of GQR decay by the g ray emission was determined to be 3 × 10^-4. This value confirms the previous result obtained for the inelastic scattering of ¹⁷O ions.

Wasilewska, M. Kmiecik, M. Ciemała, A. Maj, F.C.L. Crespi, A. Bracco, M.N. Harakeh, P. Bednarczyk, S. Bottoni, S. Brambilla, F. Camera, I. Ciepał, N. Cieplicka-Oryńczak, M. Csatlos, B. Fornal, V. Gaudilla, J. Grębosz, J. Isaak, Ł.W. Iskra, M. Jeżabek, A.J. Krasznahorkay, S. Kihel, M. Krzysiek, P. Lasko, S. Leoni, M. Lewitowicz, J. Łukasik, M. Matejska-Minda, K. Mazurek, P.J. Napiorkowski, W. Parol, P. Pawłowski, L.Q. Qi, M. Saxena, Ch. Schmitt, Y. Sobolev, B. Sowicki, M. Stanoiu, A. Tamii, O. Wieland, M. Ziębliński

γ decay to the ground state from the excitations above the neutron threshold in the ²⁰⁸Pb(p,p′γ) reaction at 85 MeV

Phys. Rev. C 105, 014310 (2022)

DOI:10.1103/PhysRevC.105.014310