Speaker
Dr
Neven Soic
(Rudjer Boskovic Institute Zagreb Croatia)
Description
Detailed knowledge on complex spectroscopy of the $^{24}$Mg nucleus at excitation energies between 14 and 19 MeV has large impact on understanding of clustering in nuclei and on carbon - carbon burning, the $^{12}$C+$^{12}$C fusion, in massive stars. The $^{12}$C+$^{12}$C and $^{16}$O+$^{8}$Be cluster structures (threshold energies are 13.9 and 14.1 MeV respectively) become active in this energy region mixing with already strong $^{20}$Ne+$^{4}$He clustering (threshold energy is 9.3 MeV). Their interplay and effects of strong $\alpha$-clustering in $^{12}$C and $^{20}$Ne lead to unique structural properties and very complex spectroscopy of the $^{24}$Mg. In this energy region are expected to exist the band heads of a number of rotational bands associated with the $^{12}$C+$^{12}$C cluster structure whose high spin members are identified at higher excitations. It is cruical to identify low spin members of these rotational bands to improve understanding of their origin. The $^{12}$C+$^{12}$C clustering has a strong effect on the C-C burning which play an essential role in many astrophysical phenomena, both quiescent and explosive. Existing data in astrophysically relevant energy range show large discrepancies in the S-factors and substantial improvements in future direct measurements are required to make further progress.
Indirect experimental approach through measurements of the $^{20}$Ne+$^{4}$He resonant elastic scattering was used to search for $^{24}$Mg states which may increase C-C burning rate. Observation of the $0^+$ (or $1^-$) resonance at excitations between 15 and 18 MeV would strongly indicate enhanced reaction rate of the $^{12}$C+$^{12}$C fusion while its non-observation would imply non-resonant nature of the C-C burning, and hence its reduced contribution in many stellar phenomena. Measurements of the $^{20}$Ne+$^{4}$He excitation functions by use of the 36.07, 45.45 and 53.17 MeV $^{20}$Ne beams delivered by the PIAVE-ALPI facility of Laboratori Nazionali di Legnaro INFN and a thick $^{4}$He gas target which stops the beam in front of the detector were performed. This beam energy range corresponds to the $^{12}$C+$^{12}$C relative energy range of prime importance for astrophysics. Scattered $\alpha$-particles were detected in large area highly segmented silicon strip detector telescope built of 20 $\mu$m thick $\Delta$E SSSD and 1000 $\mu$m thick E DSSSD. Telescope was positioned at 0$^o$. Detailed measurements of the beam energy loss and beam intensity, needed for an accurate data analysis, were performed.
Elastic scattering excitation functions were extracted for data between -5$^o$ and 5$^o$ and normalized to previously taken data. Large number of overlapping resonances is detected in the excitation functions. Strong contribution of the inelastic scattering to the first excited $^{20}$Ne state was observed and further analysis was performed for data free of inelastic scattering events. Using all available results on $^{24}$Mg states at these excitations, attempts to fully characterize the observed resonances in the excitation functions in terms of spin, parity, width and partial widths were done using R-matrix calculations. No clear evidence for the $0^+$ or $1^-$ state was found. Obtained results show the limitations of performed experiment and give clue for improved experiment. Complementary measurements using resonant scattering technique with the $^{20}$Ne beam and low density $^{4}$He gas target which will provide high resolution data for larger angular range were recently performed at LNL INFN and obtained data are being analysed.
Primary authors
Dr
Neven Soic
(Rudjer Boskovic Institute Zagreb Croatia)
Dr
Vedrana Tokic
(Rudjer Boskovic Institute Zagreb Croatia)
Co-authors
Dr
Gloria Marquinez Duran
(Department of Applied Physics, University of Huelva, Spain)
Prof.
Ismael Martel
(Department of Applied Physics, University of Huelva, Spain)
Dr
Joe Walshe
(School of Physics and Astronomy, University of Birmingham, United Kingdom)
Juan Pablo Fernandez Garcia
(Laboratori Nazionali del Sud INFN, Catania, Italy)
Dr
Lovro Prepolec
(Rudjer Boskovic Institute, Zagreb, Croatia)
Dr
Luis Acosta
(Department of Applied Physics, University of Huelva, Spain)
Marcello Lattuada
(LNS)
Mrs
Maria Fisichella
(LNS)
Prof.
Matko Milin
(Department of Physics, Faculty of Science, University of Zagreb, Croatia)
Dr
Milivoj Uroic
(Rudjer Boskovic Institute Zagreb Croatia)
Mr
Natko Skukan
(Rudjer Boskovic Institute, Zagreb, Croatia)
Pierpaolo Figuera
(LNS)
Mr
Rob Smith
(School of Physics and Astronomy, University of Birmingham, United Kingdom)
Sam Bailey
(School of Physics and Astronomy, University of Birmingham, United Kingdom)
Dr
Suzana Szilner
(Ruder Boskovic Institute)
Dr
Tea Mijatovic
(Rudjer Boskovic Institute, Zagreb, Croatia)
