The existence of fusion hindrance in the light heavy-ion systems of astrophysical interest is not well established, so investigating slightly heavier cases may allow a reliable extrapolation towards the lighter ones. The recent observation of a very high hindrance threshold in 12C + 24Mg (with a positive Q value for fusion) at σ = 0 . 75 mb, misses a valid interpretation within current theoretical models. Our aim has been to search evidence for fusion hindrances in the nearby system 12 C + 26Mg also having a positive fusion Q-value, and to obtain information on the underlying physics from a comparison of the two cases and from coupled-channels calculations. The experiment was performed in inverse kinematics using the 26Mg beam from the XTU Tandem accelerator of Laboratori Nazionali di Legnaro (LNL). The targets were thin 12C evaporations isotopically enriched to 99.9%. The fusion-evaporation residues were detected at small angles by a E- DE-ToF detector telescope following an electrostatic beam deflector. The fusion excitation function of 12C + 26Mg has been measured down to ≈ 5 µb. The astrophysical S factor shows a maximum at an energy where the cross section is ≈0 . 03 mb, significantly lower than for 12C + 24Mg. This difference is confirmed by the comparison of the two S factors. coupled channel calculations give a good account of the data, but they overpredict the cross sections below ≈ 0 . 03 mb. The logarithmic slopes of the two excitation functions are superimposable to a large extent, with visible oscillations, more noticeable for 12 C + 24 Mg. The hindrance phenomenon is clearly observed in 12C + 26Mg. The difference between the corresponding threshold energies for 12C + 24 , 26Mg might (only qualitatively) be attributed to the α-like structure of 24Mg. In Jiang’s phenomenological systematics, the different behaviours of 12C + 24 , 26Mg make the situation more complex, and call into question the extrapolation procedure toward the lighter systems of astrophysical interest.
Sub-barrier fusion in C 12 + Mg 26 , 24 : Hindrance and oscillations
M. Del Fabbro;
2023
Abstract
The existence of fusion hindrance in the light heavy-ion systems of astrophysical interest is not well established, so investigating slightly heavier cases may allow a reliable extrapolation towards the lighter ones. The recent observation of a very high hindrance threshold in 12C + 24Mg (with a positive Q value for fusion) at σ = 0 . 75 mb, misses a valid interpretation within current theoretical models. Our aim has been to search evidence for fusion hindrances in the nearby system 12 C + 26Mg also having a positive fusion Q-value, and to obtain information on the underlying physics from a comparison of the two cases and from coupled-channels calculations. The experiment was performed in inverse kinematics using the 26Mg beam from the XTU Tandem accelerator of Laboratori Nazionali di Legnaro (LNL). The targets were thin 12C evaporations isotopically enriched to 99.9%. The fusion-evaporation residues were detected at small angles by a E- DE-ToF detector telescope following an electrostatic beam deflector. The fusion excitation function of 12C + 26Mg has been measured down to ≈ 5 µb. The astrophysical S factor shows a maximum at an energy where the cross section is ≈0 . 03 mb, significantly lower than for 12C + 24Mg. This difference is confirmed by the comparison of the two S factors. coupled channel calculations give a good account of the data, but they overpredict the cross sections below ≈ 0 . 03 mb. The logarithmic slopes of the two excitation functions are superimposable to a large extent, with visible oscillations, more noticeable for 12 C + 24 Mg. The hindrance phenomenon is clearly observed in 12C + 26Mg. The difference between the corresponding threshold energies for 12C + 24 , 26Mg might (only qualitatively) be attributed to the α-like structure of 24Mg. In Jiang’s phenomenological systematics, the different behaviours of 12C + 24 , 26Mg make the situation more complex, and call into question the extrapolation procedure toward the lighter systems of astrophysical interest.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
