Speaker
Description
In recent years, the study of heavy-ion fusion reactions at the sub-barrier energies has attracted considerable attention in both experimental and theoretical investigations. One of the interesting phenomena observed in this energy regime is the sub-barrier fusion enhancement. The enhancement observed in the sub-barrier fusion cross sections over the predictions of one-dimensional barrier penetration model (1D-BPM) has been attributed to the coupling of the various internal degrees of freedom of colliding nuclei, such as deformation, collective vibrations, or positive Q-value nucleon transfer (PQNT) channels [1]. These couplings split the single barrier into multiple barriers and hence, reducing the height of the original barrier, which results in the sub-barrier fusion. The role of the deformations and collective vibrations in the sub-barrier fusion enhancement is well established [2]. However, the role of neutron transfer is still not fully understood in the sub-barrier fusion [3]. In order to investigate the role of PQNT in sub-barrier region, we have measured the fusion excitation function (EF) of $^{28}$Si+$^{130}$Te reaction.
The experiment was performed using Heavy Ion Reaction Analyser (HIRA) facility at Inter-University Accelerator Centre (IUAC), New Delhi [4]. The enriched target $^{130}$Te of thickness $170$ $\mu \text{g}/\text{cm}^2$ with carbon backing of thickness $15$ $\mu \text{g}/\text{cm}^2$ was bombarded with the $^{28}$Si pulsed beam. Two silicon surface barrier detectors (SSBDs), called monitor detectors were mounted at the angles $\pm 20^\circ$ in the target chamber to calculate the normalized cross sections of evaporation residues (ERs). In order to detect the ERs, a position-sensitive MWPC of an active area $150 \times 50\,\text{mm}^2$ was installed at the focal plane of HIRA.
The HIRA facility was operated at $0^\circ$ angle with respect to the beam direction.
HIRA setting was optimized by looking at the maximum transmission efficiency and clear separation between beam-like particles and ERs at the focal plane. The transmission efficiency of HIRA was estimated using the Monte-Carlo simulation code TERS [5]. The ERs were identified by making an electronic gate between the energy loss of ERs in MWPC ($\Delta \text{E}$) and time-of-flight of ERs (TOF).
The fusion EF was obtained from the measured cross sections of ERs in the energy range $95-124\,\text{MeV}$. The experimentally measured EF was found to be enhanced significantly with respect to 1D-BPM in the sub-barrier region. To understand the fusion enhancement observed in the sub-barrier region, further investigation has been carried out by including the inelastic excitations of the interacting nuclei using CCFULL code [6]. The coupled-channels (CC) calculations were performed by employing Woods-Saxon potential with Akyuz-Winther parametrization [7]. The coupling of inelastic excitations effectively reproduced the measured EF at the energies above the Coulomb barrier, but underpredicted the measured EF at the sub-barrier energies. Since, $^{28}$Si+$^{130}$Te system has six PQNT channels from one to six neutron pickup, the $+2n$ transfer channels was incorporated in CC calculations, which fairly reproduced the measured EF in the sub-barrier energy range, further details will be presented during the conference.
References
[1] A. B. Balantekin et al., Rev. Mod. Phys. 70 (1998) 77.
[2] B. B. Back et al., Rev. Mod. Phys. 86 (2014) 317.
[3] R. Prajapat et al., Phys. Rev. C 107 (2023) 064616.
[4] A. K. Sinha et al., Nucl. Instrum. Methods Phys. Res. A 339 (1994) 543.
[5] S. Nath, Comput. Phys. Commun. 180 (2009) 2392.
[6] K. Hagino et al., Comput. Phys. Commun. 123 (1999) 143.
[7] R. A. Broglia et al., Heavy Ion Reactions (Benjamin Cummings, San Francisco, 1981).
Acknowledgement
The research fellowships from UGC and Ministry of Education, Government of India, are gratefully acknowledged. We also thank our colleagues from the TASISPEC Lab at IIT Roorkee, for their support.