Signature of clustering in quantum many-body systems probed by the giant dipole resonance

Abstract

The present experimental study illustrates how large deformations attained by nuclei due to cluster formation are perceived through the giant dipole resonance (GDR) strength function. The high energy GDR γ-rays have been measured from 32 S at different angular momenta (J) but similar temperatures in the reactions 4 He(E lab =45MeV) + 28 Si and 20 Ne(E lab =145MeV) + 12 C. The experimental data at lower J (∼ 10h) suggests a normal deformation, similar to the ground state value, showing no potential signature of clustering. However, it is found that the GDR lineshape is fragmented into two prominent peaks at high J (∼ 20h) providing a direct measurement of the large deformation developed in the nucleus. The observed lineshape is also completely different from the ones seen for Jacobi shape transition at high J pointing towards the formation of cluster structure in super-deformed states of 32 S at such high spin. Thus, the GDR can be regarded as a unique tool to study cluster formation at high excitation energies and angular momenta.

Study of the Jacobi shape transition in A≈30 nuclei

“…Recently, similar observation-namely, the absence of Jacobi shape transition, was reported in 32 S populated via 20 Ne+ 12 C reaction [23]. In both these cases ( 32 S and 28 Si), projectile-target involve self-conjugate α-cluster nuclei.…”

“…In addition, the role of possible binary shapes on GDR, at large excitations needs to be investigated. It is important to note that the 32 S GDR data [7,23] has been analyzed only within the statistical model framework. However, deformations deduced for both 32 S, 28 Si from the conventional statistical model analysis are large (β 2 > 0.6) and point towards the elongated structure.…”

“…Such an orbiting dinuclear system can attain complicated exotic shapes as compared to a shape equilibrated compound nucleus [10,17,[19][20][21]. Interestingly, recent studies of GDR spectrum from the 32 S nucleus populated with J > J C in the reaction 20 Ne+ 12 C, did not show evidence of the Jacobi shape transition [7,23] and the result was interpreted in terms of the formation of 16 O + 16 O molecular structure in a superdeformed state of 32 S. The observation of a narrow resonance in 24 Mg+ 24 Mg at J = 36 h [22] was interpreted in terms of the highly deformed shape corresponding to a molecular state, but no clear signature of the Jacobi shape transition was observed. Therefore, experimental studies of the exotic shapes of different nuclei with J > J C are crucial to understand the different mechanisms like the nuclear orbiting, cluster formation and Jacobi shape transition.…”