Measurement of giant dipole resonance width at low temperature: A new experimental perspective

Abstract

The systematic evolution of the giant dipole resonance (GDR) width in the temperature region of 0.9 ∼ 1.4 MeV has been measured experimentally for 119 Sb using alpha induced fusion reaction and employing the LAMBDA high energy photon spectrometer. The temperatures have been precisely determined by simultaneously extracting the vital level density parameter from the neutron evaporation spectrum and the angular momentum from gamma multiplicity filter using a realistic approach. The systematic trend of the data seems to disagree with the thermal shape fluctuation model (TSFM). The model predicts the gradual increase of GDR width from its ground state value for T > 0 MeV whereas the measured GDR widths appear to remain constant at the ground state value till T ∼ 1 MeV and increase thereafter indicating towards a failure of the adiabatic assumption of the model at low temperature.

Damping of Giant Dipole Resonance in Highly Excited Nuclei

“…(5). Assuming that, at the highest T max ≃ 5 -6 MeV where the GDR can still exist, the GDR width Γ(T ) cannot exceed Γ max ≃ 3Γ(0) ≃ 0.9E GDR (0) [23], and E GDR (T ) ≃ E GDR (0), one obtains from Eq.…”

“…The GDR built on the ground state of heavy nuclei has a small width (∼ 4 -5 MeV) and the integrated cross section up to around 30 MeV that exhausts the Thomas-Reich-Kuhn (TRK) sum rule. The GDR built on highly excited compound (CN) nuclei was observed for the first time in 1981 [1], and at present a wealth of experimental data has been accumulated for the GDR widths at finite temperature T and angular momentum J in various medium and heavy nuclei formed in heavy ion fusions [2], deep inelastic scattering of light particles on heavy targets [3,4], and α induced fusions [5]. The common features of the hot GDR are: (1) Its energy is nearly independent of T and J, (2) Its full width at half maximum (FWHM) remains mostly unchanged in the region of T ≤ 1 MeV, but increases sharply with T within 1≤ T ≤ 2.5 -3 MeV, and seems to saturate at T ≥ 4 MeV.…”

Effects of thermal shape fluctuations and pairing fluctuations on the giant dipole resonance in warm nuclei

“…Several earlier works on GDR focused on the high-J regime [2,3] whereas recent studies at extreme isospins have potential astrophysical implications [4][5][6][7]. The GDR at low T is also relatively less explored and its studies have gained acceleration in recent times [8][9][10][11]. Experimentally, it is very difficult to populate nuclei at low excitation energies, but it is still feasible due to recent developments in the experimental facilities.…”

“…Very recently, GDR measurements in the low-T regions were carried out at the Variable Energy Cyclotron Centre, Kolkata [9][10][11]29] and highlighted the interesting nuclear properties at low T . In a recent work [11], it has been mentioned that it would also be interesting to compare the data with TSFM calculations by including the effect of thermal pairing.…”

“…In a recent work [11], it has been mentioned that it would also be interesting to compare the data with TSFM calculations by including the effect of thermal pairing. In some of these recent works [9][10][11], the empirical parametrizations (which mimic the results of TSFM at higher T ) were reported to fail in explaining the experimental data at low T . It has to be noted that, at low T , the application of even the proper TSFM is incomplete and hence the corresponding parametrizations would also fail.…”