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Register a new userGiant Dipole Resonance studies in Ba isotopes at $textbf{ E/A}sim$ 5 MeV
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Exclusive measurements of high energy $gamma$-rays are performed in $rm ^{124}Ba$ and $rm ^{136}Ba$ at the same excitation energy ($sim$ 49 MeV), to study properties of the giant dipole resonance (GDR) over a wider $N/Z$ range. The high energy $gamma$-rays are measured in coincidence with the multiplicity of low energy $gamma$-rays to disentangle the effect of temperature ($T$) and angular momentum ($J$). The GDR parameters are extracted employing a simulated Monte Carlo statistical model analysis. The observed $gamma$-ray spectra of $rm ^{124}Ba$ can be explained with prolate deformation, whereas a single component Lorentzian function which corresponds to a spherical shape could explain the $gamma$-ray spectra from $rm ^{136}Ba$. The observed GDR width in $rm ^{136}Ba$ is narrower compared to that of $rm ^{124}Ba$. The statistical model best fit GDR cross sections are found to be in good agreement with the thermal shape fluctuation model (TSFM) calculations. Further, it is shown that the variation of GDR width with $T$ is well reproduced by the TSFM calculations over the temperature range of 1.1--1.7MeV.
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High energy gamma-rays in coincidence with low energy yrast gamma-rays have been measured from 113Sb, at excitation energies of 109 and 122 MeV, formed by bombarding 20Ne on 93Nb at projectile energies of 145 and 160 MeV respectively to study the role of angular momentum (J) and temperature (T) over Giant Dipole Resonance (GDR) width. The maximum populated angular momenta for fusion were 67hbar and 73hbar respectively for the above-mentioned beam energies. The high energy photons were detected using a Large Area Modular BaF2 Detector Array (LAMBDA) along with a 24-element multiplicity filter. After pre-equilibrium corrections, the excitation energy E* was averaged over the decay steps of the compound nucleus (CN). The average values of temperature, angular momentum, CN mass etc. have been calculated by the statistical model code CASCADE. Using those average values, results show the systematic increase of GDR width with T which is consistent with Kusnezov parametrization and the Thermal Shape Fluctuation Model. The rise of GDR width with temperature also supports the assumptions of adiabatic coupling in the Thermal Shape Fluctuation Model. But the GDR widths and corresponding reduced plots with J are not consistent with the theoretical model at high spins.
The excitation and subsequent proton decay of the isoscalar giant dipole resonance (ISGDR) in $^{208}$Pb have been investigated via the $^{208}$Pb($alpha, alpha^{prime}p)^{207}$Tl reaction at 400 MeV. Excitation of the ISGDR has been identified by the difference-of-spectra method. The enhancement of the ISGDR strength at high excitation energies observed in the multipole-decomposition-analysis of the singles $^{208}$Pb($alpha,alpha^{prime}$) spectra is not present in the excitation energy spectrum obtained in coincidence measurement. The partial branching ratios for direct proton decay of ISGDR to low-lying states of $^{207}$Tl have been determined and the results are compared with predictions of continuum random-phase-approximation (CRPA) calculations.
Proton decay from the 3$hbaromega$ isoscalar giant dipole resonance (ISGDR) in $^{58}$Ni has been measured using the ($alpha,alphap$) reaction at a bombarding energy of 386 MeV to investigate its decay properties. We have extracted the ISGDR strength under the coincidence condition between inelastically scattered $alpha$ particles at forward angles and decay protons emitted at backward angles. Branching ratios for proton decay to low-lying states of $^{57}$Co have been determined, and the results compared to predictions of recent continuum-RPA calculations. The final-state spectra of protons decaying to the low-lying states in $^{57}$Co were analyzed for a more detailed understanding of the structure of the ISGDR. It is found that there are differences in the structure of the ISGDR as a function of excitation energy.
The isoscalar giant dipole resonance (ISGDR) has been investigated in 208Pb using inelastic scattering of 400 MeV alpha particles at forward angles, including 0deg. Using the superior capabilities of the Grand Raiden spectrometer, it has been possible to obtain spectra devoid of any instrumental background. The ISGDR strength distribution has been extracted from a multipole-composition of the observed spectra. The implication of these results on the experimental value of nuclear incompressibility are discussed.
A set of high resolution zero-degree inelastic proton scattering data on 24Mg, 28Si, 32S, and 40Ca provides new insight into the long-standing puzzle of the origin of fragmentation of the Giant Dipole Resonance (GDR) in sd-shell nuclei. Understanding is provided by state-of-the-art theoretical Random Phase Approximation (RPA) calculatios for deformed nuclei using for the first time a realistic nucleon-nucleon interaction derived from the Argonne V18 potential with the unitary correlation operator method and supplemented by a phenomenological three-nucleon contact interaction. A wavelet analysis allows to extract significant scales both in the data and calculations characterizing the fine structure of the GDR. The fair agreement supports that the fine structure arises from ground-state deformation driven by alpha clustering.
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