Fine structure of the Isoscalar giant monopole resonance in 58Ni and 90Zr using alpha inelastic scattering at zero degrees

Abstract

The last few decades have proved to be quite exciting in the eld of nuclearstructure physics. High energy-resolution ( 30 keV) proton inelastic-scattering experiments have revealed that giant resonances carry ne structure as a signature of the damping mechanisms involved. For the rst time, it is now possible to perform high energy-resolution ( 70 keV) experiments with intermediateenergy (speci cally 200 MeV) alpha-particle inelastic-scattering reactions at zero degrees. This particular combination of the scattering angle and projectile was selected since it results in the preferential excitation of the Isoscalar Giant Monopole Resonance (ISGMR). These experiments were performed for a range of nuclei, including 24Mg, 58Ni, and 90Zr, using the Separated Sector Cyclotron and the K600 magnetic spectrometer at the iThemba Laboratory for Accelerator Based Sciences. The data were extracted and extensive optimisation procedures were performed. Particle identi cation was carried out to obtain accurate spectra for the ( ; 0) reaction. Accurate focal-plane position spectra were obtained following the implementation of several techniques including, amongst others, the use of look-up-table o sets, and an angle calibration to convert the focal-plane angle to the scattering angle. Lineshape correction was performed to obtain the best-possible resolution. An instrumental-background subtraction was performed and the individual data les were o set to ensure the peak positions were aligned when the data were chained by isotope. ISGMR distributions were obtained for 58Ni and 90Zr. The data underwent a Discrete Wavelet Transform background subtraction to ensure a pure ISGMR distribution. The centroid and width of the resonance for both nuclei were extracted. Continuous Wavelet Transforms (CWTs) were applied to the data in order to extract the characteristic energy scales. Theoretical calculations were analysed with the CWT so as to compare the theoretical and experimental energy scales. A good correspondence between theory and experiment was found, and a dominant damping mechanism was found for the ISGMR.