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SUMMARY:Isoscalar giant monopole resonance in 24Mg and 28Si: Effect of cou
 pling between the isoscalar monopole and quadrupole strength
DTSTART;VALUE=DATE-TIME:20231203T073500Z
DTEND;VALUE=DATE-TIME:20231203T075000Z
DTSTAMP;VALUE=DATE-TIME:20260812T015442Z
UID:indico-contribution-3367@indico.tlabs.ac.za
DESCRIPTION:Speakers: Armand Bahini (iThemba LABS)\nBackground: In highly 
 deformed nuclei\, there is a noticeable coupling of the Isoscalar Giant Mo
 nopole Resonance (ISGMR) and the $K = 0$ component of the Isoscalar Giant 
 Quadrupole Resonance (ISGQR)\, which results in a double peak structure of
  the isoscalar monopole (IS0) strength (a narrow low-energy deformation-in
 duced peak and a main broad ISGMR part). The energy of the narrow low-lyin
 g IS0 peak  is sensitive to both the incompressibility modulus  $K_\\infty
 $ and the coupling between IS0 and isoscalar quadrupole (IS2) strength.\n\
 nObjective:  This study aims to investigate the two-peaked structure of th
 e ISGMR in the prolate $^{24}$Mg and oblate $^{28}$Si nuclei and identify 
 among a variety of energy density functionals based on Skyrme parameterisa
 tions the one which best describes the experimental data. This will allow 
 for conclusions regarding the nuclear incompressibility. Because of the st
 rong IS0/IS2 coupling\, the deformation splitting of the ISGQR will also b
 e analysed.\n\nMethods: The ISGMR was excited in $^{24}$Mg and $^{28}$Si u
 sing $\\alpha$-particle inelastic scattering measurements acquired with an
  $E_\\alpha = 196$ MeV beam at scattering angles $\\theta_{\\text{Lab}} = 
 0^\\circ$ and $4^\\circ$. The K$600$ magnetic spectrometer at iThemba LABS
  was used to detect and momentum analyse the inelastically scattered $\\al
 pha$ particles. An experimental energy resolution of $\\approx 70$ keV (FW
 HM) was attained\, revealing fine structure in the excitation-energy regio
 n of the ISGMR. The IS0 strength distributions in the nuclei studied were 
 obtained with the Difference-of-Spectrum (DoS) technique. The theoretical 
 comparison is based on the quasiparticle random-phase approximation (QRPA)
  with a representative set of Skyrme forces.\n\nResults: IS0 strength dist
 ributions for $^{24}$Mg and $^{28}$Si are extracted and compared to previo
 usly published results from experiments with a lower energy resolution. Wi
 th some exceptions\, a reasonable agreement is obtained. The IS0 strength 
 is found to be separated into a narrow structure at about $13-14$ MeV in $
 ^{24}$Mg\, $17-19$ MeV in $^{28}$Si and a broad structure at $19-26$ MeV i
 n both nuclei. The data are compared with QRPA results. The results of the
  calculated characteristics of IS0 states demonstrate the strong IS0/IS2 c
 oupling in strongly prolate $^{24}$Mg and oblate $^{28}$Si. The narrow IS0
  peaks are shown to arise due to the deformation-induced IS0/IS2 coupling 
 and strong collective effects. The cluster features of the narrow IS0 peak
  at $13.87$ MeV in $^{24}$Mg  are also discussed. The best description of 
 the IS0 data is obtained using the Skyrme force SkP$^\\delta$ with an asso
 ciated low nuclear incompressibility $K_\\infty = 202$ MeV allowing for  b
 oth the energy of the peak and integral IS0 strength  in $^{24}$Mg and $^{
 28}$Si to be reproduced. The features of the ISGQR in these nuclei are als
 o investigated. An anomalous deformation splitting of the ISGQR in oblate 
 $^{28}$Si is found. The observed  structure of ISGQR in $^{24}$Mg is descr
 ibed.\n\nConclusions: The ISGMR and ISGQR in light deformed nuclei are cou
 pled and thus need to be described simultaneously. Only such a description
  is relevant and consistent. The deformation-induced narrow IS0 peaks can 
 serve as an additional sensitive measure of the nuclear incompressibility.
 \n\nhttps://indico.tlabs.ac.za/event/119/contributions/3367/
LOCATION:
URL:https://indico.tlabs.ac.za/event/119/contributions/3367/
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