SPIN EXCITATIONS IN S-D SHELL NUCLEI WITH INTERMEDIATE ENERGY PROTONS

• Main Author: SAWAFTA, REYAD ILAYAN TAWFIQ
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01-01-1987
• Subjects: Nuclear physics
• ISBN: 9780315376687; 0315376686

During the past two years significant improvements have occurred at the Medium Resolution Spectrometer (MRS) at TRIUMF, which have made possible many nuclear physics experiments over the full range of TRIUMF energies. With the help of the dispersion matching technique and a front-end wire chamber, nearly background-free (p,p$\sp\prime$) spectra with a typical resolution of 150 keV FWHM are observed at forward angles. Spin transfer experiments in (p,p$\sp\prime$) have been carried out with the newly installed focal-plane polarimeter which covers a large region of excitation energies (about 45 MeV). Cross-sections, analyzing powers, and spin-flip probabilities have been measured in the low momentum transfer region in the $\sp{24}$Mg(p,p $\sp\prime)\sp{24}$Mg* reaction at 250 MeV. The spin-flip measurements reveal a large spin-flip probability value (about 0.6) for the M1 region. However, a large spin-flip cross-section distributed uniformally over the energy for 16 to 40 MeV is also observed. The quenching factors for the combined isovector and isoscalar 1$\sp +$ states QF($\sigma$S$\sb{\rm NN}$, 1$\sp +$) in the 9-15 MeV region are in good agreement with those for the 10.71 MeV (1$\sp +$, T = 1) state, (QF = 0.7). Finally, cross-section and analyzing power data have also been obtained for the 11.45 MeV ($\Delta$T = 1) and the 9.5 MeV ($\Delta$T = 0) M1 transitions in the $\sp{28}$Si(p,p$\sp\prime)\sp{28}$Si* reaction at 200, 250, 290, 360 and 400 MeV. The quenching of the isovector and isoscaler M1 strength is found to be roughly constant as a function of energy relative to theoretical calculations using the density dependent interaction. An average quenching factor of about 0.7 and 0.58 for the strongest 1$\sp +$ isovector and isoscalar transitions in the $\sp{28}$Si(p,p$\sp\prime)\sp{28}$Si* reaction, respectively, has been obtained. This work suggests a universal quenching factor for the (p,n), (n,p) and (p,p$\sp\prime$) reactions.