Unexpected characteristics of the isoscalar monopole resonance in the A≈90 region: Implications for nuclear incompressibility. Physical Review C - Nuclear Physics Volume 88, Issue 2, 14 August 2013, Article number 021301

The isoscalar giant monopole resonances (ISGMRs) in 90,92 ,94Zr and 92,96,98,100Mo have been studied with inelastic scattering of 240-MeV α particles at small angles including 0o. Strength corresponding to approximately 100% of the ISGMR (E0) energy-weighted sum rule was identified in each nucleus. In all cases the strength consisted of two components separated by 7-9 MeV. Except for the mass 92 nuclei, the upper component contained 14-22% of the E0 energy-weighted sum rule (EWSR); however 38% and 65% of the E0 EWSR were located in the upper components in 92Zr and 92Mo, respectively. The energies of the ISGMRs for 92Zr and 92Mo are 1.22 and 2.80 MeV, respectively, higher than for 90Zr, suggesting a significant nuclear structure contribution to the energy of the ISGMR in these nuclei. This has a large effect on the compression modulus of the nucleus with the values extracted for 92Zr and 92Mo being 27 and 56 MeV, respectively, higher than that for 90Zr.