Isovector Electric Monopole Resonance in60Ni

Abstract

The isovector electric monopole resonance (IVMR) was studied by the 60 Ni͑ 7 Li, 7 Be͒ 60 Co reaction at 65A MeV and at forward scattering angles including zero degrees. We confirmed the existence of the IVMR at an excitation energy of 20 6 2 MeV with a width of 10 6 2 MeV in 60 Co, which is an analog of the T 0 1 1 isospin component of the IVMR estimated at E x ഠ 31 MeV in 60 Ni. The result presently obtained is consistent with previous results using the pion charge-exchange reaction. PACS numbers: 25.70.Kk, 24.30.Cz, 27.50. + e Isovector resonances ͑DT 1͒ in nuclei are collective motions in which protons oscillate in opposite phase with respect to neutrons. These resonances are also characterized by the electric ͑DS 0͒ and magnetic ͑DS 1͒ modes which correspond to coherent motions of the spin-nonflip and spin-flip oscillations, respectively. Resonances with various multipolarities have been theoretically predicted [1]. Among them, the monopole resonances play a crucial role in astrophysics [2]. Concerning the isoscalar mode ͑DT 0͒, the electric monopole resonance (GMR; DT 0, DS DL 0) has been well established in various inelastic scatterings. The GMR was unambiguously identified due to a sharp enhancement at u L 0 ± [3]. On the other hand, the existence of the isovector electric monopole resonance (IVMR; DT 1, DS DL 0) has been reported only by the pion charge-exchange reaction [4]. The IVMR has also been searched for by using other reaction probes such as electron scattering [5] and the ͑ 13 C, 13 N͒ reaction [6]. Confirmation of the IVMR is, however, still very desirable because of the inconclusive data from these reactions.One of the major reasons for the inconclusive data is due to a difficulty in determining the multipolarity of the resonance. The resonance is, in general, observed as a broad bump riding on a large underlying background mainly caused by a quasielastic scattering. One meets another serious difficulty when one uses hadron reaction probes with spins like ͑p, n͒ and ͑ 3 He, t͒. These reactions allow simultaneous DS 0 and DS 1 excitations, differing from the case of the pion charge-exchange reaction which proceeds only via the DS 0 transition. There is no nuclear probe allowing only the DS 0 excitation. In this respect, the ͑ 13 C, 13 N͒ reaction is expected to be a promising probe for observing isovector electric resonances because of its large Fermi matrix element ͑M F ͞M GT ϳ 5͒ [6]. In this reaction, a resonance has been observed at the relevant excitation energy, but its multipolarity is not consistent with the DL 0 assumption.In the present work, we started with the following question: Can we observe the IVMR reported by the pion charge-exchange reaction? To answer this question, we employed the ͑ 7 Li, 7 Be͒ reaction at 65A MeV on a 60 Ni target which is the target studied by various other ͑n, p͒-like reactions [4,6,7]. The ͑ 7 Li, 7 Be͒ reaction is chosen for the following two reasons. One is that the reaction predominantly proceeds via a one-step process at 65A MeV and at forward an...

Low-lying GT+strength inCo64studied via thePopescu1, Bäumer2, Berg3 et al. 2007Phys. Rev. CSelf Cite21170View full textAdd to dashboardCite

“…Because of the Fermi motion of nucleons inside the nucleus, this region is very broad [19,20]. The very broad giant resonances like the isovector spin giant dipole resonance (IVSGDR, expected around 9 MeV [21]) and the isovector spin giant monopole resonance (IVSGMR, expected around 20 MeV [21]) are overlapping with this continuum. The long tails of these resonances contribute to the low-energy region of the spectra.…”

Observation of the Isovector Giant Monopole Resonance via the Si28(Be10,Scott1, Zegers2, Almus3 et al. 2017Phys. Rev. Lett.120110View full textAdd to dashboardCite

“…However, the large width of the IVGMR (10-15 MeV) and the contribution of a strong non-resonant continuum component in the spectrum at high excitation energies significantly hampered the analysis. Evidence for the IVGMR was also reported in a study of the 60 Ni( 7 Li, 7 Be+γ) [26] reaction at 65 AMeV, in which the coincidence with the γ decay from the excited 430-keV state in 7 Be allows for the isolation of the excitation-energy spectrum associated with ∆S = 1 transitions. The spectrum for ∆S = 0 is then generated by subtracting the ∆S = 1 spectrum from the total spectrum.…”

Isospin symmetry violation in mirrorE1transitions: Coherent contributions from the giant isovector monopole resonance in the67As-67<

“…For A = 67, we assume R = 5.30 fm. The energy difference is E 0 ≈ 20 MeV in 60 Ni (according to [15] (1) and (2). Here, however, the tensor operator is the product of two factors: a vector isovector term acting on the single-particle state and a scalar isovector one acting on the core state.…”