Electric monopole transitions from low energy excitations in nuclei

Abstract

Electric monopole (E0) properties are studied across the entire nuclear mass surface. Besides an introductory discussion of various model results (shell model, geometric vibrational and rotational models, algebraic models), we point out that many of the largest E0 transition strengths, ρ 2 (E0), are associated with shape mixing. We discuss in detail the manifestation of E0 transitions and present extensive data for : single-closed shell nuclei, vibrational nuclei, well-deformed nuclei, nuclei that exhibit sudden ground-state changes, and nuclei that exhibit shape coexistence and intruder states. We also give attention to light nuclei, odd-A nuclei, and illustrate a suggested relation between ρ 2 (E0) and isotopic shifts.

Multi-quasiparticle excitation: Extending shape coexistence inA~190neutron-deficient nuclei

“…Potential-energy-surface (PES) calculations, however, show rather soft deformations for neutron-deficient lead and polonium isotopes, indicating considerable mixing between bands with different shapes (see e.g., [10,11]). This has been confirmed experimentally by the observation of E0 components in J→J transitions at low spins between bands that arise from different shapes in 188 Pb [12], which is known to be a signature of shape mixing [13]. The mixing between different shapes is itself an interesting issue, although this may lead to considerable difficulty in isolating different shapes.…”

Conversion electrons from high-statisticsβ-decay measurements with the 8πspectrometer at TRIUMF-ISAC

“…E0 transitions are sensitive to the changes in the nuclear charge-squared radii since the E0 operator is [14] …”

“…and also a measurement of the level lifetime τ. The number of ρ 2 (E0) values known is still rather limited [14,15]. The ρ 2 (E0) values can be expressed in terms of the collective variables from the Bohr model.…”

“…so that in a two-level mixing solution with quadrupole deformation parameters (β 1 , γ 1 ) and (β 2 , γ 2 ) the E0 strength is given by [14,16] …”

Low-spin collective excitations in deformed nuclei: When is a β a β vibration?

“…The expression for ρ 2 (E0) is [3] FIGURE 2. Values of ρ 2 (E0) for the first excited 0 + band from the compilation of Wood et al [3] for well-deformed rare-earth nuclei.…”