Speaker
Description
The photon strength function (PSF) of some near-shell-closure medium and heavy-mass nuclei exhibits anomalous low-energy enhancement (LEE). Angular correlation measurements demonstrate that this LEE is clearly dipole (ΔI = 1) in nature; however, its magnitude and onset at around 3–4 MeV cannot be explained by extrapolations of known mechanisms, such as the giant dipole resonance, to this energy region. This has led to speculation regarding new mechanisms that emphasize distinctly E1 or M1 dominated LEE. The asymmetry in the linear polarization of LEE γ rays is sensitive to the multipolarity of the electromagnetic transitions from which they originate. A previous measurement, leveraging GRETINA as a Compton polarimeter, measured the linear polarization of γ rays following excitation of 56Fe nuclei in (p,p′) reactions to LEE energies; however, the multipolarity of the LEE could not be conclusively determined due to large statistical uncertainties. Here we report preliminary results from a precision follow-up experiment with improved statistics and detection efficiency, aimed at conclusively determining the E1, M1, or mixed nature of LEE in a model-independent manner and thereby distinguishing between competing theoretical interpretations of its origin.
| Contribution category | Experiment |
|---|---|
| Presenter status | Postdoc |