Low-lying electric dipole γ-continuum for the unstable 62,64Fe nuclei: Strength evolution with neutron number

R Avigo,M Reese,D Mengoni,Zs Podolyák,S Riboldi,G Benzoni,N Lalović,C Nociforo,N Kurz,P Reiter,A Gottardo,R Menegazzo,M Labiche,G Guastalla,D Ralet,A Maj,A Bracco,M Górska,J Eberth,A Görgen,S Bottoni,T Habermann,V González,B Million,B Birkenbach,M Lettmann,D Bazzacco,S Leoni,N Goel,G Rainovski,D Curien,B Bruyneel,F Didierjean,P Bednarczyk,D Barrientos,F Camera,A Jungclaus,J Nyberg,I Kojouharov,O Wieland,S Brambilla,E Clément,B Quintana,A Pullia,F Ameil,A Gadea,E Gregor,A Ataç,M Kmiecik,M Ciemała,H Schaffner,F Recchia,N Blasi,N Pietralla,J Gerl,P Golubev,A I Morales ,M D Salsac ,Dirk Rudolph ,D R Napoli ,D M Cullen ,V Yu Ponomarev ,G Duchêne ,E Merchán ,E Sanchís ,O Stézowski ,L J Harkness-Brennan ,S Piétri ,W Körten ,J J Valiente-Dobón ,C Domingo‐Pardo ,Luis Sarmiento ,T Arıcı ,John Simpson ,P H Regan ,H C Boston ,F C L Crespi ,M L Cortés ,H J Wollersheim

doi:10.1016/j.physletb.2020.135951

Abstract

The γ-ray emission from the nuclei 62,64Fe following Coulomb excitation at bombarding energy of 400-440 AMeV was measured with special focus on E1 transitions in the energy region 4-8 MeV. The unstable neutron-rich nuclei 62,64Fe were produced at the FAIR-GSI laboratories and selected with the FRS spectrometer. The γ decay was detected with AGATA. From the measured γ-ray spectra the summed E1 strength is extracted and compared to microscopic quasi-particle phonon model calculations. The trend of the E1 strength with increasing neutron number is found to be fairly well reproduced with calculations that assume a rather complex structure of the 1− states (three-phonon states) inducing a strong fragmentation of the E1 nuclear response below the neutron binding energy.

Highlights

Within the study of the evolution with neutron number of the dipole strength at energies below the neutron binding energy in stable nuclei, the cases of Sn and Xe were measured, as these elements have the longest chains of isotopes
The results for Sn and Xe isotopes show a marked increase of E1 strength and of its fragmentation with increasing neutron number, which is found to be in rather good agreement with theory [19,20,21,22]
The present work concerns the nuclei 62,64Fe. It was motivated by the search of E1 strength in nuclei far from stability below the neutron binding energy, an energy region which is interesting for the modeling of the r-process where the E1 decay is competing with neutron capture

Summary

Introduction

Within the study of the evolution with neutron number of the dipole strength at energies below the neutron binding energy in stable nuclei, the cases of Sn and Xe were measured, as these elements have the longest chains of isotopes. The γ -ray spectra measured at energy larger than 3 MeV are shown in panels d) and f) for the 64Fe and 62Fe nuclei, respectively.

Results

Conclusion