Recently, the E1 photoneutron cross sections were measured consistently using quasimonochromatic laser Comptonscattering γray beams at NewSUBARU (Japan) for a set of ten oddeven nuclei, spherical as well as deformed, covering relatively widely light to heavy species and at energies ranging between the neutron threshold and 40 MeV. This consistent set of experimental photoneutron cross sections allow us to estimate the total E1 photoabsorption cross sections, through validated theoretical models, by excluding the quasideuteron component and by including the missing lowenergy and chargedparticle emission contributions. In turn, the total E1 photoabsorption cross sections are used to derive the three main moments of the E1 distributions, namely the integrated cross section, the centroid energy, and the polarizability. These socalled modeldependent experimental moments follow a rather smooth trend with atomic mass, as theoretically expected, except for the specific case of 209Bi which presents a surprising 10% increase of both the integrated strength and the polarizability with respect to its eveneven spherical neighbor 208Pb. A rather consistent value for the enhancement factor of the E1 energyweighted sum rule could be extracted from the present experimental data. The experimentally derived moments are compared for the ten oddeven systems with calculations based on the meanfield plus quasiparticle random phase approximation (QRPA). Spherical as well as axially deformed predictions based on the Skyrme and Gogny interactions are considered to discuss the results. Special attention is also paid to the approximate treatment of odd systems of nucleons in this context. It is found that in general theoretical predictions can rather well describe the data for the full set of nuclei, except for 209Bi presenting a kink in all the three main E1 moments with respect to the wellstudied 208Pb case. Such an experimental determination cannot be explained by meanfield plus QRPA calculations. New measurements of photoabsorption cross section on 208Pb and 209Bi in the 14–19 MeV range as well as future theoretical calculations, in particular of oddeven systems, may help to solve such a mystery. The present data are also used to reinvestigate the correlation between the nuclear matter symmetry energy and its slope at saturation density. The analysis based on both Skyrme and Gogny HartreeFockBogolyubov (HFB) plus QRPA calculations confirm previous results, though quantitatively larger variations of the correlation parameters are found.
E1 moments from a coherent set of measured photoneutron cross sections / S. Goriely, S. Péru, G. Colò, X. RocaMaza, I. Gheorghe, D. Filipescu, H. Utsunomiya.  In: PHYSICAL REVIEW C.  ISSN 24699985.  102:6(2020 Dec 09), pp. 064309.0643091064309.06430913. [10.1103/PhysRevC.102.064309]
E1 moments from a coherent set of measured photoneutron cross sections
G. Colò;X. RocaMaza;
2020
Abstract
Recently, the E1 photoneutron cross sections were measured consistently using quasimonochromatic laser Comptonscattering γray beams at NewSUBARU (Japan) for a set of ten oddeven nuclei, spherical as well as deformed, covering relatively widely light to heavy species and at energies ranging between the neutron threshold and 40 MeV. This consistent set of experimental photoneutron cross sections allow us to estimate the total E1 photoabsorption cross sections, through validated theoretical models, by excluding the quasideuteron component and by including the missing lowenergy and chargedparticle emission contributions. In turn, the total E1 photoabsorption cross sections are used to derive the three main moments of the E1 distributions, namely the integrated cross section, the centroid energy, and the polarizability. These socalled modeldependent experimental moments follow a rather smooth trend with atomic mass, as theoretically expected, except for the specific case of 209Bi which presents a surprising 10% increase of both the integrated strength and the polarizability with respect to its eveneven spherical neighbor 208Pb. A rather consistent value for the enhancement factor of the E1 energyweighted sum rule could be extracted from the present experimental data. The experimentally derived moments are compared for the ten oddeven systems with calculations based on the meanfield plus quasiparticle random phase approximation (QRPA). Spherical as well as axially deformed predictions based on the Skyrme and Gogny interactions are considered to discuss the results. Special attention is also paid to the approximate treatment of odd systems of nucleons in this context. It is found that in general theoretical predictions can rather well describe the data for the full set of nuclei, except for 209Bi presenting a kink in all the three main E1 moments with respect to the wellstudied 208Pb case. Such an experimental determination cannot be explained by meanfield plus QRPA calculations. New measurements of photoabsorption cross section on 208Pb and 209Bi in the 14–19 MeV range as well as future theoretical calculations, in particular of oddeven systems, may help to solve such a mystery. The present data are also used to reinvestigate the correlation between the nuclear matter symmetry energy and its slope at saturation density. The analysis based on both Skyrme and Gogny HartreeFockBogolyubov (HFB) plus QRPA calculations confirm previous results, though quantitatively larger variations of the correlation parameters are found.File  Dimensione  Formato  

PhysRevC.102.064309.pdf
accesso riservato
Tipologia:
Publisher's version/PDF
Dimensione
1.06 MB
Formato
Adobe PDF

1.06 MB  Adobe PDF  Visualizza/Apri Richiedi una copia 
Pubblicazioni consigliate
I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.