Photodisintegration cross section of ⁴He in the giant dipole resonance energy region

概要

The isovector giant dipole resonance (GDR) is one
of the most examined nuclear resonances, which is excited through the E1 transition of nuclear ground states.
It is a representative example of the collective excitation modes of atomic nuclei in which protons and neutrons coherently oscillate in antiphase, and its energyintegrated cross section exhausts approximately 100% of
the Thomas-Reiche-Kuhn sum-rule value [1]. The photodisintegration reaction is a suitable probe to investigate the GDR because the photoabsorption dominantly
induces E1 transition as the long wave-length approximation commonly holds in various nuclei.
The cross section of the 4 He photodisintegration reaction in the GDR energy region has recently attracted
research interest because it is an important aspect for
understanding nucleosynthesis process in the universe.
One example is the ν-process in the He-layer of corecollapse supernovae [2]. In this process, rare elements
such as 7 Li and 11 B are produced through a series of nuclear reactions initiated by the 4 He(ν,ν ′ n) and 4 He(ν,ν ′ p)
reactions [3]. The giant resonances, such as GDR and
spin-dipole resonances, make a dominant contribution on
these reactions because the 4 He(ν,ν ′ ) reaction primarily
excites these resonances with L = 1 [4]. The GamowTeller resonance is approximately forbidden in 4 He due
to the system’s double magicity. Because of technical
difficulties in measuring neutrino-nucleus reactions, estimation of neutrino-nucleus reaction cross sections for
examining the ν-process relies on the nuclear structure
theories. Nuclear structural information is therefore a
source of uncertainty with regard to the calculations. ...

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