gELBE施設におけるIn-115のγ線強度関数測定

The photon strength function (PSF) is an important quantity to estimate the neutron capture cross section for the understanding of astrophysical processes and applications to nuclear engineering. In the last half century, the giant dipole resonance (GDR) has been studied well. Recently, the PSF on the low-energy tail of the GDR below the neutron threshold is of particular interest because of the appearance of an extra enhancement of E1 strength called Pygmy dipole resonance (PDR), or M1 strength in addition. The nuclei heavier than iron are mainly produced via s-, r-, or p- processes. The origin of p-nuclei is said to be production via photodisintegration in the O/Ne layers of core-collapse of massive stars explosions of supernovae type I or II, or/and s-, r- processes. However, one of the p-nuclei, $^{115}$Sn still cannot be explained with its production abundance. Recently, the s-process contribution is tried to be explained at the branching point of neutron capture reaction and β-decay at $^{113}$Cd$^m$ by the following reactions: $^{112}$Cd(n,g)$^{113}$Cd$^m$(β-)$^{113}$In(n,g)$^{114}$Sn(n,g)$^{115}$Sn. It was found that an s-process contribution from $^{113}$Cd$^{m}$ is not sufficient to explain the production problem of $^{115}$Sn. In this study, we would like to shift the viewpoint to the $^{115}$In region, which is produced via the main s-process. In this region, 3 possible reactions compete between $^{115}$In(g,n)⇄(n,g)$^{114}$In(β-)$^{114}$Sn(g,n)⇄$^{115}$Sn. However, both the photodisintegration rate for $^{115}$In and the neutron capture rate for $^{114}$In have not been known experimentally well. Hence, we measured the $^{115}$In(g,g’)$^{115}$In reaction to estimate the photodisintegration rate and the rate of the inverse $^{114}$In(n,g)$^{115}$In reaction.