Photoneutron cross sections for ${}^{118\text{--}124}$Sn and the $\gamma$-ray strength function method

Photoneutron cross sections were measured for ${}^{118}$Sn, ${}^{119}$Sn, ${}^{120}$Sn, ${}^{122}$Sn, and ${}^{124}$Sn near neutron threshold with quasi-monochromatic laser-Compton scattering $\gamma$ rays. A systematic analysis of the present photoneutron data and existing neutron-capture data is made using the $\gamma$-ray strength function on the basis of the HFB + QRPA model of $E1$ strength supplemented with a pygmy dipole resonance, which was deduced from a previous study on ${}^{116}$Sn and ${}^{117}$Sn. Radiative neutron capture cross sections for two radioactive nuclei, ${}^{121}$Sn and ${}^{123}$Sn, are deduced through the $\gamma$-ray strength function method.

Figure 1

The chart of nuclei depicting an application of the $\gamma$-ray strength function method to tin isotopes. Photoneutron cross sections measured in the present experiment are shown by left arrows. Radiative neutron capture cross sections used for constraining the $\gamma$SF are show by right arrows. Photoneutron cross sections for two radioactive nuclei, ${}^{121}$Sn and ${}^{123}$Sn, are deduced with the $\gamma$-ray strength function method.

Figure 2

${}^{118}$Sn($\gamma$,$n$)${}^{117}$Sn photoneutron cross section. The full dots correspond to our new measurements and the other symbols to the former photodata [16, 17] and the evaluated cross sections [18]. The theoretical cross sections considered in this study (see text) are also shown.

Figure 3

Same as Fig. 2 for the ${}^{119}$Sn($\gamma$,$n$)${}^{118}$Sn photoneutron cross section.

Figure 4

Same as Fig. 2 for the ${}^{120}$Sn($\gamma$,$n$)${}^{119}$Sn photoneutron cross section.

Figure 5

Same as Fig. 2 for the ${}^{122}$Sn($\gamma$,$n$)${}^{121}$Sn photoneutron cross section.

Figure 6

Same as Fig. 2 for the ${}^{124}$Sn($\gamma$,$n$)${}^{123}$Sn photoneutron cross section.

Figure 7

${}^{117}$Sn($n$,$\gamma$)${}^{118}$Sn cross section obtained with the HFB + QRPA, HFB + QRPA and PR and Lorentzian $E1$ strengths (see Fig. 2) and compared with experimental data [28, 29, 30, 31].

Figure 8

Same as Fig. 7 for ${}^{118}$Sn($n$,$\gamma$)${}^{119}$Sn.

Figure 9

Same as Fig. 7 for ${}^{119}$Sn($n$,$\gamma$)${}^{120}$Sn.

Figure 10

Comparison between the HFB + QRPA strength (with and without the inclusion of the PR) and the experimental data of the Oslo group [9, 10], from photodata [18] as well as the present photoemission data, for ${}^{118}$Sn (a), ${}^{119}$Sn (b), and ${}^{122}$Sn (c).

Figure 11

${}^{121}$Sn($n$,$\gamma$)${}^{122}$Sn (a) and ${}^{123}$Sn($n$,$\gamma$)${}^{124}$Sn (b) cross sections obtained with the HFB + QRPA and PR $E1$ strengths (see Fig. 5 and 6). The uncertainties are associated with the use of different nuclear level density models [35]. The dashed, dotted, and dash-dot curves correspond to the Japanese JENDL-4.0, American ENDF/B-VII, and European JEFF-3.1 evaluations, respectively [36], whenever available.