${}^{197}\mathrm{Au}(n,2n)$ reaction cross section in the 15–21 MeV energy range

The cross section of the ${}^{197}\mathrm{Au}(n,2n){}^{196}\mathrm{Au}$ reaction has been determined at six energies ranging from 15.3–20.9 MeV by means of the activation technique, relative to the ${}^{27}\mathrm{Al}(n,\alpha ){}^{24}\mathrm{Na}$ reaction. Quasimonoenergetic neutron beams were produced via the ${}^3\mathrm{H}(d,n){}^4\mathrm{He}$ reaction at the 5.5 MV Tandem T11/25 accelerator laboratory of NCSR “Demokritos”. After the irradiations, the induced $\gamma$-ray activity of the target and reference foils was measured with high-resolution HPGe detectors. The cross section for the high spin isomeric state (${12}^{-}$) was determined along with the sum of the ground ($2^{-}$), the first ($5^{+}$), and second (${12}^{-}$) isomeric states. Theoretical calculations were carried out with the codes empire 3.2.2 and talys 1.8. Optimum input parameters were chosen in such a way as to simultaneously reproduce several experimental reaction channel cross sections in a satisfactory way, namely the ($n,\mathrm{elastic}$), ($n,2n$), ($n,3n$), ($n,p$), ($n,\alpha$), and ($n$,total) ones.

Figure 1

Simplified decay scheme for the deexcitation of the ground and isomeric states of the ${}^{196}\mathrm{Au}$ nucleus. The intensities are obtained from the Lund/LBNL library [15] and all energies are given in keV.

Figure 2

Off-line $\gamma$-ray energy spectra observed after the neutron irradiation at 15.3 MeV. $\gamma$-ray transitions from the decay of (a) the second isomeric (m2) and (b) the ground plus both isomeric states (g+m1+m2) are shown. The duration of these measurements was 16 and 19 h, respectively.

Figure 3

Experimental cross-section values for the ground and isomeric states of the ${}^{197}\mathrm{Au}(n,2n){}^{196}\mathrm{Au}$ reaction compared with previous data and IRDFF 1.05 evaluation (solid curve).

Figure 4

Experimental cross-section values for the ${}^{197}\mathrm{Au}(n,2n){}^{196}\mathrm{Au}^{m2}$ reaction. The red points correspond to the values of the third column of Table 5, with $\gamma$-ray intensities obtained from Ref. [15], while the blue ones are the results presented in the fourth column of Table 5, using the modified intensities given in Table 1.

Figure 5

Location of the experimentally known discrete states of ${}^{196}\mathrm{Au}$ on the ($E,J$) plane. The location of the liquid drop model rotational energy [26] is shown with the solid curve.

Figure 6

Cross section of seven reaction channels for the $n+{}^{197}\mathrm{Au}$ interaction. The experimental results of this work for the ($n,2n$) channels are presented along with existing data in literature [6] and theoretical calculations obtained with empire 3.2.2 and talys 1.8 codes. Each reaction channel is shown separately: (a) ${}^{197}\mathrm{Au}(n,2n){}^{196}\mathrm{Au}$, (b) ${}^{197}\mathrm{Au}(n,2n){}^{196}\mathrm{Au}^{m2}$, (c) ${}^{197}\mathrm{Au}(n,3n){}^{195}\mathrm{Au}$, (d) ${}^{197}\mathrm{Au}(n,\alpha ){}^{194}\mathrm{Ir}$, (e) ${}^{197}\mathrm{Au}(n,p){}^{197}\mathrm{Pt}^{g+m}$, (f) ${}^{197}\mathrm{Au}(n,\mathrm{elastic})$, and (g) ${}^{197}\mathrm{Au}(n,\text{total})$.