${}^{191}\mathrm{Ir}(n,2n)$ and ${}^{191}\mathrm{Ir}(n,3n)$ reaction cross sections in the 15–21 MeV energy range

The cross sections of the ${}^{191}\mathrm{Ir}(n,2n){}^{190}\mathrm{Ir}$ and ${}^{191}\mathrm{Ir}(n,3n){}^{189}\mathrm{Ir}$ reactions have been determined by means of the activation technique, relative to the ${}^{27}\mathrm{Al}(n,\alpha ){}^{24}\mathrm{Na}$ reaction, at neutron beam energies higher than 15 MeV. The quasi-monoenergetic neutron beams were produced at the 5.5 MV Tandem T11/25 Accelerator Laboratory of NCSR “Demokritos” by implementing the ${}^3\mathrm{H}(d,n){}^4\mathrm{He}$ reaction. The induced $\gamma$-ray activity of the irradiated target and reference foils was measured with high resolution, high purity germanium (HPGe) detectors. The cross section for the high-spin isomeric state (${11}^{-}$) of the ${}^{190}\mathrm{Ir}$ nucleus was determined along with the sum of the ground ($4^{-}$), the first ($1^{-}$), and the second (${11}^{-}$) isomeric states. Moreover, the cross section for the production of the ground state of the residual nucleus of $(n,3n)$ reaction, ${}^{189}\mathrm{Ir}$, was also estimated. Additionally, cross section theoretical calculations were carried out using the empire 3.2.2 and talys 1.8 codes, in which the input parameters were chosen in such a way as to simultaneously reproduce several experimental reaction channel cross sections in a satisfactory way, namely the $(n,2n)$, $(n,3n)$, $(n,p)$, $(n,\alpha )$, and $(n,\text{total})$ ones. Similar combination of theoretical model parameters had also been successfully used in the case of the neighboring ${}^{197}\mathrm{Au}$ nucleus, and this constitutes an encouraging confirmation of how accurately the theoretical models can reproduce the experimental results in this mass region.

Figure 1

Simplified decay scheme for the deexcitation of the ground and isomeric states of the ${}^{190}\mathrm{Ir}$ nucleus. The intensities are obtained from the NNDC Brookhaven National Laboratory library [14] and from Refs. [15, 16], and all energies are presented in keV.

Figure 2

Simplified decay scheme for the deexcitation of the ground state of the ${}^{189}\mathrm{Ir}$ nucleus. The intensities are obtained from the NNDC Brookhaven National Laboratory library [14] and all energies are presented in keV.

Figure 3

Off-beam $\gamma$-ray energy spectra obtained after the neutron irradiation at 15.3 MeV [(a) and (b)]. $\gamma$-ray transitions from the decay of (a) the second isomeric ($m2$) of the ${}^{190}\mathrm{Ir}$ nucleus and (b) the ground plus both isomeric states ($g+m1+0.086m2$) of the ${}^{190}\mathrm{Ir}$ nucleus are marked. The durations of these measurements were 10 and 72 h, respectively. Concerning the measurement of the ground state of the ${}^{189}\mathrm{Ir}$ nucleus (c), the 245.1 keV $\gamma$ ray is marked in the 56 h spectrum obtained after the irradiation at 20.9 MeV.

Figure 4

Experimental cross section values for the ${}^{191}\mathrm{Ir}(n,2n){}^{190}\mathrm{Ir}^{m2}$ reaction compared with previous data.

Figure 5

Experimental cross section values for the ${}^{191}\mathrm{Ir}(n,2n){}^{190}\mathrm{Ir}^{g+m1+0.086m2}$ reaction compared with previous data and ENDF/B-VIII.0 evaluation (solid curve). The datasets with an asterisk in the end correspond to the total $(n,2n)$ channel cross section, while the rest correspond to $g+m1$ cross section values.

Figure 6

Experimental cross section values for the ${}^{191}\mathrm{Ir}(n,3n){}^{189}\mathrm{Ir}$ reaction compared with previous data and ENDF/B-VIII.0 evaluation (solid curve).

Figure 7

Cross sections of six reaction channels for the $n+{}^{191}\mathrm{Ir}$ interaction. The experimental results of this work for the $(n,2n)$ channels are presented along with existing data in literature [9] and theoretical calculations obtained with empire 3.2.2 and talys 1.8 codes. Each reaction channel is shown separately: (a) ${}^{191}\mathrm{Ir}(n,2n){}^{190}\mathrm{Ir}^{g+m1+0.086m2}$, (b) ${}^{191}\mathrm{Ir}(n,2n){}^{196}\mathrm{Ir}^{m2}$, (c) ${}^{191}\mathrm{Ir}(n,3n){}^{189}\mathrm{Ir}$, (d) ${}^{191}\mathrm{Ir}(n,\alpha ){}^{188}\mathrm{Re}$, (e) ${}^{191}\mathrm{Ir}(n,p){}^{191}\mathrm{Os}$, and (f) ${}^{191}\mathrm{Ir}(n,\text{total})$.