Isomeric cross sections of fast-neutron-induced reactions on ${}^{197}$Au

Recent accurate data obtained for the isomeric cross section of the ${}^{197}$Au$(n,2n)$ reaction provide a valuable opportunity to consider the question of the effective moment of inertia of the nucleus within a local consistent model analysis of all available reaction data for the ${}^{197}$Au target nucleus. Thus, a definite proof of a moment of inertia equal to that of the rigid-body has been obtained for the ${}^{196}$Au nucleus, while indications infer about half the rigid-body for ${}^{194}$Ir.

Figure 1

Comparison of experimental [59, 86, 87], ENDF/B-VII.1 evaluated [88], and calculated cross sections of the reactions (a,c) ${}^{197}$Au$(n,2n)$${}^{196}$Au and (b,d) ${}^{197}$Au$(n,2n)$${}^{196}$Au${}^{m2}$ (with the corresponding spin, parity, and lifetime shown between square brackets), for incident energies up to (a,b) 24 MeV and (c,d) 40 MeV, by using the excitation-energy variable ratio $I/I_r$ of the nuclear moment of inertia to its rigid-body value (dashed curve) or the constant ratios 0.5 (dotted) and 1 (solid).

Figure 2

As for Fig. 1, but for (a) the $(n,3n)$ reaction and (b) the $(n,4n)$ reaction on ${}^{197}$Au.

Figure 3

As for Fig. 1, but for the $(n,p)$ reaction and population of (a) the g.s. and (b) the isomeric state of the residual nucleus ${}^{197}$Pt, and (b) the same comparison for the isomeric ratio.

Figure 4

As for Fig. 1, but for (a) $(n,\alpha )$ reaction cross sections for the target nucleus ${}^{197}$Au and (b) population of the g.s and isomeric state of the residual nucleus ${}^{194}$Ir. The actual evaluation data [89] are shown for the spin and parity of the isomeric state while the value 11${}^{-}$ has been used in the calculation (see text for details).

Figure 5

The excitation-energy dependence of the level density spin cutoff for the nucleus ${}^{196}$Au corresponding to rigid-body (solid curve) and half rigid-body (dashed) moments of inertia, the energy-dependent parametrization of Ref. [45] (dash-dot-dotted), the discrete spin cutoff (dash-dotted) and its global value (dotted) of Ref. [47], and given by the maximum likelihood estimator [90] (solid circles). The latest quantity is also shown for the nucleus ${}^{194}$Ir (open circles).

Figure 6

Comparison of experimental [87], ENDF/B-VII.1 evaluated [88], and calculated $(n,xn)$ reaction cross sections for the target nucleus ${}^{197}$Au, by using the model assumptions and parameters given in the text (solid curves) and the alternative replacement of either the Fermi energy value $F=40$ MeV (dotted) or the FG energy dependence of the s.p.l. density $g$ of PE excited particles (dashed), or use of only the BSFG formula for the nuclear level density (dash-dotted).