Neutron activation cross sections at 14.4 MeV For some naturally occurring heavy elements in the region 76 ≦ Z ≦ 82

Abstract

Abstract Neutron activation cross sections at 14.4 MeV were determined for isotopes of the following naturally occurring heavy elements: Os, Pt, Au, Hg, Tl and Pb. The mixed-powder method with Ge(Li) γ-detection was used, and the cross sections in mb are as follows. For (n, 2n) reactions ( m = metastable ; g = ground state ); 192 Os, 1993±200 ( m+g ); 192 Pt , 2035±150; 198 Pt , 1009±100 ( m ); 198 Pt , 707±85 ( g ); 197 Au , 151 ±18 ( m ); 197 Au , 1986±150( m+g ); 196 Hg , 1617±160( m ); 196 Hg , 363±54( g ); 198 Hg , 885±80( m ); 198 Hg , 1125±100( g ); 200Hg, 789±120( m ); 204 Hg , 2077±166; 203 TI , 1950±200; 204 Pb , 1737±140 . For (n, n′) reactions: 199Hg, 128±20( m ); 204 Pb , 51±10( m ) . For (n, 3n) reactions: 197Au, 61±20. For (n, p) reactions: 194Pt, 4.3±0.6; 196 Pt , 1.1±0.2; 198 Hg , 4.5±0.5; 199 Hg , 2.3±0.3; 208 Pb , 0.46±0.06 . For the (n, α) reaction; 203Tl, 2.2±0.4. For the [(n, np)+(n, pn)+(n, d)] reaction: 199Hg, 0.40±0.06. Cross sections calculated with the statistical-model equation of Pearlstein and an optimized level-density parameter equation are compared with a consistent set of measured (n, 2n) values over the region 30 ≦ Z ≦ 82; it is shown that deviations of the calculated cross sections from the respective measured values become larger as the energy needed to emit the second neutron increases, probably because fewer exit channels are available and the continuum assumption in the statistical model of the compound nucleus becomes invalid.