Total radiative thermal neutron-capture γ-ray cross sections for the 182,183,184,186W isotopes were measured using guided neutron beams from the Budapest Research Reactor to induce prompt and delayed γ rays from natural and isotopically-enriched tungsten targets. These cross sections were determined from the sum of measured γ-ray cross sections feeding the ground state from low-lying levels below a cutoff energy, Ecrit, where the level scheme is completely known, and continuum γ rays from levels above Ecrit, calculated using the Monte Carlo statistical-decay code dicebox. The new cross sections determined in this work for the tungsten nuclides are σ0(182W)=20.5(14) b and σ11/2+(183Wm,5.2s)=0.177(18) b; σ0(183W)=9.37(38) b and σ5-(184Wm,8.33μs)=0.0247(55) b; σ0(184W)=1.43(10) b and σ11/2+(185Wm,1.67min)=0.0062(16) b; and, σ0(186W)=33.33(62) b and σ9/2+(187Wm,1.38μs)=0.400(16) b. These results are consistent with earlier measurements in the literature. The 186W cross section was also independently confirmed from an activation measurement, following the decay of 187W, yielding values for σ0(186W) that are consistent with our prompt γ-ray measurement. The cross-section measurements were found to be insensitive to choice of level density or photon strength model and only weakly dependent on Ecrit. Total radiative-capture widths calculated with dicebox showed much greater model dependence; however, the recommended values could be reproduced with selected model choices. The decay schemes for all tungsten isotopes were improved in these analyses. We were also able to determine new neutron-separation energies from our primary γ-ray measurements for the respective (n,γ) compounds: 183W [Sn=6190.88(6) keV]; 184W [Sn=7411.11(13) keV]; 185W [Sn=5753.74(5) keV]; and, 187W [Sn=5466.62(7) keV].
ASJC Scopus subject areas
- Nuclear and High Energy Physics