Exploratory study of the 180m
Ta reaction with mono-energetic low-energy photon beams at HIγS
© 2019 Elsevier B.V. For the first time the de-excitation cross section of the isomeric-state nuclide 180m Ta has been measured with mono-energetic photon beams in the 1.56 MeV to 3.70 MeV energy range. The measurement of this inelastic scattering cross section on nature's rarest isotope was performed at eight energies at the High-Intensity Gamma-Ray Source Facility with natural tantalum targets. After irradiation for typically 20 h with photon fluxes ranging from 0.3×10 7 γ/(cm 2 × s) to 3.2×10 7 γ/(cm 2 × s), the 180m Ta de-excitation cross section was obtained from the yield of the K α1 and K α2 X rays of 180m Hf at 55.79 keV and 54.61 keV, respectively, produced after electron capture on the unstable 180m Ta ground state. The cross-section values found vary between (2.0±0.7) mb and (4.7±1.5) mb, providing a very large cross section for the de-excitation of 180m Ta. Extensive tests were performed to check on the reliability of the present data. The effect of bremsstrahlung photons of higher energy than the mono-energetic beam was carefully studied and corrected for. It was found that even a very small contamination of the mono-energetic photon beam by bremsstrahlung photons with E γ >7.6MeV can provide a sizable yield of 180m Hf X rays via the reaction 181 Ta(γ,n) 180 Ta, if a natural tantalum target is used, which contain four orders of magnitude more 181 Ta nuclei than 180m Ta nuclei available for the 180m Ta(γ,γ ′ ) 180 Ta reaction of interest.
Tornow, W; Bhike, M; Finch, SW; Krishichayan,
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