A study of photoneutron reactions on ${}^{159}\mathrm{Tb}$ was performed by using quasimonochromatic laser Compton scattering $\gamma$-ray beams provided at the NewSUBARU facility, Japan, along with a high-and-flat efficiency moderated array of ${}^3\mathrm{He}$ counters and an associated neutron multiplicity sorting method. The $(\gamma ,1nX)$, $(\gamma ,2nX)$, $(\gamma ,3nX)$, and $(\gamma ,4nX)$ photoneutron cross sections and average energies of the corresponding photoneutron spectra were measured in the 8.25 to 42.23 MeV energy range, from the vicinity of the neutron emission threshold up to well above the giant dipole resonance region. This dataset constitutes the first measurement of average photoneutron energies in ${}^{159}\mathrm{Tb}$ to date. The total photoneutron cross section $\sigma (\gamma ,sn)$ was determined by summing the partial $(\gamma ,inX)$ components. Our $(\gamma ,1nX)$ and $(\gamma ,sn)$ cross sections show reasonable agreement with those measured by R. Bergère et al. [Nucl. Phys. A 121, 463 (1968)] at Saclay, while our $(\gamma ,2nX)$ results align well with the Livermore measurements by R. L. Bramblett et al. [Phys. Rev. 133, B869 (1964)]. This contradicts the recommendation of B. L. Berman et al. [Phys. Rev. C 36, 1286 (1987)] to resolve the Saclay-Livermore discrepancies by applying a uniform scaling factor across all reaction channels. The present experimental excitation functions and photoneutron energies were compared with statistical model calculations performed with the empire and talys codes. We found that the competition between the $(\gamma ,inX)$ reaction channels is better reproduced using the Modified Lorentzian (MLO2) photon strength function (PSF) model than with the Simple Modified Lorentzian (SMLO) PSF model. After adjustment of the PSF on the photoabsorption cross section, the experimental photoneutron emission cross sections are found to be rather well reproduced by both the empire and talys codes. However, average neutron energies are fairly described only at the lowest photon energies. Based on the present centroid energies of the first and second giant dipole resonance peaks, we obtained the hydrodynamic model prediction of $+6.99\left(42\right)$ b for the intrinsic electric-quadrupole moment of the ${}^{159}\mathrm{Tb}$ ground state.

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• Gamma-ray strength functions
• Giant resonances
• Nuclear reactions
• Photonuclear reactions
• 150 ≤ A ≤ 189
• Radiation detectors