Photo-neutron cross-section of $${}^{{\mathrm {nat}}}{\mathrm {Dy}}$$ in the bremsstrahlung end-point energies of 12, 14, 16, 65, and 75 MeV
The flux-weighted average cross-sections of 
$${}^{\mathrm {nat}}{\mathrm {Dy}}(\upgamma , {\mathrm {xn}}){}^{{159,157,155}}{\mathrm {Dy}}$$

 reactions were measured at the bremsstrahlung end-point energies of 12, 14, 16, 65 and 75 MeV with the activation and off-line 
$$\upgamma $$

-ray spectrometric technique using the 20 MeV Electron Linac for beams with high Brilliance and low Emittance (ELBE) at Helmholtz-Zentrum Dresden-Rossendorf, Dresden, Germany and the 100 MeV electron linac at the Pohang Accelerator Laboratory, Korea. The 
$${}^{\mathrm {nat}}{\mathrm {Dy}}(\upgamma , {\mathrm {xn}}){}^{{157,155}}{\mathrm {Dy}}$$

 reaction cross-sections as a function of photon energy were also calculated theoretically using TALYS 1.9 code. Then the flux-weighted average values at different end-point energies were obtained based on the theoretical values of mono-energetic photons. These values were compared with the flux-weighted values of present work and are found to be in general agreement. It was also found that the experimental and theoretical formation cross sections of 
$${}^{159}{\mathrm {Dy}}$$

, 
$${}^{157}{\mathrm {Dy}}$$

 and 
$${}^{155}{\mathrm {Dy}}$$

 from the 
$${}^{\mathrm {nat}}{\mathrm {Dy}}(\upgamma , {\mathrm {xn}})$$

 reactions increased from their respective threshold values to a certain energy where other reaction channels opened. After reaching a maximum value, the individual reaction cross-sections slowly decreased with the increase of the bremsstrahlung energy due to the initiation of other competing reactions at higher energy, which indicates the impact of the excitation energy. However, the production cross sections of 
$${}^{157}{\mathrm {Dy}}$$

 and 
$${}^{155}{\mathrm {Dy}}$$

 from the 
$${}^{\mathrm {nat}}{\mathrm {Dy}}(\upgamma , {\mathrm {xn}})$$

 reactions slightly increase in between and then decreased slowly with bremsstrahlung energy, which is due to the contributing reactions of higher mass isotopes.