This is the preprocessed raw data and analysis code of the photonuclear experiment on the γ-decay Behavior of the Giant Dipole Resonances of ¹⁵⁴Sm and ¹⁴⁰Ce performed in 2021 at the High Intensity γ-ray Source (HIγS) located at the Triangle Universities Nuclear Laboratory (TUNL), Durham, NC, USA by the Technische Universität Darmstadt and TUNL collaboration. It is published at TUdatalib, TU Darmstadt's institutional repository for all research data generated or worked with at TU Darmstadt (https://tudatalib.ulb.tu-darmstadt.de). The data forms the basis of the doctoral studies of Jörn Kleemann (https://orcid.org/0000-0003-2596-3762) under the supervision of Prof. Norbert Pietralla (https://orcid.org/0000-0002-4797-3032) at the Technische Universität Darmstadt, Germany and was mainly analyzed by him. The resulting dissertation (J. Kleemann, "Probing the Giant Dipole Resonance Using Nuclear Resonance Fluorescence", Dissertation, Technische Universität Darmstadt, Darmstadt (2024)) is published with TUprints, the e-publishing-service of TU Darmstadt, and is openly accessible at https://tuprints.ulb.tu-darmstadt.de/27008 and https://doi.org/10.26083/tuprints-00027008 . Furthermore, a paper on part of the results was accepted for publication in Physical Review Letters (J. Kleemann et al., "Gamma decay of the ¹⁵⁴Sm Isovector Giant Dipole Resonance: Smekal-Raman Scattering as a Novel Probe of Nuclear Ground-State Deformation", Phys. Rev. Lett., to be published (2025)), with the preprint already being available at https://arxiv.org/abs/2406.19695 . This data publication is directly related to both the dissertation and the peer-reviewed publication and allows for the full reproduction of the analysis and results presented in these works and the creation of all figures contained in them.