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 dissertation work 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 dissertation of Jörn Kleemann is still in preparation, but should be available at https://tuprints.ulb.tu-darmstadt.de/27008 and/or https://doi.org/10.26083/tuprints-00027008 once its published. Furthermore, a peer-reviewed publication of part of the results is in preparation (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" (2024), in preparation). Once the dissertation is ready for publication, there might be an updated version of this repository, which would be cited by the dissertation and also be published at TUdatalib (https://tudatalib.ulb.tu-darmstadt.de), so please check there for the most recent version of this repository and the data and codes contained in it.