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Identifying the unknown geometric and material information of a multi-shield object by analyzing the radiation signature measurements is always an important problem in national and global security.In order to identify the unknown shielding layer thicknesses of a source/shield system with gamma-ray spectra,we have developed a derivative-free inverse radiation transport model based on a differential evolution algorithm with global and local neighbourhoods (IRT-DEGL).In the present paper,the IRT-DEGL model is further extended for estimating the unknown thicknesses with random initial guesses and material mass densities of multi-shielding layers as well as their combinations.Using the detected gamma-ray spectra,the illustration of inverse studies is implemented and the main influence factors for inverse results are also analyzed.