Identification of short-lived fission products in delayed gamma-ray spectra for nuclear material signature verifications

Short-lived Fission Products (FPs) of both uranium (U) and plutonium (Pu) isotopes were identified in neutron irradiated nuclear material (NM) standards in the high-energy gamma-rays range in the perspective of the utilisation of the Delayed Gamma-ray Spectrometry (DGS) technique for nuclear material signature verifications. DGS is a promising active Non-Destructive Assay (NDA) technique that found applications not only in nuclear safeguards but also in nuclear security. This paper presents results of measurement campaigns that include the development of experimental set-up, sample irradiation, gamma-ray spectra acquisitions and qualitative analysis of the obtained gamma-spectra. The experimental setup-up is based on an HPGe planar detector of high-energy resolution and an irradiation chamber made of high-density polyethylene (HDPE) that accommodates a sealed Cf-252 source of 50 MBq activity. The delayed gamma-ray spectra of standard samples of U and Pu neutron interrogated samples are successfully acquired using the cyclic neutron irradiation method. 35 and 24 FPs with half-lives ranging from dozens seconds to minutes were identified in the irradiated U and Pu samples, respectively. In the energy range 2-4.9 MeV of the acquired DGS gamma-ray spectra; we have successfully identified 72 gamma-ray peaks of 21 FPs in U and Pu standard samples. This large number of identified FPs is auspicious to the full development of DGS as new active NDA technique for nuclear signature verifications.