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

Abstract

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 252Cf 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.