Abstract
As part of its R&xD activities in the fields of radioactivewaste drum storage and homeland security, the NuclearMeasurement Laboratory of CEA Cadarache has started studiesrelated to the detection of induced delayed fission gamma rays asa signature of U/Pu presence either in radioactive wastes or incargo containers and luggage. The study described in the presentpaper explores the feasibility of detecting fission delayed gammarays of nuclear materials interrogated by a pulsed neutrongenerator. For this purpose, Monte Carlo simulations have beenperformed with ACT, the MNCP6 Activation Control Card.Simulated results have been compared with experimental data tovalidate the numerical model. Samples of uranium andplutonium have been irradiated for 2 hours with a pulsed D-Tneutron generator delivering 14 MeV neutrons with an averageemission of 8.107n/s, which are thermalised in a graphite cellcalled REGAIN. At the end of irradiation, activated nuclearmaterials were placed in a low-background, high-resolutiongamma spectroscopy station in order to detect delayed gammarays emitted by fission products. Anomalies have been observedin the calculated time decay curve of fission delayed gamma rayswith MCNP6 ACT card, but the time behavior is correct for non-fission activated materials like aluminum or copper. On the otherhand, the number of counts recorded in the main simulatedgamma ray lines from activated nuclear material fission productsis consistent with the experimental results, thus validating thesimulation scheme in view of further studies on thecharacterization of radioactive waste drums or special nuclearmaterial detection in cargo containers.
Highlights
Delayed gamma rays detection emitted after neutron-induced fission or photo-fission is being studied in the fields of radioactive waste drum characterization and for homeland security [1] [2] [3] [4]
The study presented in this paper mainly focuses on the detection of delayed gamma rays emitted by fission fragments of nuclear materials (235U and 239Pu) or by non-nuclear materials activated during neutron irradiation
The ACT card allowing evolution transport calculation in MCNP 6.1 was used to model neutron-induced fission delayed gamma rays, as well as activation gamma rays from nonfissionable materials
Summary
Delayed gamma rays detection emitted after neutron-induced fission or photo-fission is being studied in the fields of radioactive waste drum characterization and for homeland security [1] [2] [3] [4]. The relative intensities of these delayed gamma rays provide additional information on the nature of the interrogated isotopes, such as 235U and 239Pu, which have different fission yields [5]. In this context, it is important to test and qualify simulation tools in view to further design nondestructive measurement systems based on the detection of induced-fission delayed gamma rays. The study presented in this paper mainly focuses on the detection of delayed gamma rays emitted by fission fragments of nuclear materials (235U and 239Pu) or by non-nuclear materials activated during neutron irradiation. The simulation results obtained for these delayed gamma rays were confronted to experimental data in order to validate a calculation scheme adapted to further feasibility studies related to delayed gamma-ray measurements after neutron irradiation
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