Functionalized Polystyrene Sensor for Selective Extraction and Assay of Plutonium at Ultratrace Level in Complex Radionuclide Matrices

The present study focuses on the development of a scintillation sensor specifically designed for the selective extraction and ultratrace detection of Pu in the presence of other α and β-γ emitting radionuclides. To achieve this, a polystyrene (PS) film, embedded with the fluorophore 2,5-diphenyloxazole (PPO) and the activator 1,4-bis(2-methylstyryl)benzene (MSB), has been prepared as the substrate owing to its excellent pulse height response. The Pu selective functional groups have been introduced onto the PS substrate by surface grafting of bis(2-(methacryloyloxy)ethyl) phosphate (BMEP) monomer using in situ ultraviolet (UV) polymerization. The scintillation sensor could be successfully tested for Pu detection in the presence of α (Am, Cm, U) and β-γ (Cs, Ba, and Eu) emitting radionuclides. The sensor has been successfully applied for the uptake and estimation of Pu from a legacy sample containing high activities of ¹³⁷Cs and ²⁴¹Am. In order to test the response of the Pu-loaded sensor in the most complex scenario, it has been exposed to a freshly prepared fission product solution. In this case, the uptake of fission product (⁹⁵Zr and ⁹⁵Nb) has been observed along with Pu, which introduced significant interference from β particles in the scintillation pulse height spectra of Pu. With optimization of the thickness of the PS substrate, the β contribution could be reduced and Pu could be estimated in such a complex scenario. If the Pu activity is sufficiently high, the PS film can also be subjected to α spectrometry using solid-state Si detectors for quantification of Pu. The developed sensor has been found to be sensitive, selective, and reusable and has a linear response over a wide range of Pu concentrations. Moreover, these sensors are deployable for field applications with the capability of remote monitoring, enabling low-level detection of Pu even in the presence of other interfering radionuclides.