Fast Spectroscopic Gamma Scintillation Using Hafnium Oxide Nanoparticles–Plastic Nanocomposites

Abstract

Fast scintillators with a spectroscopic gamma response are essential in nuclear security and medical imaging. However, few individual scintillation materials exhibit both fast scintillation decay and high photopeak energy resolution. We report a nanocomposite scintillator comprising 40 wt % of hafnium oxide nanoparticles uniformly dispersed in a luminescent plastic matrix. The nanoparticles have an average diameter of 4.2 nm and are covalently attached to the polymer matrix to prevent agglomeration and thus achieve high optical transparency across nanocomposite monoliths up to 8.5 mm thick. The measured transmittance is around 80% across the emission range. Gamma pulse scintillation has a fast decay time constant of 2.5 ns and high light output of 8000−9000 photons/MeV. The gamma scintillation shows energy proportionality from 32 to 1275 keV. A 1.93 cm 3 nanocomposite produces photopeaks at 32 and 662 keV for 137 Cs and at 511 and 1275 keV for 22 Na. The photopeak energy resolution at 662 keV is 7.2−9.1%.

Nanocomposite Scintillators Loaded With Hafnium Oxide and Phosphorescent Host and Guest for Gamma Spectroscopy

“…Hafnium oxide nanoparticles were synthesized according to a literature protocol. ,, Typically, 50 mL trifluoroacetic acid was added dropwise to 30 mmol (9.6 g) hafnium­(IV) chloride, then stirred at 40 °C overnight. Purification was performed through rotary evaporation and vacuum drying, yielding hafnium trifluoroacetate.…”

“…For surface modification of the hafnium oxide nanoparticles, the pristine oleylamine ligand was partially exchanged by bis­(2-(methacryloyloxy)­ethyl) phosphate as described in a literature protocol. ,− After ligand exchange, the nanoparticles were vacuum-dried, transferred into a nitrogen-filled glovebox, and dispersed into a degassed formulation containing 5 vol % divinylbenzene in methylstyrene, after which FIrPic, Luperox-231 (thermal initiator, 0.1 vol %), mCP, and MF were dissolved into the solution. The curing solution was transferred to a glass vial (cleaned with 3:1 sulfuric acid/30 wt % hydrogen peroxide and treated with trichloro­(1 H ,1 H ,2 H ,2 H -tridecafluoro- n -octyl)­silane) and sealed with a plastic lid and polytetrafluoroethylene (PTFE) film.…”

“…Measurements were performed using a home-built system constructed in a light proof box and follow a previously reported literature protocol, with minor modifications. ,, Typically, the plastic scintillator or nanocomposite was placed in a PTFE sample holder and coupled to a Hamamatsu R878 photomultiplier tube (PMT) using EJ-550 optical grade silicone grease. A Cs-137 source was placed outside the PTFE sample holder, and a PTFE back reflector was used to optimize photon collection by the PMT while also excluding the influence of concomitantly emitted β rays from the Cs-137 source.…”

“…Using high- Z plastic scintillators for spectroscopic identification of radionuclides is made possible by comparing the measured energies that result from the interaction of gamma rays with high- Z elements against known radionuclide standards . Thus, as long as plastic materials demonstrate satisfactory light yield and are able to incorporate high- Z elements, they remain viable competitors against other gamma radiation detection technologies, as shown by our group’s previous work that incorporated high- Z nanoparticles into a fluorene-enhanced organic matrix. , Unfortunately, these high- Z plastic scintillators often see a trade-off between high light yield and high loading of high- Z components, as high- Z nanoparticles are non luminescent and photoelectric energy deposited in the nanoparticles do not contribute to the scintillation light yield. Therefore, the development of a plastic matrix with exceptionally high light yield becomes critical, especially at high nanoparticle loading.…”

From Gel to Crystal: Mechanism of HfO2 and ZrO2 Nanocrystal Synthesis in Benzyl Alcohol

“…Hafnium oxide nanocrystals are particularly interesting since they are relevant for memory devices, − as X-ray CT contrast agents, − for scintillators, ,, for catalysis, or for radiotherapy . While HfO 2 can be synthesized in benzyl alcohol from HfCl 4 in a pressure bomb (autoclave), the reaction can also be performed in a microwave reactor, considerably shortening the reaction time to 3–4 h .…”