Nanomaterials have shown promise for a variety of medical applications due to their unique properties and form factors compared to their bulk counterparts. Several novel medical technologies leveraging these properties are in various stages of development for applications including drug delivery, anti-microbial, diagnostic, or therapy technologies. A subset of these technologies, namely radiation therapy applications, require the nanoparticles to retain their structure and properties in radiation environments. It has been demonstrated that nanoparticle irradiation response can vary greatly from bulk materials response, as damage effects become dominated by sputtering and surface effects. As such, the stability, or rather the resistance of these materials towards radiation-induced degradation needs to be well understood to gauge the efficacy of candidate nanoparticles for these applications. This presentation details ongoing efforts at the In-situ Ion Irradiation Transmission Electron Microscopy (I3TEM) facility at Sandia National Laboratories to study and characterize the structural evolution of nanoparticles utilizing both in-situ and ex-situ ion beam irradiation techniques. Materials systems of interest include CeO2 nanoparticles, used for protecting healthy cells from radiation damage, and Au and HfO2 nanoparticles, used to increase local dose from proton therapies. Observed nanoparticle responses were varied and included stability, coalescence, ablation, cratering, sputtering, and swelling, depending on particle species, morphology, and irradiation condition. This diversity in nanoparticle irradiation response demonstrates the need for additional systematic study to determine the ultimate usefulness of various nanoparticle species for radiation therapy applications.
Scintillating nanomaterials are being investigated as replacements for fragile, difficult to synthesize single crystal
radiation detectors, but greater insight into their structural stability when exposed to extreme environments is needed to
determine long-term performance. An initial study using high-Z cadmium tungstate (CdWO4) nanorods and an in-situ
ion irradiation transmission electron microscope (I3TEM) was performed to determine the feasibility of these extreme
environment experiments. The I3TEM presents a unique capability that permits the real time characterization of
nanostructures exposed to various types of ion irradiation. In this work, we investigated the structural evolution of
CdWO4 nanorods exposed to 50 nA of 3 MeV copper (3+) ions. During the first several minutes of exposure, the
nanorods underwent significant structural evolution. This appears to occur in two steps where the nanorods are first
segmented into smaller sections followed by the sintering of adjacent particles into larger nanostructures. An additional
study combined in-situ ion irradiation with electron tomography to record tilt series after each irradiation dose; which
were then processed into 3D reconstructions to show radiation damage to the material over time. Analyses to understand
the mechanisms and structure-property relationships involved are ongoing.
Particle size effects of nano- and polycrystalline metal tungstate MWO4 (M = Ca, Pb, Cd) scintillators were examined
through a comparison of commercially available powders and solution precipitation prepared nanoscaled materials. The
scintillation behaviors of nanoparticles and commercial powders were examined with ion beam induced luminescence
(IBIL), photoluminescence (PL), and cathodoluminescence (CL) spectroscopy techniques. For commercial microns
sized MWO4 powders, spectral emission differences between CL and PL were only observed for Cd and Pb tungstates
when compared to reported single crystals. The IBIL wavelength emissions also differed from the commercial MWO4
CL and PL data and were red shifted by 28 and 14 nm for CaWO4 and CdWO4; respectively, while PbWO4 had no
significant change. IBIL analysis on CaWO4 nanoparticles produced a 40 nm blue shift from the commercial powder
emission. These preliminary results suggest that both size and cation Z may affect the emission properties of the MWO4
scintillators.
The ion photon emission microscope (IPEM), a new radiation effects microscope for the imaging of single event effects
from penetrating radiation, is being developed at Sandia National Laboratories and implemented on the 88" cyclotron at
Lawrence Berkeley National Laboratories. The microscope is designed to permit the direct correlation between the
locations of high-energy heavy-ion strikes and single event effects in microelectronic devices. The development of this
microscope has required the production of a robust optical system that is compatible with the ion beam lines, design and
assembly of a fast single photon sensitive measurement system to provide the necessary coincidence, and the
development and testing of many scintillating films. A wide range of scintillating material for application to the ion
photon emission microscope has been tested with few meeting the stringent radiation hardness, intensity, and photon
lifetime requirements. The initial results of these luminescence studies and the current operation of the ion photon
emission microscope will be presented. Finally, the planned development for future microscopes and ion luminescence
testing chambers will be discussed.
Conference Committee Involvement (8)
Radiation Detectors in Medicine, Industry, and National Security XIX
22 August 2018 | San Diego, California, United States
Radiation Detectors in Medicine, Industry, and National Security XVIII
9 August 2017 | San Diego, California, United States
Radiation Detectors: Systems and Applications XVII
31 August 2016 | San Diego, California, United States
Radiation Detectors: Systems and Applications XVI
12 August 2015 | San Diego, California, United States
Radiation Detectors: Systems and Applications XV
19 August 2014 | San Diego, California, United States
Penetrating Radiation Systems and Applications XIV
28 August 2013 | San Diego, California, United States
Penetrating Radiation Systems and Applications XIII
14 August 2012 | San Diego, California, United States
Penetrating Radiation Systems and Applications XII
22 August 2011 | San Diego, California, United States
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