An Overview of Current and Propose Radioactive Nano- Particle Creation and Use

1. An Overview of Current and Propose Radioactive Nano-Particle Creation and Use L. Scott Walker Los Alamos National Laboratory 03/17/08

2. Unique Radioactive Nanoparticle Hazards • Radioactive nanoparticles present several unique hazards all of which are associated with the size of the material. • 1 nm diameter particle is made of approximately 10,000 atoms. • An experiment was conducted with 1 gram of 5 nm uranium particles last year. There were 1 X 1017 particles in 1 gm. The surface area presented by these particles was ~144 square meters. • Nanometer particles potentially present new hazards based upon size, shape, surface area, chemical presentation, electrostatic charge and radioactivity (there is no longer any beta or alpha radiation self absorption).

3. Unique Radioactive Nanoparticle Hazards Continued • Since nanoparticles are so fine, dry nanoparticles are readily aerosolized and dispersible. • An experiment was completed by Skrable et all in 1975 (Health Physics, 29 pages 796-798) where 20% of the <10 nanometer particles passed through the filter media. By continuing to pass air through the media the experimenters re-aerosolized 20% of the material they captured and it passed thought the filter media. • It is questionable whether HEPA Current test measurements have not repeated the experimental results and have in fact shown that HEPA filters do a very effective job of removing nanoparticles.

4. Unique Radioactive Nanoparticle Hazards Continued • Because of their small size, self absorption of the radiation emitted by nanoparticles is almost completely excluded. (Approximately 25% of the atoms are on the outside of the particle and there are approximately 10,000 atoms per 1 nm particle). • Radioactive nanoparticles behave differently than larger particles and are not necessarily constrained to the media in which they are deposited. • The nano size can completely alter the way the material behaves chemically, alter its normal color and electrostatic charge (or the lack there of) may in itself alter the way the particle interacts with other materials.

5. Unique Radioactive Nanoparticle Hazards Continued • Researchers go to great lengths to avoid creating nanoparticles with an electrostatic charge. Non-charged particles flow more freely in certain environments but may also be less reactive. • As with other research, radioactivity allows the location and interaction of nanoparticles to be followed more accurately. Thus there are advantages to using radioactively tagged nanoparticles for research. • Nanoparticles are so small they require electron microscope to view them.

6. Sources of Radioactive Nanoparticles • Currently, the primary use of radioactive nanoparticles is in radio-pharmaceutics and as a means of cancer treatment. • Their use is confined primarily to research institutions. Several institutions have used radioactivity tagged particles to enhance understanding of particle migration. • Other research is being carried on a materials research centers but radioactive nanoparticles are gradually finding their way out of research institutions and into main stream industry.

7. Medical Uses of Radioactive Nanoparticles • Through the use of radiopharmaceuticals, radioactive nanoparticles can be targeted to deposit in certain organs. • Imaging the organ requires small amounts but killing cancer requires relatively large concentrations. • Colloidal Gold nanoparticles are finding significant use. Gold isotopes have relatively short half lives but as a result have high activity.

8. Further Nanoparticle Medical Uses • Certain “free” nanoparticles are finding use as medical radionuclides. • Magnetic, radioactive nanoparticles (Fe-59 sulfate for instance) can be directed to specific organs by placing magnets over the organ of interest.

9. Dispersal • As you have probably determined from previous slides, nanomaterils have the potential to disperse over huge areas. • Finding these materials (especially if they are low activity, long half life materials) may become a significant problem. • If the materials are prepared so they are not ionized, they may be easily re-aerosolized and re-dispersed.

10. Background Radiation • There is approximately 1 ton of Uranium and 2 tons of Thorium in the first six inches of top soil per square mile. • A one pound dispersal of 5 nanometer uranium oxide particles would not be distinguishable from the uranium in the first inch of top soil. • Background radiation would make finding all but very large concentrations of nanoparticles very difficult.

11. Measurement • Radioactive nanoparticles are easy to measure and identify in comparison to non-radioactive nanoparticles. Instrumentation for these determinations is quite expensive. • In approximately 1 hour we breath in 12 billion nanoparticles from the background in environment (i.e. there are approximately 50,000 nanoparticle per cm3 of air). Many of these background particles may be radioactive. • Small highly radioactive particles are easy to see but very hard to located with standard instrument probes.

12. Measurement and Cleanup • An instrument kit should include both alpha and pancake β/γ probes. Low activity alpha emitters may present a particular measurement problem. • Argonne National Laboratory has recently developed a cleaning system for nanoparticles that will remove them from surfaces and pores and suspend them in a media that is easy to cleanup and reduces to small volumes for disposal. Information about this system is available at: http://www.anl.gov/Media_Center/News/2004/news040702.htm

13. Conclusions • Radioactive nanoparticles are becoming more common and finding more uses in medicine and industry. Current industrial uses are limited, but their application in both medicine and industry will only continue to increase in the coming years. • Only small volumes of material are required to create rather large contamination events.