Properties of Technegas: Careful observations in our lab by Rod Browitt, reveal an intriguing mechanism for the creation of Technegas. It was always somewhat counter-intuitive that Technetium metal should suddenly volatilise a little way above its melting temperature (2157°C) when its boiling point is 4165°C. Also, although graphite has a steep partial pressure profile with temperature in the 2-3000°K range, some 6 orders of magnitude, predominantly releasing Carbon as C-C-C triplets, (“Thermodynamic properties of carbon up to the critical point”. Leider HR, Krikorian OH, young DA. Carbon 11: 555-563; 1973.) it still did not explain the sudden “lifting off” and Technegas production. It is now hypothesized that the sudden lift-off is caused by the striking of an AC arc from the intense thermionic plasma inside the crucible, and that it is this arc that ablates the technetium and graphite simultaneously. Evidence for the validity of this theory comes from the interesting fact that if the crucible is heated by direct current, Technegas production is greatly impaired and is not sudden. It would seem the peaks of the 12V AC sine wave are necessary to trigger the arc and hence produce rapid and efficient Technegas production. Ignition of this arc may also explain the abundance of pure Fullerenes observed in the vapour. Mass spectrometry reveals a large spectrum of Fullerenes, but no mass shift to suggest they carry Tc atoms.

Co-condensation in the gas phase: An experiment was conducted in which Technegas from about 2GBq of 99mTc- Pertechnetate in the crucible was produced with the generator unit against the collimator of a gamma camera set to run in cine mode. The sequence very clearly shows the sudden lift off and “spout” of activity rising rapidly for about 10cm. It then appears to pause momentarily before dispersing convectively in the chamber. We believe this pause point represents the condensation of the Tc vapour to the solid crystalline state and the assembly of the Carbon triplets into 6 member rings and then graphitic sheets to coat it. We are trying to get the image data translated into a modern format to reproduce here.

Although the aerodynamic characteristics of the particles are not known, it is clear from their dimensions that they will suspend in air indefinitely under stable thermal conditions, supported by the kinetic energy of the surrounding air molecules, and diffusing rapidly in all directions from their point of insertion into the atmosphere.

From experiments with the ground-state Tc-99 nuclide, so far unpublished, it is clear that the particles are inert in the rat for periods of up to three months, whether inhaled or injected. No experiments beyond that point have been performed to date. But there is no reason to suggest that the graphite coat will not remain intact indefinitely once formed. Some early work in vitro showed the cocoon of graphite was stable to several hundred degrees around the Tc metal crystal.

The particles are clearly hydrophobic, which is of considerable importance in a lung agent as they will repel from aqueous surfaces and water vapour, only being trapped by the surfactant material present in abundance in the alveolar (respiring airways) region. Imaging of lungs of volunteers up to 22 hours following Technegas inhalation has shown a less than 3% loss of activity from the lung field in that time. The combination of this observation and that a 5 second breathold on end inspiration during the breathing manoeuvre raises the per breath retention from 20% to 80%, demonstrate unequivocally that virtually all the activity reaches beyond the 16th division of the bronchial tree ( the foot of the muco-ciliary escalator ) to the respiring airways.

They are not strictly metallo-fullerenes because there is more than one layer of graphitic coating and there is currently no evidence of five membered rings in the structure. This animation depicts a conceptual view of the Technegas particle. The 5 to 30 nm central crystal of technetium metal is covered by a thin, but multi-layered graphitic shell.

The fact that the carbon shell is layered is known from transmission electron microscopy. The structure of the carbon in the plane of the layers is unclear. For more information please contact Dr. Tim Senden at The Dept. Applied Mathematics, ANU.