Medical Isotopes

Radioactivity as Medicine

The world of atoms, nuclei and elementary particles is usually perceived as being completely beyond intuitive understanding, being way below the scales that can be perceived by the human sensory instrumentarium. According to Johann Wolfgang von Goethe, this would actually mean that particles are non-existent or at least that their physics adds nothing to our understanding of nature, as according to Geothe, everything worth knowing can be found by observation with the naked eye: Perception is already the entire theory.

But astronauts dream of fireflies: A single energy-packed ion from the depths of space creates a perceivable glowing trail on human retinae. A fog chamber that can be assembled on a kitchen table shows the flightpaths of individual particles as fleeting contrails.

What makes radioactivity eerie in the eyes of some turns it into an extremely powerful tool: Due to the high energie involved, it is measurable with fantastic precision. Single nuclear decays can be registered. That way, it also helps us study the human body accurately.

In nuclear medicine, radioactive isotopes are added to molecules which gather at the desired spot in the body. That way, bone fractures, carcinomas, heart- and brain maladies can be localized precisely or, using SPECT (Single photon emission computed tomography), even imaged in three dimensions.

Of course, these methods of examination cause a certain exposure of the patient to radiation. The doses are very small, though (as even tiniest amounts of radiotracer suffice to create a measurable signal!), so that the increase in cancer risk is negligible.

The most common and versatile trace is technetium 99m, a weak gamma emitter. It is produced as a decay product of molybdenum 99 with a half-life of three days. Currently, molybdenum 99 is created in a complex process at research reactors by irradiation of highly enriched uranium: Supply bottlenecks can occur, as was shown by the worldwide molybdenum crisis 2009/10. Power plants are not suitable for production: Due to the short half-life, the fuel would have to be constantly removed and the molybdenum filtered out — far too expensive and effortful. If there only was a reactor with liquid fuel separating fission products on-line…!

Molybdenum 99 from the DFR

A single DFR (3000 MW thermal) produces 300 gram per year, correspondig to world consumption within a single day(!). The PPU delivers the desired nuclide cleanly: Together with noble metal fission products it deposits on the surface of the argon bubbles that permeate the liquid prior to thermal distillation. From this chemically inert metal mixture it can be easily separated. The technetium generators can be assembled in the power plant itself — massive reduction of complexity of the distribution chain.

Extreme cost reduction will follow! This should trigger an avalanche of new applications, in medicine as well as other fields.