In a YouTube video produced by Carl Willis, a nuclear engineer shows us around radioactive sites with a Geiger counter and documenting his finds. In a video from 2011, Willis explores Chernobyl’s Number 5 reactor, eventually finding a “hot spot” he traces down to a tiny speck no larger than a grain of salt.
After some rudimentary tests, Willis concludes the small particle is a fragment of spent nuclear fuel, likely ejected in 1986 when the Number 4 reactor exploded.
In this video, I dig up one of these hot spots, and learn that the object responsible for the prominent radiation is a hard black fleck a mere 0.5 mm on a side.
What is it? I collected the specimen and brought it back to the Interinform hotel for further explorations. The CDV-700 Geiger probe measures 35-40,000 cpm on contact with the beta window closed, translating into about 60 milliroentgen / hr and an activity of about 40 microcuries by comparison with other, known Cs-137 sources. Next I illustrate a rudimentary form of scintillation gamma spectrometry making use of my netbook’s sound card and a clever piece of free pulse analysis software called PRA, written by Australian physicist Marek Dolleiser. This spectrometer arrangement works on the AC-coupled linear scintillation pulses from the Ludlum 12 preamp, and displays a pulse-height spectrum that conclusively identifies the medium-lived fission product Cs-137 as the nuclide responsible for all the gamma radiation from this particle. No surprise.
About the only reasonable assumption based on the high activity (~20 mCi / g) is that this particle is a fragment of spent fuel that was ejected from Unit 4 at the time of the accident there. In color and appearance it is consistent with sintered uranium dioxide fuel, and the activity is broadly consistent as my calculation at the end of the video shows.