Collecting a spent nuclear fuel fragment at Chernobyl
Channel: Carl Willis
Date: 2011-08-07

**Please watch in HD format for best results**

The area surrounding the incomplete natural-draft cooling towers at ChNPP's Unit 5 construction site is littered with local hot spots that are easy to find with a scintillation detector.  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.