Older lantern mantles contain Thorium as the incadescent material. All Thorium isotopes are radioactive and this radiation can easily be detected with the setup used here. Note that most new lantern mantles use Yttrium instead of Thorium and are not radioactive. The mantles used in this study are shown below.
Note that the mantles were not removed from their packaging in this study to minimize exposure to the radioactive material inside.
The resulting gamma-ray spectrum for the lantern mantles is shown below. Four 0.093" thick Plexiglass sheets were used between the mantles and the probe to block the beta particle that the mantles also emit. These beta particles otherwise produce a background continuum that swamps most of the peaks visible in the spectrum.
An attempt has been made at identifying the peaks visible and they are labelled on the plot. All of the peaks shown are produced by daughter products in the Thorium decay chain.
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