E., Plutonium Isotopic Composition by Gamma-Ray Spectroscopy (1986).

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The Soviet Union cooked up more plutonium than any other nation.

Most of this was slated for the noble purpose of containing capitalist imperialism, but some found its way into commercial ionization smoke detectors like the KI-1, RID-1, and RID-6M.

w=200" data-large-file="https://carlwillis.files.wordpress.com/2017/02/dscf0054_v1.jpg? w=450" src="https://carlwillis.files.wordpress.com/2017/02/dscf0054_v1.jpg? w=209&h=314" width="209" height="314" data-original-width="209" data-original-height="314" itemprop=" title="dscf0054_v1" alt="Smoke detector source in graded Cd and Cu attenuator" style="width: 209px; height: 314px;" / Graded attenuator capsule (copper pipe) holding the smoke detector source is placed in front of the HPGe detector.

" data-medium-file="https://carlwillis.files.wordpress.com/2017/02/dscf0064_v1.jpg? w=300" data-large-file="https://carlwillis.files.wordpress.com/2017/02/dscf0064_v1.jpg? w=450" src="https://carlwillis.files.wordpress.com/2017/02/dscf0064_v1.jpg? w=233&h=155" width="233" height="155" data-original-width="233" data-original-height="155" itemprop=" title="dscf0064_v1" alt="Graded attenuator capsule (copper pipe) holding the smoke detector source is placed in front of the HPGe detector." style="width: 233px; height: 155px;" / HPGe detector (right, on floor) and associated NIM electronics.

" data-medium-file="https://carlwillis.files.wordpress.com/2017/02/geometry.jpg? w=300" data-large-file="https://carlwillis.files.wordpress.com/2017/02/geometry.jpg? w=450" src="https://carlwillis.files.wordpress.com/2017/02/geometry.jpg? w=233&h=155" width="233" height="155" data-original-width="233" data-original-height="155" itemprop=" title="geometry" alt="HPGe detector (right, on floor) and associated NIM electronics." style="width: 233px; height: 155px;" / The gamma spectrum is shown, annotated, in the gallery below.

It can be downloaded in ASCII format as an Excel spreadsheet here.

" data-medium-file="https://carlwillis.files.wordpress.com/2017/02/dscf0029_v1.jpg? w=200" data-large-file="https://carlwillis.files.wordpress.com/2017/02/dscf0029_v1.jpg? w=450" src="https://carlwillis.files.wordpress.com/2017/02/dscf0029_v1.jpg? w=136&h=204" width="136" height="204" data-original-width="136" data-original-height="204" itemprop=" title="dscf0029_v1" alt="Cute, isn't it?

This is the ~1-milligram plutonium source from a Soviet KI-1 smoke detector." style="width: 136px; height: 204px;" / Plutonium source from the Soviet KI-1 smoke detector " data-medium-file="https://carlwillis.files.wordpress.com/2017/02/dscf0021_v1.jpg?

In quantitative gamma spec measurements, another important point is to avoid getting the source too close to the detector. With the right attenuation and geometry, all that remains is to gather a statistically-useful number of counts in the spectrum–in this case, about 42 hours of counting.

Smoke detector source in graded Cd and Cu attenuator " data-medium-file="https://carlwillis.files.wordpress.com/2017/02/dscf0054_v1.jpg?

w=200" data-large-file="https://carlwillis.files.wordpress.com/2017/02/dscf0021_v1.jpg? w=450" src="https://carlwillis.files.wordpress.com/2017/02/dscf0021_v1.jpg? w=446&h=669" width="446" height="669" data-original-width="446" data-original-height="669" itemprop=" title="dscf0021_v1" alt="Plutonium source from the Soviet KI-1 smoke detector" style="width: 446px; height: 669px;" / High-resolution gamma spectroscopic measurements allow direct determination of the relative concentrations of Pu-238, Pu-239, Pu-240, and Pu-241 in a plutonium sample.