Geiger-Muller counters cannot detect alpha particles?!

Not true for pancake mica-window tube!

I refute this unsophisticated claim thus (click image). The source is 241Am, normally well shielded within an old smoke detector. For Rocky Flats monitoring (including whole body scans for workers) this isotope was used until the mid-1970s as a proxy for Pu isotopes, which emit so few gamma rays that aerial surveys for Pu are not possible. Gamma rays from 241Am have very low energy (59.5 keV).

Processing bGeigie nano log files for fun but no profit

Places background radiation around Rocky Flats in the context of a trip from Arvada to Grand Junction and back, and decomposes into terrestrial (soil) radiation and cosmic rays.

A well-calibrated data-logging, GPS-enabled Geiger counter permits rapid mapping of areas and trajectories.

A well calibrated, GPS-enabled data logging pancake Geiger-Muller counter permits quick, precise mapping of paths and trajectories, albeit less so at highway speeds.


Most homeowners in Colorado know all about radon. You can learn much more in these two documents.

  • Radon: how it builds up and how it drops after mitigation
  • ‘Daughters’ from decay of radon and thoron, measured in my basement. Identifying what’s in your air.

The details

Radon daughters

Gamma spectroscopy confirmation of radon daughters

Count rate (counts/min) for furnace filter paper as measured with a Geiger-Muller counter, most sensitive to beta particles

Gamma ray spectrometry

Gamma rays are specific to each radioisotope, in the same way visible light (like neon or sodium vapor lights) is particular to particular atoms). An amateur gamma ray spectrometer is not too expensive and can characterize what’s around and how much of dose you get. Unsurprisingly, around Colorado (and Rocky Flats) it’s all natural. Trace amounts of soil plutonium which are present are undetectable because Pu emits tiny amounts of gamma rays.

Sample (logarithmic) scintillator/PMT based gamma spectrometer data for a 1980s-era Coleman thorium salt based lantern mantle. Peak widths and locations may be fit; vertical blue lines are nominal values for 232Th and decay daughters.