Documents here are primarily of interest to people who do their own radiation measurements, including the processing of long trajectories of data-logging or the work flow of people doing amateur gamma ray spectrometry.
SAFECAST bGeigie Nano data-logging GPS-enabled Geiger-Müller counter
- LongLongAnalysis.pdf Document on using SAFECAST QGIS (version 3.x) plugin version 2 for post-processing bGN log files. Compares data from Spatial variations in natural background radiation: absorbed dose rates in air in Colorado by Stone, Whicker, Ibrahim, and Whicker with recent car measurements at 80 km/h or higher. Details on how to combine ‘there’ and ‘back’ legs of a trip using a moving average or the wavelet-denoised data. Analysis of the approximate spatial resolution.
- Mathematica notebook used to process 4-column dataset from plugin QGIS data. Denoises ADER data using wavelet transforms and detects and rejects outliers. Using parameterization of Cinelli et al, decomposes ADER into cosmic ray and terrestrial contributions. Produces ready-to-use graphics and exports x-y data files for: altitude vs. distance, speed vs. distance, ADER vs. distance, terrestrial and cosmic ray contributions too.
- DeadTime.pdf Careful analysis of calibration data for bGN carried out by and how it in fact reflects counter dead time rather than calibration. The default calibration of the bGeigie Nano is already excellent: as noted in documents elsewhere, my measurements in the Refuge (and Kim Griffith’s measurements in the COU) both yielded an ambient dose equivalent rate (ADER) of 0.140 microSv per hour, to be compared with 0.140 reported using a pressurized ionization chamber (a much larger and more expensive device which is much more sensitive than a GM tube and whose gamma ray energy response is known to be smoother than for a GM tube.
Impact of radon abatement
As may be found elsewhere on the website, radon exposure is the single most important source of radiation exposure to people living in Colorado. Radon isotopes occur in both the 232Th and 238U decay chains.
- An interesting mathematical physics exercise I assigned a couple of times (and had to solve myself) concerns using scaled (`non-dimensionalized’) variables to solve for the time and spatial dependence of the concentration of a gas which seeps through the floor (bottom boundary) at a constant rate. The transverse dimensions of the rectangular box room are assumed much larger than the height of the room above the floor.
- Data on how the radon concentration is measured to change before and after installation of a Rn mitigation system. When you sell your house you will have to produce proof that this has been done, but it is never done by builders when a house is being built.
Setting up a home gamma ray spectrometer: shielding, calibration, changing PMT gain
A scintillation detector attached to a photomultiplier tube is the bare bones of an affordable gamma ray spectrometer. Until the 1970s such systems were used as whole-body counters and detectors at the Rocky Flats plant. (As we noted, Pu isotopes emit so few gamma rays that 241Am was used as a proxy for Pu (since 241Am is a decay product of the trace contaminant 241Pu in weapons grade plutonium). As mentioned in our science documents, the chemical identity of radionuclides is very specifically encoded in their gamma ray spectrum. The 1.46 MeV gamma from the very common radioisotope 40K is the dominant feature in a gamma ray spectrum (even with as much lead shielding as I could afford) in a basement. The 241Am spectrum comes from an old smoke detector source and the 232Th spectrum from a 1980s-era unopened Coleman lantern mantle.