Geiger counters for detecting nuclear radiation (gamma rays, etc)

see also:

• electromagnetic radiation
• radio basics

• consumer Geiger counters can be handy for a number of reasons:
  • learn about background radiation in your area or whilst camping
  • discover sources of low radiation emissions such as old camera lenses, crockery, smoke alarms, etc
  • in the event of a nuclear disaster, can help you avoid high radiation areas
  • if you work in nuclear medical facilities in may be useful for personal protection
  • if you are interested in searching for radioactive minerals - perhaps not the safest of past times!
  • and if it has spectral analysis, it can detect potential radioactive contamination in foods, etc such as by cesium-137 in Europe and Japan
• the old Geiger counters as well as the cheap ones available online are generally very slow in measuring and can take 10-20secs which means walking very slowly if searching an area of ground
• new ones such as those from Radiacode are much faster and can even plot measurements on a map as you move around, as well as providing spectral analysis which means you can often work out which radioactive material is producing the gamma rays
  • NB. although these do not detect alpha particles or low energy beta particles, they can still often detect these sources as their breakdown elements are usually unstable and they themselves further break down, often giving off signature gamma rays

• these are waves at the high energy end of the electromagnetic spectrum and unlike light and radio waves are usually specified by their energy level in electron-Volts rather than by their wavelength or frequency
• X-rays generally have photon energies ranging from about 100 electron volts (eV) up to around 100 keV
• gamma rays typically have photon energies greater than 100 keV, starting where X-rays end and extending up to several MeV or even much higher in astrophysical contexts
  • common gamma ray signatures:
    • Cesium-137 ⇒ 662 keV (actually emitted by ^137mBa, the metastable daughter product)
      • ⇒ X-rays at 32 keV (from barium electron transitions) are also present but less intense
      • ⇒ beta particles emitted have endpoints around 512 keV and 1173 keV depending on the beta decay branch

• these can be useful but take 10-20sec to perform measurement and have lower sensitivity which reduces their versatility
• generally do not provide a spectral analysis function to identify isotopes, etc
• can usually detect (alpha?,) beta as well as gamma and high energy X-Rays
  • a Geiger counter can detect X-rays, but due to lower efficiency and certain technical limitations, it is less precise compared to other detectors like ionization chambers for X-ray measurement
  • at very low X-ray energies (below ~25 keV): Detection is primarily due to direct ionization of the gas inside the tube. However, the tube wall (often steel) can attenuate these low-energy X-rays, reducing sensitivity.
  • at higher X-ray energies: The detection relies on photoelectric interaction in the tube wall material (often a high atomic number material like stainless steel). This interaction produces free electrons that enter the gas and ionize it. The efficiency at these energies depends on the tube wall composition and thickness
• weak X-rays given off by alpha emitters are nearly undetectable with standard Geiger counters but can be detected by scintillation meters
• the GM M4011/J321 Geiger Muller counter tube itself is very inexpensive and can be bought for under $AU10
• often combined in a EMF meter, for example:
  • FNIRSI GC-03 3-IN-1
    • M4011/J321 Geiger Muller counter tube
      • Range: 0.01usv/h-999.99usv/h; Dose Current Rate: 0.00-10000uSv/h (10mSv/h); Cumulative Dose Equivalent: 0.00uSv-500.0mSv; Energy Range: 48keV-1.5MeV ≤ ±30% (for 137Cs-);
      • Sensitivity: 80CPM/uSv; chart over time display;
    • electric field and magnetic field measurements
    • USB-C charging; 1500mAh Li ion battery; Auto-off option after 5-15min;

• scintillators are luminescent materials that emit light when exposed to ionizing radiation, have revolutionized the field of radiation detection and imaging, luminescent materials that emit light when exposed to ionizing radiation, have revolutionized the field of radiation detection and imaging
• example scintillator crystal options include CeBr3, Ga3Al2Ga3O12(Ce) GAGG, and Cs2HfCl6, as well as traditional scintillators like NaI(Tl), CsI(Tl), CsI(Na), and 6LiI(Eu)

• a great option for most enthusiasts
• provides generally adequate spectral analysis capability for most purposes but may not suffice for accurate uranium products given their complexity
• the crystal emits light at ~500 nm where it is very effectively read out by silicon photodiodes
• it is slightly hygroscopic and soluble in water and thus the crystal is encased in a sealed chamber to protect it from moisture
• do not detect alpha or low energy beta particles
• RADEX OBSIDIAN Radiation Dosimeter
  • https://www.radonmarket.com/product/radex-obsidian-radiation-dosimeter/ 267EUR
• Radiacode 102
  • very capable, USB-C rechargeable pocket sized device with spectral analysis
  • Bluetooth to smartphone apps which can display the spectral analysis better and also plot measurements according to GPS location
  • https://www.radiacode.com/products ~$AU349
  • see https://www.youtube.com/watch?v=8Dtm0-HSkHA Youtuber review of this model compared to a Radiacode 103G
• Radiacode 103
  • updated version of the 102 with improved energy resolution 8.4% or 54kEv for 662kEv line compared with 9.4% or 63kEV for the Radiacode 102 ¹⁾
  • https://www.radiacode.com/products ~$AU449
  • see https://www.youtube.com/watch?v=TxD71kAYITU
• Radiacode 110
  • as with 103 but detector is 3x the volume giving greater sensitivity at 77cps instead of 30cps per 1 microSv/hr for Cs-137 (but max 400microSv/hr instead of 1000) and 1500mAh Li poly battery instead of 1000mAh
  • https://www.radiacode.com/products ~$AU559
• Raysid
  • https://raysid.com/
  • smaller than Radiacode and without a screen but 5x the crystal size and much more expensive starting at 399.99 EUR for < 13% FWHM - 699.99 EUR for < 7% FWHM at at 662keV (Full Width at Half Maximum)
  • https://www.youtube.com/watch?v=ceAR0MX5umo

• more expensive Csl(Tl) and provides ~1.5x more sensitivity and improved spectral analysis with high energy gamma rays but may not detect low energy X-rays as well (below 20KeV may not be displayed)
• do not detect alpha or low energy beta particles or low energy X-rays
• Radiacode 103G
  • same form factor and functionality as with the Radiacode 103 but with different sensitivity characteristics - energy resolution 7.4%
  • does not display X-Rays below 20KeV
  • https://www.radiacode.com/products ~$AU849
  • see https://www.radiacode.com/knowledge/differences-between-radiacode-models-103-and-103g
  • see https://www.youtube.com/watch?v=8Dtm0-HSkHA Youtuber review of this model compared to a Radiacode 102

• new 2026 product
• allows measurement of up to 9 mSv/h instead of being limited to limited to 1 mSv/h as is the case with the above models, but lacks their advanced analytical tools for detailed environmental and material assessment
• Radiacode Zero
  • see https://www.radiacode.com/zero