Radiation Monitor
One of the Microship's many environmental data collection channels is radiation – we're still trying to decide whether to be content with general ambient levels or add a second channel that looks at the water. In either case, the key components are a family of wonderful, low-cost units from International Medcom in Sebastopol, CA. They have a variety of units with different features and sensivities, and a long history of doing very interesting projects (including a packet radio-linked network of sensors around Three Mile Island).

The units output a pulse for every particle hit, and are interfaced to the Microshipnet via a simple counter that lets us see "counts per minute" directly. This adequately averages the data, with typical values around 25-30 CPM here in our lab. The number doubles when you lay the unit in the catbox, as the clay has a low-level radioactivity, and an old Coleman lantern mantle drives it berserk.

Specs on this model, the Inspector, are:

  • Detector: Halogen-quenched Geiger-Mueller tube. Effective diameter 1.75" (45 mm). Mica window density 1.5-2.0 mg/cm2
  • Display: 4-digit liquid crystal display with mode indicators Averaging Periods: Display updates every 3 seconds, showing the average for the past 30-second time period at normal levels. The averaging period decreases as the radiation level increases. User can select fast 3-second averaging period.
  • Operating Range: mR/hr: .001 to 100.0; CPM: 0 to 300,000; Total: 1 to 9,999,000 counts; mSv/hr: .01 to 1,000; CPS: 0 to 5,000
  • Efficiency: Sr-90 (546KeV, 2.3MeV b max): approx. 75%; C-14 (156KeV b max): approx. 11%; Bi-210 (1.2 MeV b max): approx. 64%; Am-241 (5.5 MeV a): approx. 36%
  • Sensitivity: 3500 CPM/mR/hr referenced to Cs-137
  • Accuracy: ± 15%
  • Timer: Can set 1-10 minute sampling periods in 1-minute increments, 10-50 minute sampling periods in 10-minute increments, and 1-24 hour sampling periods in 1-hour increments
  • Count Light: Red LED flashes with each radiation event
  • Audio: Beeper beeps with each radiation event; can be muted
  • Outputs: Dual miniature jack drives CMOS or TTL devices, sending counts to computer or data logger. Submini jack allows for electronic calibration.
  • Anti-Saturation: Readout holds at full scale in fields up to 100 times the maximum reading
  • Temperature Range: -10° to +50° C , 14° to 122° F
  • Power: One 9-volt alkaline battery; battery life is minimum 200 hours at normal background, minimum 24 hours at 1 mR/hr
  • Size: 150 x 80 x 30 mm (5.9"; x 3.2"; x 1.2")
  • Weight: 350 grams (12.5 oz) with battery
  • Options: Wipe Test Plate; External scintillation probe

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