Pictures:
First picture shows both the SBM20 and the SBM20U (shorter, with only one cap connector). The third picture shows the SBM-19 and the SBM-20 for size comparison. The SBM-19 is larger and approximately 4 times more sensitive than the SBM-20.
Details:
Geiger-Muller tube for gamma and hard beta radiation. The main radiation detection element in the uRADMonitor detectors.
Notes on sensitivity:
This is a moderately sensitive tube. It's relatively small size, makes it a convenient choice as a radiation detection element in handheld dosimeters and DIY circuits, however for monitoring equipment larger volume tubes, such as the SBM-19 or the SI-22G should be used. The following chart shows the average of the background readings over a period of 24 hours and each point in the chart was computed using another average of 60 independent, consecutive measurements. The dosimeter used to take the measurements has 1 minute resolution.
Background readings: 19CPM for a background radiation level of 0.12uSv/h
Datasheet:
General specifications
Gas Filling: Ne + Br2 + Ar
Cathode Material: Stainless Steel, 50 mkm
Maximum Length (mm): 108 / 101
Effective Length (mm): 91.0 / 83.5
Maximum Diameter (mm): 11
Effective Diameter (mm): 10
Connector: Pin
Operating Temperature Range: -60 to +70 C
WALL SPECIFICATIONS
Areal Density (mg/cm2): 40
Thickness (mm): 0.05
ELECTRICAL SPECIFICATIONS
Minimum Anode Resistor (meg ohm): 1.0
Recommended Anode Resistor (meg ohm): 5.1
Recommended Operating Voltage (volts): 400
Operating Voltage Range (volts): 350 - 475
Initial voltage (volts): 260 - 320
Plateau length (volts): at least 100
Maximum Plateau Slope (%/100 volts): 10
Minimum Dead Time (at U=400V, micro sec): 190
Working range (mkR/s): 0.004 - 40
Working range (mR/h): 0.014 - 144
Gamma Sensitivity Ra226 (cps/mR/hr): 29
Gamma Sensitivity Co60 (cps/mR/hr): 22
Inherent counter background (cps): 1
Tube Capacitance (pf): 4.2
Life (pulses): at least 2*1010
Weight (grams): 10 / 9
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