Description
The Analog Radiation Detector – Monitor 4 & Monitor 4EC are versatile and dependable survey instruments designed for detecting alpha, beta, gamma, and X-ray radiation in a wide range of field applications. Commonly used for checking industrial gauges containing Cesium-137, locating radioactive sources, personal protection, and general radiation surveying, both models feature a rugged analog meter that provides immediate, easy-to-interpret readings. Their wide operating ranges and selectable scales make them suitable for both low-level background monitoring and higher radiation environments.
The Monitor 4 uses an uncompensated GM tube with a thin mica window for high sensitivity to alpha and beta radiation, while the Monitor 4EC adds energy compensation for a flatter and more accurate gamma and X-ray response across a broad energy range. Both models include audible indication, anti-saturation protection, long battery life, and pulse output for external analysis. Lightweight, portable, and trusted worldwide, the Monitor 4 series offers reliable performance for professionals, safety officers, and training environments, with optional SI scale meters and software support to suit various monitoring needs.
Specifications
Detector
| Model |
Detector Description |
| Monitor 4 (M4) |
Halogen-quenched uncompensated GM tube with thin mica window (1.5–2.0 mg/cm²). Effective window diameter: 9.1 mm (0.36 in). |
| Monitor 4EC (M4EC) |
Halogen-quenched GM tube with energy-compensated sidewall (2 mm thin filter) and thin mica window (1.5–2.0 mg/cm²). Effective window diameter: 9.1 mm (0.36 in). |
Operating Range
| Measurement Mode |
Range |
| Dose Rate |
0–0.5 / 0–5 / 0–50 mR/hr |
| Count Rate |
0–500 / 0–5,000 / 0–50,000 CPM |
| SI Scale (Optional) |
0–5 / 0–50 / 0–500 µSv/hr |
Energy Sensitivity & Radiation Detection
| Parameter |
Details |
| Gamma Sensitivity |
1,000 CPM/mR/hr (¹³⁷Cs) |
| Energy Response – M4EC |
Flat within +61% / −26% (40–100 keV)
Flat within +35% / −17% (100 keV – 1.3 MeV) |
| Beta Detection |
50 keV beta: ~35% efficiency
150 keV beta: ~75% efficiency |
| Alpha Detection (Both Models) |
Detects alpha down to 2.5 MeV
>80% efficiency at 3.6 MeV |
| Gamma & X-Ray Detection – M4 |
Down to 10 keV (through window)
40 keV minimum (through case) |
| Gamma & X-Ray Detection – M4EC |
Down to 10 keV (through window, non-compensated)
40 keV (through sidewall) |
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| Monitor 4: Detects alpha down to 2.5 MeV; typical detection efficiency at 3.6 MeV is greater than 80%. Detects gamma and x-rays down to 10 keV typical through the window, 40 keV minimum through the case. |
Monitor 4EC: Detects alpha down to 2.5 MeV; typical detection efficiency at 3.6 MeV is greater than 80%. Detects gamma and x-rays down to 10 keV typical through the window (non-compensated), 40 keV through the sidewall. |
Range Switch
X1, X10, X100, Battery Check.
Accuracy & Controls
| Specification |
Details |
| Accuracy |
Typically ±15% of reading (¹³⁷Cs) |
| Range Switch |
X1, X10, X100, Battery Check |
| Display |
Analog meter, CPM & mR/hr scale
Holds full scale in fields up to 100× maximum reading |
| SI Display Option |
Optional SI scale meter available |
Indicators & Outputs
| Specification |
Details |
| Audio Indicator |
Internal beeper (can be turned off for silent operation) |
| Output |
3.5 mm jack with pulse output |
Power & Environmental
| Specification |
Details |
| Power Requirements |
9 V alkaline battery |
| Battery Life |
Approx. 2,000 hours at normal background |
| Temperature Range |
−20°C to +55°C (−4°F to +131°F) |
Physical Characteristics
| Specification |
Monitor 4 |
Monitor 4EC |
| Weight |
200 g (7.1 oz) |
224 g (7.9 oz) |
| Size |
209 × 71 × 50 mm (8.2 × 2.8 × 1.9 in.) |
Same as M4 |
Included Items, Options & Warranty
| Category |
Details |
| Included |
Carrying case with belt clip |
| Options |
SI Meter Option, Observer Software |
| Warranty |
1 year limited warranty |
| Kits |
Monitor 4 kits available (educational / build-your-own option) |
