lamaPLC: RadiationD Geiger counter module and tubes

The RadiationD-v1.1 is a popular DIY Geiger counter module for measuring ionising radiation, often paired with microcontrollers like the ESP32 or Arduino. It typically utilizes a Miller tube (Geiger-Müller tube) to detect gamma rays and some beta particles.

The RadiationD-v1.1 module’s measuring limits are primarily determined by the specific Geiger-Müller (GM) tube installed on the board. Most kits use either the J305 or M4011 glass tubes.

☢️ Radiation Type Limits

• Gamma (Γ): Excellent detection. It is most accurate for Gamma rays (like those from Cesium-137).
• Beta (β): Detects high-energy (“hard”) Beta particles. Low-energy Beta may not penetrate the glass tube wall.
• Alpha (α): Detection is only possible with the LND-712 tube. All other tubes have glass walls that are too thick for alpha particles to penetrate; they are either blocked by the glass or even a few centimeters of air.

The RadiationD-v1.1 (also known as the CAJOE module) is highly versatile and supports most Geiger-Müller (GM) tubes that operate with an anode voltage between 350V and 500V.

¹: This defines the minimum energy a particle must have to “get inside” the tube.
²: This defines the maximum amount of radiation the tube can count before it becomes “choked” (Saturation).

• Low Energy Limit: When detecting weak radiation, such as from food or granite, the J-series glass tubes may fail to register it because the energy is too low to penetrate the glass.
• Saturation (The Danger Zone): When these tubes are near a high-radiation source, like an X-ray machine or a major leak, they will reach their Max CPM and stop detecting additional radiation. A flat reading around 30,000 CPM usually indicates radiation levels are actually much higher than the display suggests.
• LND-712 Advantage: This model is unique in being able to detect Alpha particles, like those from Americium in smoke detectors, as Alpha particles are very weak and cannot pass through glass or steel.

• Light Sensitivity: These act like solar cells. If you don't wrap them in black tape or put them in a dark box, the sun will cause thousands of “fake” counts.
• Beta Detection: They can only detect “hard” Beta. The glass walls are too thick for Beta particles to penetrate.

• J305: Excel at detecting Beta radiation, which makes them popular in medical radiology experiments. They are very fragile.
• J321: Concentrates on Gamma detection with improved linear response features, making it perfect for environmental security monitoring.
• M4011: Exhibits high sensitivity to both Beta and Gamma rays, making it ideal for scientific research and broad industrial monitoring.

• Durability: These are metal tubes. They won't break if you drop them, and they are completely immune to light interference.
• Size: The STS-5 (~112mm) is longer than the SBM-20 (~108mm). Neither usually fits the standard “clips” on the RadiationD board (85-90mm) without modification or the use of wires.
• Voltage Tuning: These tubes love 400V. You will need to use a multimeter to adjust the P1 blue potentiometer on the RadiationD board to ensure it stays in the “plateau” range (350V–475V).
• Connection: These tubes use “pin” ends. Most users use fuse clips or small springs to hold them, rather than soldering directly to the tube (which can damage the seal).

The LND-712 is a professional-grade, American-made tube. It is rarely used by beginners because the tube alone often costs $80–$150, which is 5-10 times the price of the RadiationD module.

• Alpha Detection: This is the only tube on your list with a Mica end-window. This window is thin enough to let Alpha particles through.
• Voltage: It requires the higher end of the RadiationD's power range (near 500V). You must adjust the blue potentiometer (P1) while measuring the voltage with a high-impedance multimeter.
• Usage: To detect Alpha, you must point the “window” end directly at the source (within 1–2 cm).
• Warning: The Mica window is extremely fragile—touching it with a finger or a tool will destroy the tube instantly
• Mounting: The LND-712 is much shorter (approx. 50mm) and has a different pin configuration. It will not fit the clips. You must solder custom lead wires.
• Use for mineral collectors: Users hunting for “hot” rocks (Autunite, Torbernite) where Alpha emission is the primary indicator.

To operate the RadiationD-v1.1 with an Arduino, connect it as an external interrupt source. Since radiation events occur randomly and very quickly, relying on a standard digitalRead is not dependable.

Wiring Diagram

Simple RadiationD & Arduino Code

This script counts the pulses and calculates CPM (Counts Per Minute).

#define LOG_PERIOD 15000 // Log period in milliseconds (15 seconds)
unsigned long counts;     // Variable to store pulses
unsigned long previousMillis;
 
void ICACHE_RAM_ATTR countPulse() {
  counts++;
}
 
void setup() {
  Serial.begin(9600);
  pinMode(2, INPUT); 
  // RadiationD pulses LOW when radiation is detected
  attachInterrupt(digitalPinToInterrupt(2), countPulse, FALLING);
}
 
void loop() {
  unsigned long currentMillis = millis();
  if (currentMillis - previousMillis > LOG_PERIOD) {
    previousMillis = currentMillis;
 
    // Calculate CPM (Counts Per Minute)
    float cpm = counts * (60000.0 / LOG_PERIOD);
 
    Serial.print("CPM: ");
    Serial.println(cpm);
 
    counts = 0; // Reset count for next period
  }
}

Converting CPM to µSv/h

To get a usable dose reading, you multiply the CPM by the conversion factor specific to your tube.

• J305 / M4011: µSv/h = CPM * 0.0081
• SBM-20: µSv/h = CPM * 0.0057
• Example: If your Arduino calculates 20 CPM with a J305 tube:20 * 0.0081 = 0.162 µSv/h (Normal background radiation).

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