Radiation Monitor: Geiger Counter with Data Logging

Measuring radiation is essential for nuclear safety, geological survey, and even building material testing. India operates 22 nuclear power reactors, and communities near these facilities benefit from independent radiation monitoring. A DIY Geiger counter with Arduino data logging provides real-time counts per minute (CPM) and dose rate in microsieverts, giving you and your community peace of mind.

Understanding Ionising Radiation

Ionising radiation comes in three main forms: alpha particles (stopped by paper), beta particles (stopped by aluminium), and gamma rays (penetrate most materials). A Geiger-Mueller (GM) tube detects all three by ionising gas inside the tube, producing an electrical pulse for each radiation event.

Background radiation in India averages 2.4 millisieverts (mSv) per year, mainly from cosmic rays, soil, and building materials. Some areas of Kerala and Tamil Nadu have naturally elevated levels (5-15 mSv/year) due to thorium-rich monazite sands — these are the highest natural background levels in the world.

Geiger-Mueller Tube Selection

For a DIY radiation monitor, the GM tube is the most critical component:

• SBM-20 (Russian) — The most popular hobby tube. Detects beta and gamma radiation. Length: 108mm, voltage: 400V. Available for ₹1,500-2,500 on Indian electronics marketplaces.
• J305β — Chinese equivalent of SBM-20. Lower cost (₹800-1,200) but adequate for background monitoring.
• SBM-21 (miniature) — Tiny tube for portable devices. Lower sensitivity but fits in pocket-sized enclosures.

Components for a Radiation Monitor

Complete parts list:

• GM tube (SBM-20 or J305β)
• Arduino Nano or ESP32
• HV boost converter module (adjustable, set to 400V for SBM-20)
• 10M ohm anode resistor
• 100pF coupling capacitor
• Buzzer for audible clicks
• OLED display for CPM and dose rate
• SD card module for data logging
• 9V battery or 18650 lithium cell

Total cost: ₹3,000-5,000 depending on tube choice.

High-Voltage Power Supply Design

The GM tube requires 380-420V to operate, but draws only microamps of current. Use a commercial HV boost module (available for ₹200-400) that converts 5V to 400V. These modules use a flyback oscillator — do not touch the output, it can deliver a painful shock.

Safety precautions: add a discharge resistor (10M ohm) across the HV output, use insulated wire rated for 600V+, and enclose the HV section in a separate compartment. Label it clearly with a high-voltage warning.

Arduino Code for CPM and Dose Rate

// Geiger Counter - Arduino
volatile unsigned long counts = 0;
unsigned long lastTime = 0;
const int geigerPin = 2; // Interrupt pin

void countPulse() { counts++; }

void setup() {
  Serial.begin(9600);
  pinMode(geigerPin, INPUT);
  attachInterrupt(digitalPinToInterrupt(geigerPin), countPulse, FALLING);
}

void loop() {
  if (millis() - lastTime >= 60000) { // Every minute
    noInterrupts();
    unsigned long cpm = counts;
    counts = 0;
    interrupts();

    // Convert CPM to microsieverts/hour (SBM-20: 1 uSv/h ≈ 151 CPM)
    float usvh = cpm / 151.0;

    Serial.print("CPM: "); Serial.print(cpm);
    Serial.print("  Dose: "); Serial.print(usvh);
    Serial.println(" uSv/h");

    lastTime = millis();
  }
}

Safety Thresholds and Alerts

Normal background radiation thresholds:

• 0.05-0.15 μSv/h — Normal background for most of India
• 0.15-0.30 μSv/h — Elevated background (granite buildings, high-altitude areas)
• 0.30-0.50 μSv/h — Investigate source (building materials, nearby industry)
• Above 0.50 μSv/h — Alert. Identify and isolate the radiation source
• Above 1.0 μSv/h — Significant. Contact the Atomic Energy Regulatory Board (AERB)

Background Radiation Mapping in India

Create a radiation map of your area by walking with a portable Geiger counter and logging GPS coordinates (from your phone) alongside CPM readings. Common findings in India:

• Granite countertops and tiles emit 0.15-0.30 μSv/h (radon from uranium decay)
• Kerala/Tamil Nadu beach sand can read 1-5 μSv/h (monazite thorium)
• Altitude increases cosmic radiation — Ladakh reads 50-100% higher than sea level
• Hospital X-ray rooms should read zero outside the shielding — test this!

Applications Beyond Radiation Detection

Beyond radiation safety, your Geiger counter can test food imports for contamination, check antique ceramics (some contain uranium glaze), verify X-ray shielding effectiveness, and even detect radon gas in basements when paired with a charcoal sample collection technique.