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Rad Pro Reference Manual

This manual provides technical reference for the Rad Pro custom firmware.

Measurements

Instantaneous Rate

The instantaneous radiation rate is calculated by dividing the number of pulses, minus one, by the time interval between the first and last pulse within the averaging window.

Average Rate

Calculates the average radiation rate over a time window, using the same formula as the instantaneous rate.

Cumulative Dose

The cumulative dose tracks the total number of pulses recorded during the measurement time.

History

At startup, the history is loaded from the data log and updates every second using the instantaneous rate.

To clear the history, go to Settings > Data log > Reset.

Electric and Magnetic Field Strength (If Supported)

Calculates the electric and magnetic field strength over a 400 ms window.

Important: The device's built-in buzzer and USB connection can interfere with electric field measurements. For highest accuracy, disable audio feedback and disconnect USB during measurements.

Sensitivity

Sensitivity indicates how effectively a Geiger-Müller tube detects ionizing radiation. It is usually expressed in counts per minute (cpm) per microsievert per hour (µSv/h) — in other words, how many counts are registered for a given rate.

Rad Pro includes default sensitivity values derived from numerical simulations using Rad Lab. These values are calculated for a standard Cs-137 gamma source and apply to the most commonly used GM tubes:

  • J305: 135.200 cpm/µSv/h
  • M4011: 108.345 cpm/µSv/h
  • J321: 108.345 cpm/µSv/h
  • HH614: 30.157 cpm/µSv/h
  • СБМ20 (SBM20): 106.105 cpm/µSv/h
  • СИЗБГ (SI3BG): 3.267 cpm/µSv/h
  • LND 7317: 252.567 cpm/µSv/h

To set a custom sensitivity value, go to Settings > Geiger tube > Sensitivity and select the appropriate value.

Important: Accurate dose-rate readings require the correct sensitivity for the radiation type and energy being measured. Using an incorrect value will lead to inaccurate results.

Note: For high sensitivity tubes (≥ 600 cpm/µSv/h), pulse indication is capped at the equivalent of 600 cpm/µSv/h to prevent uncomfortable clicking. This limit affects pulse feedback only and does not reduce the accuracy of the measurements.

Source Compensation

When the source of ionizing radiation is known, Rad Pro can improve measurement accuracy by applying source compensation. This corrects for the energy-dependent response of Geiger–Müller tubes.

To enable it, go to Settings > Measurements > Source compensation and select the appropriate source from the list.

Notes:

  • Source compensation applies to gamma emitters only. Beta radiation changes its energy spectrum with distance — beta particles are attenuated as they travel through air, while gamma rays are far more penetrating and maintain a more consistent spectrum.
  • To suppress beta radiation — especially important for mixed sources — place a metal shield between the source and the detector. For home use, placing the detector inside a steel pot is a practical option: it blocks most beta particles while attenuating gamma rays only minimally.
  • All compensation factors are relative to Cs-137.
  • Compensation requires radiation levels at least 10× above background; otherwise, background spectral contributions may distort results. This requirement does not apply when compensating for background radiation itself.
  • Correction factors are theoretically derived using Rad Lab and do not account for the voltage-dependent slope of the Geiger–Müller plateau.
  • Real Geiger tubes may exhibit individual characteristics — erroneous gas fill, self-activity from radioactive construction materials, or mechanical defects — that reduce accuracy. Calibration with a check source is always preferable. Source compensation is provided as the next best alternative.

Compensation Factors by Tube and Source

Source J305 M4011/J321 HH614 СБМ20 (SBM20) СИЗБГ (SI3BG) LND 7317
Cs-137 1 1 1 1 1 1
Co-60 1.114 1.119 1.371 0.791 1.397 0.998
Tc-99m 6.38 6.401 2.567 3.267 2.419 2.466
I-131 0.99 0.998 0.761 0.918 0.762 0.943
Lu-177 3.487 3.516 1.109 1.424 1.104 1.443
Am-241 11.925 11.88 4.468 6.774 0.554 3.123
Radium 1.062 1.066 0.979 0.869 0.991 0.99
Uranium ore 1.21 1.214 0.973 0.961 0.978 1.068
Uranium glass 1.367 1.37 0.973 1.054 1.015 1.123
Depleted uranium 1.353 1.356 1.089 1.05 1.1 1.118
Thorium ore 1.113 1.118 0.416 0.858 0.697 1.011
X-rays (60 kV) 5.486 5.465 2.424 5.686 0.125 2.806
K-40 1.052 1.058 1.398 0.735 1.478 0.987
Background radiation 1.338 1.345 1.099 1.012 1.028 1.15

Data Logging

To start logging:

  1. Ensure the device's time zone, date and time are set correctly.
  2. Enable data logging in Settings. Data logs automatically in the background.
  3. When memory is full, older data is overwritten.

USB connection: Some devices require enabling Data mode in settings. Disable it after use to save power.

Downloading/logging: Use GeigerLog to download logs or log live data. The CPS (counts per second) data is raw; use the MvAvg function to average it.

Note: Data logging pauses during downloads.

Instantaneous Rate Averaging

Choose from these averaging options to balance response speed and precision:

  • Adaptive fast: Averages the last 20 pulses, targeting a ±50% confidence interval. Ideal for general use. See response curves: instantaneousaveraging-adaptivefast.ipynb
  • Adaptive precision: Extends Adaptive fast with a minimum 5-second averaging time for greater precision at high radiation levels, but slower response. See response curves: instantaneousaveraging-adaptiveprecision.ipynb
  • Fixed intervals (1 minute, 30 seconds and 10 seconds): Uses a fixed averaging window. If zero or one pulse is detected during the averaging interval, the rate registers as zero.

Instantaneous Rate Alerts

Alerts trigger only when the confidence interval falls below 75% to reduce false alarms.

Dead-Time Compensation

Dead time is the brief interval (50–200 µs) after a radiation event during which a Geiger-Müller tube cannot detect another event, leading to undercounting at high radiation levels. Rad Pro can compensate for these missed counts.

To measure dead time, go to Settings > Statistics and monitor the Dead time value. Measure several hours at normal radiation levels for accuracy, or use a radioactive source to speed up the process.

Rad Pro compensates dead time using the non-paralyzable model:

$$n = \frac{m}{1 - m \tau}$$

Where:

  • $m$: Uncompensated rate (counts per seconds).
  • $\tau$: Dead time (seconds).
  • $n$: Compensated rate (counts per second).

The compensation factor is capped at 10 to prevent overflow. Compensation applies to instantaneous rate, average rate, cumulative dose, and history but not to tube life pulse count or data logs.

HV Profiles (If Supported)

High-voltage (HV) profiles control the voltage supplied to the Geiger-Müller tube, balancing power consumption and accuracy. Preconfigured profiles are included, or you can create a custom profile.

⚠️ Incorrect HV settings may damage the tube or switching transistor due to overvoltage or overcurrent.

Higher PWM frequency provides more stable voltage but increases power consumption. Lower PWM frequency reduces power consumption but may decrease measurement accuracy due to higher ripple.

The recommended HV for most supported tubes (M4011, J305, J321, HH614, SBM20) is 440 V.

Measuring HV with a Multimeter (Recommended)

⚠️ High voltage can be lethal.

  1. Use a high-quality multimeter (10 MΩ input impedance) set to the 20 V range.
  2. Connect a clean 1 GΩ resistor (or ten 10 MΩ resistors in series) in series with the multimeter's positive terminal.
  3. Connect the negative terminal to ground and the free end of the resistor to the tube's anode.
  4. Calculate voltage: Multimeter reading × 101 (or × 11 when using 10 MΩ resistors).

Setting HV without a Multimeter (Lower Accuracy)

  1. Set PWM frequency to 2.5 kHz.
  2. Start with the lowest duty cycle and increase slowly until the tube begins producing counts (note this value).
  3. Continue increasing slowly until the displayed rate exceeds background radiation (> 0.3 µSv/h).
  4. Choose the average of the two duty-cycle values as the operating point.

⚠️ Leaving the counter running at the higher PWM duty cycle can damage the tube.

Tube Fault Alarm

The device triggers an alarm if:

  • No pulses are detected within a safety interval, indicating a faulty high-voltage generator or tube. The safety interval $t_s$ (in seconds) is $t_s = \frac{12000}{S}$, where $S$ is the tube's sensitivity (cpm/µSv/h).
  • The tube is saturated (due to high radiation) or shorted (due to malfunction).

Random Generator

The random number generator uses pulse timing to produce random outcomes in multiple formats:

  • ASCII, alphanumeric, hexadecimal, decimal and binary: up to 16 outcomes per run.
  • Die rolls, coin flips: one outcome per run.

Generation process:

  1. Measures time of pulses with microsecond precision.
  2. Extracts randomness from the two least significant bits of each timing measurement.
  3. Stores bits in a 128-bit buffer.
  4. Processes bits using the Fast Dice Roller algorithm.
  5. Bit consumption depends on output format:
    • ~7 bits: ASCII, 100-sided die
    • ~6 bits: alphanumeric
    • ~4 bits: hexadecimal, decimal, 10/12-sided die
    • ~3 bits: 6/8-sided die
    • ~2 bits: 4-sided die
    • 1 bit: binary, coin flip

Tips:

  • Use a radioactive source for faster bit generation.
  • Disable sound/vibration notifications in Settings > Alerts if you want silent operation when the generator runs to completion.

radpro-tool

radpro-tool enables low-level device access from a computer for tasks like downloading logs, live logging, submitting data to radiation monitoring websites, retrieving device info, setting HV profiles (on supported devices), and syncing the clock.

Setup:

  1. Install Python and PIP.

  2. Install requirements:

    pip install -r tools/requirements.txt

Commands:

  • Get help:

    python tools/radpro-tool.py --help

  • Sync clock (e.g., COM13):

    python tools/radpro-tool.py --port COM13

  • Download data log to datalog.csv:

    python tools/radpro-tool.py --port COM13 --download-datalog datalog.csv

  • Log pulse data live to live.csv every minute:

    python tools/radpro-tool.py --port COM13 --log-pulsedata live.csv --period 60

  • Submit data to gmcmap.com:

    python tools/radpro-tool.py --port COM13 --submit-gmcmap [USER_ACCOUNT_ID] [GEIGER_COUNTER_ID]

  • Submit data to radmon.org:

    python tools/radpro-tool.py --port COM13 --submit-radmon [USERNAME] [DATA_SENDING_PASSWORD]

  • Submit data to safecast.org:

    python tools/radpro-tool.py --port COM13 --submit-safecast [API_KEY] [DEVICE_ID]

  • Submit data to safecast.org with location data:

    python tools/radpro-tool.py --port COM13 --submit-safecast [API_KEY] [DEVICE_ID] --safecast-latitude 37.7749 --safecast-longitude -122.4194 --safecast-height 100.5

  • Submit data to opensensemap.org:

    python tools/radpro-tool.py --port COM13 --submit-opensensemap [SENSE_BOX_ID] [API_KEY] --opensensemap-sensor-id [SENSOR_ID]

Data Communications

Refer to the communications protocol description for USB serial port communication details.

Further Resources