The main finality of the Radiation Sensor Board for Raspberry Pi is to help people in Japan to measure the levels of radiation in their everyday life after the unfortunate earthquake and tsunami struck Japan in March 2011 and cause the nuclear radiation leakages in Fukushima. We want to give the chance to measure by themselves this levels instead of trusting in the general advises which are being broadcasted. The usage of this sensor board along with the affordable and easy to use Raspberry Pi platform helps people to get radiation values from specific places.
As technical guys, we feel the responsibility of providing our support in those areas where we can contribute. As a result, first batch has been shipped to Japan at no charge to the Tokyo Hackerspace and other working groups.
The design of the board is open hardware and the source code is released under GPL.
The Libelium Team. April 2011.
The radiation board has two main parts, the power circuit and the signal circuit.
The power part is used to provide the voltage necessary for the tube (400V – 1000V) and the signal circuit is used to adapt the pulses output from the tube and connect it to the input of the microcontroller.
Once the tube is powered, we can receive the pulses in the microcontroller and count them, then with an easy calculation we can get the value of radiation.
The code we use for the board is counting pulses for 10 seconds, then we multiply the number of pulses by 6, so we get the number of pulses by minute (cpm), then, according to the tubes documentation we divide cpm by the conversion factor of the tube (360 by default) and we have the value of radiation in µSV/h.
Depending on the tube you use, maybe you need to change the calculation, you should try with different values and comment us witch value is working better.
The electronic used in the radiation board could be divided in five parts:
- High voltage power supplyFor the high voltage power supply we use a circuit based on an oscillator connected to a voltage multiplier made with diodes, transistors, resistors and capacitors (see schematic for detail). With this circuit we get a power of 500V in the tube. We've added a line of zener diodes connected in series that can be used if we need more than 500V for powering the tube. We'll add as volts to the output as volts in zener diodes we add.
- Adaptation circuit for the Geiger outputThe adaptation circuit for the output is based on a NPN transistor, this transistor will trigger the interrupt pin in the microcontroller, this transistor is also activating/deactivating the piezo speaker and LED indicator generating the audio/visual signal.
- Piezo speaker and LED indicatorThe piezo speaker and LED indicator are connected to the adaptation circuit, so the LED will blink with each pulse and the speaker will sound with each pulse.
- LCD screenThe LCD screen is connected to the microcontroller using the 4-bit mode (4 data lines in addition to RS, Enable and RW control lines).
- LED barThe LED bar is made with five standard LEDs, 3 green and 2 red. These leds are connected to digital pins of the microconroller with a series resistor.
Connecting the Radiation board to Raspberry Pi
The board is connected to Raspberry Pi through the Raspberry Pi to Arduino Shield Connection Bridge
If the board is connected to Raspberry Pi, the power is taken from the 5V pin. The pulses can be counted using the interruption on digital pin 2.
The Geiger Tube
A Geiger–Müller tube consists of a tube filled with a low-pressure (~0.1 Atm) inert gas such as helium, neon or argon (usually neon), in some cases in a Penning mixture, and an organic vapor or a halogen gas. The tube contains electrodes, between which there is a potential difference of several hundred volts (~500V), but no current flowing. The walls of the tube are either entirely metal or have their inside surface coated with a conductor to form the cathode while the anode is a wire passing up the center of the tube.
When ionizing radiation passes through the tube, some of the gas molecules are ionized, creating positively charged ions, and electrons. The strong electric field created by the tube's electrodes accelerates the ions towards the cathode and the electrons towards the anode. The ion pairs gain sufficient energy to ionize further gas molecules through collisions on the way, creating an avalanche of charged particles.
This results in a short, intense pulse of current which passes (or cascades) from the negative electrode to the positive electrode and is measured or counted.
Types of Radiation
- Alpha:Alpha radiation consists of positively (+2) charged particles emitted from the nucleus of an atom in the process of decay. These particles are also very dense which, with their strong positive charge, precludes them from penetrating more than an inch of air or a sheet of paper. Because of this, Alpha particles are not a serious health hazard, except when they are emitted from within the body as a result of ingestion, for instance, when their high energy poses an extreme hazard to sensitive living tissue. A weak form of ionizing radiation detectable on some models of Geiger counters, typically those that incorporate a thin mica window at one end of the Geiger -Mueller tube.
- Beta:Beta radiation consists of negatively charged (-1) particles emitted from an atom in the process of decay. These particles are relatively light and can penetrate somewhat better than an Alpha particle, though still only through a few millimeters of aluminium at best. If ingested, Beta radiation can be hazardous to living tissue. A relatively weak form of ionizing radiation detectable on many Geiger counters, generally dependent on the thickness of the Geiger-Mueller tube wall or the existence of a window at the end of the tube.
- Gamma:Gamma radiation represents one extreme of the electromagnetic spectrum, particularly that radiation with the highest frequency and shortest wavelength. (That same spectrum also includes the more familiar X-rays, ultraviolet light, visible light, infrared rays, microwaves, and radio waves, listed in order of decreasing frequency and increasing wavelength from Gamma rays.) Gamma rays can pass through virtually anything, and are effectively shielded or absorbed only by materials of high atomic weight such as lead. Gamma rays are produced naturally by the sun and other bodies in outer space, their transmission to earth being known as “cosmic radiation”. A very powerful and potentially very dangerous type of ionizing radiation detectable on virtually all Geiger counters.
For more detail: Geiger Counter – Radiation Sensor Board for Raspberry Pi tutorial