Quick disclaimer before we begin: I'm not a physicist. The information in here must be taken with a pinch of salt. This project started as a personal learning exercise and by sharing it I hope to get valuable feedback from the community!
Radiation monitoring is a technical challenge at many levels. We basically want to detect particles that travel very fast and have weak interactions with matter. This involves lots of physics, mechanics and electronics.
Most radiation detectors don't read the particles directly. Instead, they monitor a volume of matter and watch out for ionization events that occur when high energy particles interact with the material. Here is a brief overview on some of the existing detector types:
- Geiger counters are by far the most popular type of detector. They work by applying a high voltage to an electrode inside a low pressure gas tube. Each time a high energy particle goes through the tube, they ionize some of the gas and discharge the electrode. These events are read by an electronic circuit that translates them into audible "clicks".
- Scintillation counters use scintillation as the detection principle. They include a special crystal that flashes whenever a particle passes through. These scientific grade detectors are way more accurate, but also more expensive and complex.
- Ionization chambers are similar to Geiger counters, but have a lower voltage applied to the electrode. A weak electric field is enough to separate the ion-electron pairs that are generated each time a high energy particle passes through the chamber. Instead of watching for individual ionization events, these detectors measure the aggregated currents that are induced in the electrodes when the ions arrive. For more information check out this fantastic page by Charles Wenzel.
- Spark detectors are a special case, and are very well explained in this video by Carl Willis:
My favourite type of detector. You can almost see the particles!
- There are many other techniques such as using photo-diodes to measure gamma radiation. See a related project also in Hackaday: https://hackaday.io/project/1749-solid-state-ionising-radiation-detector
For the Open Radiation Detector, we will use an open-air ionization chamber like the ones studied by Charles Wenzel & Alan Yates (http://www.techlib.com/science/ion.html & http://www.vk2zay.net/category/30) among others. These decision comes from the following facts:
- Ionization chambers don't require high voltages (they are safe).
- They can work at ambient pressure and temperature (they are robust & easy to build since no vacuum is involved).
- As opposed to counting detectors, ionization chambers have a linear response. Reading is proportional to the amount of radiation (less corrections are needed).
- The detection circuit is basically a current amplifier (it can be simple & low cost).
- Another consideration is that ionization chambers are specially sensitive to alpha radiation. Most Geiger counters block alpha radiation, giving false readings when presented with pure alpha sources. So this feature would complement many commercial counters very well.
Theory is soo pretty, isn't it? (It should be!). However there are some practical considerations that must be taken into account when designing a detector of this type.
In the following updates we will show you some of the prototypes and iterations that have been necessary towards a validation of the final design.
Thanks for reading! Please share your questions or concerns in the comments section below.