Fascinating patterns drawn by radiation: Particle physics in your pocket.
The miniature particle tracking and imaging detectors of ADVACAM such as MiniPIX can record very small levels of radioactivity which is present everywhere: In the air, you breathe, in the water you drink, in the food, you eat and, yes, even in your own body.
NASA uses 7 of these units on board of International Space Station ISS as radiation environment monitors REM.
It is enough to plug the MiniPIX device into the USB port of your PC and start the software. The fascinating images of ionizing particles will start to appear in front of you.
Watching it for while you start to recognize some typical often occurring cases: Large blobs, straight strikes,
This animation shows radiation recorded during two hours on the table of my office.
From time to time one can observe some rare particles and their interactions which can create funny pictures like flowers or even letters. All of it is just a random manifestation of natural radioactivity in the normal environment.
So, there is, unfortunately, no secret message “347” send by god:
All the boring physics turns into wonderful exploration. There are hundreds of questions you can explore with this device:
Is there a difference between day and night radiation? Does the radiation change when somebody enters the room? What happens if I would place a piece of granite close to the detector? And what about ash? Or air filter? Is there some preference in the directions of muons? And beta rays? Does the neodymium magnet affect the particles? Can I find some new particles in mountains? Or in mines? Or onboard of the plane? What about lightning during the storm? Can I use natural radiation to make an image of something?
The device can be used with great advantage during courses of physics for direct visualization of principles described in textbooks. Students or teachers can perform real nuclear experiments on their tables.
What do we see?
Alpha particles are observed as large roundish blobs in our pictures. They originate from the decay of certain unstable atomic nuclei such as Radon. The alpha particle is composed of two protons and two neutrons (which is in fact nucleus of Helium). They are electrically charged (carrying two positive charges of protons). Alpha particles are large and heavy -that is why they don’t penetrate deep into objects. In the air, they would fly less than 5 cm till they would stop and change into normal helium atoms (stealing two electrons from atoms around). Since they cannot penetrate through the dead layer of human skin, they present a substantial risk for people only if generated inside of the body, typically in the lungs, causing internal irradiation and potentially cancer.
Radon is the main source of alpha particles in our environment is generated from radium in the solid grains of the rock in the soil, they emanate the radon atom toward pore gases or fluids in the intergranular space. Then radon migrates at significant distances from the site of generation reaching houses of people where it can accumulate if not ventilated properly.
Beta radiation or beta rays
formed by electron or positron (anti-electrons) flying at high speed (close to the speed of light). Such fast-flying electrons can be generated during the decay of unstable atoms or they can start as normal electron accelerated by other particles flying around (e.g. hit by gamma-ray, cosmic muon …). They are relatively lightweight and charged so they often change direction during collisions with other electrons when flying through the material. That is why we see them in our detector as crooked lines like “worms”. During these interactions, they decelerate gradually losing all their energy, stop and become normal electrons. Depending on original speed (energy) they can fly tens of centimeters or even meters in the air. Since they interact so often they present a high risk for the human body.
are photons of electromagnetic radiation. They have zero rest mass and no electric charge. They are of the same nature as photons of visible light just with a much shorter wavelength and, therefore, much more energy and, therefore, much more penetrating. They originate in the nucleus of the atom during transitions from an excited state to a state with less energy – this happens usually just after radioactive decay. They don’t interact very often with the material. They can fly tens of meters in the air or more. They penetrate the human body easily interacting just rarely. They are stopped by large and heavy materials. That is why radiation shielding is usually made of thick lead.
When flying through the mater they would interact mostly with electrons. During such interactions, they spent either all energy (photo effect) or part of it (Compton scattering) recoiling an electron which continues similarly as a beta ray. Therefore in our images, we cannot distinguish original beta rays caused by radioactive decay from electrons recoiled by energetic gamma photons – they cannot be distinguished, they are identical.
We can identify gamma rays reliably only if their energy is low and the electrons they recoil don’t fly far from the interaction point. Because beta rays of the same energy would be absorbed in the air and they would not reach the detector. Therefore we see those gamma rays as small dots.
The penetration power of gamma rays is used with great advantage for medical imaging. The patient gets a “radiomarker” injected into his blood containing a radioactive agent emitting gamma rays (e.g. Technetium or radioactive isotope of Iodine). Such agents get accumulated in specific organs (e.g. Iodine goes to the Thyroid). Gamma rays are then emitted from that organ penetrating the body tissues easily. Observing this with a gamma camera we can create an image of the organ. This technique is used for the visualization of some types of tumors or metastasis.
Mouns are generated during interactions of cosmic rays in the upper layers of the atmosphere. They are charged and 207 times heavier than electrons. They are fast and heavy which is why they don’t change the direction of flight often. We see them as narrow straight strikes. They are unstable with a mean lifetime of 2 microseconds. The fact that we can detect them on the ground level is a nice demonstration of the validity of Einsteins’ relativity theory. If the relativity principles would not be valid, muons would fly only about 600 meters till they would decay.
Combinations of multiple effects
Alpha and beta decay often happen in sequence. For example, during the decay of Radon, we see that during the transition from Radium C to Radium C’ single beta ray is emitted. Then in 164 microseconds emission of alpha particle follows. In our images we see it as a flower where a large blossom of alpha is attached to the stem of an electron:
Delta electrons: A muon flying at high speed through the sensor can recoil the electron which continues forming a typical worm shape. These recoiled electrons are often referred to as delta electrons:
Scattering of Muons: Muon flying through the sensor can hit the nucleus of the atom. It happens rarely. Since the nucleus (Cd or Te) is about 1000 times heavier than the muon. It would not recoil during the collision. It is similar to the situation when a cyclist would hit a train. The train would not recoil but the cyclist would bounce back or sideways depending on the angle of impact.
There are many other nice interactions we can observe. Much more very interesting shapes of particle tracks you can see when flying in a plane. I will come to this topic in some of my future articles.
MiniPIX EDU: Detector optimized for use in schools
A special simplified detector version MiniPIX_EDU affordable for schools, teachers, and even students is available now. It provides the same functionality as our standard MiniPIX operated on board of ISS by NASA. Less robust mechanics, less strict qualification criteria (schools are less demanding than NASA) and shortened manufacturing process allowed more than 50% price reduction.