Seeing Inside of the Things With Muon Scanning Tomography

_{Img Source: pxhere.com (CC Public Domain)}

Intro

We are all under a violent radiation bomber at any moment. Don’t panic! It’s not harmful that much. Relax and go on reading. Every minute thousands of subatomic particles pierce our bodies with a terrible speed. This is not the "curse of modern life", nor is it a disaster from nature. Even if you move away from cities and settled in a powerless mountain village, you can not get rid of it. Because this radiation is completely natural!

As I said above, there's nothing to be scared of. Natural radiation in the environment was always part of the evolutionary process; From the very beginning, life has developed as an adaptation to repair the damage caused by radiation. It means we are fully adapted to it. There are several sources of natural radiation: radioactive elements on earth, radioactive elements in the air we breathe, and cosmic rays. The subject of my essay explains the effects of the last source I have spoken and the possibilities of exploiting it.

It Is Rainy Every Day. And Cosmic Rays Cause It to Happen

Space is not completely empty. It is a hard and dangerous environment. There are electrons and protons gushing out of solar explosions. Moreover, very high energy particles fill the space, coming from the depths of space, called "cosmic rays". Cosmic rays are not electromagnetic radiation. They are composed of nuclei of 90% proton, 9% alpha particle (helium nucleus), 1% electrons and heavy helium atoms. Cosmic rays have energies that can be said to be extremely high for particles, such as a few billion electron-volts. (For comparison, the energy of molecules in the air is 0.04 electron-volts, the energy of electrons in tube TVs is 20 000 electron-volt, the energy of an alpha particle coming from the decay of radioactive nuclei is a few million electron-volts). The particles accelerated in the plasma clouds in the depths of space travel in the space void without losing anything from their energies because they do not encounter friction. Those who meet the Earth collide with the molecules at the top of the atmosphere. As a result of these collisions, reactions between atomic nuclei create new and strange particles.The first product that emerges when cosmic rays strike the atoms of the atmosphere are particles called pions. These are three species, positively charged, negatively charged, and uncharged. Their lives are very short. Charged ones turn into two separate particles, decay, and the muon neutrino, decaying less than a hundred millionth of a second.

_{By Simon Swordy,Public domain, via Wikimedia Commons}

The uncharged pion is first decayed into two gamma-ray photons. They also produce electrons and positrons. All these particles fall into the earth like a rain.We know the electrons; the basic components of atoms. Positron is not an alien, it is an antiparticle of electrons. We can say positively charged electrons. Neutrino is also a fundamental particle. Neutrino enters from one side of the world and comes out from the other because there is hardly any interaction with the matter. Let's not add them to the account.

Muons, the main subject of this post, were discovered during the cosmic ray surveys in 1937. When the deviations in the magnetic field were measured, it was understood that the electric charges were the same as the electrons, but their masses were two hundred times more than the electrons and one-ninth of the mass of the proton.

The muons are fundamental particles, like electrons. So, as far as we know, there are no other building blocks in them. Proton and neutrons are not fundamental particles, they are composed of three quarks. However, unlike electrons, muons are unstable particles. Their average lifetime is only 2.2 microseconds (a billionth of a second). Because of this instability, and because we need a lot of energy to produce a new muon, there are no roles in our everyday life.

If we look at their short-lived lives, it is surprising at first glance whether we can detect the muons on the earth. Normally, a particle with a lifetime of about 1 / 500,000 of a second cannot have enough time to descend to the sea level below 100 kilometers from the upper part of the atmosphere. This is not because they cannot be fast enough. On the contrary, the muons produced by energetic cosmic rays are so fast, they travel almost at the speed of light. But even at the speed of light, they will only last a very short lifespan of five to six hundred meters.

There is no contradiction here, of course, only the effects of special relativity have not accounted for. In objects close to the speed of light, time passes slower than ours. On this count, the life of the "muon" extends for us and it is possible to remain without any decay until the particle reaches the earth.From the perspective of the muon, there is no question of a lifetime extension. But when viewed from the "window" of the muon, the distance to the earth is narrowed by Lorentz contradiction, which the particle can reach even in the short lifespan. Indeed, the fact that muons can be detected on earth is considered one of the experimental proofs of special relativity theory.

It’s So Interesting But These Muons And The Pyramids Are Somehow Related.

The Cosmic Rain is like a slow-pouring rain more than an intense heavy rain. There drops 1 muon per 1 cm² of an area in 1 minute on average. that is one or two muons per second, regularly in an area of your hand.

As they are charged particles, they are exposed to an electric field as they pass near an atomic nucleus. This, in turn, diverts their path slightly. They are very fast, so this deviation is not much, but if they pass through a dense material, they can follow a zigzag path with successive deviations, and they can decay and disappear without going too far.

Luis Alvarez (1911-1988) was an experimental particle physicist who devoted his scientific career to the perfection of particle detectors and received the Nobel Prize for Physics in 1968 in honor of his new discoveries.He had a very agile intelligence and he liked to apply physics knowledge to interdisciplinary problems. For example, he did an analysis of the 'Zapruder Film' that recorded Kennedy's assassination.Alvarez thought in 1960 to use particle detectors to determine if there were hidden rooms inside the Egyptian pyramids. The idea was simple and based on the same principle as the X-ray in the hospitals. Now imagine the thick and dense walls of the pyramids for a second. Muon particles that fall like rain can be somewhat inhibited by such dense substances.

_{By U S Government, Public domain, via Wikimedia Commons}

The thicker the wall, the greater the number of blocked particles. If we put a particle detector in the pyramid and measure the number of muons by turning this detector in various directions and find out that the number of muons coming from some directions is higher,

then we can understand that it is not a rock but space. By 1967, Alvarez had a new job. He worked with some American and Egyptian physicists and archaeologists. He put a muon detector into the Pyramid which is known as Kefren (the second largest pyramid after the Pyramid of Keops).

_{Img Source: pxhere.com, CC0 Public Domain}

The experiment could not be finished quickly because it needed to be left in place for months to allow muon counting at the required amount.Although the technical problems such as the deterioration of the detectors were overcome, the Six Day War broke out between Egypt and Israel as it began to be fully tested. Diplomatic relations between Egypt and the United States ceased. Alvarez and his friends had to return to their countries. Luckily, after months, the political climate was partly normal, but they could go back and continue experimenting.

If we talk about the end of the experiment; there appeared to be no space on the pyramid walls. This experiment is the first successful example of a method called muon transmission tomography. In fact, these experiments are still going on today. Some physicists and archaeologists are likewise scanning tomographies of the Mayan Pyramids.

This Technique Is Used For Volcanoes And Fukushima!

Our beautiful muons are actually doing a very good job. They also make it possible to understand how the inner structures of the volcanoes are. Because they can pass through unbelievably thick rocks almost without blocking.In fact, in a volcano, the process that takes place before the explosion is as follows: The molten magma slowly approaches the mouth of the volcano crater. If this gentle approach can be followed, it can be determined when the explosion will occur. This will be a great opportunity for people around that volcano to leave before the explosion takes place. But you know that things will not be that easy. Under normal conditions, there is no window to see what is in the volcano. But our beautiful, helpful muons are ready to work with us at this point.

As Alvarez did, it's easy to put a muon detector in a pyramid. But placing it in a volcano is not like that. It is not possible to do such a thing. You can not place anything into a volcano. For this reason, the detector is placed horizontally on the edge of the volcano. In this way, the muons coming from the horizon can be counted which are passed through the mountain. If the dense magma is raised in the mountain, the number of muons falling in the detector decreases, so the height of the lava column can be estimated.This technique was first developed by the Japanese. Researchers from Tokyo University, in 2007, displayed the top of Asama volcano. Following this success, the interiors of the Puy de Dome of France, La Soufriere of Guadaloupe, Etna and Vesuvius in Italy could be displayed in the same way.

_{By KDS4444, CC BY-SA 4.0, via Wikimedia Commons}

Muon tomography can also be used for nuclear power plant security. The cleanup of the Fukushima Daichi nuclear power plant, which was destroyed by a tsunami in 2011, is still underway. One of the most difficult tasks of this laborious task is to determine where the fused radioactive material is collected after liquefaction. Since radioactivity is at a very high level, it is impossible to get in and look inside; Even a robot cannot be sent in. Because there is a danger of radiation leakage from any door that opens. Without entering Fukushima, muon tomography technique is still in place to determine where the radioactive substance is.

Los Alamos National Laboratory (LANL), one of the USA's most important research laboratories, is working with Toshiba to prepare a muon detector that can be used in nuclear power plants. With such a detector it will be possible to determine where the radioactive material from heavy atoms is collected.

The biggest nightmare of border security is the secretive or inevitable abduction of nuclear fuel that can be used to build a bomb. Although borders are being searched, cargoes are scanned by various devices, smugglers can take precautions against these methods. Those who want to smuggle large quantities of radioactive material in a truck or container will hide them between the metal objects that will prevent them from viewing to make detection difficult. The missing substance may be placed in a lead box so that the emitted neutron or gamma rays cannot be detected.

_{By Schtone GFDL CC-BY-SA-3.0, via Wikimedia Commons}

Muon tomography provides a good solution to this problem. First of all, the muons are very energetic. They can penetrate deep into the material to be scanned. Other materials in the bag will not block them. (A typical muon with 3 billion electron-volts of energy can pass through a two-meter thick solid lead). Second, muons are a part of natural radiation and are always around. Thus, they do not create any additional health risks for the people in the vicinity during the scan, and the power requirements of the scanner devices are low. Their third advantage is that the material they pass through is precisely depended on the atomic weight of the material, so they can be used to detect particularly heavy radioactive atoms.

_{Img Source: pixabay.com}

Easy Explanation Of Muon Scattering Tomography

This event can be explained as follows. Muons deviate significantly when passing through near heavy atoms such as Uranium or Plutonium. If such a deviation is seen, it means that there is a body of heavy elements in the cargo. In such a case, the thing inside the cargo can be suspected and inspected.The detector system required for scattering tomography is more complex than that used in 'through' tomography. The volume to be investigated should have six separate particle detectors, and each face should have two detector plates.

A fast-descending muon from the top down passes first through the top two plates. During the transition, the detector causes ionization in the material. With this ionization, the detector's electronic part can detect that a muon has passed through a specific pixel. Because the muon is so energetic, he goes on without hesitation and goes through the second plate on the top. The difference between the two plate crossings, allows us to determine the direction of muon going. The going muon, like a bullet, passes through the material and reaches the bottom plate, and the same process is repeated there. We look at the difference in angle between the directions at the inlet and outlet, and using mathematical relations, we can see what is the material that will provide a deviation in this quantity.

It's a very basic principle, but it's not as easy as it looks because in practice it takes a lot of trouble. To detect such small deviations, you have to have very high-resolution detectors. Your Pixels need to be very, very small. That's why we use semiconductor detectors, which we can obtain high resolution.

Conclusion

Another problem in practice is that muons do not fall so much to earth. You do not have that much time to scan the cargo. You only need to finish this process in 1 or 2 minutes. Because if you want to scan for long periods of time, you'll expect a lot of muons to fall on the earth. In such case like this, millions of vehicles will collect in the back for making their luggage to be scanned. To overcome the 'short time' problem, it is necessary to develop very complex algorithms.At the time of commercialization, there will be a price tag of $ 1 million. Many countries will need this device for nuclear safety. Although there are still problems based on technology and production, it will surely be used at many customs control points after resolving these problems.

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REFERENCES

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