A revolutionary approach to observing matter, time and place - Research article showcases the possibilities of muography

This novel technology of the future is called muography. It is already in use, and the industry is on the upswing. Muography helps tackle many technical problems of global and even space-reaching scales.

The study was just published in the prestigious journal Nature Reviews Methods Primers. It provides an extensive review of new developments in muography and gives a glimpse of the new directions this young field is branching towards.

A new type of X-ray vision

Marko Holma, a researcher at the University of Oulu who has worked with muography for many years, is one of the many authors of the international study. He is also the CEO of Muon Solutions, a company developing muography. This startup originated from the research projects of the universities of Oulu and Jyväskylä in 2016 and develops muographic density imaging systems mainly for the mining industry's needs. The company strives to make the industry more sustainable and responsible.

- Muon imaging is one of the many methods of muography. It is easily compared to X-ray imaging, in the sense that both techniques are used to distinguish more and less dense areas from each other. However, in muon imaging, we just passively look at harmless muons that naturally zoom down from the sky. They help us see through objects up to kilometers wide, without dangerous radiation or lead aprons. Muons are totally safe and do not disturb the target, Holma describes.

From groundwater surveys to scanning shipping containers and monitoring volcanoes

Muon imaging is good for more than just scanning rocks. It can be used to monitor bridges and tunnels, as well as to scan ruins and archaeological sites. Muon imaging has been utilized in the search for previously unknown chambers in pyramids. The technology works in groundwater surveys and has been used to look inside storm clouds. It even helped notice a tsunami wave caused by a distant underwater volcanic eruption. Large muon imaging devices are used at ports of entry to safely see through shipping containers and vehicles.

In Japan, muon imaging is used to continuously monitor active volcanoes. This technique aids in detecting the movements of magma deep inside the volcano. It provides an advance warning system of a possible upcoming eruption. However, a muographic imaging device must be placed either under or to the side of the target, making the technique best suited for large central volcanoes. Many volcanic regions, such as Iceland, also harbor lower-relief eruptive fissure systems, where muographic monitoring would not be that easy.

From positioning technology to clock synchronization

Muon positioning systems can reach an accuracy of centimeters. They are especially suitable when the coverage from satellite positioning systems is patchy or non-existent. Such places include, for example, indoor spaces, underground tunnels and mines, and underwater environments.

Muons can also be used to synchronize and calibrate precise clocks. The particles are useful in encryption techniques, coding and transmission of data, and encryption key storage. Muons are suitable as a guarantee of wireless security and the basis of cloud-based authentication systems.

Muography allows the development of many applications that previously seemed impossible

Muons are elementary particles similar to electrons, though 207 times heavier. They are formed at altitudes of 15–25 kilometers, as cosmic rays coming from space collide with atoms in our atmosphere. This creates a continuous rain of muons travelling downwards at almost the speed of light. At sea level, about 150–200 muons pass through an area of one square meter every second. They even penetrate the bedrock, passing down to a depth of roughly one kilometer.

Good penetration, extremely fast speed, and an uninterrupted flow of particles make muons very useful for many purposes.

Muography is a young field. Its theoretical foundations were laid already in the 1960s, but the technology has matured enough for practical use only in the last 10–15 years. The sector has grown quickly, especially in recent years. Muons have become an efficient and versatile tool that can be used to implement many technical solutions that previously seemed impossible. Best of all, these technologies are similarly applicable around the globe, regardless of latitude or the time of year or day. The most notable advantages of muographic methods are their safety, environmental friendliness, and low energy consumption.

Muon imaging has even been projected to be of great help outside our own planet. Scanning the internal structures of the Moon, Mars, and asteroids with muons may prove invaluable in our future conquest of space.

Article:
Hiroyuki K. M. Tanaka ym. 2023. Muography. Nature Reviews Methods Primers.