Muography lets scientists see through solid rock. It could help with carbon storage systems

By Tim Hornyak

At more than 4,500 years, the Great Pyramid of Giza is the oldest of the Seven Wonders of the Ancient World. But despite years of study, mysteries about its origin and purpose continue to deepen.

In 2017, a team of Japanese and French scien­tists announced they had studied the structure for two years and discovered that it contains a cavity some 30m long. To make this discovery, they used a power­ful new tech­­nique called muography that promises to open new areas of collaboration between the UK and Japan for scientific research and commercial applications.

Pyramid peeking

The discovery of two voids has been controversial, and some experts question their significance. With no way to access the cavities, it’s impossible to say what they may contain or why they were incorporated into the monument to Pharaoh Khufu, who reigned from 2589 to 2566 BC as the second pharaoh of the Fourth Dynasty of ancient Egypt. One theory is that they were designed to relieve weight from the roof of the Great Gallery, the passage that ascends to the King’s Chamber.

Those secrets may be revealed by muography, a technique that makes use of particles called muons, the heavier cousins of electrons. Muons are created when cosmic rays flying through space collide with air molecules in Earth’s atmosphere. Every square centimetre of our planet is showered with muons at all times. But as they move at near the speed of light and interact weakly with matter, we do not notice them. Compared with imaging techniques such as X-rays, muons are freely available and can be found just about anywhere.

“High-energy muons can penetrate as far as 2km within solid rock and, therefore, similar in prac­tice to X-ray machines, can be used as an imaging tech­­ni­que”

Hiroyuki Tanaka

“High-energy muons can penetrate as far as 2km within solid rock and, therefore, similar in prac­tice to X-ray machines, can be used as an imaging tech­­ni­que to see within gigan­tic objects such as volca­­noes, pyramids and nuclear reactors,” Hiroyuki Tanaka, a professor and director at The University of Tokyo’s International Muography Research Organization (MUOGRAPHIX), told ACUMEN. “Along with being capable of imaging potential minerals or energy resources under­­ground, muography is also a non-destructive technique”.

Tanaka has been studying muography for decades and is a pioneer in the field. He has collaborated with other researchers—including those from the UK—to study a range of uses for muography. These include scanning under­ground water tables as well as seismic fault zones and volcanoes—an important application for a seismically active country such as Japan, which is home to the still-active Mount Asama.

Commercial value

Aside from shedding light on geological features, muography also has industrial applications. In 2016, Japanese researchers installed a muon detector—about the size of a washing machine—in the Unit 2 reactor of the crippled Fukushima Daiichi Nuclear Power Plant. The researchers were able to get a virtual peek inside the highly radio­active pressure vessel and deduce the presence of nuclear fuel debris.

“Social infrastructure—including silos for nuclear waste, bridges, highways, underground pipe systems—constructed in the 1950s is getting old and needs to be maintained, but there was no practical method to evaluate the degree of ageing,” explained Tanaka. “Muography can offer a completely new visualisation tech­nique for non-destructive evaluation and testing of these structures. Muography will, in particular, contri­bute to industry, innovation and infra­structure for global safety, part of the United Nations Sustainable Development Goals (SDGs)”.

Read the rest of the article at BCCJ Acumen.