Cosmic rays reveal ancient burial chamber hidden under Naples – Ars Technica

The ruins of the ancient Neapolis necropolis lie about 10 meters (about 33 feet) below the city of Naples, Italy. But the site is in a densely populated urban area, making it difficult to conduct accurate archaeological excavations for those ruins. So a team of scientists turned to cosmic rays for help — specifically an imaging technique called radiography, or Muon tomographyAnd a burial chamber previously hidden underground was discovered, according to A The last paper Published in Scientific Reports.

As we reported, there is a long history of using muons in Image of archaeological structuresThe process is made easier because cosmic rays provide a steady supply of these particles. An engineer named E.P. George used them to take measurements of an Australian tunnel in the 1950s. But Nobel Prize-winning physicist Luis Alvarez put muon imaging on the map when he teamed up with Egyptian archaeologists to use the technique to search for hidden chambers in the pyramid of Khafre at Giza. Although it worked in principle, they didn’t find any hidden rooms.

Muon is also used Chase illegally moved Nuclear material at border crossings and monitoring of active volcanoes, hoping to detect when they might erupt. In 2008, scientists at the University of Texas, Austin, worked, trying to follow in Alvarez’s footsteps, reusing ancient muon detectors to search for possible hidden Mayan ruins in Belize. Physicists at Los Alamos National Laboratory have been developing portable versions of muon imaging systems to unlock the secrets of building the dome above Earth. Cathedral of Saint Mary of Venus In Florence, Italy, it was designed by Filippo Brunelleschi in the early 15th century. The dome has been plagued by cracks for centuries, and muon imaging can help conservationists figure out how to fix them.

In 2016, scientists used muon imaging Pick up the signals It points to a passage hidden behind the famous chevron blocks on the north face of the The Great Pyramid of Giza in Egypt. The following year, the same team discovered a mysterious void in another area of ​​the pyramid, believing it could be a hidden chamber, which was later painted using two different muon imaging Methods.

There are many different forms of muon imaging, but they all usually involve gas-filled chambers. As muons zip through the gas, they collide with gas molecules and emit a flash of light that the detector records, allowing scientists to calculate the particle’s energy and trajectory. It’s similar to X-rays or ground-penetrating radar, except that higher-energy muons occur naturally instead of X-rays or radio waves. This high energy makes it possible to image dense and thick materials such as the stones used to build the pyramids. The denser the imaged object, the more muons are blocked, which cast telltale shadows. Hidden chambers will appear in the final image because they block fewer particles.

Neapolis was a Hellenistic city in a mountainous region rich in volcanic rocks. This made it soft enough to carve out tombs, places of worship, or caves for housing. One such construction was the cemetery in what is now the Sanita district of Naples, used for burials from the late fourth century BC to the early first century AD. The site has been buried in sediment over time by a series of natural disasters, most notably floods Lava de Virginie (“Lava of the Virgins”). Unlike the lava that famously engulfed Pompeii, this “lava” was made up of mud and boulders that had broken off from the hills during heavy rains.

The exact size of the cemetery is unknown, but it likely contained dozens of tombs, each with multiple bodies. Four such tombs, now known as Ipogeo dei Cristallini, were discovered in the late 19th century under the di Donato family mansion on Via Cristallini. (Current owners Opening graves for public tours last year.) After the 1980 earthquake prompted a three-dimensional structural analysis of the area, two more burial chambers were discovered: Ipogeo dei Togati and Ipogeo dei Melograni.

These discoveries raised hopes that more hidden burial chambers would be found. Researchers at the University of Naples Federico II, the National Institute of Nuclear Physics in Naples, and Nagoya University in Japan believe that radiography would be an ideal way to do this. “Due to its non-invasive nature, this technique is particularly suitable for urban environments where applications for active inspection methods such as seismic waves or boreholes are unimaginable,” the authors wrote. They were based on their detectors nuclear emulsion technology; Emulsion detectors are very simple and compact and do not require an external power source.

The development of the nuclear emulsion from radioactive research in the early 20th century. Physicist Ernest Rutherford began using commercial photographic plates to capture alpha rays emitted by various radioactive materials, which cause the plates to darken. His colleague, Kinoshita Suikiti, modified the basic approach, preparing gelatin emulsion films with a high concentration of very fine silver halide grains for alpha particle detection. These grains act as sensors, which are triggered when a charged particle passes through the emulsion and loses its charge. Once recorded, the tracks become visible under a microscope after the plates are developed, allowing scientists to measure their location and orientation.

Nuclear emulsion was popular in the study of cosmic rays, which led to the discovery of pi-meson and parity violation in K-mesons. When more powerful particle detectors and accelerators came on the scene, nuclear emulsion fell out of use. However, it is still useful in some physics experiments (eg opera and CERN’s FASER Project) as well as medical, biological and archaeological applications.

The authors of the cemetery study used two reagent units, each containing a stack of four emulsion films sealed inside an envelope to control light and humidity, and left them in an underground vault (single-use aged ham) from March 10 to April 7, 2018. Once the exposure period ended Emulsions were developed the next day. For comparison purposes, they relied on a 3D laser-scanning spatial model of all accessible underground structures.

The radiographs revealed evidence (in the form of an increase in the expected number of muons) of a new underground structure, as well as enough information for the authors to estimate the size and location of this structure. The structure corresponds to a rectangular burial chamber, likely partially filled with rock and sediment. It measures 6.5 by 11.5 feet (2 by 3.5 metres) and is similar in structure to Ipogei dei Togati and Ipogeo dei Melograni. The authors believe that the burial chamber dates back to the late fourth / early third century BC, and may have been the tomb of a wealthy individual or family.

DOI: Scientific Reports, 2023. 10.1038 / s41598-023-32626-0 (about DOIs).