The Great Pyramid, or Khufu's Pyramid, was built on the Giza plateau in Egypt during the fourth dynasty by the pharaoh Khufu (Cheops), who reigned from 2509 bc to 2483 bc. Despite being one of the oldest and largest monuments on Earth, there is no consensus about how it was built. To understand its internal structure better, we imaged the pyramid using muons, which are by-products of cosmic rays that are only partially absorbed by stone. The resulting cosmic-ray muon radiography allows us to visualize the known and any unknown voids in the pyramid in a non-invasive way. Here we report the discovery of a large void (with a cross-section similar to that of the Grand Gallery and a minimum length of 30 metres) situated above the Grand Gallery. This constitutes the first major inner structure found in the Great Pyramid since the nineteenth century. The void, named ScanPyramids' Big Void, was first observed with nuclear emulsion films installed in the Queen's chamber, then confirmed with scintillator hodoscopes set up in the same chamber and finally re-confirmed with gas detectors outside the pyramid. This large void has therefore been detected with high confidence by three different muon detection technologies and three independent analyses. These results constitute a breakthrough for the understanding of the internal structure of Khufu's Pyramid. Although there is currently no information about the intended purpose of this void, these findings show how modern particle physics can shed new light on the world's archaeological heritage.

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Khufu’s Pyramid is one of the largest archaeological monument all over the world, which still holds many mysteries. In 2016 and 2017, the ScanPyramids team reported on several discoveries of previously unknown voids by cosmic-ray muon radiography that is a non-destructive technique ideal for the investigation of large-scale structures. Among these discoveries, a corridor-shaped structure has been observed behind the so-called Chevron zone on the North face, with a length of at least 5 meters. A dedicated study of this structure was thus necessary to better understand its function in relation with the enigmatic architectural role of this Chevron. Here we report on new measurements of excellent sensitivity obtained with nuclear emulsion films from Nagoya University and gaseous detectors from CEA, revealing a structure of about 9 m length with a transverse section of about 2.0 m by 2.0 m.

Muon radiography is nondestruction research technic for large structure like a pyramid, volcano, blast furnace. The technology measures the density length (=material density × path length) by PoS(KMI2017)075 Development of nuclear emulsion with using thick type plastic base for improvement of angular accuracy MANABE Yuta

A nuclear emulsion is a three dimensional tracking detector which is able to record minimum ionizing particles with micrometric accuracy. We are developing the nuclear emulsion for observation of cosmic rays and its analysis techniques. We have been applying nuclear emulsions to cosmic ray radiography for measuring the inner structure of nuclear power plants, volcanoes and so on. Since 2015, we have been observing cosmic rays inside the pyramids, which are the Bent Pyramid at Dahshur and Khufu's Pyramid at Giza, in Egypt through ScanPyramids. In this project, we produced nuclear emulsions and installed them into the pyramids to measure cosmic ray muons. We observed over ten million muons passed through the pyramids and reconstructed the angular distribution of detected muons. Through the analysis, the validity of cosmic ray radiography for investigation of a pyramid was confirmed and the new space inside the Khufu's Pyramid was discovered. In this paper, nuclear emulsions for the observation and latest results are described.

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