FROM LEFT: T. TIBBITTS; NAGOYA UNIV.24 SCIENCE NEWS | April 23, 2022L. BONECHI, R. D’ALESSANDRO AND A. GIAMMANCO/REVIEWS IN PHYSICS2020FEATURE |MUONS OPEN DOORS
unexpected rooms, but proved that the technique
worked.
Still, the idea took time to take off, because muon
detectors of the era tended to be bulky and worked
best in well-controlled laboratory conditions. To
spot the muons, Alvarez’s team used detectors
called spark chambers. Spark chambers are filled
with gas and metal plates under high voltage, so
that charged particles passing through create trails
of sparks.
Now, thanks to advances in particle phys-
ics technologies, spark chambers have largely
been replaced. “We can make very compact, very
sturdy detectors,” says nuclear physicist Edmundo
Garcia-Solis of Chicago State University. Those
detectors can be designed to work outside a care-
fully controlled lab.
One type of resilient detector is built with plas-
tic containing a chemical called scintillator, which
releases light when a muon or other charged par-
ticle passes through (SN Online: 8/5/21). The light
is then captured and measured by electronics.
Later this year, physicists will use these detectors
to take another look at Khafre’s pyramid, Kouzes
and colleagues reported February 23 in the Journal
for Advanced Instrumentation in Science. Compact
enough to fit within two large carrying cases, the
detector “can be carried into the pyramid and then
operated with a laptop and that’s all,” Kouzes says.
A different but particularly low-maintenance
type of detector, called a nuclear emulsion film,
was crucial to uncovering the Great Pyramid’s
hidden void in 2017. Nuclear emulsions record
particle tracks in a special type of photographic
film. The detectors are left in place for a period of
time, then brought back to a lab for analysis of thetracks imprinted in them.
Particle physicist Kunihiro Morishima of Nagoya
University in Japan helped discover the secret
chamber through work on an international proj-
ect called ScanPyramids. “Nuclear emulsions are
lightweight, compact and do not require a power
supply,” he explains. That meant that multiple
detectors could be placed in prime viewing loca-
tions in one of the pyramid’s rooms, the Queen’s
Chamber, and a small niche next to it. The detec-
tors’ measurements were supplemented with
plastic scintillator detectors inside the Queen’s
Chamber, and gas-based detectors outside
the pyramid.
Since the discovery of the void, Morishima and
colleagues have been taking additional measure-
ments to better sketch out its properties. The team
placed emulsion detectors in 20 locations in the
pyramid, as well as gas detectors in several differ-
ent spots. Using their new array of instruments,
the researchers determined that the void is over
40 meters long. Its purpose is still unknown.
A more extensive survey of the Great Pyramid,
placing much larger detectors outside the pyr-
amid, is being planned by another team of
researchers. The detectors will be periodically
moved to measure muons from multiple angles,
the team reported March 6 in the Journal for
Advanced Instrumentation in Science. The result,
says co author and particle physicist Alan Bross
of Fermilab in Batavia, Ill., will offer a 3-D view of
what’s inside.
Pyramids in other parts of the world are also get-
ting closer scrutiny. Garcia-Solis and colleagues
are now planning muography of the Maya pyramid
known as El Castillo at Chichén Itzá in Mexico.A look inside
Scientists placed three
different types of muon
detectors in and around
the Great Pyramid to
map out the density of
the structure and search
for hidden chambers.
SOURCE: K. MORISHIMA ET AL/
NATURE 2017Nuclear emulsion detectors are compact enough to be installed in
a small niche next to the Queen’s Chamber in the Great Pyramid.Grand Gas detectors
GalleryScintillator
and nuclear
emulsion
detectorsKing’s
ChamberQueen’s
ChamberSubterranean chamberSouth Northmuons.indd 24muons.indd 24 4/6/22 9:15 AM4/6/22 9:15 AM