Review of Muography

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Review of Muography

• Hiroyuki Tanaka

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Particles for Earth Studies
The investigation into the basic properties of
the earth has been a particularly active area of
research in the field of solid earth science, and
has mainly been conducted by using the "classical
probe" such as seismic waves.
Proceeding into the 21st century, research may
expand to utilize quantum probes, such as muons
and neutrinos towards solving current questions
in solid earth science.
We are currently investigating the possibility
that these new quantum probes may provide another
method for surveys in solid earth science.
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quantum probes
photon
muon
neutrino
(x-ray) photography
neutrinography
muogrphay
Topic of this talk
Scale
Mm
m
km
Since its original discovery by Rontgen in 1895,
the x-ray has played a prominent role in
anatomical studies in the medical field.
Despite of the great motivation to survey the
earths interior, we now know that x-rays are not
sufficiently penetrative to successfully target
geophysical-scale objects.
Our current knowledge about the cross sections of
the muon and the neutrino with matter solves the
problem of how to study the interior of objects
beyond the inspectable size limit of x-rays.
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Utilizing muons that arrive at a near-horizontal
angle, muography can be applied to
kilometer-sized objects located at elevations
above where the detector is placed.
Position Sensitive Plane (PSP)

Pb
Fe
Fe
muon

N1 Ny
N1 Nx
What are muons? Primary cosmic rays reacting with
the nitrogen and oxygen nuclei at the top of the
earths atmosphere produce muons
Fe Pb
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The reactions of muons with matter fall
completely within the framework of the standard
model of particle physics.
Thickness (density) of the rock determine the
amount of muons that successfully pass through
the rock and reach the detector.
The penetrating flux refers to the number of
muons that have enough energy to continue
traversing through a given thickness of rock.
By calculating the muon path length multiplied by
the average density along the muon path we find
the density length in units of kmwe
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The objective of muography is to detect a muon
signal efficiently in order to take a
radiographic image of the target object.
Detectors designed for muogaphy measurements
utilize nuclear emulsion, gaseous and
scintillation technologies.
The goal is to figure out how existing
technologies can be adapted to design a device
that can survive in a variety of environmental
restrictions
but each detector has cons and pros
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50 microns
The nuclear-emulsion-based muon detector has
major advantages of both superior high resolution
and an ability to run without any electric power.
It is a practical detector to use particularly
when the commercial electricity is not available.
The nuclear emulsion needs to be developed like a
regular photographic film.
Nuclear emulsions are designed to create a single
image within an observation time
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The scintillation detector has the potential to
take time-dependent multiple images.
The detector consists of two or more PSPs. Each
PSP consists of Nx and Ny adjacent scintilltor
strips which together form a segmented plane with
Nx x Ny segments. All the vertex points of the
strips that output the signals are considered to
reconstruct the muons path, but only the
vertices along one straight line are exploited.
The scintillator is the most essential component
of the scintillation detector since it
efficiently facilitates the conversion of muon
events to photons.
Photons are then transferred to the PMT so that
the electric current signals can be measured.
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In 2006, the Tokyo-Nagoya collaboration team
first imaged the internal structure of the peak
region of Asama volcano.
In 2009, additional muography data from Asama
supported conclusions of the 2006 survey
Muography captured images both before and after
the 2009 Asama eruption.
The image was reconstructed from the muon
trajectories recorded in the nuclear emulsion
detector.
The scintillation detector was accessed from a
remote PC
The image was interpreted that magma did not flow
up the pathway in the 2009 eruption, and instead,
high-pressure vapor simply blasted through the
old magma deposit that acts as a plug of the
pathway.
The superior spatial resolution capabilities of
muography were confirmed.
This low-density region has been interpreted as a
magma pathway that is plugged by magma deposited
on the crater floor. We can expect that if magma
ascends and gas is released from the
depressurized magma in the pathway of Asama
volcano, high gas pressure will cause the plug to
explode, rapidly releasing fragments of the old
magma deposit.
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The actual magma body was also imaged with
muography under the Tokyo-KEK-AIST collaboration
Muography imaged a large, shallow depth,
low-density region existing beneath the crater
floor.
The Satsuma-Iwojima volcano continuously
discharges large amounts of volcanic gasses
without significant magma discharge.
With the assumption that the conduit has a
cylindrical shape, it can be inferred that the
density corresponded to liquid water.
One of the proposed mechanisms of this continuous
gas discharge is conduit magma convection
(Stevenson and Blake, 1998).
However, liquid water is not likely to exist
below the hot crater floor, where hot fumaroles
are observed with the maximum temperature gt
800oC.
In this hypothesis, a magma conduit is connected
to a deep magma chamber and a "degassing"
phenomenon propels convection.
Muography measurements have also revealed a
low-density region at the uppermost point of the
magma conduit, substantiating the convection
models prediction of degassing magma being
present at this location.
A continuous supply of non-degassed magma from
the magma chamber ensures that there is
compensation for the degassed magma and the cycle
continues.
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Various lava domes were also muographically
imaged.
DIAPHANE collaborators targeting the lava dome of
La Soufurier, measured the region that may
indicate a high density rock layer generated in
between the hydrothermal region and deeper
regions. We would expect the region to be over
pressured when the geothermal energy flux
increases, functioning similarly to the plug
observed in Asama volcano.
TOMUVOL experiment has created a muographic image
of Puy de Dome. As a result, the shallow
structure of the dome was clearly imaged
revealing two independent higher density regions
indicated near the top of the dome.
The image of Showa-shinzan lava dome taken by the
Tokyo-Nagoya-Hokkaido team in 2006 is shown for
comparison. The magma pathway is plugged with
magma. The structure beneath the Puy de Dome is
unclear mainly due to low statistics. However, if
the higher density region indicated beneath the
dome is the magma pathway of Puy de Dome, it
corresponds to the structure of Showa-shinzan.
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Three factors intrinsically affect eruption
prediction starting time, location and the
magnitude of the eruption (which is directly
related to how long the eruption will last).
The first factor, starting time, is increasingly
easier to predict based on recent progress of
technologies in monitoring volcanic tremors and
land deformation.
However it is still very difficult to accurately
forecast the latter two factors. An important
first step towards addressing these factors has
been achieved with the previously mentioned
muographic images, as measured before and after
the 2009 Asama eruption
We anticipate that as muography develops, it will
become capable of estimating the eruption
sequence with increasing precision. Visualization
of the internal structure of a volcano with
muography provides unique information. By
accumulating information about worldwide volcanic
eruption events into muography databases, we will
increase the reliability of this method towards
this application.