The French National Research Agency (ANR) annually develops an Action Plan that outlines research priorities and funding instruments. The agency’s roadmap for the coming year, this document is drawn up in consultation with research stakeholders (the five Alliances, the CNRS and the Ministry in charge of Research and Innovation, which coordinates interministerial action between the ministries concerned) in line with the National Research Strategy (SNR).

A pioneer project in muography in France

The DIAPHANE project was initiated in 2008 by a collaboration between several academic institutions, experts in particle physics on the one hand and in geophysics on the other hand:

• Institut de Physique Nucléaire de Lyon, IPNL, UMR 5822, Université de Lyon, CNRS-IN2P3
• Géosciences Rennes, OSUR, UMR 6118, Université de Rennes, CNRS-INSU
• Institut de Physique du Globe de Paris, IPGP, UMR 7154, Université Sorbonne Paris Cité, CNRS-INSU

It was this project that introduced muon tomography in France after trials in the field of archaeology in Egypt by an American team (Alvarez, 1970) and volcanology in Japan (Nagamine, 1993).

The project was initiated to study the active dome of the Soufrière in Guadeloupe. It went well beyond the scope of this study to allow the validation of technological choices, methodological developments and valorization in different geophysical fields:

• characterization of geological layers in a landfill or long-term storage issue
  • application for the downstream of the nuclear power cycle (Mont-Terri underground laboratory)
  • application to CO2 storage (Mont-Terri underground laboratory)
  • characterization of the dynamics of a hydrothermal system
  • methodological development through live monitoring of the contents of a water tower
  • application to hydrogeology (Tournemire underground laboratory, Rustrel low noise underground laboratory)
  • application to the study of geothermal sources (Soufrière)
• characterization of an urban subsoil
  • application to the detection of anomalies in the subsoil (Croix-Rousse tunnel in Lyon)
  • application to the reconnaissance of the progress of a tunnel boring machine (digging of line 15 as part of the Grand Paris Express)
• non-invasive non-destructive testing (NIND) of the contents of industrial plants
  • application to ArcelorMittal’s blast furnaces in Fos/Mer
  • application to ORANO evaporators in La Hague
• CNIND of Archaeological Structures: Application to Greek Mounds
• characterization of atmospheric parameters
  • application to the measurement of effective atmospheric temperature (Mont-Terri underground laboratory)
  • application to the detection of rare events such as sudden stratospheric warming (Mont-Terri underground laboratory)
  • application to the development of atmospheric muon flux models

Technological choices

The muon detectors developed in the framework of the DIAPHANE project are plane trajectographs with a plastic scintillator. The trajectory of the particle is reconstructed from the data of at least two pairs of coordinates (X,Y). The spatial resolution is constrained by the segmentation of the front and back planes. A third central plane is added to eliminate fortuitous coincidences. The configuration of the trajectographs has evolved, the first version V1 being based on a segmentation of the extreme planes into 16×16 channels, the second version V2 on a segmentation of these planes into 32×32 channels for the same active area. The central plane is 16×16 channels in both versions.

The optoelectronic reading chain uses a multianode photomultiplier and a « smart sensor » acquisition type developed at the IPNL. The self-triggered electronics allows amplification, reading, time marking and digitization of analog signals, and the shaping, compression, temporary storage and transfer of digital signals.

The on-board reading system includes a processor, a clock synchronization card, a network switch, a relay system controlled in an independent box referenced as CTRL BOX.

The system operates on independent power supply if required (solar, wind, heat pump). A WiFi type network connection on POE ensures the possibility of remote control.

Total production :

• 18 shots of 16×16 channels [pixels 5cm×5cm].
• 12 shots of 32×32 channels [pixels 2.5cm×2.5cm].
• → 10 active telescopes (4 V1, 6 V2)

Two special detectors have been built:

• a small “mini-telescope” trajectograph to instrument a fault in the Soufrière (3 planes 10×10 channels)
• Cylindrical geometry trajectograph to instrument a borehole (62 reading channels)

Figure 1 – Top: photo of the inside of a V1 (left) and V2 (right) detection plane. Bottom: schematic diagram of a complete V1 telescope (left) and a complete installation (right). Source: DIAPHANE.

From detection to image

The use of muon tomography in non-invasive and non-destructive testing.
The observable quantity is the opacity, measured in g/cm², which represents the density of the crossed material (in g/cm³) integrated along the trajectory of the particle.

An example of muography in volcanology is given in Fig.2. The muon detector placed on the side of the volcanic structure measures the flux of muons crossing in all accessible directions (in red). The comparison with the theoretical flow, in the absence of obstacles, gives access to the opacity of the structure. This phase of analysis corresponds to the direct problem.
To go back to the material density distribution inside the structure, we introduce a priori knowledge about the target, in particular its topography, since a given opacity value, product of two variables, can be obtained by multiple combinations. This phase of analysis constitutes the inverse problem, whose solutions are the most probable distributions of matter within the target. The reconstructed density scale map is given in Fig. 1.

Figure 2 – Principle of muography applied to the study of the domes of active volcanoes and reconstructed density map: the blue zones correspond to the least dense zones, the red zones to the most dense zones.

The measurement of the flow of incident muons as a function of time makes it possible to take X-rays at different times and to perform functional imaging of the target by looking at the temporal evolution of the reconstructed density. This capacity to monitor a target has many applications both in an industrial context – emptying / filling of tanks, flow analysis, gauge controls, injection / replacement of material etc. – and in a geological context – geothermal, hydrogeology, dynamics of a hydrothermal system etc. – and in a geological context.

In the particular context of volcanoes likely to erupt into water (explosion of a cavity mainly under vapor pressure), we have demonstrated the feasibility of a temporal monitoring of the water content of the dome, the drop in density in a given area signalling the vaporization of water initially in liquid form (Fig.3, left).

Imaging by muon absorption does not escape the problem of solution degeneration when only one shot is available. Indeed the measurement of an opacity value, convolution of a density by a length can correspond to different realizations: a long trajectory in a low density medium can have the same opacity as a short trajectory in a very dense medium.

To solve these problems, one can either multiply the shots around the target, or couple the muon tomography measurements with other geotechnical techniques, which allows to generate 3D images, or more simply to switch from radiography to scanner. An example of a result obtained by coupling between muon tomography and gravimetry is given in Fig.3, on the right.

Figure 3 – Left: temporal variation of the muon flow through the Soufrière dome. Right: Sections of a 3D image of the dome made by “muon-gravimetry” coupling. Source: DIAPHANE.

Soufrière de Guadeloupe (French West Indies)

Objectives: structural imaging of the active dome, study of the dynamics of the hydrothermal system, methodological developments, coupled geophysical measurements, modeling of the dome destabilization constraints, hazard management, stations that can be integrated into a monitoring network.

Dates: July 2010 – experiment in progress

Academic funding (BQR, ANR)

Detectors: progressive instrumentation of 6 sites around the dome: Mule Savannah, Matylis, Split Rock, August 30 Fault, Southwestern Savannah, Northern Slot:

• 2010 – 2014: a V1 mobile detector moved to several sites
• 2015: 3 V1 detectors + mini-telescope deployed around the dome
• 2016: 5th detector (V2)
• 2017: 6th detector (V2, first instrumentation of the North Slot site)

Complementary instrumentation:

• permanent system of geotechnical probes at the top of the dome:
  • temperature sensors
  • geophones (seismicity)
  • magnetometers
• temporary use of gravimeters for coupled measurements

Main methods developed:

• Bayesian inversion,
• filtering of the upward flow by time of flight analysis,
• coupled measurements (with gravimetry, electric tomography, seismicity)
• temporal analysis in main components
• highlighting of mass transfers within the hydrothermal system
• 3D structural imaging

Figure 4 – Installations on the Soufrière de Guadeloupe. 1. 30 August fault (mini-telescope). 2. Matylis (V1). 3. Reconstructed density map. 4. Temporal monitoring by zones: evidence of an abrupt increase in muon flux correlated with seismicity. Source: DIAPHANE.

Ongoing

Generic call for proposals 2019

• NEWFUN (NEW energy FUnctional for heavy Nuclei)
• MEGaMU (Monitoring with ERT Gravimetry and Muons)

Generic call for proposals 2018

• BAMBI (Beta-particle Attachment to Molecules of Biological Interest)
• VISIONs (Vibrations and losS In amorphous OptIcal coatiNgs)

Bilateral call for proposals ANR – JST 2018

• QuantumFilters (Manipulation of an optomechanically coupled oscillator using a quantum filter)

Generic call for proposals 2017

• PROFILE (PRObing the aqueous interface of a Ionic Liquid during Extraction)

Ended

Generic call for proposals 2015

• EXSQUEEZ (EXperimental SQUEEZing for optomechanics)

Generic call for proposals 2014

• DIAPHANE (Functional and Structural Imaging of Volcanoes with Cosmic Rays)
• CHONRAD (RADiosensitizing nanoparticules for therapy against CHONDrosarcoma. A preclinical proof of concept.)

White call for proposals 2013

• FastTRACK (Development of a fast processing electronics for track trigger for Hadron Collider Experiments)