NEXUS WP2 - France

vendredi 6 févr. 2026, 08:30 → 10:00 Europe/Paris

Fairouz Malek (LPSC-Grenoble, CNRS-IN2P3, UGA)

1 Muography activities (T2.1/T2.2/T2.3)

Commitment from Lyon Team (Jacques)
- write a paper on the 2024-2025 muon measurements (Matias, JM) ;
- build a mobile muon detector of smaller size wrt the one we used last year and which had the main advantage of existing (typically we target a 60cmx60cmx60cm detector) (Jean-Christophe, JM) ;
- perform a measurement campaign, coupled ideally with gravimetry measurements (involving geophysicists, from SU ? Wits ?) to improve the quality of the 2024 campaign (Matias, Jean-Christophe, JM) ;
- join the measurements with the ones of our SU colleagues developing their detectors (to perform 3D analysis) (Matias for analysis, Jean-Christophe for tech transfer if needed) ;
- leave the detector on site for long time series, implications on the physics of the atmosphere etc (Matias for analysis, JM for data quality check).

2 Tunnel caracterization (T2.7)

3 Characterization and measurement of neutrons spectral and flux (T2.4)

4 Radon and other Gamma measurements (T2.5/T2.6)

5 Work Package 2

Task 2.1 (O2.1) Measurement of angular muons spectrum.
Measurement of a precise angular muon’s spectrum. Simultaneous measurements by several emulsion detectors located in different positions are possible in the tunnel where the future South African laboratory (PAUL) will be located. Combined measurement of emulsion and electronic detectors can be performed.
We propose to perform similar measurements in other ULs (UKRI, SURF, LSC).

Task 2.2 (O2.1) Geophysical measurements.
Installation of a permanent muon monitoring station to perform geophysical measurements (joint gravimetry inversion + hydrological studies) to characterize the Huguenot Tunnel at maximum overburden for the future PAUL facility design and study.

Task 2.3 (O2.1): Installation of muons detector.
Development of a local muon detector system in South Africa. As part of this objective, SU also recognizes this as an opportunity to train students and ensure knowledge and skills transfer (WP5). The network of existing UL expertise, in especially European institutions, offers an ideal channel for staff exchange wherein staff and students can be trained in the best measurement techniques, tomography, technical know-how of muon detectors and detector development.

Task 2.4 (O2.2): Characterization and measurement of neutrons spectral and flux.
The neutron spectral and flux characterization in an underground laboratory is one of the most important measurements to be performed to understand the background of any rare event detector installed in UL. The LPSC (CNRS-IN2P3) has developed a directional neutron spectrometer, a neutron flux monitor detector, and other complementary detectors able to perform a fast and thermal neutron characterization of UL, such a Spherical Proportional Counter (SPC) and He-3 counters. The LNGS has developed a new method for precise measurement of directional and energetic spectrum of neutrons in sub-MeV using nuclear emulsion detector (NIT: nano imaging tracker). We will perform neutron characterization in South-Africa (Huguenot-Tunnel and the future PAUL), at SURF and at SNOLAB using all these new technologies. SU in collaboration with CNRS-LPSC-LSM is already planning to construct and install an SPC-neutron detector to measure the neutron flux in South Africa in the Huguenot tunnel. To ensure the long-term sustainability and autonomy of the South African team, we aim also to train students (WP5). A PhD student from SU has already started to work on the subject and had the opportunity to be trained on the instrumentation and the simulation at LSM in 2024.

Task 2.5 (O2.3) Measurement of radon level.
The important issue of radon exhalation from materials used in the detection systems of low activity experiments is addressed in WP1. However, the radon gas concentration in the laboratory from exhalation from the walls of an underground laboratory (UL) is also of great importance. For the new PAUL laboratory in South Africa, the radon level in the present road tunnel has been measured and found to be relatively low, but the closed environment of the laboratory could be more challenging. Secondments are necessary to consider the best practice in the ULs in Europe and to support measurements in South Africa.

Task 2.6 (O2.3) Measurement of gamma background.
Gamma rays from environmental radioactivity (40K plus the 238U and 232Th series) is an important source of background in underground laboratories. These gamma rays are of relatively low energy (up to 3.5 MeV) compared to the cosmic muon energies, but the underground experiments still need to be shielded from these rays. We propose to measure the gamma radiation from the rock faces in different places in the Huguenot Tunnel to test what shielding is required for the future PAUL facility. Since the Paarl Mountain contains granite rocks, this needs to be done carefully.

Task 2.7 (O2.4) Design and study of the future UL in South Africa.
The geotechnical layout of the tunnel in which the future PAUL facility is proposed to be constructed is unique in layers presented and widths. However other UL would have faced similar challenges when preparing construction methodologies, tie-ins to operational tunnels and how the co-operation between the different service providers are managed. Staff exchange visits are required to consider the best practice in the UL in Europe to understand the different construction approaches undertaken and best options for South Africa. The design and engineering consultants have provided some recommendations but there is a need for knowledge exchange on construction methodology and tunnel management and other information relevant for the future facility.