Paarl Africa Underground Laboratory (PAUL) is envisaged being constructed inside a the Huguenot Tunnel connecting the towns of Paarl and Worcester in the Western Cape Province of South Africa.
The PAUL will house various scientific equipment in order to do research on, amongst others, the following topics:
- search for Dark Matter,
- low radiation measurements with many areas of application,
- biology and radiation damage studies, and
- detection of antineutrinos (from Koeberg Nuclear Power Station)
In order to reduce the background from cosmic rays the PAUL should be located where the rock overburden is maximal. The underground lab facility will be under the 1300 m Du Toitskloof mountain with ∼ 800 m of rock overburden for the Huguenot tunnel, see Figures 1 and 2.
Muons: Figure 1: The Huguenot-Tunnel: Pictures of the North-Bore service tunnel (left) and the South-Bore Road tunnel (right). 2024
Figure 2: The Huguenot-Tunel crossing the Du Tooitskloof mountain.
A muon detector developed by Jacques Marteau, physicist at IP2I Lyon France, has been loaned to universities in South Africa. The project involves measuring the background and muon flux in the tunnel and imaging the bedrock geology above and around the tunnel. This will determine the criteria for constructing PAUL in a tunnel and will be important for the design of the future detectors.
The muon detector arrived in December 2023 where it was put into service at Stellenbosch University (SU). A series of measurements “open sky” at SU and the University of Western Cape (UWC) were carried out from December 2023 to March 2024. Then since April at three key locations in the tunnel, Figures 3 and 4.
Figure 3: Diagram of the tunnel under the Du Toitskloof mountain and the 3 reference points (Vehicle Cross Cut): Until October 2024 at VCC2 and 200 m towards VCC1 where the cosmic flux measurements were carried out, at the point of maximum overload of the rock. Then at VCC3 since October 2024.
Figure 4: The muon detector in the service tunnel: (left) at VCC2; (right) 200 m towards VCC1.
The measurements will continue until June 2025. A series of analyses and other studies (gravimetry, gamma rays, neutrons, nature of the rock around the maximum over burden) will be carried out to determine the characteristics of the mountain and the tunnel in order to participate in the definition of the future laboratory.