Natural radionuclides as background sources in the Modane underground laboratory

Area of Science:

• Nuclear and particle physics
• Astrophysics
• Environmental physics

Background:

• The Modane underground laboratory (LSM) offers a low-background environment crucial for sensitive experiments.
• Understanding background sources is vital for accurate scientific measurements.

Purpose of the Study:

• To identify and quantify dominant background sources at the Modane underground laboratory (LSM).
• To characterize contributions from cosmic rays, muon-induced neutrons, and environmental radionuclides.

Main Methods:

• Analysis of radioactive contamination in construction materials.
• Assessment of radon contamination in laboratory air.
• Quantification of neutron production from (α, n) reactions and spontaneous fission.

Main Results:

• Radioactive contamination of materials and radon are significant background contributors.
• Neutrons from (α, n) reactions in low Z materials range from 10⁻⁷–10⁻⁴ n s⁻¹ Bq⁻¹.
• Spontaneous fission of Uranium-238 contributes 1.1×10⁻⁶ n s⁻¹ Bq⁻¹ to neutron background.

Conclusions:

• Radioactive contamination, radon, and neutrons are the primary background sources at LSM.
• Neutron production from (α, n) reactions and 238U fission are the largest neutron contributors.
• Mitigation of these sources is essential for future low-background research at LSM.