Ultra-Sensitive
Nuclear Measurements

Detecting and measuring very
small amounts of radioactivity

Physicist Emily Mace loads a copper detector with a low-level radioactive gas sample into an Ultra-Low-Background Counting System in PNNL’s Shallow Underground Laboratory.

(Photo by Andrea Starr | Pacific Northwest National Laboratory)

One of our signature capabilities at Pacific Northwest National Laboratory (PNNL) is the detection and measurement of very small amounts of radioactivity. This ultra-sensitive nuclear measurements capability is built on four main elements: ultra-pure materials, ultra-sensitive radiation detection systems, measurements inaccessible by other means, and the applications uniquely enabled by these measurements. The mission space for this capability spans national security, fundamental physics, and environmental science applications.

All of these elements come together in PNNL's Shallow Underground Laboratory. This cleanroom facility, located 40 feet underground, provides shielding against radioactive backgrounds induced by cosmic rays.

PNNL's Shallow Underground Laboratory

National security

Ultra-sensitive nuclear measurements support a range of nuclear nonproliferation applications and are foundational for detecting nuclear explosions for compliance with the Comprehensive Nuclear-Test-Ban Treaty. The radioactive isotope argon-37 can be produced in nuclear explosions, which means argon-37 can also be used to detect them. PNNL is one of only two laboratories worldwide that can measure argon-37 at environmental levels.

PNNL researchers are also exploring how analytical and computational techniques such as machine learning can further reduce backgrounds and provide quantitative reporting from these ultra-sensitive measurements.

Scientist uses ultra-low background detector — Physicist Stephanie Lyons uses the Ultra-Low Background Liquid Scintillation Counter (ULB-LSC) in PNNL’s Shallow Underground Laboratory. (Photo by Andrea Starr | Pacific Northwest National Laboratory)

Fundamental physics

Ultra-sensitive nuclear measurements support increasingly more sensitive searches for dark matter and rare nuclear interactions that can expand our understanding of the universe. For example, the ultra-pure materials that are part of this capability are key design elements in large international fundamental physics experiments like the Majorana Demonstrator. The Majorana Demonstrator experiment searches for evidence of non-standard properties of neutrinos, subatomic particles important for understanding the composition of the universe and solar evolution.

Environmental science

The detection and measurement of very small amounts of radioactivity can be used to increase our understanding of environmental systems and pathways. As an example, PNNL is one of only two laboratories worldwide that can use ultra-sensitive radiation detection to determine the age of groundwater by measuring the abundance of the radioactive isotope argon-39 at levels far below those seen in the atmosphere. Scientists can use this information to determine residence time of water in aquifers and better understand this critical natural resource.