Dark matter research provides starting point for radiation detector

CNL's work has been enabled by Atomic Energy of Canada Ltd's Federal Nuclear Science and Technology Work Plan, which leverages the experience and expertise at the Chalk River Laboratories science and technology complex to contribute to the Canadian government’s health, science, innovation and climate change objectives. As part of that plan, CNL has since 2016 been working to develop disruptive technologies for applications in non-proliferation and nuclear counter terrorism.

The ALARM (A Liquid Argon Radiation Monitor) detector is based on the DEAP-3600 detector, developed through the international DEAP Collaboration which is working to directly observe and identify the dark matter component of the universe. Dark matter is believed to make up about 25% of the universe, but its existence has so far been inferred by its gravitational effect on stars and galaxies. DEAP-3600 is located over two kilometres underground at the SNOLAB underground laboratory in Sudbury, Ontario, to protect the ultra-sensitive detector from cosmic rays and muons that would compromise its effectiveness.

DEAP-3600 uses an ultraclean acrylic vessel loaded with over 3 tonnes of liquid argon kept at a very low temperature (around minus 186°C). The argon emits an intense flash of ultraviolet light when it interacts with a neutron or other ionising radiation. Andrew Erlandson, applied physicist at CNL, said DEAP is effectively one of the most sensitive neutron detectors on Earth. "Though DEAP is not searching for neutrons per se, they’ve effectively laid all the ground work for demonstrating the efficacy of liquid argon as a detection medium for radiation," he said.

Liquid argon - or LAr - can simultaneously detect both gamma and neutron radiation with high precision, and potentially offer significant improvements over existing neutron detection technology, CNL said. Liquid argon-based detectors can easily be scaled to a range of sizes from kilograms to tonnes, and can be customised to specific applications.

The technology used by DEAP is a strong candidate for detecting so-called special nuclear materials in border security applications, said Oleg Kamaev, head of Simulations & Measurements for the Advanced Radiation Technologies section in CNL’s Applied Physics Branch. The collaborative project brings two of Canada’s "big science" teams in SNOLAB and CNL, he added. "We are optimistic that this new LAr prototype will lead to further developments in passive detection techniques which could be deployed in Canadian radiation portal monitors at the ports of entry, ultimately making a difference in global security."

ALARM is in the final stages of assembly and commissioning of the hardware is expected this year.