A new underground detector in the Boulby Laboratory will attempt to spot nuclear reactors from tens of kilometres away by catching the ghostly particles they emit. Nuclear reactors produce a flood of anti-neutrinos—subatomic particles that pass through almost anything. Existing detectors can pick them up only at close range. The WATCHMAN detector tackles this by adding gadolinium to a water-filled tank, which makes the detector sensitive to the neutron released when an anti-neutrino interacts. This creates a distinct two-part signal—positron plus neutron—that tags the particle as an anti-neutrino rather than a harmless neutrino. If the technology works, it could allow inspectors to monitor suspected nuclear sites from a safe distance, since anti-neutrinos cannot be shielded or hidden. This would give non-proliferation efforts a new tool to detect clandestine reactors. The same facility will also test faster light sensors and water-based liquid scintillators, which could later extend detection range and enable fundamental physics searches, such as geoneutrino studies and neutrinoless double-beta decay. The project is a technology demonstrator, not an operational system, but success would prove a concept that could quietly strengthen global security.
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The Advanced Instrumentation Testbed (AIT) is a new facility, to be sited in the Boulby Underground Laboratory, that aims to explore new technologies for the purposes of nuclear non-proliferation and particle physics. The first phase of AIT is the WATer CHerenkov Monitor for Anti-Neutrinos (WATCHMAN). WATCHMAN construction is primarily funded through the US National Nuclear Security Administration (NNSA). UK involvement is a partnership between our industrial partners in the Atomic Weapons Establishment (AWE), the STFC-Boulby laboratory, and the Universities of Sheffield, Edinburgh, and Liverpool. The WATCHMAN detector is a technology demonstrator, which will attempt the first monitoring of nuclear reactors from a standoff distance of tens of kilometres. The mechanism for this monitoring is anti-neutrino detection. Nuclear reactions all produce a large flux of anti-neutrinos, which cannot be shielded. The WATCHMAN detector combines the decades-old technology of water Cherenkov neutrino detectors with the new technique of gadolinium loading. Adding gadolinium to the detector makes it sensitive to the neutron that is produced in an anti-neutrino interaction, but not a low-energy neutrino interaction. As such, the coincident signature of positron plus neutron can be used to tag anti-neutrinos. If successful, the techniques pioneered by WATCHMAN could be used to search for clandestine nuclear reactors as a means of non-proliferation and nuclear threat reduction. The AIT also includes a significant component of research and development into new detection materials and technologies. For this purpose, AIT will be investigating fast photosensors such as the Large Area Picosecond Photo-Detector (LAPPD), and new detector materials, such as water-based liquid scintillator. These can be used in future phases of the project to enhance the reactor detection range, as well as to enable particle physics goals such as geoneutrino studies and searches for neutrinoless double-beta decay.
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