High-Efficiency Gamma-Beta Blind Alpha Spectrometry for Nuclear Energy Applications

A novel, centrifugally tensioned metastable fluid detector (CTMFD) sensor technology has been developed over the last decade to demonstrate high selective sensitivity and detection efficiency to various forms of radiation for wide-ranging conditions (e.g., power, safeguards, security, and health physics) relevant to the nuclear energy industry. The CTMFD operates by tensioning a liquid with centrifugal force to weaken the bonds in the liquid to the point whereby even femtoscale nuclear particle interactions can break the fluid and cause a detectable vaporization cascade. The operating principle has only peripheral similarity to the superheated bubble chamber-based superheated droplet detectors (SDD). Instead, CTMFDs utilize mechanical “tension pressure” instead of thermal superheat, offering a lot of practical advantages. CTMFDs have been used to detect a variety of alpha- and neutron-emitting sources in near real time. The CTMFD is blind to gamma photons and betas allowing for detection of alphas and neutrons in extreme gamma/beta background environments such as spent fuel reprocessing plants. The selective sensitivity allows for differentiation between alpha emitters including the isotopes of plutonium. Mixtures of plutonium isotopes have been measured in ratios of $1∶1$⁠, $2∶1$⁠, and $3∶1$ Pu-238:Pu-239 with successful differentiation. Due to the lack of gamma-beta background interference, the CTMFD is inherently more sensitive than scintillation-based alpha spectrometers or SDDs and has been proved capable to detect below femtogram quantities of plutonium-238. Plutonium is also easily distinguishable from neptunium, making it easy to measure the plutonium concentration in the NPEX stream of a UREX reprocessing facility. The CTMFD has been calibrated for alphas from americium (5.5 MeV) and curium (⁠$∼6MeV$⁠) as well. Furthermore, the CTMFD has, recently, also been used to detect spontaneous and induced fission events, which can be differentiated from alpha decay, allowing for detection of fissionable material in a mixture of isotopes. This paper discusses these transformational developments, which are also being considered for real-world commercial use.