Abstract
The monitoring of neutron radiation in extreme high ≈1014 (#/cm2-s) neutron/photon fields and at extremely-low (≈10−3 #/cm2-s) levels poses daunting challenges—important in fields spanning nuclear energy, special nuclear material processing/security, nuclear medicine (e.g., photon-based cancer therapy), and high energy (e.g., dark-matter) research. Variably proportioned (neutron, gammas, X-ray) radiation, spanning 10−2–109 eV in energy, is omnipresent from ultra-low (Bq) activity levels (e.g., cosmic rays/ bananas), to extreme high (>1020 Bq) levels. E.g., in nuclear reactor cores; in spent nuclear fuel bearing nuclear-explosive-relevant safeguard-sensitive isotopes, such as Pu-239; and in cancer therapy accelerators. The corresponding high to low radiation dose range spans a daunting 1016:1 spread—alongside ancillary challenges such as high temperatures, pressure, and humidity. Commonly used neutron sensors get readily saturated even in modest (<1 R/h) photon fields; importantly, they are unable to decipher trace neutron radiation relative to 1014 times greater gamma radiation. This paper focuses on sensing ultra-low to high neutron radiation in extremely high photon (gamma-X ray) backgrounds. It summarizes the state-of-art compared to the novel tensioned metastable fluid detector (TMFD) sensor technology, which offers physics-based 100% gamma-blind, high (60–95%) intrinsic efficiency for neutron-alpha-fission detection, even under extreme (≈103 R/h) gamma radiation.
Highlights
IntroductionFluids, like solids, can sustain tension (i.e., the intermolecular bonds holding the molecules together can be “stretched” and weakened)
Just what do we mean by “extremely high” radiation fields that pose challenges to the status quo of neutron monitoring? In order to address this question, one must start with a baseline of sorts.1.1
We first start with radiation in everyday life for which monitoring is readily accomplished, and relative to such radiation levels we consider radiation levels that are “extreme high”—quantitatively specified, for which state-of-art sensors fail to perform satisfactorily, and for which we describe the novel tensioned metastable fluid detector (TMFD) sensor technology and its validation for applicability in various challenging environments
Summary
Fluids, like solids, can sustain tension (i.e., the intermolecular bonds holding the molecules together can be “stretched” and weakened). Ordinary fluids, such as water, at room temperature can be stretched (i.e., tensioned) to include negative (Pneg ) pressures (yes—even below perfect vacuum), as scientifically confirmed only a few decades ago, leading to the novel TMFD sensor class [10,11,12,13,14,15,16]. A separate unusual security-safeguards arises for extreme radiation fields once a a reactor is shut and down and the spent nuclear fuel challenge assemblies (SNFAs) are removed for reprocessing. Figure the relatively small inventory of SNM decay from spontaneous fission (SF).
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