Monitoring Neutron Radiation in Extreme GammaXRay Radiation Fields The monitoring of neutron radiation in extreme high xe2x89x881014 (cm2s) neutronphoton fields and at extremelylow (xe2x89x8810xe2x88x923 cm2s) levels poses daunting challengesxe2x80x94important in fields spanning nuclear energy, special nuclear material processingsecurity, nuclear medicine (e.g., photonbased cancer therapy), and high energy (e.g., darkmatter) research. Variably proportioned (neutron, gammas, Xray) radiation, spanning 10xe2x88x922xe2x80x93109 eV in energy, is omnipresent from ultralow (Bq) activity levels (e.g., cosmic rays bananas), to extreme high (u003e1020 Bq) levels. E.g., in nuclear reactor cores; in spent nuclear fuel bearing nuclearexplosiverelevant safeguardsensitive isotopes, such as Pu239; and in cancer therapy accelerators. The corresponding high to low radiation dose range spans a daunting 1016:1 spreadxe2x80x94alongside ancillary challenges such as high temperatures, pressure, and humidity. Commonly used neutron sensors get readily saturated even in modest (u003c1 Rh) photon fields; importantly, they are unable to decipher trace neutron radiation relative to 1014 times greater gamma radiation. This paper focuses on sensing ultralow to high neutron radiation in extremely high photon (gammaX ray) backgrounds. It summarizes the stateofart compared to the novel tensioned metastable fluid detector (TMFD) sensor technology, which offers physicsbased 100% gammablind, high (60xe2x80x9395%) intrinsic efficiency for neutronalphafission detection, even under extreme (xe2x89x88103 Rh) gamma radiation.

Sensors for Ultrasonic Nondestructive Testing (NDT) in Harsh Environments In this special issue of Sensors, seven peerreviewed manuscripts appear on the topic of ultrasonic transducer design and operation in harsh environments: elevated temperature, high gamma and neutron fields, or the presence of chemically aggressive species. Motivations for these research and development projects are strongly focused on nuclear power plant inspections (particularly liquidsodium cooled reactors), and nondestructive testing of hightemperature piping installations. It is anticipated that we may eventually see extensive use of permanently mounted robust transducers for inservice monitoring of petrochemical plants and power generations stations; quality control in manufacturing plants; and primary and secondary process monitoring in the fabrication of engineering materials.