A new ground level neutron monitor for space weather assessment.

We report on a new ground-level neutron monitor design for studying cosmic rays and fluxes of solar energetic particles at the Earth's surface. The first-of-its-kind instrument, named the NM-2023 after the year it was standardised and following convention, will be installed at a United Kingdom Meteorological Office observatory (expected completion mid 2024) and will reintroduce such monitoring in the UK for the first time since ca. 1984. Monte Carlo radiation transport code is used for the development and application of parameterised models to investigate alternative neutron detectors, their location and bulk material geometry in a realistic cosmic ray neutron field. Benchmarked against a model of the current and most widespread design standardised in 1964 (the NM-64), two main parameterisation studies are conducted; a simplified standard model and a concept slab parameterisation. We show that the NM-64 standard is well optimised for the intended large-diameter boron trifluoride (BF 3 ) proportional counters but not for multiple smaller diameter counters. The new design (based on a novel slab arrangement) produces comparable counting efficiencies to an NM-64 with six BF 3 counters and has the added advantage of being more compact, lower cost and avoids the use of highly toxic BF 3 .

Real-Time Avoidance of Ionising Radiation Using Layered Costmaps for Mobile Robots.

Humans in hazardous environments take actions to reduce unnecessary risk, including limiting exposure to radioactive materials where ionising radiation can be a threat to human health. Robots can adopt the same approach of risk avoidance to minimise exposure to radiation, therefore limiting damage to electronics and materials. Reducing a robot's exposure to radiation results in longer operational lifetime and better return on investment for nuclear sector stakeholders. This work achieves radiation avoidance through the use of layered costmaps, to inform path planning algorithms of this additional risk. Interpolation of radiation observations into the configuration space of the robot is accomplished using an inverse distance weighting approach. This technique was successfully demonstrated using an unmanned ground vehicle running the Robot Operating System equipped with compatible gamma radiation sensors, both in simulation and in real-world mock inspection missions, where the vehicle was exposed to radioactive materials in Lancaster University's Neutron Laboratory. The addition of radiation avoidance functionality was shown to reduce total accumulated dose to background levels in real-world deployment and up to a factor of 10 in simulation.

Use of Gaussian process regression for radiation mapping of a nuclear reactor with a mobile robot.

Collection and interpolation of radiation observations is of vital importance to support routine operations in the nuclear sector globally, as well as for completing surveys during crisis response. To reduce exposure to ionizing radiation that human workers can be subjected to during such surveys, there is a strong desire to utilise robotic systems. Previous approaches to interpolate measurements taken from nuclear facilities to reconstruct radiological maps of an environment cannot be applied accurately to data collected from a robotic survey as they are unable to cope well with irregularly spaced, noisy, low count data. In this work, a novel approach to interpolating radiation measurements collected from a robot is proposed that overcomes the problems associated with sparse and noisy measurements. The proposed method integrates an appropriate kernel, benchmarked against the radiation transport code MCNP6, into the Gaussian Process Regression technique. The suitability of the proposed technique is demonstrated through its application to data collected from a bespoke robotic system used to conduct a survey of the Joz̆ef Stefan Institute TRIGA Mark II nuclear reactor during steady state operation, where it is shown to successfully reconstruct gamma dosimetry estimates in the reactor hall and aid in identifying sources of ionizing radiation.

Local and global trace plutonium contributions in fast breeder legacy soils.

Trace-level plutonium in the environment often comprises local and global contributions, and is usually anthropogenic in origin. Here, we report estimates of local and global contributions to trace-level plutonium in soil from a former, fast-breeder reactor site. The measured 240Pu/239Pu ratio is anomalously low, as per the reduced 240Pu yield expected in plutonium bred with fast neutrons. Anomalies in plutonium concentration and isotopic ratio suggest forensic insight into specific activities on site, such as clean-up or structural change. Local and global 239Pu contributions on-site are estimated at (34 ± 1)% and (66 ± 3)%, respectively, with mass concentrations of (183 ± 6) fg g-1 and (362 ± 13) fg g-1. The latter is consistent with levels at undisturbed and distant sites, (384 ± 44) fg g-1, where no local contribution is expected. The 240Pu/239Pu ratio for site-derived material is estimated at 0.05 ± 0.04. Our study demonstrates the multi-faceted potential of trace plutonium assay to inform clean-up strategies of fast breeder legacies.

Detection of Simulated Fukushima Daichii Fuel Debris Using a Remotely Operated Vehicle at the Naraha Test Facility.

The use of robotics in harsh environments, such as nuclear decommissioning, has increased in recent years. Environments such as the Fukushima Daiichi accident site from 2011 and the Sellafield legacy ponds highlight the need for robotic systems capable of deployment in hazardous environments unsafe for human workers. To characterise these environments, it is important to develop robust and accurate localization systems that can be combined with mapping techniques to create 3D reconstructions of the unknown environment. This paper describes the development and experimental verification of a localization system for an underwater robot, which enabled the collection of sonar data to create 3D images of submerged simulated fuel debris. The system was demonstrated at the Naraha test facility, Fukushima prefecture, Japan. Using a camera with a bird's-eye view of the simulated primary containment vessel, the 3D position and attitude of the robot was obtained using coloured LED markers (active markers) on the robot, landmarks on the test-rig (passive markers), and a depth sensor on the robot. The successful reconstruction of a 3D image has been created through use of a robot operating system (ROS) node in real-time.

Remediation of 137Cs contaminated concrete using electrokinetic phenomena and ionic salt washes in nuclear energy contexts.

This work describes the first known the use of electrokinetic treatments and ionic salt washes to remediate concrete contaminated with 137Cs. A series of experiments were performed on concrete samples, contaminated with K+ and 137Cs, using a bespoke migration cell and an applied electric field (60V potential gradient and current limit of 35mA). Additionally, two samples were treated with an ionic salt wash (≤400molm-3 of KCl) alongside the electrokinetic treatment. The results show that the combined treatment produces removal efficiencies three times higher (>60%) than the electrokinetic treatment alone and that the decontamination efficiency appears to be proportional to the initial degree of contamination. Furthermore, the decontamination efficiencies are equivalent to previous electrokinetic studies that utilised hazardous chemical enhancement agents demonstrating the potential of the technique for use on nuclear licensed site. The results highlight the relationship between the initial contamination concentration within the concrete and achievable removal efficiency of electrokinetic treatment and other treatments. This information would be useful when selecting the most appropriate decontamination techniques for particular contamination scenarios.

High-intensity power-resolved radiation imaging of an operational nuclear reactor.

Knowledge of the neutron distribution in a nuclear reactor is necessary to ensure the safe and efficient burnup of reactor fuel. Currently these measurements are performed by in-core systems in what are extremely hostile environments and in most reactor accident scenarios it is likely that these systems would be damaged. Here we present a compact and portable radiation imaging system with the ability to image high-intensity fast-neutron and gamma-ray fields simultaneously. This system has been deployed to image radiation fields emitted during the operation of a TRIGA test reactor allowing a spatial visualization of the internal reactor conditions to be obtained. The imaged flux in each case is found to scale linearly with reactor power indicating that this method may be used for power-resolved reactor monitoring and for the assay of ongoing nuclear criticalities in damaged nuclear reactors.

The analysis of complex mixed-radiation fields using near real-time imaging.

A new mixed-field imaging system has been constructed at Lancaster University using the principles of collimation and back projection to passively locate and assess sources of neutron and gamma-ray radiation. The system was set up at the University of Manchester where three radiation sources: (252)Cf, a lead-shielded (241)Am/Be and a (22)Na source were imaged. Real-time discrimination was used to find the respective components of the neutron and gamma-ray fields detected by a single EJ-301 liquid scintillator, allowing separate images of neutron and gamma-ray emitters to be formed. (252)Cf and (22)Na were successfully observed and located in the gamma-ray image; however, the (241)Am/Be was not seen owing to surrounding lead shielding. The (252)Cf and (241)Am/Be neutron sources were seen clearly in the neutron image, demonstrating the advantage of this mixed-field technique over a gamma-ray-only image where the (241)Am/Be source would have gone undetected.

Depth profiling 137Cs and 60Co non-intrusively for a suite of industrial shielding materials and at depths beyond 50 mm.

A phantom has been used to position two radiation sources, separately, when buried under dry-silica sand at depths between 5 and 50 mm. A γ-ray energy spectrum was then measured at every 1 mm depth. Principal component analysis has been conducted, which has led to a non-linear fit being established, allowing the depth of entrainment to be accurately inferred. The technique has been expanded for additional shielding media: water, aggregate and both wet and dry soil. The technique has also been expanded beyond the previous depth constraint of 50 mm.

Determination of the depth of localized radioactive contamination by 137Cs and 60Co in sand with principal component analysis.

A method to determine the depth of buried localized radioactive contamination nonintrusively and nondestructively using principal component analysis is described. The γ-ray spectra from two radionuclides, cesium-137 and cobalt-60, have been analyzed to derive the two principal components that change most significantly as a result of varying the depth of the sources in a bespoke sand-filled phantom. The relationship between depth (d) and the angle (θ) between the first two principal component coefficients has been derived for both cases, viz. d(Φ) = x + y log(e) Φ where x and y are constants dependent on the shielding material and the γ-ray energy spectrum of the radioactivity in question, and φ is a function of θ. The technique enables the depth of a localized radioactive source to be determined nonintrusively in the range 5 to 50 mm with an accuracy of ±1 mm.

Profiling the depth of caesium-137 contamination in concrete via a relative linear attenuation model.

An application of the relative attenuation of X rays and gamma rays for the measurement of depth of radioactive contamination in concrete and is described, based upon the photon energy spectrum of caesium-137. This has been tested on two bespoke phantoms with pressed/cast concrete and silica sand highlighting the potential for sub-millimetre depth resolution. This research highlights the importance of the ease of calibration, prior to application in the field, and improved knowledge of materials composition in legacy facilities.

Time-dependent rheology of starch thickeners and the clinical implications for dysphagia therapy.

The viscosity of nonsolid foods and the stability of their viscosity over time is critical in managing dysphagia. The time-dependent viscosity of liquids thickened with starch-based thickeners was measured at constant temperature and shear rate. Viscosity was measured between 30-min intervals of rest (zero shear) over a period of 17 h at 20.0 degrees C. Two common types of thickeners were evaluated: maize-based and maltodextrin-based (the latter commonly used in pediatrics). The maize-based thickeners undergo a significant decrease in viscosity over the initial 1-4 h following preparation. The maltodextrin-based thickener's viscosity increases significantly 30 min following preparation and is then more stable over time than its maize-based equivalent. These findings suggest that the success of current dysphagia therapies that use thickeners could be influenced by the time-dependent nature of thickened fluid viscosity. Acknowledgment and appropriate selection of the thickener type is shown to be of great importance.

Radiation-induced statistical uncertainty in the threshold voltage measurement of MOSFET dosimeters.

The results of a recent study on the limiting uncertainties in the measurement of photon radiation dose with MOSFET dosimeters are reported. The statistical uncertainty in dose measurement from a single device has been measured before and after irradiation. The resulting increase in 1/f noise with radiation dose has been investigated via various analytical models. The limit of uncertainty in the ubiquitous linear trend of threshold voltage with dose has been measured and compared to two nonlinear models. Inter-device uncertainty has been investigated in a group of 40 devices, and preliminary evidence for kurtosis and skewness in the distributions for devices without external bias has been observed.

Novel developments in the MOSFET dosemeter for neutron dosimetry applications.

The feasibility of large-geometry Metal Oxide Semiconductor Field Effect Transistor (MOSFET) devices has been assessed for both active and passive neutron dosimetry and use in radiotherapy environments. Neutron sensitivity has been enhanced with the use of polymeric cement surrounding the gate region. Neutron activation via nuclear interaction processes is a potential problem with conventionally packaged and fabricated devices. To overcome this problem, a unique low-activation device design is described. Standard Dual in-Line devices, modified with polymeric cement and boron loaded cement have been exposed to gamma rays (60Co) and neutrons (gamma-ray shielded 252Cf) to provide neutron sensitivity estimates. The results show that the neutron sensitivity can be increased by a factor of approximately three by the use of a thin layer of polymeric cement over the gate region. Essentially zero activation is observed in the activation-reduced design compared with 1000 cps in the conventional design MOSFET when both are exposed under identical conditions to a neutron field from a gamma-ray shielded 252Cf isotopic source.