The characteristics of the Solid-state Neutron Detector, under development for neutron-scattering measurements at the European Spallation Source, have been simulated with a Geant4-based computer ...code. The code models the interactions of thermal neutrons and ionising radiation in the 6Li-doped scintillating glass of the detector, the production of scintillation light and the transport of optical, scintillation photons through the scintillator, en route to the photocathode of the attached multi-anode photomultiplier. Factors which affect the optical-photon transport, such as surface finish, pixelation of the glass sheet, provision of a front reflector and optical coupling media are compared. Predictions of the detector response are compared with measurements made with neutron and gamma-ray sources, a collimated alpha source and finely collimated beams of 2.5 MeV protons and deuterons.
The response of a position-sensitive Li-glass based scintillation detector being developed for thermal-neutron detection with 6 mm position resolution has been investigated using focused beams of ...2.5MeV protons and deuterons. The beams were scanned across the detector in 0.5 mm horizontal and vertical steps perpendicular to the beams. Scintillation light was registered using an 8 × 8 pixel multi-anode photomultiplier tube. The signal amplitudes were recorded for each pixel on an event-by-event basis. Several pixels generally registered considerable signals at each beam location. To optimize planned detector operation at the European Spallation Source, the number of pixels above set thresholds was investigated, with the maximization of the single-hit efficiency over the largest possible area as the primary goal. For both beams, at a threshold of ∼50% of the mean of the full-deposition peak, ∼80% of the events were registered in a single pixel, resulting in an effective position resolution of ∼5 mm in X and Y. Lower thresholds resulted in higher pixel multiplicities. These events could also be localized with the same effective position resolution.
The response of a position-sensitive Li-glass scintillator detector to alpha-particles from a collimated Am-241 source scanned across the face of the detector has been measured. Scintillation light ...was read out by an 8 x 8 pixel multi-anode photomultiplier and the signal amplitude for each pixel has been recorded for every position on a scan. The pixel signal is strongly dependent on position and in general several pixels will register a signal (a hit) above a given threshold. The effect of this threshold on hit multiplicity is studied, with a view to optimize the single-hit efficiency of the detector.
We present the development of a specialized concrete for neutron shielding at neutron research facilities, based on the addition of hydrogen atoms in the form of polyethylene and also B 4 C for ...enhancing the neutron capture properties of the concrete. We show information on the mechanical properties of the concrete and the neutronics, in particular its relevance to modern spallation neutron sources, such as the European Spallation Source (ESS), currently under construction in Lund, Sweden. The new concrete exhibits a 15% lower mass density, a compressible strength of 50% relative to a standard concrete and a significant increase in performance of shielding against MeV neutrons and lower energies. The concrete could find application at the ESS in for example common shielding components, individual beamline shielding and instrument caves. Initial neutronic tests of the concrete, carried out at Lund University, have also verified the performance in the MeV neutron energy range and the results are presented.
The response of a position-sensitive Li-glass scintillator detector to α-particles from a collimated 241Am source scanned across the face of the detector has been measured. Scintillation light was ...read out by an 8 × 8 pixel multi-anode photomultiplier and the signal amplitude for each pixel has been recorded for every position on a scan. The pixel signal is strongly dependent on position and in general several pixels will register a signal (a hit) above a given threshold. The effect of this threshold on hit multiplicity is studied, with a view to optimize the single-hit efficiency of the detector.
Coincidence and time-of-flight measurement techniques are employed to tag fission neutrons emitted from a Cf-252 source sealed on one side with a very thin layer of Au. The source is positioned ...within a gaseous He-4 scintillator detector. Together with a particles, both light and heavy fission fragments pass through the thin layer of Au and are detected. The fragments enable the corresponding fission neutrons, which are detected in a NE-213 liquid-scintillator detector, to be tagged. The resulting continuous polychromatic beam of tagged neutrons has an energy dependence that agrees qualitatively with expectations. We anticipate that this technique will provide a cost-effective means for the characterization of neutron-detector efficiency in the energy range 1-6 MeV.
Adversarial Path Planning Analysis of Urban Radiation Detection Networks Raji, D. M.; Rofors, E.; Cooper, R. ...
2023 IEEE Nuclear Science Symposium, Medical Imaging Conference and International Symposium on Room-Temperature Semiconductor Detectors (NSS MIC RTSD),
2023-Nov.-4
Conference Proceeding
Networks of radiation sensing-nodes in urban areas have been conceptualized to better detect and track mobile radiological/nuclear sources. However, these systems are complex and difficult to ...practically evaluate. This effort models intelligent adversarial behavior as a means to this end using the city of Chicago as a case study environment. The ability of this analysis to plan paths through the urban area containing the network without being observed is quantified to assess network coverage and avoidability. A selection of samples of adversarial paths created along with quantitative distributions of paths' observance rates under different network scenarios is provided. We then propose an approach to couple dynamic optimization of the network's detector placement strategy and the adversarial path planning. Feedback from each model is used to improve the other in a competitive manner. To this end, a non-stationary multi-objective evolutionary algorithm (MOEA) is designed and applied. Results including approximated Pareto fronts are discussed.
To address the threat posed by the nefarious use of radiological/nuclear sources, there is a growing interest in deploying connected static detector networks in cities. Connected detector networks ...can have improved detection sensitivity over unconnected networks by using the correlations between detectors. We explore the use of graph neural networks (GNNs) to exploit such correlations in a minimal detector network of two nodes and one edge in downtown Chicago. We compare a GNN model with and without message passing, and find that the model with message passing performs significantly better (p = 0.03), suggesting that it is leveraging spatiotemporal relationships to improve detection performance. Future work includes assessing the performance of GNN models on larger detector networks and benchmarking them against existing algorithms.
Deep Learning for Tritium Detection Using Scientific CCDs Rofors, E.; Cooper, R.; Heller, R. ...
2023 IEEE Nuclear Science Symposium, Medical Imaging Conference and International Symposium on Room-Temperature Semiconductor Detectors (NSS MIC RTSD),
2023-Nov.-4
Conference Proceeding
Utilizing recent advances in image recognition, we explore the possibilities of applying deep learning to to the challenging problem of tritium detection and quantification using thick, fully ...depleted, highly-pixelated, scientific Charge Coupled Devices (CCDs.) We present a simulation framework developed to study signals from both tritium decay products and background radiation. Simulated particle tracks are used to train a Convolutional Neural Network (CNN) to perform track-based particle identification. The importance of thin CCD dead layers are discussed, as 50% of tritium decay particles don't penetrate deeper than 50 nm in silicon.
Knowledge of the neutron light-yield response is crucial to the understanding of scintillator-based neutron detectors. In this work, neutrons from 2--6 MeV have been used to study the scintillation ...light-yield response of the liquid scintillators NE 213A, EJ 305, EJ 331 and EJ 321P using event-by-event waveform digitization. Energy calibration was performed using a GEANT model to locate the edge positions of the Compton distributions produced by gamma-ray sources. The simulated light yield for neutrons from a PuBe source was compared to measured recoil proton distributions, where neutron energy was selected by time-of-flight. This resulted in an energy-dependent Birks parametrization to characterize the non-linear response to the lower energy neutrons. The NE 213A and EJ 305 results agree very well with existing data and are reproduced nicely by the simulation. New results for EJ 331 and EJ 321P, where the simulation also reproduces the data well, are presented.
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