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Gamma Imagers for Nuclear Security and Nuclear Forensics: Recommendations based on results from a side-by-side intercomparison
L. E. Sinclair, P. R. B. Saull, A. McCann, A. M. L. MacLeod, N. J. Murtha, A. El-Jaby, G. Jonkmans
https://arxiv.org/abs/2602.00826 https://arxiv.org/pdf/2602.00826 https://arxiv.org/html/2602.00826
arXiv:2602.00826v1 Announce Type: new
Abstract: Nuclear security operations and forensic investigations require the utilization of a suite of instruments ranging from passive gamma spectrometers to high-precision laboratory sample analyzers. Gamma spectroscopy survey is further broken down into wide-area search performed with large-volume scintillator-based mobile survey spectrometers which are integrated with geographic position sensors for mapping and identification of hot zones, and high-precision long-dwell measurements using solid state spectrometers for follow-on characterization to establish isotopic content and ratios. While performing well at detecting the presence, quantity and type of radioactivity, all of these methods have limited ability to determine the location of a source of radioactivity. In recent years, technology advances have resulted in gamma imager devices which can create an image of the distribution of radioactive sources using the gamma emissions which accompany radioactive decay, and overlay this on an optical photograph of the environment. These gamma imaging devices have arisen out of methods developed for medical physics, experimental particle physics, and astrophysics, resulting in a proliferation of different technological approaches. Those responsible for establishing a nuclear security concept of operations, require guidance to choose the proper gamma imager for each of the application spaces in a tiered response. Here the results of an intercomparison of two gamma imagers based on two widely different technologies, semiconductor and scintillator detectors, are presented. The optimal utilization of these imaging technologies in a tiered response is discussed based on the results of the trial. Finally, an outlook on future directions for gamma imaging advances is provided.
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Counterflow around a cylinder
Matheus P. Severino, Leandro F. Souza, Elmer M. Gennaro, Daniel Rodr\'iguez, Fernando F. Fachini
https://arxiv.org/abs/2602.22022 https://arxiv.org/pdf/2602.22022 https://arxiv.org/html/2602.22022
arXiv:2602.22022v1 Announce Type: new
Abstract: The incompressible flow around a circular cylinder, positioned at the center of an unconfined planar counterflow, is studied by means of numerical solutions of the conservation equations and linear stability analysis. The flow is completely defined by the Reynolds number ($\Rey$) -- based on the cylinder radius, the strain rate defining the counterflow, and the kinematic viscosity. For very low values of $\Rey$, the flow is steady, two-dimensional, and fully attached to the cylinder wall. Increasing $\Rey$ above $\Rey_s \approx 16.86$, the flow separates, giving rise to two symmetric, counter-rotating recirculation regions on each side of the cylinder. Further increasing $\Rey$ leads to a progressive enlargement of the recirculation regions and the appearance of multiple recirculation centers, akin to Moffatt eddies. However, the convective acceleration imposed by the counterflow limits their size. An oscillatory mode becomes linearly unstable for $\Rey_{c} \approx 4146$. This mode gives rise to a sinuous meandering of the wake flow, on each side of the cylinder, being analogous to the well-known von K\'arm\'an instability. The frequency of this mode is directly proportional to the strain rate defining the counterflow.
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🚨Job Alert!🚨 Three (3) tenure track positions at Tohuku University: #Mathematics, #Physics, #Astronomy, #Geophysics

Regret-Guided Search Control for Efficient Learning in AlphaZero
Yun-Jui Tsai, Wei-Yu Chen, Yan-Ru Ju, Yu-Hung Chang, Ti-Rong Wu
https://arxiv.org/abs/2602.20809 https://arxiv.org/pdf/2602.20809 https://arxiv.org/html/2602.20809
arXiv:2602.20809v1 Announce Type: new
Abstract: Reinforcement learning (RL) agents achieve remarkable performance but remain far less learning-efficient than humans. While RL agents require extensive self-play games to extract useful signals, humans often need only a few games, improving rapidly by repeatedly revisiting states where mistakes occurred. This idea, known as search control, aims to restart from valuable states rather than always from the initial state. In AlphaZero, prior work Go-Exploit applies this idea by sampling past states from self-play or search trees, but it treats all states equally, regardless of their learning potential. We propose Regret-Guided Search Control (RGSC), which extends AlphaZero with a regret network that learns to identify high-regret states, where the agent's evaluation diverges most from the actual outcome. These states are collected from both self-play trajectories and MCTS nodes, stored in a prioritized regret buffer, and reused as new starting positions. Across 9x9 Go, 10x10 Othello, and 11x11 Hex, RGSC outperforms AlphaZero and Go-Exploit by an average of 77 and 89 Elo, respectively. When training on a well-trained 9x9 Go model, RGSC further improves the win rate against KataGo from 69.3% to 78.2%, while both baselines show no improvement. These results demonstrate that RGSC provides an effective mechanism for search control, improving both efficiency and robustness of AlphaZero training. Our code is available at https://rlg.iis.sinica.edu.tw/papers/rgsc.
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Application of RFSoC Technology for Beam Position Monitors at the SuperKEKB Storage Rings Injection Points
B. Urbschat, G. Mitsuka, L. Ruckman
https://arxiv.org/abs/2602.14870 https://arxiv.org/pdf/2602.14870 https://arxiv.org/html/2602.14870
arXiv:2602.14870v1 Announce Type: new
Abstract: In order to achieve its ambitious luminosity target, the SuperKEKB collider must achieve and sustain high beam currents on the order of Ampere in its storage rings. This requires continuous top-up injection and operation with a two-bunch injection scheme, injecting two 96 ns spaced bunches in a single injection cycle. An important input for tuning the injection beam is the position reading from a dedicated beam position monitor (BPM), located after the septum magnets, slightly upstream of where the injected and stored beams converge. Previously, the readout electronics used for these special BPMs were not capable of independent measurement of both bunches in the two-bunch injection mode and modification of the concerned devices and their firmware was not feasible. The opportunity was taken to develop a new readout device based on the AMD/Xilinx RF System on a Chip (RFSoC) platform with the goal of not only providing a sufficiently flexible and performant readout solution for the concerned BPMs, but also to evaluate and gain experience with the platform for beam monitor electronics applications. This paper is concerned with the details of this development as well as evaluation and operation of the developed device.
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A minimal wake-vortex model explains formation flight of flapping birds
Olivia Pomerenk, Kenneth S. Breuer
https://arxiv.org/abs/2602.22043 https://arxiv.org/pdf/2602.22043 https://arxiv.org/html/2602.22043
arXiv:2602.22043v1 Announce Type: new
Abstract: Collective patterns of motion emerge across biological taxa: insects swarm, fish school, and birds flock. In particular, large migratory birds form strikingly ordered V-shaped formations, which experiments and direct numerical simulations have demonstrated provide substantial energetic benefits during long-distance flight. However, the precise aerodynamic and morphological mechanisms underlying these benefits remain unclear. In this work, we develop a reduced-order model of the wake-vortex interactions between two flapping birds flying in tandem. The model retains essential unsteady flapping dynamics while remaining computationally tractable. By optimizing over a six-dimensional state space, which comprises the follower's three-dimensional relative position and three independent flapping parameters, we identify the energetically optimal leader-follower configuration of northern bald ibises. The predicted optimum agrees quantitatively with live-bird measurements. Because of its simplicity, the model allows for direct interrogation of the physical mechanisms responsible for this optimum. In particular, it isolates precisely how the follower's wing kinematics interact with the leader's wake to enhance aerodynamic efficiency. The model predicts an 11% reduction in total mechanical power for a follower in formation flight -- consistent with experimental estimates -- and shows that this saving arises from reductions in both induced and profile power, dominated by decreased profile power enabled primarily through reduced flapping amplitude and, secondarily, reduced upstroke flexion. These results provide a mechanistic explanation for the structure of V-formations and offer new insight into the aerodynamic principles governing collective flight.
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Toward a Fully Autonomous, AI-Native Particle Accelerator
Chris Tennant
https://arxiv.org/abs/2602.17536 https://arxiv.org/pdf/2602.17536 https://arxiv.org/html/2602.17536
arXiv:2602.17536v1 Announce Type: new
Abstract: This position paper presents a vision for self-driving particle accelerators that operate autonomously with minimal human intervention. We propose that future facilities be designed through artificial intelligence (AI) co-design, where AI jointly optimizes the accelerator lattice, diagnostics, and science application from inception to maximize performance while enabling autonomous operation. Rather than retrofitting AI onto human-centric systems, we envision facilities designed from the ground up as AI-native platforms. We outline nine critical research thrusts spanning agentic control architectures, knowledge integration, adaptive learning, digital twins, health monitoring, safety frameworks, modular hardware design, multimodal data fusion, and cross-domain collaboration. This roadmap aims to guide the accelerator community toward a future where AI-driven design and operation deliver unprecedented science output and reliability.
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FLUKA-Based Optimization of Muon Production Target Design for a Muon Collider Demonstrator
Ruaa Al-Harthy
https://arxiv.org/abs/2602.16672 https://arxiv.org/pdf/2602.16672 https://arxiv.org/html/2602.16672
arXiv:2602.16672v1 Announce Type: new
Abstract: This study investigates how target geometry and material influence pion and muon production from an 8 GeV proton beam, in support of target-system design for a muon collider demonstrator. A 2 m long, 0.7 m radius solenoid with a 5 T peak magnetic field is used to capture secondary particles, with the target positioned at its center. We examine how variations in target radius, length, and material affect secondary-beam yield and emittance at the solenoid exit. In parallel, we evaluate temperature rise within the target to assess material limitations and guide future work on thermal and structural survivability. The results provide initial intuition for optimizing both particle yield and target durability in muon collider front-end systems.
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