[论文解读] Non-Destructive Beam Monitoring via Secondary Radiation Detection with Ce-Doped Silica Fibers

Alexander Gottstein, Pierluigi Casolaro+8 more|arXiv (Cornell University)|Jan 26, 2026

Advanced Radiotherapy Techniques被引用 0

一句话总结

论文评估了一种外部 Ce 掺杂二氧化硅光纤监测器（EFM），通过检测二次辐射来监测医疗回旋加速器 beamline 上的束流强度、损失和位置，而不对束流进行干预。

ABSTRACT

Non-destructive beam diagnostics are essential for low-energy medical cyclotrons, where even thin interceptive devices can severely degrade beam quality. We investigate an external fiber monitor (EFM) based on Ce-doped silica scintillating fibers that detects secondary radiation generated at existing beamline components of the 18 MeV Bern Medical Cyclotron beam transfer line (BTL). Three use cases were studied: (i) beam intensity monitoring around an electrically isolated, water-cooled beam dump; (ii) beam-loss monitoring around a 10 mm collimator under varying the beam focusing; and (iii) by steering a 6.5 mm $ imes$ 6.5 mm beam spot on a beam dump. For case (i), the summed EFM signal exhibits a linear dependence on the current on target over nearly three orders of magnitude. In case (ii), a normalized EFM-based beam-loss proxy scales monotonically with an electrical loss proxy across several focusing settings. Furthermore, opposing-fiber signal ratios provide decoupled, monotonic sensitivity to horizontal and vertical beam displacements.

研究动机与目标

• Motivate non-destructive beam diagnostics for low-energy medical cyclotrons where interceptive devices perturb the beam.
• Evaluate the external fiber monitor (EFM) concept using Ce-doped silica fibers to detect secondary radiation around existing beamline components.
• Characterize EFM performance for three use cases: beam intensity monitoring, beam-loss monitoring, and beam-position monitoring.
• Assess linearity, calibration, and potential systematics to inform retrofitting and routine operation.

提出的方法

• Utilize Ce-doped silica fibers mounted around beamline components to convert secondary radiation into scintillation light.
• Route light to an external readout chain comprising an IDQ single-photon detector and a Vertilon eight-channel counter system.
• Test three configurations on the Bern Medical Cyclotron beam transfer line: (i) around a water-cooled beam dump for linearity, (ii) around a collimator for beam loss, (iii) around a beam dump with an array for position sensing.
• Compare EFM signals against reference measurements such as beam dump current, UniBEaM profiles, and Pi2 beam profiler to establish correlations.
• Use background-subtracted signals and, where relevant, derive proxies (e.g., S_I, S_EFM) for calibration in loss scenarios.

Figure 1 : Schematic of the measurement setup. The proton beam (in blue) strikes an aluminium beam dump, producing secondary radiation that excites the Ce-doped fibers; the resulting scintillation light is read out with a single-photon counter, connected to a DAQ.

实验结果

研究问题

• RQ1 Can the EFM provide a linear, non-destructive response to beam current over a broad range?
• RQ2 Is the EFM signal correlated monotonically with beam losses at a collimator under varying focusing conditions?
• RQ3 Can an opposing-fiber array yield decoupled, monotonic sensitivity to horizontal and vertical beam displacement?
• RQ4 How do geometry, materials, and activation affect the EFM response and required site-specific calibration?

主要发现

• The summed EFM signal shows a linear dependence on beam current over nearly three orders of magnitude with small residual drift within ±3%.
• A beam-loss proxy from EFM signals scales monotonically with an electrical loss proxy across several focusing settings, enabling empirical calibration to infer losses.
• Opposing-fiber signal ratios provide decoupled, monotonic sensitivity to horizontal and vertical beam displacements.
• The EFM is non-interceptive and retrofit-friendly, suitable for continuous monitoring without perturbing the beam, given site-specific calibration.
• A second-order limitation notes geometry- and material-dependence of the response, requiring careful calibration and potential background mitigation.

Figure 2 : On the left, a photograph of the water-cooled target installed on the BTL is shown. The four EFM sensing fibers (1) are mounted around the beam dump (2). The four transport fibers with the SMA connectors are labelled with (3) in the picture on the left. They are routed away from the beam