Recovery of Plastic Scintillators after Radiation Damage By Ultra-High Dose Rate Protons
Abstract
Purpose
To quantify recovery of damaged plastic scintillators and optical fiber after exposure to ultra-high dose rate (UHDR) protons, in terms of light output and spectral signature.
Methods
A 5-channel plastic scintillation detector (PSD) comprising of four scintillators, BCF-12, EJ-212, BCF-60 and Scint02, and a blank PMMA optical fiber, was damaged by a cumulative dose of 10.4kGy delivered with UHDR protons (~255Gy/s). To track recovery of light output after radiation damage, a reference 500 MUs measurement using the 6 MV beam of a TrueBeam linac was repeated on multiple time points (3-256 days), while spectral recovery was measured using the on-board imager kV tube. Output and spectral responses were compared to undamaged response measured before proton irradiations. The Hyperscint RP-200 dosimetry platform was used to measure light spectra.
Results
Damaged PSDs maintained their linearity to dose, but radiation damage caused a decrease of light output (1.29-4.04%/kGy), a spectral shift towards yellower wavelengths and a preferential quenching of scintillation emission in the 380-500nm range. Minimal output recovery (2.7-4.9%) was observed for blue-emitting BCF-12, EJ-212 and Scint02, leaving (10.9±0.9)% permanent damage after 256 days of rest. While green-emitting BCF-60 was about twice more radiation-hard compared to other scintillators, its output did not recover after long-term rest and even decreased by 6.6%, leaving (15±1)% permanent damage. Spectral recovery was (99.3±0.2)% complete for scintillators after full rest, indicating that different mechanisms may be involved in recovery of output and spectral signature.
Conclusion
This work represents the first systematic investigation of recovery processes in PSDs after radiation damage by UHDR protons, a step towards the use of PSDs for real-time UHDR dosimetry. Such processes are complex and depend on cumulative dose, particle type and scintillator composition. Care must be taken in selecting scintillators for FLASH applications, considering radiation hardness, recovery capacity and response stability.