Background and Aims

To characterize the biological "FLASH effect", it is necessary to have dosimeters available for reliable real-time measurements at ultra-high dose rates (> 40 Gy/s) and ultra-high dose-per-pulse (DPP > 0.6 Gy/pulse). A promising approach are detectors based on synthetic single crystal diamond working as Schottky photodiodes like the microDiamond T60019. The aim of this work is to investigate the dose response linearity of this detector type at ultra-high DPP.

Methods

Several different microDiamond detectors were investigated at PTB's research electron accelerator (20 MeV, 5 Hz, 2.5 µs pulse duration). To determine the DPP reference, the beam current monitor was calibrated against alanine.

Results

All microDiamonds respond linearly at low DPP (Figure 1). The response deviates from linearity with increasing DPP and finally reaches saturation. The DPP value at which non-linear behavior becomes significant varies between 0.1 and 2 Gy/pulse for the commercially available microDiamonds and is exemplar-dependent (SN). However, prototypes (B1, C1) demonstrated that the linear range can be extended.

Figure 1. Measured vs. actual DPP for different microDiamonds

Conclusions

The dose response of various microDiamond exemplars was investigated as a function of DPP. Commercially available microDiamonds have limitations in ultra-high DPP range. However, it has been shown with microDiamond prototypes that the linear range can be extended to the ultra-high DPP range. This shows that the microDiamond is in principle suitable for FLASH-RT dosimetry.

This project 18HLT04 UHDpulse has received funding from the EMPIR programme co-financed by the Participating States and from the European Union’s Horizon 2020 research and innovation programme.