Changes in the phosphorescence lifetime τ (a and c) and
phosphorescence decay initial amplitude (b and d) measured in a buffered
solution (20 mM phosphate, pH 7.2) containing BSA (2%) (a, b) and in pure water
(c, d) at 22°C. Probe: of Oxyphor PtG4 (1 μM). The solutions were
subjected to irradiation by proton FLASH: for (a, b) - 7 exposures of 30 Gy,
then 3 exposures of 100 Gy; for (c, d) - all exposures were 30 Gy. In all cases,
the dose rate was ~105 Gy/s. Inset in (b): [O2]-trace derived
from the τ-trace shown in (a). Insets in (c) and (d): expanded sections
of the traces encircled in the main graphs. Asterisks in (d) mark the regions
corresponding to high-speed recordings, where the determination of the initial
amplitudes was obscured by noise.