  This work aims to characterize ultra high dose rate pulses (UHDpulse)
electron beams using the hybrid semiconductor pixel detector. The Timepix3
(TPX3) ASIC chip was used to measure the composition, spatial, time, and
spectral characteristics of the secondary radiation fields from pulsed 15 to 23
MeV electron beams. The challenge is to develop a single compact detector that
could extract spectrometric and dosimetric information on such high flux short
pulsed fields. For secondary beam measurements, PMMA plates of 1 and 8 cm
thickness were placed in front of the electron beam, with a pulse duration of
3.5 microseconds. Timepix3 detectors with silicon sensors of 100 and 500
micrometers thickness were placed on a shifting stage allowing for data
acquisition at various lateral positions to the beam axis. The use of the
detector in FLEXI configuration enables suitable measurements in situ and
minimal self shielding. Preliminary results highlight both the technique and
the detector's ability to measure individual UHDpulses of electron beams
delivered in short pulses. In addition, the use of the two signal chains per
pixel enables the estimation of particle flux and the scattered dose rates
(DRs) at various distances from the beam core, in mixed radiation fields.
