  We have designed and implemented an experiment to measure the angular
distributions and the energy spectra of the transition radiation X-rays emitted
by fast electrons and positrons crossing different radiators. Our experiment
was selected among the proposals of the 2021 Beamline for Schools contest, a
competition for high-school students organized every year by CERN and DESY, and
was performed at the DESY II Test Beam facility area TB21, using a high-purity
beam of electrons or positrons with momenta in the range from 1 to 6 GeV/c. The
measurements were performed using a 100 um thick silicon pixel detector, with a
pitch of 55 um. Our results are consistent with the expectations from the
theoretical models describing the production of transition radiation in
multilayer regular radiators.
