This paper considers the process of Thomson scattering of coherent diffract
ion radiation (CDR) produced by the preceding electron bunch in the acceler
ator onto one of the subsequent bunches. it is shown that the yield of scat
tered hard photons is proportional to N-e(3), where N-e is the number of el
ectrons per bunch. A geometry is chosen for the CDR generation and an expre
ssion is obtained for the scattered-photon spectrum, with regard to the geo
metry used, that depends explicitly on the bunch size. A technique is propo
sed for measuring the bunch length using scattered radiation characteristic
s. [S1063-651X(99)03408-X].