Photon-flux determination by the Poisson-fitting technique with quenching corrections

摘要

Single- and multi-photon spectra of pulsedγ-ray beams produced at 17, 34, and 40 MeV in the laser Compton scattering were measured with an 8”×12” NaI(Tl) detector. By using the experimental single-photon spectra as the probability function of generating random numbers, response functions of the NaI(Tl) detector toj-fold photons (j= 2, 3, 4 ...) were constructed. The least-square fits to the experimental multi-photon spectra by the Poisson distribution consisting of the response functions were made. The multi-photon spectra measured at 17 and 34 MeV follow the Poisson distribution. A quenching phenomenon of multi-photon spectra was observed for 40 MeVγ-rays as a result of the saturation at the photomultiplier tube of the NaI(Tl) detector. The original Poisson distributions were restored from the quenched spectra using a saturation curve in the form ofy=a⋅xηwithη=e−bx. We discuss the accuracy of photon-flux determination.