CSI(TL) YIELD MONITOR FOR QUASI-MONOCHROMATIC PHOTONS FROM COMPTON BACKSCATTERING OF LASER-LIGHT AT ETL

A CsI(Tl) yield monitor has been constructed for the detection of quasi-monochromatic photons generated by Compton backscattering of laser light at the Electrotechnical laboratory (ETL). The monitor has dimensions of 150*150*300 mm3, consisting of 9-CsI(Tl) crystals. The fundamental performances of the CsI(Tl) monitor were measured with Radio Isotope (RI) sources and a quasi-monochromatic photon beam. The detection efficiency was measured, and 100% efficiency was achieved for 20 MeV quasi-monochromatic photons. This monitor was also used as a photon spectrometer. The overall energy resolution was 3% for 3.2 MeV and 7% for 20 MeV quasi-monochromatic photons. Precise measurements of the LCS photon yield were done with the CsI(Tl) monitor. We confirmed that the photon yield was correctly expressed by the theoretical calculation.