Absolute Measurement Of Extremely High Intense Photons Using Calorimetric Method

The absolute intensity of intense photon beam at the high flux beamline, BL40XU, of SPring‐8 was measured directly with high accuracy by using calorimetric method in a short period irradiation from 0.2 to 10 s. The results of the measurements agree with each other within 2 % for different irradiation periods and about 23 % difference was recognized between the intensities of the direct measurements using calorimeter and the extrapolation from the intensities at the weak current of the storage ring.