The cross section function of the Ca40(gamma,3p3n)Cl 34 reaction was determined by radiochemical techniques up to 70 Mev with the Iowa State College synchrotron. The Intensity of the X-ray beam was experimentally calibrated by three methods: (1) Known cross section for Cu63(gamma,n)Cu62 reaction; (2) Roentgen dosage measured with a thick wall ionisation chamber; (3) Calorimetrically calibrated ionization chamber. The three methods were evaluated;Reaction modes were discussed. The implication of the results were examined in terms of the statistical and hydrodynamic nuclear models.