Radiographic x-ray flux monitoring during explosive experiments by copper activation

During radiographic experiments involving explosives, it is valuable to have a method of monitoring the X-ray flux ratio between the dynamic experiment and an X-ray taken of a static object for comparison. The standard method of monitoring with thermoluminescent detectors suffers the disadvantages of being sensitive to temperature, shock, UV radiation, cleanliness and saturation. We are studying an additional flux monitoring system which is not subject to any of the above disadvantages and is based upon the 63Cu(photon,n)62Cu reaction. The 62Cu has a 10 min. half-life and is counted by a nuclear pulse-counting system within a few minutes of an explosive test. 170 MicroCoulomb of 19.3 MeV electrons hitting 1.18mm of Ta produces X-rays which illuminate a 0.8mm thick by 1.6cm diameter Cu disk placed 46cm from the Ta. The activated Cu is placed in a counting system with a window between 400-600 keV and produces about 42500 counts in the first 100 sec counting period. Less than 0.2% of the initial activity is due to other reactions. Photo-induced neutrons in Be parts of the system are shown to produce a negligible effect in the Cu. The main disadvantage of the Cu activation is its sensitivity to electron energy. Monte-Carlo calculations of the excitation function for our accelerator are shown, along with excitation functions for three other configurations