The direct measurement of dose enhancement in gamma test facilities

The design and use of a dual-cavity ionization chamber for routine measurement of dose-enhancement factors in Co-60 gamma test facilities are described. The enhancement factors can be derived directly from the chamber measurements without recourse to reference data that may be difficult to obtain. It is shown, in agreement with earlier work, that the maximum dose-enhancement factors can be altered by a factor of two as a result of Compton scatter from relatively small amounts of low- or high-atomic-number materials next to the target. The dual chamber permits the ready detection of such effects. This relatively simple device reliably reproduced earlier results obtained by more involved equipment and procedures. The chamber can be calibrated to give an absolute dose reading for silicon, gallium arsenide, or any other material together with the associated enhancement factor. Measured enhancement factors are also reported for material combinations not previously examined and compared with recent calculations.>