Investigations of the transient responses of several semiconductor photocells employed in clinical dosimetry

Conclusions

1. It has been shown that the rise time for both kinds of phototransducers is approximately the same when the signal across the load resistance is equal. Consequently, the choice as a component in a detector for ionizing radiation of a silicon or gallium arsenide transducer is dictated by other factors (temperature stability, sensitivity, etc.).

2. When the light excitation levels are low (for instance, when a combination detector is employed in clinical dosimetry) and the load resistances are in the order of several kilohms, the time constants of the Si and GaAs transducers investigated amounted to between 0.2 and 0.6 µsec. Such a short rise time was entirely satisfactory for making the majority of dosimetry measurements and made it possible (in a number of cases) to simplify the amplifier portion of the dosimetry apparatus.

3. In those cases where higher requirements are imposed on the response speed of detectors (for the adjustment of x-ray apparatus, etc.), a series connection of several semiconductor components of the type mentioned must be employed.

4. In order to reduce errors during the measurement of the average current value for a pulse or for pulsed radiation, it is advisable to include additional capacity in the measuring circuit.