Application of Transimpedance Amplifiers in PIN Photodiode Dosimetry

This paper analyzes the properties of commercial silicon PIN photodiodes BPW34 as direct
$\gamma$
-radiation sensors. Sample is formed by four photodiodes connected in parallel and polarized reversely. Current to voltage conversion and amplification is performed using a prototype circuit with a low noise transimpedance (TIA) operational amplifier with input current range of 1 nA -
$3.3 \mu \mathrm{A}$
. The voltage characteristic from the amplifier circuit and induced current characteristic is measured by source measuring unit (SMU) Keithley 2636A for the same irradiation dose rates. Sample is irradiated for 140 s using a 60Co
$\gamma$
-ray source. Obtained results have shown very good linearity between amplification circuit output voltage and induced photocurrent measured with SMU Keithley 2636A for dose rates ranging from 2.5 Gy/h to 11 Gy/h. Using voltage to current conversion formula, amplification of circuit input current is calculated and compared to induced photo current measured with SMU. These results show amplification circuit current error offset. Also, non-linearity results are shown for photo current under 1 nA. Due to offset error, but good linearity response, an output voltage vs. radiation dose calibration curve is given.