ACCURATE is a dedicated ASIC developed to be the next generation of read-out electronics for CROME radiation monitoring. It is designed to measure the current generated by ionization chamber from fA to 20μ A. It exists as a mixed-signal chip (ACCURATE2M) in which the analog signals are directly processed to be sent via serial communication or in an analog-only version (ACCURATE2V1), where the digital section is embedded in a FPGA.
After characterizing it with a reference current source, it was needed to test it when connected to ionization chambers. A first test was done at the calibration lab where Cs137 sources were used to generate dose rates ranging from 5nSv/h to 150mSv/h. Three different ionization chambers were used (Centronic IG5-A20 and IG32 and PTW T32006) and the chip successfully measured current from 0.1pA to 300nA.
To extend the tested current range, a similar experiment was done at the Co60 facility where dose rate ranging from approximately 160mSv/h to 7.4Sv/h. These two values are based on a measurement done with a secondary ionization chamber placed next to the main one, thus it does not represent very precisely the real dose rate that was delivered. Nevertheless, this is sufficient since all measurements were done by comparing ACCRUATE’s output to a reference electrometer (Keithley 6517B).
Mixed-signal and analog versions of the ACCURATE current measurement ASIC were successfully tested at the Co60 facility under dose rate ranging from 180mSv/h to 7.4Sv/h. These tests showed that the ASIC can measure current up to 5.5μ A when connected to an ionization chamber with a global error smaller than ±6%. This extends the range in which the chips were tested in real conditions, however, the 20μ A limit was not reached. Placing the ionization chamber closer to the collimator to increase the dose rate with a given radioactive source was unfortunately limited by geometrical consideration, as a smaller part of the chamber volume would be covered by the beam.
For pulsed radiation, we have used the same setup at PS-AIF above AD. The result are very promising and will be published soon.