Photomultiplier tube circuit

[Vlad.]

Hello guys, I am working with some R7600 MapMTs from Hamamatsu, and i try to read the dark current.
This is the circuit that I have proposed to use for this purpose. Can someone with experience look at this schematic?
I need to measure current about 2..20nA.
Thank you.

 

[FvM]

AD8009 is the wrong device. You'll use a CMOS or FET input OP with low input current.

By a second stage gain of 151, the input current range is limited to +/- 1.5 nA, so it won't work for intended pupose.

 

[chuckey]

Do not photomultiplier tube operate with > 600V and a high value load resistor? I would have thought the main problem is keeping the 600V out of your metering circuits.
Frank