Experimentation with JFET for an ion chamber detector

I am trying out an experiment using a JFET to detect ionizing radiation, but so far I can't find the MPSW45A's I need. Anyone tried this experiment.
http://www.techlib.com/science/ion.html

Looking at the simple ion chamber circut.....

 

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Thats a cool project, you might be able to make your own darlington pair from normal transistors which would have a really high gain, not too sure what the leakage current would be, it should be very low, sometimes a resistor is put between base and emitter of the two transistors to prevent leakage current.

try this site for your mpsw45a's, if you click on order samples and say you are using them for developing a new product they will probably give them to you for free.

https://www.onsemi.com/site/products/availability/0,4413,,00.html?searchString=mpsw45a

 

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