In this web page: http://physicsopenlab.org/2017/09/27/charge-sensitive-preamplifier/
If I do the quick computation (see below), I deduce that the web page made an error in the sign of the output voltage: it should be a voltage that goes more and more negative, and not as they show: more and more positive.
Am I right or is the web page right?
Now, a related question: if electrons would be created in the detector by an ionizing particle, will the current "id" be a positive pulse or a negative pulse ? I would believe that actually, id should be a negative pulse. In this case, we would obtain the positive output voltage.
Here is my computation: