And is it possible that you (pito) may make a circuit diagram or something for me
Both circuits are depicted in the pdf above.. Just connect the LM311 one to the output of the diode amplifier, and do power the LM311 with 5V instead of 9V (power it from arduino's 5V). Connect output of the LM311 (let R6 there) to an arduino input. Read the pdf article.
Use a 10turn potentiometer as the P2 - the comparator trigger level to set will be difficult otherwise. The "issue" with this kind of detector is the amplitude of the pulses from the amplifier differs based on the particle's energy. So proper setting of the P2 will be the key here..