You can purchase an off-the-shelf adjustable high voltage power supply suitable for this project. Using the power supply we wire up our components as detailed in the schematic, photo of set-up is shown below.
The metal plate has two 1/8" plastic squares next to it. The prototyping board rests on the plastic squares as shown. The wires are positioned approximately 0.1" above the metal plate.
Next bring an alpha particle source close to the detector you will be an electrical discharge between the wires and HV plate.
Power is applied to the detector. There should not be any electrical discharge until an alpha particle shown is brought near the detector. If your detector immediately begins to arc, (have a discharge between the wires and plate) use the potentiometer on the adjustable power supply to reduce power. If that doesn't work, you need to increase the space between the wires and the plate. Also note, the .003 copper wires should be soldered taunt across the opening so that they do not droop down close to the plate.