Hi, I thought I would write a guide for the person interested in radiation measurements. The first instrument you should buy is a CDV-700 which was made during the cold war early years. The CDV-700 is able to detect High Energy Beta and Gamma radiation. It uses a 6993 detector tube which has a thick wall steel enclosure, and because of this cannot detect Low Energy Beta or Alpha radiation.
You will then want to purchase a Thin Window Pancake Geiger Muller detector like a Ludlum 44-9 wand.
This detector can detect Alpha, Beta and Gamma and is the principal detector of choice for both civilian and government workers who are interested in contamination by radiological contaminants.
A Scintillation detector is very important next. This detector is typically a NaI(Tl) Sodium Iodide doped with Thallium - Scintillation Crystal which produces visible spectrum photons when exposed to Gamma Radiation and the photons are detected with a Photo Multiplier Tube and converted to a radiance measurement.
If you have questions about these types of equipment, please email me at richwestfall@comcast.net and I will try to answer your questions.

Thanks - Rich Westfall 303-433-1978