Last week I launched two geiger counters into near space. The mission was for KU aerospace engineering students and I got to send my experiments along in the tracking capsule.
The first geiger counter is the reliable Aware Electronics RM-60. I've flown this geiger counter dozens of times and really love it. It measures everything, alphas, betas, and gammas. Aware has a range of geiger counter products that you'll love. See them at http://www.aw-el.com/
The second geiger counter was built from a kit that's available from Electronics Goldmine. The tube is Russian built and does not include a mica window for alpha particles. Here's the webpage for this product. http://www.goldmine-elec-products.com/prodinfo.asp?number=c6979
The Russian tube is suppose to be pretty sensitive. In my tests, it detects more background radiation. However, I don't have a calibrated source that I can verify that it's actually detecting properly. I have s short video on a test that you can watch on my YouTube channel, www.youtube.com/nearsys.
Below is a chart I produced with data from NearSys-10A. Note how much more radiation the Goldmine geiger counter is detecting.
Normally the RM-60 shows a drop off at 62,000 feet. The driop off doesn't happen until closer to 70,000 feet and it doesn't show up well at all for the Goldmine detector.
So much more to learn!