■ This LED should
be flashing, rather
than remaining on
constantly.
the ON position.
That is, it would
produce a
continuous signal
rather than the
click-click of cosmic
ray detections. So
to be sure, I loaded
the Geiger counter
and nine volt
battery into the
clear plastic jar of
my environmental
test chamber and
pumped it down.
Initially, the Geiger
counter behaved as normal, giving the occasional click as
the chamber was brought to a vacuum. Then, around 28
inches of vacuum (roughly 70 mb of pressure), the
indicator LED began flashing faster until it remained on
constantly. Oops, corona discharge. Corona discharge can
be a real pain to locate because it often can’t be seen. I
initially assumed the discharge was occurring from the
high voltage traces on the underside of the PCB. I applied
a liberal coat of hot glue over these traces and exposed
the Geiger counter to the vacuum a second time. It was
still arcing, but at a lower pressure now, so hot glue was
covering up some of the problem. On the second fix, I
coated both ends of the GM tube in hot glue and tried
again. That did it; I could pump the vacuum chamber to
as high of a vacuum as my pump could handle without
the Geiger counter suffering from corona discharge.
FLIGHT RESULTS WITH THE
NEW GEIGER COUNTER
Last April 17th, I launched my first near space flight of
2010 in conjunction with the University of Kansas. The
AE360 class — Introduction to Aeronautical Engineering —
had built BalloonSats and was ready to fly them. I
provided two tracking capsules as the student BalloonSats
■ Not pretty, but hot glue is very insulating. Best of all, it
can be removed more easily than epoxy.
70
July 2010
did not contain GPS receivers or radios. (I like to think I’m
providing the Space Shuttle that students are flying their
experiments onboard.) The flight reached 102,500 feet
and landed in a tree, about 40 feet above the ground.
Along with a weather station and camera, I flew the
RM- 60 and Electronic Goldmine Geiger counters. The
number of detections (clicks) from both units was counted
for 10 seconds at 30 second intervals. I converted the
counts for each detector into counts per minute and
graphed the results. The first thing to notice is that the
Goldmine Geiger counter always detects more radiation
than the RM- 60 (even when its multiple pulses per detection
are taken into consideration). Even on the ground, there
are more detections by the Goldmine Geiger counter. Why
this is the case, I’m not sure. Aware Electronics makes a
calibrated Geiger counter that’s suitable for serious studies,
so I trust the numbers of the RM- 60.
Next, I noticed that the Goldmine Geiger counter
detected a drop in the cosmic ray flux for the first 3,000
feet. This is pretty much what Hess detected. Above 3,000
feet, the cosmic ray flux increased as the altitude
increased for both Geiger counters. This was also
expected as there is less air to filter secondary cosmic rays
as the balloon climbs higher. Around 62,000 feet, the flux
dropped off as the balloon began sampling more primary
cosmic rays before they could create a secondary shower.
The RM- 60 Geiger counter had always shown this peak,
however, the other Geiger counter showed it weakly, if at
all. What about that drop-off that begins at 101,000 feet?
It looked too substantial to be a glitch or random
variation. To clear that up, I’m going to have to fly the
Geiger counters again.
WHAT DOES IT MEAN?
After some discussion with near space groups on
GPSL, we figured the Goldmine Geiger counter GM tube
has a larger volume and therefore detects more radiation
■ Trees are near space magnets. There was plenty of open
space around our recovery site, but against the odds, we
landed in a tree too high to climb. Now, where is that rope?
