Re: High Altitude Radiation?

[mcnaught@lanl.gov (Mike McNaughton)]

>Our campus amateur radio club recently launched a balloon with an
>amateur radio package attached.  In addition to the amateur radio
>gear, there was a Geiger counter and data acquisition system on board.
>They looked at the data and then came to me with questions.  They
>basically were looking at counting rate versus altitude.  The numbers
>they got are (cpm = counts per minute):
>    ground - 16cpm
>    60,000ft - 800cpm
>    90,000ft - 600cpm
>
>According to the manufacturers calibration data, 1cpm = 1 microR/hour.

Reply:
This is an approximation that is only true for a certain spectrum of radiation.

>Their questions are:
>1) Why is the counting rate higher at 60,000 than 90,000?

At very high altitude cosmic rays consist of a smaller number of particles
each with a higher energy (typically GeV, often TeV, sometimes more). When
one of these high energy particles hits the atmosphere it creates a
"shower", i.e. a larger number of particles and photons each with a lower
energy.  The Geiger counter counts particles without regard to the energy
of individual particles. Thus at higher altitude its count rate is lower,
though the total dose rate may be higher.

>2) What kind of radiations are they seeing (x-rays, mesons)?

Just about everything. Cosmic rays are mostly protons in the GeV to TeV
range to begin with. At lower elevations the shower consists of muons,
electrons, photons, and anything else that can possibly be made from the
original amount of energy.


"Shlala gashle" (Zulu greeting, meaning "Stay safe")
mike (mcnaught@LANL.GOV)