On the first balloon flight, at the last minute, Tom Boucher suggested putting some film aboard. Perhaps the elevated radiation rate at high altitude might expose the film. We ended buying a package of 4 x 6 photographic paper, placing sheets of aluminum foil in between (all this in the dark bathroom of the dark hotel room), and sending it up with the stack facing vertical. The flight went to 120,000 feet altitude for about 12 hours. What developed ? The scale here : the top picture's black streak is about 2 cm long. Are these black streaks caused by cosmic rays ?

For the October flight, we prepared a similar package, without the foil, but using papers of varying sensitivities...

For scale, the above streak is about 2 cm long.

(above) ~ 1 cm long streaks

(above) ~ .5 cm long streaks

(above) ~ 1 cm long streaks

(above) ~ .2 cm long streaks

(above) ~ .5 cm long streaks

(above) ~ .5 cm long streaks

(above) ~ .5 cm long streaks