ABSTRACT
Comparative data on the daily concentration of fission
products in the air and the actual fallout on the ground have
been collected. For short times after a test, fallout was
very much dependent on rainfall. In many cases, the air
concentration wasaffected relatively little. On the average,
the apparent: “rate of fallout” was about 4 X 10‘ feet per day.
Screens made of cloth or metal mounted on a vane and
exposed to the wind were efficient collectors of fission
. products dispersed in the atmosphere. In some cases, 10
to 100 times as much activity was deposited on a vertical
screen as onan equal horizontal area. Nodefinite correlation
between gummed-paper, screen, and filter collections has
been noted.
Direct interception by the small fibers of vegetation, as
distinguished from simple fallout, may account for a large
fraction of the total fission product activity adsorbed on such
ground.cover.
_
Additional measurements were made on the distribution _ofactivity with particle size by the use of filter media of
different retention characteristics.
PROBLEM STATUS
This is an interim report; work on the problem is
continuing.
"AUTHORIZATION
NRL Problem A02-13
Project No. NR 612-130
Manuscript submitted August 20, 1955