478
LOCKHART, PATTERSON, SAUNDERS, AND BLACK
in the troposphere; indeed, there was little information on levels of
either fission products or natural radioactivity in the air of the southern hemisphere.
Preliminary discussions were also underway during this period
regarding the advisability of including in the forthcoming International
Geophysical Year (IGY) program a study of atmospheric nuclear radiation, following the suggestion of The Netherlands. In this regard, it may
be of interest to note here that the U.S. Naval Research Laboratory
(NRL) had previously, in 1954, recommended that the U.S. National
Committee for the IGY propose to the international organization a
comprehensive program of measurement of both natural and fissionproduct activity in the air; this recommendation was not carried out,
however.
It was with this background information in mind that representa-
tives of NRL, the Division of Biology and Medicine of the U. S. Atomic
Energy Commission (AEC), and the U. S. Weather Bureau met and con-
cluded that a program of measurement of fission-product activity in
the air was desirable, regardless of whether or not it later became a
part of the proposed nuclear-radiation study of the IGY. Everyone contacted in regard to participation in this program was enthusiastic about
it, and excellent cooperation was obtained from all participating groups.
This program has been financed jointly by the Office of Naval Research
and the Division of Biology and Medicine, AEC.
Actual operation of a portion of the network of stations began in
May 1956; air filters were used at a few sites, and standard AEC
gummed-film fallout collectors and experimental NRL cheesecloth collectors were employed at others. As they became available, filters and
blower units were supplied to all stations. Later, cheesecloth and
gummed-film collections were discontinued because of their lack of
correlation with air-concentration measurements. By the start of the
IGY in July 1957, an effective 80th meridian network was in operation,
with daily collections of gross fission-product activity from the air at
ground level being taken. The sampling sites and cooperating agencies
participating in this program are listed in Table 1.
In December 1962 NRL voluntarily terminated its association with
the 80th meridian network and transferred direction to the Health and
Safety Laboratory (HASL), AEC. A complete listing of NRL reports and
publications resulting from this AEC-sponsored program is included
in the reference section (Refs. 1 to 26),
PROCEDURES
Positive-displacement blowers were used to draw air through 8-
in.-diameter absolute filters (Navy equivalent of ACC type 6 cellulose —