TRAY AND CLOTH SAMPLES, LRL, BERKELEY
Two static-sampling devices are utilized for monitoring ambient outdoor
air.
These are trays and cloth screens.
A coated metal tray of 17" x 14" x 7/8" size 1s clamped on a plywood
turntable.
A vane on the table is the means of facing the same long side
of the tray to the wind.
Wo provision is made for retention or drainage
of rain water. A cloth screen, open weave of fiberglasea material, is
mounted in an eight inch square frame underneath the turntable and just
back of center. Thus the screen ia always faced to the wind and is
sheltered from all but driving rains.
Five sampling stations of one tray and screen each are widely spaced
about the project. A sixth station is maintained for reference purposes
approximately 70 miles north of San Francisco Bay at St. Helena. All
samplers are mounted on five to eight foot high posts away from wind
obatructions.
Periodically, the samplers are changed; the period varies with unrelated
factors, such as available manpower and nuclear testing.
After 48-hour decay, processing of samples involves radioautographing
the pans and screens, and in addition, instrument counting of the latter.
Kodak type KK x-ray film size 16 7/8 x 13 7/8 is placed against the tray
and/or screen for one-week exposure. The number of resultant "spots" on
the developed film is taken as a measure of the activity. A "spot" is
defined as that area bounded by the circumference of a circle (in which
the darker portion just fades to the film background) which touches
the four sides or overlaps the smallest square of a particular size
graph paper.
The "spote" are counted on a back-illuminated glass plate covered with
& graph paper.
1)
2)
3)
The various size graph papers used are as follows:
10x 10 to one-half inch, Keuffel and Esser #359-11L
10x 10 to inch, K & E #359-5DG
5 x 5 to inch, K & E #359-2
A Q.M. tube (see Daily Air Samples, LRL, Berkeley) is used to obtain the
beta-gamma counts.
counts.
A zinc-sulfide crystal is used to obtain the alpha
Information prior to the reporting period is included in the data compilation below. This is done to give the reader a "feel" for the variability
of the determinations; the method, after all, is considered in the exploratory stage.
For the purpose of this report mich of the data has been compressed into
averages, and only the total number of "spots" greater than 1/20" diameter
considered.