NAVAL RESEARCH LABORATORY
5
TABLE 4
Comparison of One-Week Screen and Cloth
Collections at Washington, D. C.
;
ernie
3/28
4/4
4/11
4/18
4/25
5/2
80-Mesh
Stainless-
Cheesecloth
(d/m)
(d/m)
Steel Screen
~
Coneoon
‘|
.
Screen
fin)
,
- 4/4
-4/11
- 4/18
~ 4/25
~ 5/2
~-5/9
7, 700
3, 800
75, 000
1,500
1,900
14, 000
6, 300
6, 700
140, 000
7,100
3,600
23, 000
0
0.07
1.50
0.47
| 0.40
0.01
5/16 - 5/23
5/23 - 5/31
4, 700
---
59, 000
24, 000
0. 50
1.11
5/9 - 5/16
2,600
9,800
{1.62
TABLE 5
Comparison of Gummed-Paper and Cloth-Screen
Collections at Washington, D. C.
™“
(3/28/55 to 5/31/55)
.
.
Total Activity Collected
Total Activity Deposited Total Activity Collected
by Filter Papers
on Gummed Papers
{by Cloth Screens
1.9 * 10°
"2.8105
- (d/m/ft?)
(3x 10° cu ft of air)’
(a/m)
(d/m)
1.8 x 10°
An attempt was madeto relate the mesh size of the screen to the amount of activity.
collected. Comparative measurements of various one-week collections by electrically
grounded screens are shown in Table 6 for four screen sizes. There does not seem to
’ be a significant difference between the collections obtained with any of the screensizes
used in the above experiments. The amountof activity was also not appreciably affected
by the screen’s being electrically grounded or well-insulated. However, the insulated
~ screen collected considerably more solid matter. The available information indicates
that screens collect activity through an impaction process. In the absence of rain, the
impaction of particulate matter on small fibers may be the most important means for the
removal of fission debris from the air.
Pack filters have been used to effect rough particle size differentiation of fission
products dispersed in the air. The filter pack consisted of three separate filter papers:
a top paper with a penetration of about 90% at one micron, a middle paper having approximately 50% penetration at this particle diameter, and a bottom paper having essentially
100% efficiency for particles as small as 0.1 micron in diameter.
Table 7 compares data obtained from collections of residual activity before the TEAPOT
tests with similar collections during the tests. Both sets of samples were measured at
.
approximately the same time on 30 March, andare not believed to be significantly different.
The data are in fair agreement with that obtained during Operation GREENHOUSE.
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