Table 3.
a
«“
Survey area
SumMARY oF 1962-63 SuRVEY RESULTS
No.
Dose-rate range (ur./h)
Date
Loc. (naturally)
(fall-out y)
New York State
(1) South and west
(2) North
(3) New York City
Vermont
New Hampshire
South-eastern U.S.*
(1) South Carolina
(2) North Carolina
Western U.S.
(1) Black Hills, 8.D.
(2) Seattle, Wash.
(3) Olympic Peninsula, Wash.
{4) San Francisco, Cal.
(5) Nevada-Utah
(6) Denver—Colorado
Springs, Col.
Central U.S.t
8/63
3/63
5-9/62
5-9/63
7/62
35
19
3
3
26
5-7
4-38
5-10
7
4-8
3-4
3-5
3+5
4-5
2-3
7/62
6/63
9/63
4/63
4/63
4/63
39
5
10
3
6
2
6-15
6-8
6-15
3-7
3-10
15-140
2-3
3-6
3-5
4-7
4-7
2-4
10/62
10/63
10/62
10/62
16/62
10/63
10/62
10/63
10/62
10/63
10/62
10/63
6
4
3
9
6
6
6
3
9
10
15
11
68
6-3
4
3-5
4-8
5-8
5-9
5-9
9-14
9-15
7-9
7-9
2-5
3-4
2
1-4
1-2
1
1-4
2-3
2-3
1-2
3-6
2-4
8/63
6
4-8
4-5
* Includes locations in Texas (2), Louisiana (1), Arkansas (1), Alabama(2),
Tennessee (1), and Georgia (1).
¢ Includes locations in Wisconsin (1), Minnesota (1), Eastern South Dakota
(4), [ilinois (4), Kansas (3) and Missouri (2).
near ontrances from outside.
Spiers* has observed dose
rate increases inside various structures during periods
of high fall-out deposition, although these were generally
of lesser amplitude than the corresponding outdoor
changes.
It is evident that the effect of deposition of
fission products in the environment on indoor y-radiation
levels must be strongly dependent on the type of building
material, thickness of the walls, the number and size of
apertures in the walls (that is, doors and windows), the
location of rooms, the presence of other buildings nearby,
as well as the degree to which the fall-out is tracked
indoors. Spiers® has suggested applying a shielding factor
of about two to outdoor measurements as a means of
estimating an upper limit to the dose-rate contribution
of fall-out to general population exposure, this figure being
derived from ground-floor observations in houses. The
removal of artificial radioactivity from hard surfaces by
weathering processes plays a part in reducing the outdoor
exposure-level of the population, particularly in urban
areas where a large number of people see very little open
ground.
It is probable that open field measurements
provide a substantial overestimate of the total exposure
of the population to fall-out y-radiation.
Table 3 presents a summary of the results obtained
during the 1962 and 1963 survey trips with respect to
both natural and falJ-out y-levels. The dose-rate ranges
quoted generally include about 80-90 per cent of the
individual measurements at various locations in the
particular areas. The detailed data for individual loca8