fined to one station only, showed that the deposition rate increased after the thermonuclear
tests in the Pacific in 1954 and maintained a mean value of 2.3 mc/km*/year throughout the
period ending April 1956. This result was shown to be consistent with the fact, established
independently, that the debris from large-scale nuclear explosions is stored in the stratosphere
and is returned to earth slowly over a number of years.
With only one sampling station it was not possible to deal with the important questions of
the uniformity of this deposition over the U. K. and over the earth’s surface. A network of six
stations in the U. K. and thirteen in other parts of the world has now been set up, at which rain
water is collected over three-month periods and analyzed for Sr®*, sr®, ce'*, and Cs". Some
of these stations have been in operation since the middle of 1955 and an accountis given in this
report of the results obtained so far. The non-uniformity observed in the world pattern of
deposition shows that such global surveys are essential for a true assessmentof the fallout
problem, while the results as a whole throw someinteresting light on the mechanism whereby
fission products are transferred from the stratosphere to the troposphere and deposited on the
ground by rain water.
Table 1— LIST OF RAIN WATER COLLECTION STATIONS
Station
Mean annual
Longitude
Kinloss
57° 39'N
OF 34°W
70
January 1956
Liverpool
Snowdon*
Abingdon
53° 21/N
53° 04'°N
51° 41’N
51° 41’N
02° 58’°W
04° O1°W
o1° 18°W
05° 09°W
85
300
65
January 1956
October 1956
July 1955
Felixstowe
51° 58’N
OL 20'E
55
January 1957
Bodo
Esquimalt
67° 17°N
49° 30'N
14° 22°E
123° 00°W
87
79
July 1957
October 1957
July 1955
Milford Havent
Tromso
69° 42'N
rainfall, ems
Sampling
Latitude
19° OVE
75° 41°W
75
commenced
May 1954
68
June 1957
Ottawa
45° 20’N
100
Gibraltar
36° 10’N
65° 21°W
90
Caenwood
18° 13'N
76° 35°W
280
July 1957
Palisadoes
17° 56’°N
76° 47°W
80
July 1957
Port Harcourt
Singapore
04° 45'N
01° 19°N
07° 20’°E
103° 49°E
250
240
Suva
18° 05’8
178° 28°E
290
Melbourne
Ohakea
37° 45°S
40° 12’S
144° 50’E
175° 23/E
65
100
Port Stanley
51° 42’8
57° 52°W
65
July 1956
January 1956
July 1955
July 1955
—:
January 1956
July 1955
February 1956
* Two stations one 335 m higher than the other.
{1 Monthly and three-month samples.
2
NETWORK OF RAIN WATER COLLECTION STATIONS
A list of the stations in current operation, arranged in order of latitude is given in Table 1
together with the dates when sampling commenced. The period of sampling at all stations is
three months (January to March, April to June, etc.) but the monthly sampling at Milford Haven,
which was started in May 1954 has been continued to provide somefiner detail. The stations in
the mountainous region near Snowdon were chosen because the rainfall there is about four times
the average for the U. K.; one of the two Stations is at an altitude 335 metres above the other.
The recently commissioned stations in the West Indies, Caenwood and Palisadoes, were selected
because they have quite different rainfall patterns although they are close together geographically.
Sampling at latitudes north and south of 60°N and 55°S, respectively, is difficult because of
the lack of suitable stations and because of the problems associated with snow sampling.
Through the kindness of T. Hvinden of the Norwegian Defence Research Establishment, snow
cores and samples of summer rain have been obtained from latitudes up to 70°N. Through the
232
ipearsageatas