GLOBAL DISTRIBUTION OF TRITIUM
647
DESCRIPTION OF PROJECT
The International Atomic Energy Agency (IAEA) and the World
Meteorological Organization (WMO) have been jointly conducting a
worldwide survey of tritium in precipitation since 1961. The objectives
of the project are to compile data on the ground-level global distribution of tritium in precipitation, to analyze its migration patterns, and
to provide an accurate inventory in both area and time. Sample collection began in early 1961 at numerous Sites, and thus it has been possible to establish the base level for tritium prior to the resumption of
weapons testing in late 1961, to follow the rise of the tritium levels
through 1962 and 1963, and to detect the incipient decay in 1964.
The global sampling network is provided by WMO,It includes
102 stations distributed strategically over land and ocean areas in both
hemispheres. Collections of precipitation for one sample are made
over a period of one month in a standard rain gauge (usually 8 in.).
All collections are made at ground level. Samples of oceanic precipitation are taken at island stations and aboard weather ships.
The samples are sent from the collection stationsto IAEA and other
cooperating tritium laboratories for measurement of their tritium concentration. The organizations that contribute to tritium measurements
and their identifying code letters used in this paper are given as
follows:
International Atomic Energy Agency
International Meteorological Institute, Stockholm
Chalk River, Environmental Studies Group
Scripps Institute of Oceanography
Weizman Institute
New Zealand Institute of Nuclear Studies
Tata Institute of Fundamental] Research, Bombay
IA
Ss
CR
LJ
Ww
NZ
T
Additional data for North America provided by the U. S. Geological
Survey have been used in this report. The identifying code for these
data is GS.
The IAEA laboratory is now responsible for measurements from
approximately one-half of the stations in the network. In addition to
this, IAEA has the responsibility for the routine operation of the sample
transmission system, conducts periodic laboratory intercomparisons
to ensure the reliability of the data, assembles data from laboratories
outside the network which voluntarily contribute, and publishes net-
work and contributed data in Tritium Water Lists. Five of these lists
have been issued so far.
Measurement Technique
The tritium measurements are made according to the procedure
of Bainbridge et al.' by direct counting for “hot” samples and after