the region of the whole of the Baltic Sea (14.10. to
3.11.).

04.12.1986

Commencement of the investigations with RV "Gauss"” in
the German Bight (04.12. to 15.12.).

Investigations in the marine environment

4.1

Radiological measurement network

The radioactivity of the sea is registered, in the DHI's radiological
 measurement network, which consists of the fixed stations

Light Vessel "Borkumriff”",
Light Vessel "Elbe 1”,
Research Platform "Nordsee"
"Helgoland",
Light Vessel "Fehmarnbelt",

and the mobile stations

RV "Gauss”,
SWSV "Atair”",
and
SWSV "Süderoog”"

with an NaIl-Gamma radiation probe, with a continuously flushed,
lead-shielded measurement container. The water suction connections,
each according to station, are in 3 m to 5m water depth. The measurement
 probe on the Research Platform "Nordsee" is mounted direct
in open water at 15 m depth. The positions of the measurement network
 stations are shown in Fig. 1.

The first information about increasing radioactivity in the sea was
reported at the station Light Vessel "Borkumriff". On 03.05., at
about 21.00 hrs. - with the set in of thunder showers - the indicator
 on the equipment rose from a previous 480 impulses/min (Ipm)
to 900 Ipm., corresponding to circa 40 Bq/1l (see Fig. 2).

Ihe indicator at the station "Elbe 1” rose slowly, beginning at
03.05, from 22,00 hrs., from a previous 850 Ipm until 04.05., 00.00
hrs., to 900 Ipm, then further until 01.00 hrs. to 1200 Ipm, and until
 03.00 hrs. to 1300 Ipm. The increased count rates correspond
each time to 5 Bq/l, 35 Bq/l, and 45 Bq/l. The measurement values
continued to rise slowly in the days following. Nevertheless, this
could be traced back to contamination of the measurement container,
and could be counteracted by cleaning. On the station "Helgoland", a
first increase of the activity in the water was ascertained on