4.1. PHYSICAL MONITORING
The physical monitoring has been carried out since the summer of 1993 in
full range (Figure 2). The radio ecological status of the Rila Mountain
was studied by measuring the local gamma background and radon 222 for each
sampling point. Laboratory determination of radioactivity in samples representative
for the ecosystem was made.
Figure 2. Physical monitoring
Environmental gamma background counting was carried
out directly during the time of sampling and by long-term measurements
using Bulgarian termoluminescent detectors (TLD) [2,3]
or computerized and automated SBN90 SAPHYMO detectors [9],
placed in Shoumen, Sofia, Kurtovo and Hotovo.
A method based on combination of TLD [2,3]
and French solid-state track detectors (SSTD) [4] for
integrated measurements of soil-gas radon 222 concentrations was developed
and applied [5].
The radioactivity was determined by gamma spectrometry
[5,6,7] and total
beta activity [7,8] measurements
in more than 
600
samples of various origin selected to be representative for the ecosystem
at altitudes between 1100 – 2925m a.s.l. The total beta- activities were
controlled by low background measurements [4,7]
realized by beta low- intensity devices. The total alpha activity was controlled
by TLD and track detectors estimating the ratio [238Pu/(238Pu+ 240Pu) ].
Gamma spectrometric analysis was carried out on sediments from the lakes,
as well as on soil samples from the lake surroundings [8].
The elements Pb-210, Cs-134 and Cs-137 were determined.
The results obtained for the radio ecological status
[8,10,11,12]
of the investigated region can be summarized as follows:
-
the radiation background primarily depends on the presence and concentration
of natural radio nuclides as well as on the altitude;
-
the presence of artificial radio nuclides is due to the atmospheric transfer.
The impact of the Chernobyl disaster is still dominant. It is most evident
in the total beta activity of litter layers;
-
the river water samples show normal values for total beta activity;
-
the experimental results vary within relatively narrow limits for soil
samples, while their variability is considerably higher for biological
monitors.
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