This thesis deals with the detection and analysis of low-level natural and induced radioactivity. Using high energy-resolution Ge detectors in low-level counting areas airborne radioactivity’s like Be-7 and Cs-137 have been investigated. The experimental facilities and techniques are described in some detail.
One of the aims in this work is the studying of change detection in the amount of the activity received on the earth from events that happen at the solar system. Information about this is achieved by measuring the activity of the Be-7 isotope, which is a very good indicator of the solar protons that reach the atmosphere of the Earth. Therefore Be-7 probes the variation of the boundary conditions on the Earth related to solar events as well as transportation between the atmospheric layers, troposphere and stratosphere, which are the layers nearest to the ground. Results obtained by this work refer to the seasonal variation and the eleven years sun cycle in addition to the two to three years cycle expected by some scientists. These results are shown in many figures of the activity measurements and the Fourier transformation of the intensity of the Be-7.
The effect of the man-made radiation in the air was studied by collection of Cs-137, which was contaminating most of countries in the world after the Chernobyl accident. Our search for low levels of Cs-137 shows how important it is to use a Low Level Laboratory, like the one at AlbaNova, for measurements of novelty and change.
Studying the airborne activity in Sweden and Finland at the same time and time interval gives us a possibility to look for correlations of the fall down of the Be-7 activity from the upper layers of the atmosphere simultaneously in both countries.
This thesis also involves the results of Neutron Activation Analysis Technique applied to the general human food, milk, vegetables and grains. The experiments were performed at the neutron beam of the Iraqi reactor IRT 5000 at Baghdad. The goal of the experiments was to determine iodine and other trace elements after the Chernobyl accident compared to results from different countries.
An exploratory, preliminary study of airborne activities, following e.g. an accident at a nuclear power plant, or leakage of radiation from any source of contamination at any region, using a small, expendable unmanned aerial vehicle is also discussed briefly.
Stockholm: Fysik , 2007.
2007-06-05, Sal F32, AlbaNova universitetcentrum, Roslagstullsbacken 21, Stockholm, 10:00