Abstract. This paper proposes an empirical study of inductive Genetic Programming with Decision Trees. An approach to development of fitness functions for efficient navigation of the search process is presented. It relies on analysis of the fitness landscape structure and suggests measuring its characteristics with statistical correlations. We demonstrate that this approach increases the global landscape correlation, and thus leads to mitigation of the search difficulties. Another claim is that the elaborated fitness functions help to produce decision trees with low syntactic complexity and high predictive accuracy.

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We describe a fast method for the determination of ""Sr and 89 Sractivity in environmental samples. In case of a nuclear event it allows to get information within two days about the contamination of soil. After sample ashing, strontium is separated from the matrix as sulphate. Radiochemical cleaning is continued by combined use of an extraction column and of a Chromate scavenger. With 50% chemical yield, the minimal detectable activity of 89 Sr in the liquid scintillation vial depends on the background caused by potassium-40 contained in the vial material. Detection limits (DIN 25482) of 0.78 and 0.52 Bq can be obtained within two days for 89 Sr given ""Sr-activities of 1 and 0 Bq, respectively. For routine environmental monitoring the technique can be adjusted for exclusive '"Sr-determination. Assuming a 100 g soil sample and a 50% chemical yield for ^Sr, a detection limit of 0.20 Bq kg"' is reached within two weeks. The new method is exemplarily applied to the analysis of ^'Sr in Ukrainian soil profiles. The results are discussed in comparison to depth profiles of ,37 Cs and to deposition from global weapons fallout.

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