Activity concentration and distribution of ⁴⁰K in the soil profile of the Rostov agglomeration

The activity concentration of ⁴⁰K in soils of Rostov agglomeration was studied. Natural and anthropogenically modified soils of Rostov agglomeration were studied: Haplic Chernozems, Haplic Chernozems (Technic), Urbic Technosols. Activity concentration ⁴⁰K in soils was measured by gamma-spectrometric method of radionuclide analysis. The total mass fraction of K₂O was determined by X-ray fluorescence method on a Spectroscan MAKS-GV instrument. Knowing the total mass fraction of K₂O, we calculated its potential radioactivity based on the fact that one gram of natural potassium has an activity concentration of 28.5 Bq. Comparison of the two methods allows estimating the involvement of ⁴⁰K in biogenic cycles. No significant differences between the actual and calculated activity concentration of ⁴⁰K in the soil-forming rock were revealed, while in horizons A and B the calculated activity is significantly higher. At the same time, there are no reliable differences between native and their buried analogs. The direct influence of the granulometric composition on the activity concentration of ⁴⁰K was not established, but in the urban horizons with lightened granulometric composition the average activity of ⁴⁰K is the lowest by reliably significant values when comparing this index with native, buried horizons and the group of heavy urban horizons. This implies that ⁴⁰K is more actively involved in biogenic cycles than its stable isotopes. The burial under urban deposits is accompanied by a weak change in the activity concentration of ⁴⁰K in the profile, while the difference between genetic horizons is leveled out.