RADIOLOGICAL CHARACTERIZATION OF PHOSPHATE FERTILIZERS: COMPARISON BETWEEN ALPHA AND GAMMA SPECTROMETRY

The natural radioactivity, 238U, 234U, 235U, 228Th, 230Th , 232Th 210Pb , 210Po 226Ra , 228Ra and40K, has been measured in phosphate fertilizers used in central Italy. Radiological characterization of phosphate fertilizers was performed by alpha and gamma spectrometry and the comparison between the results obtained by these two techniques was done. The concentration activities for the different radionuclides found in the fertilizer samples are different; it can be due to the different concentration of uranium and thorium series radionuclides in the raw material (phosphatic rock) and to the different composition of fertilizers. In the samples analyzed it is possible to observe that the 234U/238U activity ratio is approximately one. While the 226Ra/234U and 210Po/234U activity ratios are clearly lower than one indicating that the majority of 210Po and 226Ra tends to remain in the phosphogypsum. While the U-isotopes tend to be in solution with phosphoric acid from which all fertilizers derive. A very good correlation exists between the activity concentrations found by alpha spectrometry and those found by gamma spectrometry . Continued application of phosphate fertilizers to soil over a period of many years could eventually increase the radium and uranium content of the soil, which would result in an increase of the dose to bone. In any case in order to estimate the environmental impact of fertilizers use, it is necessary to evaluate the transfer of radionuclides and their concentration distribution in the environmental matrices such as soil,vegetation, milk, etc. and the individual doses by using mathematical models.