COMPTON TAIL BACKGROUND DUE TO SODIUM ELEMENT IN BIOLOGICAL SAMPLES

The influence of Compton tail background on the PIXE detection limit is discussed in the case of human serum as an example of biological samples containing sodium element. The PIXE spectrum of the human serum for 3 MeV proton bombardment was measured with a Si(Li) x-ray detector and the Compton tail edge of 440keV γ-rays from ²³Na in the serum was observed at the x-ray energy of 278.4 keV. The spectrum of the Compton tail was measured for the 511 keV γ-rays from a ²²Na source and compared with a theoretical one. It is found that the intensity of the experimental Compton tail below 35 keV is two~three times larger than the theoretical one. Minimum detection limits for the elements of Z=35~55 in the human serum were estimated by using experimental Compton tail background.