Experimental investigation of the KLL Auger spectrum of 88Sr from the EC-decay of 88Y

According to the calculations, intensity of the KL1L2(3P0) Auger transition should drastically increase with increasing atomic number Z due to the relativistic effects. However, this behavior was experimentally proved only for very few elements. A lack of enough precise experimental data in the atomic number region Z<45 does not enable one to distinguish between relativistic and non-relativistic approaches in this region. Thus for Z=38 the KL1L2(3P0/1P1) intensity ratio was determined with relative uncertainty of 63 % in the only measurement with external excitation. Here we present results of our investigation of the KLL Auger electron spectrum of 88Sr generated in the EC decay of 88Y (T1/2= 106.6 d). Electron spectra were measured with the 11 eV instrumental resolution using a combined electrostatic spectrometer. The present value of the KL2L3(1D2) absolute transition energy in Sr is higher by 7.4 eV (i.e. more than 3σ) then that obtained in the previous measurement which agrees with the prediction within uncertainties. Taking into account a chemical form of 88Y in our source and available experimental data on chemical shifts of Sr Auger transition energies one can make a conclusion that the discrepancy found can only be caused by the 'atomic structure effect' and a value of this 'atomic structure effect' shift should be higher than 7.4 eV. The obtained value of 0.14(3) for the KL1L2(3P0/1P1) transition intensity ratio is much more precise than the previous one of 0.19(12) and agrees within 1σ with the relativistic calculations but differ by 4σ from the non-relativistic approach. Thus an influence of the relativistic effects on the KL1L2(3P0) transition intensity at Z=38 is evident