An experimental comparison of the K- and L-Auger electron spectra generated in the decays of 140Nd and 111In.

The low-energy electron spectra generated in the decay of 140Nd have been measured using a combined electrostatic spectrometer adjusted to the 4, 7, and 35 eV instrumental resolution. In order to estimate the therapeutic potential of low-energy electrons associated with the decay of 140Nd, similar experiments have been performed with 111In. Relative Auger electron intensity ratios per decay are: 111In(K-Auger)/140Nd(K-Auger)=1.47(12), 111In(L-Auger) /140Nd(L-Auger)=1.1(4), and 111In(L-Auger [2.8-7 keV])/140Nd(L-Auger [2.8-7 keV])=0.24(11). The obtained K-Auger group intensity ratios have been compared with results of calculations. The good agreement found for the experimental and estimated values indicates that such information can be also derived using available nuclear and atomic data. The relative intensity of L-Auger electrons emitted within the 2.8-7 keV interval is higher for 140Nd by a factor of about 4 compared to 111In. As the L-Auger emission is dominating relative to that of the K-Auger group, this implicates that any potential endotherapeutic strategy using 140Nd-labelled targeting vectors requires a maximum accumulation of the endoradiotherapeutical close to the cell nucleus or the DNA of the tumour cell.