Possible background reductions in double beta decay experiments

The background induced by radioactive impurities of ${}^{208}\mathrm{T}\mathrm{l}$ and ${}^{214}\mathrm{B}\mathrm{i}$ in the source of the double beta experiment NEMO-3 has been investigated. New methods of data analysis which decrease the background from the above mentioned contamination are identified. The techniques can also be applied to other double beta decay experiments capable of measuring independently the energies of the two electrons.