  In the framework of rare event searches, the identification of radioactive
contaminants in ultra-pure samples is a challenging task, because the signal is
often at the same level of the instrumental background. This is a rather common
situation for $\alpha$-spectrometers and other detectors used for low-activity
measurements. In order to obtain the target sensitivity without extending the
data taking live-time, analysis strategies that highlight the presence of the
signal sought should be developed. In this paper, we show how to improve the
contaminant tagging capability relying on the time-correlation of radioactive
decay sequences. We validate the proposed technique by measuring the impurity
level of both contaminated and ultra-pure copper samples, demonstrating the
potential of this analysis tool in disentangling different background sources
and providing an effective way to mitigate their impact in rare event searches.
