How did ernest rutherfors deduce that he had observed a transmutation in his cloud chamber?

Ernest Rutherford deduced that he had observed a transmutation in his cloud chamber when he detected alpha particles emitted from radium that transformed into helium nuclei. By analyzing the tracks left by these particles in the cloud chamber, he noted that the characteristics of the emitted particles differed from the original radium, indicating a change in atomic structure. This observation suggested that one element was changing into another, leading to the conclusion that a transmutation had occurred.