Actinium (89)
Periodic Table's 89 th atom is Actinium This atom is a radioactive, long-lived, small traces in nature. It is used cancer medicine and neutron sources.
Thorium (90)
Periodic Table's 90 th atom is Thorium This atom is a radioactive, long-lived, most abundant radioactive element, nuclear reactor fuel, gas lamp mantles, tungsten filaments.
Protactinium (91)
Periodic Table's 91 th atom is Protactinium This atom is radioactive, long-lived, dense. Small traces in nature and no uses
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