Environmental Chemistry
Environmental chemistry.com: Periodic Table Actinium
A great site for just about anything you could ever need or want to know about actinium.
Web Elements
Web Elements Periodic Table: Actinium
WebElements offers a nice set of basic data and information on the physical and chemical properties of actinium.
Florida-Spectrum Environmental Services
Florida Spectrum: Chemical Fact Sheet: Actinium
Some basic information stressing isotopes and half lives.
Royal Society of Chemistry
Chemical Society: Actinium
A short summary of some basic historical information on actinium.
TED Talks
Ted: Ted Ed: Actinium: Periodic Table of Videos
The team at periodicvideos has created a TED-Ed Lesson for every element of the periodic table. Actinium is element number 89, and first of the actinide series. [1:44]
Thomas Jefferson National Accelerator Facility
Jefferson Lab: It's Elemental the Element Actinium
Facts and historical information on the element of Actinium.
Chemicool
Chemicool: Actinium
A set of data tables with most of the key chemical and physical properties of actinium.
Corrosion Source
Corrosion Source: Actinium
This resource provides a summary of basic data and information on the properties of actinium.