Completely safe for use in the science laboratory! Each source is mounted in a one-inch diameter sealed disc and is completely safe for student use. Three radioactive sources are available; Alpha, Beta, and Gamma. Perfect for showing the different properties of radiation. For instance, students will be able to see that alpha particles can be blocked very easily yet gamma rays are nearly impossible to block. These sources also allow you to compare different types of radiation. The isotope name, type of radiation, activity in microcuries, and half life is written on each sealed disc. Cobalt-60, Polonium-210 and Strontium-90 are included in the Radioactive Source Kit AP8796. Best if used within four months of delivery due to half life of polonium.Nuclide Activity half Life Type of Radiation Polonium-210 0.1 ï¿½Ci 138 days AlphaThallium-204 1.0 ï¿½Ci 3.78 years Beta Cobalt-60 1.0 ï¿½Ci 5.27 years Gamma Strontium-90 0.1 ï¿½Ci 28.6 years Beta You may purchase three types of radioactive sources separately.