These check sources are a plastic discs. The small quantity of radioactive material is sealed in the plastic with epoxy to prevent leakage and contamination. The transmission window is sufficiently thin to transmit both beta and gamma emissions without undue absorption. Disc sources are available in 1 inch and 2 inch diameter plastic disc with 1 inch being standard and other sizes on special orders. Pricing for a standard check source Cs-137, 10uCi is $150 plus applicable tax.