The University of Iowa

SAFETYmatters - Uranyl Acetate

Uranyl acetate (UAc) is a yellow compound that contains a small amount of radioactive uranium.  There are three isotopes of uranium that occur in nature, and each is radioactive.  U-238 makes up the bulk of naturally occurring uranium, at 99.27%, with U-235 and U-234 making up 0.72% and 0.006% respectively.  The effective half-life of uranium is close to 4.5 billion years, which means it takes nearly 4.5 billion years for only half of all uranium atoms to decay to a different element.  The elements formed by the initial decay go through several more nuclear transmutations on their journey to becoming a stable (non-radioactive) isotope of lead.  The fact that there is an abundance of lead on the earth is evidence to the relative age of our home planet.

Commercially available uranyl acetate typically contains quantities of radioactivity that are below the level at which many of the regulations and licensing requirements for radioactive material apply.  In fact, it is generally purchased as a chemical compound without regard to its radioactivity.  Uranyl acetate is extensively used as a negative stain in electron microscopy.  In fact, most procedures in electron microscopy for biology require the use of uranyl acetate.  Although not a significant hazard from a radiation safety standpoint, uranyl acetate does represent a chemical hazard, and as such must be handled with care.  Skin contact should be avoided due to the potential for skin irritation.  In addition, measures to prevent ingestion and inhalation must be taken, as UAc is potentially harmful to the lungs, kidneys, and blood.  Please contact EHS if you have questions on the safe handling and use of uranyl acetate. 

EHS uses a powdered form of this compound to make instrument functionality check sources which are typically affixed to the side of radiation detection equipment used throughout campus and UI Healthcare.  You may have seen these – a small amount of UAc is epoxied to the surface of the instrument, then covered with a protective metal seal containing the radiation symbol.  The epoxy and seal prevent the release of any UAc from the source.  The small amount of radioactivity in the UAc is sufficient to check the response of the instrument to ensure it is detecting radiation prior to using it for survey measurements.

Disposal of uranyl acetate must be done by EHS staff.  It is treated as chemical waste so you must complete a waste pickup request form: