Answer to Question #1646 Submitted to "Ask the Experts"

Q

I want to know the bioassay procedure for radiochemical determination of ³⁵S, ³²P, ¹⁴C in the urine of an occupational worker.

A

The three radionuclides (³⁵S, ³²P, ¹⁴C) indicated in the question each emit beta particles (electrons) as their primary radiations. The common method to detect these radionuclides in a urine sample is liquid scintillation. This involves putting a small amount of urine in a vial along with a scintillation "cocktail." This cocktail is a solution in which the urine dissolves and emits visible light when a beta particle interacts. This visible light is detected using "photomultiplier tubes" that convert the light energy detected into an electronic pulse. This procedure is used if it is known that there is only the possibility of a single one of these radionuclides in the sample. If there is another beta-particle-emitting radionuclide for which the energy of the emitted beta particle is similar to the energy of the first, more work must be done. First, each individual radionuclide must be extracted from the sample by radiochemical means. This usually involves either getting the radionuclide into a form where it is a solid in a liquid phase and can be filtered, or getting the radionuclide into a charge state where an "ion exchange resin" can be used to remove the radionuclide from the sample. The final form of these samples is usually either a nickel disk with the radionuclide electroplated on it or a filter. These samples would be counted on a "proportional counter" which collects ionizations created by beta particle interactions in a gas inside of the detector. C.A. Gus Potter, PhD, CHP Sandia National Laboratories