The use of an inductively coupled argon plasma atomic emission spectrometer (ICP-AES) system for analysis of radioactive materials at Pacific Northwest Laboratory (PNL) began about three years ago on completion of the installation of a modified Applied Research Laboratory (ARL) Model 3560 inductively coupled plasma (ICP) spectrometer. At that time, the system consisted of a direct reader interfaced with a lead-shielded glove box containing the source stand. Further modification a year later added a sequential spectrometer for increased analytical capabilities.
An important concern in radioactive analyses is limiting the operator exposure to high-energy β and δ rays emitted by various radioisotopes. Scientists at PNL decided that an ICP-AES interfaced with a lead-shielded glove box would provide minimum operator exposure as well as radioactive material containment. The system was selected on the basis of a number of criteria that met this mandate, including the following features:
(a) a direct reader capable of analyzing up to 40 elements simultaneously to minimize the sample volume;
(b) availability of a simple, compact autosampler and software that allowed remote handling;
(c) electronic and gas control systems that were easily removable from the torch stand so that only the stand would be inside the glove box;
(d) torch and sample aspiration systems that were easily replaced and maintained without affecting the optical alignment, and
(e) availability of a sequential analyzer as a field-installed module.
Most critical to the installation was the interface between the spectrometer and a lead-shielded glove box weighing over 1360 kg (1½ tons). A neoprene gasket around the interface plate serves to keep the optical path properly aligned.
Retrofit installation of a sequential system involved the mounting of a second spectrometer directly above the first. Spectral emissions can be directed upward to the sequential spectrometer with a system of mirrors. To verify the integrity of the simultaneous system, the same solution containing 20 μg/mL of selected ion elements was analyzed before and after the installation of the sequential spectrometer. Comparison of the intensities after 20 integrations indicated little change.
Operation and maintenance of the system has been fairly problem-free. Plugging of the aspiration system occurs, as well as signal drift; but both these problems are common in the operation of any ICP spectrometer.
Funding for the purchase and installation of the ICP-AES was provided by the Nuclear Waste Materials Characterization Center (MCC) established at PNL by the U.S. Department of Energy in 1979. Reference glasses prepared by the MCC have been analyzed on the ICP-AES. Other samples analyzed relate to the methods of storage for nuclear waste. Radionuclide-doped glass samples leached in a brine solution simulate storage in a salt bed. Vitrification of waste slurries involves their analysis before being fed into the ceramic melter, characterization of off-gas and condensate samples taken during melting, and analysis of the glass produced.