Instrument Description
TIMS is an analytical technique that requires the deposition of a sample onto a sample holder (filament in this case), whereafter the sample filament and ionizing filament are loaded into a carousel and placed into the instrument (in the ion source housing chamber). The ion source housing chamber is evacuated and the filaments are heated under controlled conditions to promote volatilization and ionization of the sample.
The ionized analyte is then directed through an accelerating section of the instrument and into a magnetic analyzing sector of the mass spectrometer for identification. The sample may arrive in any number of forms, but must be put into solution of sufficient concentration before it is deposited onto the sample filament. A solid sample will typically be dissolved in nitric acid. A sample that is too dilute will be evaporated down—either to reduce volume or bring to incipient dryness. A sample in an acid other than nitric will also be brought to incipient dryness and brought back to an appropriate volume by adding nitric acid. All work with radionuclides is conducted in an approved hood.
Prepared samples are loaded on filaments and inserted into the mass spectrometer for analysis. The TRITON TIMS ionizes the samples and measures the isotopic ratios of the element(s).
TIMS is widely viewed as the gold standard for low uncertainty isotopic analysis for Pu and U. Coupled with isotope dilution methods uncertainties as small as ±0.5% can be achieved allowing for precise and accurate isotopic measurements. It is the only method currently approved for safeguards and accountability measurements of Pu and U isotopics. Another advantage of TIMS is the small size of sample loadings (1 ng or less), effectively reducing exposure to the researcher and waste costs associated with disposal.
Applications
For uranium and plutonium, simultaneously measures ions generated from the thermal ionization of sample.
Performs nuclear material accountability measurements by TIMS isotope dilution; can do isotopic analysis on a single element.
Makes very precise measurements of isotope ratios of elements that can be ionized thermally.
Comparison of the voltages corresponding to individual ion beams yields precise isotope ratios, which are used for isotope dilution mass spectrometry analyses.
Specifications
Samples typically are either dried in a 10-ml beaker or exist as liquids.
Samples may arrive in containers of various sizes up to a nominal volume of 100 ml, but are generally in, or are transferred to, 5- or 10-ml vials.
Liquid volumes are typically less than 100 ml.
The loading of samples is <10 µl on the filament with U and Pu amounts <5 mg.