Analysis Request Form (PDF, DOC, ODT)

THERMAL IONIZATION MASS SPECTROMETER

Isotopes arethe atoms of the same element those having same proton but different neutron numbers thus different masses. Atoms produced by the radioactive decay of other nuclides are termed as radiogenic isotopes. Radiogenic isotopes are not only used for radiometric dating but also as a tracer providing important data on the origin and formation processes of materials.

TRITON TI Mass Spectrometer

The device is designed for high-precision analyses of radiogenic isotopes and is mainly used to measure the isotopic ratios and elemental concentrations in the Rb-Sr, Sm-Nd, U-Pb systems.

Sample Preparation and Measurement

Before whole-rock isotope analyses, rocks are crushed, pulverized and sieved to the clay-size, and homogenized. If minerals to be analyzed, coarse pulverization is followed by enrichment of mineral fraction via shaking table, magnetic and heavy liquid separation methods, and hand-picking under microscope. Afterwards rock and mineral samples are dissolved in a proper acid (For samples other than rocks and minerals suitable methods should be determined).

Element ofwhich isotopic ratios and concentrations to be determined is separated from other elements by ion chromatography and isotope dilution methods. Element weighing about few hundred nanograms is load on the filament (Re, Ta or W) in a solution. Filaments are mounted on the sample magazine which is put into the thermal ion source housing. Analysis is started when necessary vacuum conditions are reached. A current is passed through the filament, which causes the isotopes in the sample to ionize at the necessary temperature. The ions are accelerated through a magnetic field, resulting in separation of the ions by mass, and the number of ions of each isotope are counted by multicollector.

Schematic view of the device and thumbnail photos of some parts are shown in the figure:

1. The sample magazine in the ion source housing,
2. Top view of the internal part of the multi-collector and
3. A single Faraday cup.

Specifications

• Elements ofwhich isotopic ratios can be determined: Rb, Sr, Nd, Sm, U, Pb, Th, Ca, Li, Hf, Os, B etc.

• External and internal precision on Nd and Sr isotope ratios is <5 ppm, both in static and multidynamic acquisition.

• Ion source: Highly sensitive, optimized for maximum ion transmission for both single and double filament techniques.

• Multicollector: Comprise seven carbon Faraday cups, 1 fixed and 6 moveable.

• Amplifier: The extended dynamic range of 50 V in positive mode and 12 V in negative mode supports the measurement of large isotope ratios. Virtual amplifier concept covers a relay matrix for sequential switching of all amplifiers to different Faraday cups to eliminate gain calibration errors.

Applications

Common applications are determination of ⁸⁷Sr/⁸⁶Sr, ¹⁴³Nd/¹⁴⁴Nd, ^206Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb, and ²⁰⁸Pb/²⁰⁴Pb isotope ratios and radiometric dating by U/Pb, Rb/Sr and Nd/Sm methods for researches in the fields of

• Geochronology and isotope geochemistry

• Nuclear energy researches

• Environmental pollution control

• Archeology etc.

Sample Requirements

Sr and Nd isotope ratios are measured in our laboratory, and ⁸⁷Sr/⁸⁶Sr and
¹⁴³Nd/¹⁴⁴Nd ratios are determined from the whole-rock and mineral samples. Sample requirements depends on the method and sample characteristics. For the whole-rock analyses more than 3-4 kg representative samples are required.