Science Center Objects

Radiogenic isotopes are daughter nuclides derived from natural decay of radioactive parent nuclides. They are useful for determining radiometric ages of rocks, minerals, and soils, and can be used as natural tracers of lithologic, hydrologic, and biologic materials.  GEC scientists are currently focused on radiometric dating by U-Pb, U-Th, Sm-Nd, and Rb-Sr, as well as tracer studies using natural isotopes of U (234U/238U), Pb (204Pb-206Pb-207Pb-208Pb), Sr (87Sr/86Sr), and Nd (143Nd/144Nd); however, investigations of other isotope systems are possible.  Those data support a number of GEC projects funded primarily by the National Cooperative Geologic Mapping Program and Land Resources Program. Radiogenic isotope studies contribute to projects from around the nation and the world in collaboration with scientists from GEC and other USGS Science Centers, and with colleagues from other Federal Agencies and academic institutions.  Establishing and maintaining an in-house radiogenic isotope analytical capability is critical as these analyses are generally not available from the private sector.  

[The use of firm, trade, and brand names is for identification purposes only and does not constitute endorsement by the U.S. government.]

The GEC Science Center supports a laboratory facility that includes sample preparation labs, class-10,000 or better clean labs for chemical processing, and an instrument lab with multiple thermal ionization mass spectrometers (TIMS).  The laboratory was recently moved to newly renovated space in Building 95 of the Denver Federal Center.  It is effectively shared between multiple Science Centers and provides a model for efficient use of space and communal resources.  

USGS class-10,000 clean lab

Class-10,000 clean lab used to separate and purify elements of interest from samples of powdered rocks, minerals, and water.

Shared instrument lab

Shared instrument lab housing solid-source, multi-collector, thermal-ionization mass spectrometers in the medium- and fore-ground.  The shared space also houses USGS GSIL (GGG-Stable Isotope Laboratory) instruments in the background.


The facility houses four TIMS instruments, including an Isotopx Phoenix (installed July 2017), Thermo Finnigan Triton (installed 2004), and two older VG instruments installed in the 1980s.  All instruments are capable of running in fully automated modes.  Newer instruments can be run manually from remote locations through a secured internet connection.  Three of the four instruments have moveable faraday cups allowing static or dynamic simultaneous multi-collection of large ion beams. Small ion beams are measured by single-collector peak-hopping methods using either a discrete-dynode electron multiplier or Daly-knob /photomultiplier collector.  Resulting data are competitive with other state-of-the-art TIMS labs around the world.  


Scientist Wayne Premo working on a thermal-ionization mass spectrometer

Wayne Premo analyzing the isotopic composition of neodymium on the Phoenix thermal-ionization mass spectrometer.


USGS ThermoFinnigan Triton thermal-ionization mass spectrometer

Prior to TIMS analyses, chemical processing is required to separate and purify the element of interest. This typically involves acid-digestion and evaporation followed by ion chromatographic exchange on small, resin-filled columns. The newly built clean lab includes multiple HEPA-filtered work stations and evaporation boxes that provide class-1000 or better work spaces.  As a result, samples are exposed to minimal environmental contamination during processing allowing analyses of very small samples.  


Portion of the Class-10,000 clean lab with HEPA-filtered laminar-flow hoods

Portion of the Class-10,000 clean lab with HEPA-filtered laminar-flow hoods (left) used for chromatographic column separations and four-tier, ULPA-filtered exhausting dry-down boxes with Teflon-coated hotplates for sample digestion and evaporation.


Ion-chromatographic columns loaded with anion resin

Ion-chromatographic columns loaded with anion resin and used to separate and purify uranium and thorium prior to isotope analysis


Jim Paces working in USGS Radiogenic Isotope Lab

Disassembling a source magazine consisting of 21 individual filament locations recently run for U and Th isotope analysis




The Denver Radiogenic Isotope Lab is cooperatively run by a number of principle investigators, post-docs, and support staff.  

  • James Paces: Research Geologist, Geosciences and Environmental Change Science Center

  • Wayne Premo: Research Geologist, Geosciences and Environmental Change Science Center

  • Kathleen Simmons: Geologist, Geosciences and Environmental Change Science Center

  • Leonid Neymark: Research Chemist, Geology, Geophysics, Geochemistry Science Center

  • Adam Hudson: Research Geologist (post-doc), Geosciences and Environmental Change Science Center

  • Aaron Pietruszka: Research Geologist, Geology, Geophysics, Geochemistry Science Center

  • Janet Paces: Volunteer