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The USGS TRIGA® Reactor (GSTR) is a low–enriched uranium–fueled, pool–type reactor. The mission of the TRIGA® is to support USGS science by providing information on geologic, plant, and animal specimens to advance methods and techniques unique to nuclear reactors.

The reactor facility is supported by programs across the USGS and is organizationally under the Associate Director for Energy and Minerals. Samples from around the world are submitted to the USGS for analysis using the reactor facility. Qualitative and quantitative elemental analyses, spatial elemental analyses, and geochronology are performed. Few research reactor facilities in the United States are equipped to handle the large number of samples processed at the GSTR. Historically, more than 475,000 sample irradiations have been performed at the USGS facility. Providing impartial scientific information to resource managers, planners, and other interested parties throughout the world is an integral part of the research effort of the USGS.

The USGS TRIGA® reactor has been in operation since the late 1960s in support of nuclear–based research for the USGS and a number of universities across the nation. It is the only research reactor in the Department of the Interior and the only research reactor within a 350–mile radius of Denver, Colo. The reactor design is similar to research and training reactors at universities throughout the United States. The reactor provides an intense neutron source for experiments and is capable of continuous steady–state operation at 1,000 kilowatts (thermal). Also, it may be pulsed to a peak power of approximately 1,600 megawatts.

What the GSTR Can Do

Services at GSTR include but are not limited to the following:

  • Neutron irradiations for argon isotopic dating
  • Neutron activation analysis
  • Isotope production
  • Fission track experiments
  • Gamma spectrometry

These routine operations at the GSTR involve the irradiation of samples to produce nuclear changes in the samples. This change or “transmutation” of the original elements in the sample is accomplished when neutrons from the reactor strike the sample and change its nuclear composition. This technique, where the specimen is “activated” and then analyzed to determine its elemental composition, is called neutron activation analysis (NAA). Most elements can be detected at a level of a few nanograms or less. An advantage of NAA is that the samples can be analyzed without any chemical processing before or after the activation. This composition information is useful in determining geological sources and origins and in discovering mineral deposits.

The reactor is also used to produce nuclear changes in rock and mineral samples to determine their ages. Elemental analyses using other methods often result in data of less precision and/or less accuracy. The GSTR provides high–quality data on rock and mineral elemental composition using state–of–the–art techniques while providing the research tools needed to develop new and improved analytical techniques.

A large range of radioisotopes can be produced at the GSTR, in gaseous, liquid, or solid form, and with a wide range of half–lives.

Irradiation Facilities

Position               Neutrons/cm2s

Central Thimble   ˜3 x 1013

Lazy Susan          ˜4 x 1012

Dry Tube              ˜1 x 1012 

Experiments can be irradiated in several locations. Maximum neutron flux is in the central thimble, directly in the center of the core. A rotating specimen rack can hold many samples for concurrent irradiation. Several locations are also provided for irradiation external to the core. A pneumatic transfer system provides quick transfer of samples from their irradiation position to the counting lab. This system is computer–controlled and allows irradiation and analysis without manual handling of the samples. A fixed 6” diameter beam tube is located at the outer edge of the reactor tank and a moveable 8” diameter beam tube may be located at any position between the reflector edge and the outer tank wall. Contact the facility for details on irradiations and pricing.


The GSTR staff has provided training in areas of radiation measurements, radiation instruments and calibration, radiation saftey. Training services are available on a limited basis for facility customers.


Irradiation Only1                                  $564 Per Operating Hour2

NAA (irradiation and analysis)    Varies from $65 to $250 per sample, depending on analytical complexity.2

1"Irradiation only" requires radioactive materials license to receive samples after the irradiation.

2Discounts are available for public academic institutions and federal agencies. Please contact us for more information.


Tours of the GSTR are available to members of the general public as well as to high school, college, and university groups. Group size is limited to 25 persons. Tours normally last 60-90 minutes. Please contact us to schedule a tour and discuss specifics for your group.


Phone: 303-236-4726