Gamma-Ray Spectrometry's Greatest Hits Available On CD

April 15, 1999

For a musician, the score for a symphony is a map that leads to sublime expression. To a nuclear physicist, a radioactive isotope has a rhythmic syncopation that produces a song as sweet as a Mozart concerto. This visible song, or spectrum, is the map that leads a physicist to knowledge and understanding.

A CD containing the most comprehensive collection of gamma-ray spectra compiled to date will be disseminated at an upcoming conference sponsored by the National Institute of Standards and Technology. Researchers from the Department of Energy Idaho National Engineering and Environmental Laboratory will be sponsoring a booth at the Tenth International Conference on Modern Trends in Activation Analysis (MTAA-10), April 19-23 in Bethesda, MD.

Naturally occurring elements can be stable or unstable. Unstable elements, called radionuclides, are like sand in the upper chamber of an hour-glass timer -- they are drawn over time to a position of rest, a stable state. The sand gives up energy as it falls to rest -- radionuclides must also expend energy to achieve stability through a process termed 'decay.'

One type of energy emitted from radionuclides is a massless photon called a gamma-ray. Researchers use detectors that convert the energy from these photons into electronic pulses. These signals are digitized and displayed as a visual spectrum (the physicist's song) that can be used to identify the original source radionuclide, just like a signature or a musical score.

Researchers in diverse fields such as nuclear medicine, environmental science, and health physics use gamma-ray spectrometry to identify and quantify radioactive materials. In nuclear medicine, a physician must precisely measure the amount of the radioisotope in order to calculate the correct dosage for a diagnostic test or radiation treatment for a patient. An environmental scientist must understand what radionuclides are contained in a radioactive waste so that it is properly disposed of without polluting the environment.

As a radionuclide decays to a stable state over time, it literally becomes something else -- a different element entirely. Researchers can now predict how a radionuclide will decay. These predictive models are called decay schemes. The Catalogue contains 315 reference spectra identifying specific radionuclides and more than 371 associated decay schemes. The decay schemes are constantly being updated as additional data strengthens the predictive models.

The instruments used to measure gamma-rays are called gamma-ray spectrometers and are widely used in academic and industrial laboratories worldwide. The INEEL has traditionally taken a lead role in the development of this technology, publishing a number of books and technical journal papers, including the Nal(TI) and Ge Gamma-Ray Spectrum Catalogues. The late INEEL physicist Russell Heath published the first Catalogue in 1974, and it has been a widely used resource ever since.

INEEL physicists Richard Helmer and Robert Gehrke plan future expansions of this Catalogue to include actinide radionuclides commonly found in waste forms and contaminated facilities resulting from the Department of Defense weapons program activities. Gamma spectra from prompt gamma emission immediately following nuclear reactions are also presently under consideration.

Working with Heath prior to his death, and with Helmer and Gehrke afterwards, INEEL engineer Jim Davidson has spent the last several years updating the Catalogues and making them available in the CD-ROM format. "This is exactly the kind of thing that a national laboratory should be doing," said engineer Jim Davidson, "making information freely available to the scientific community for the benefit of all."

In the new catalogues, the spectra have been replotted, color coded, and the peaks relabeled. Partial decay schemes have been added. Zooming capability features to see individual data points and half-life details have been added.

The Catalogues are also freely available on the INEEL Gamma-Ray Spectrometry Center homepage at

The research behind development of this Catalogue and the on-line versions of the data was funded through the INEEL's discretionary research program, and the DOE's Office of Science, Basic Energy Sciences.
The Idaho National Engineering and Environmental Laboratory is operated for the U.S. Department of Energy by Lockheed Martin Idaho Technologies Company. The Laboratory will celebrate its 50th Anniversary this summer. Visit our web site at

Editor's Notes: Richard Helmer can be contacted at 208-526-4157, or Robert Gehrke can be contacted at 208-526-4155, or, and Jim Davidson can be contacted at 208-526-0422, or

DOE/Idaho National Laboratory

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