GAMMA RAY
SPECTROMETRY

Technique

Gamma-ray spectrometry measures the gamma-rays emitted from natural or man-made radioactive elements that are present in solid and liquid samples. The natural decay of U and Th produce a series of radionuclides with different half-lives that can be used to determine the absolute ages and accumulation rates of sediments, including marine deposits, ferromanganese nodules and marine phosphorites. The U-series and Th-series elements that emit gamma-rays include ²³⁴Th, ²²⁶Ra, ²¹⁴Pb, ²¹⁰Pb and ²²⁸Ac. Emission rates from these radionuclides can be quantitatively measured utilizing high-resolution semiconductor detectors. In addition, gamma-ray spectrometry can identify the presence of man-made radionuclides including ¹³⁷Cs from radioactive fallout and ⁶⁰Co, ¹⁴⁴Ce and ¹²⁵Sb from activation products.

Elements:

²³⁴Th, ²²⁶Ra, ²¹⁴Pb, ²¹⁰Pb, ²²⁸Ac, ¹³⁷Cs, ⁶⁰Co, ¹⁴⁴Ce, ¹²⁵Sb

Material:

Any solid or liquid matrix.

Form:

Any

Precision:

Typically 5-10% depending on the activity level.

Applications:

Dating, fractionation of U-series and Th-series by natural and man-made processes, radioactive contamination.

Costs:

$30 per sample.

Special Peripherals:

Ge-Well detector utilized for small samples (high-energy determinations only)

Automation:

None, because sample containers may be of varying dimensions.

Sample Size:

50-200 grams (2-5 grams for Ge-Well analysis)

| Capabilities |
| Chemical Analyses |

URL http://geology.cr.usgs.gov/capabilities/chema/grspec/tech.html