Subsurface Gamma Radiation Detection

Description

At many U.S. Department of Energy (DOE) sites, restoration planning requires characterization of radiation fields below the surface for both for contaminated soil and groundwater. Because gamma radiation is more penetrating and travels further than alpha or beta radiation, and because most radionuclides produce some gamma radiation, gamma detection is the most common form of radiation detection. The crucial component of any gamma-measuring device is the detector, which is a component producing electrical signals as a result of the interactions of the gamma radiation. The following are descriptions of the most recent innovations that DOE has demonstrated and evaluated to detect gamma radiation in the subsurface.

Spectral Gamma Probe
The Spectral Gamma Probe is designed for the in-situ detection of subsurface radionuclides. The gamma radiation detection system is driven into the subsurface using a Site Characterization and Analysis Penetrometer System (SCAPS) or other cone penetrometer truck. The sensor uses a NaI (sodium iodide) scintillation crystal to detect gamma radiation in the subsurface at the probe tip. Gamma rays emitted by the radioactive waste are collected and this energy spectrum is analyzed to identify radioactive constituents and their relative concentrations. This technology can be used anywhere to characterize underground gamma radioactivity assuming that the subsurface is conducive to cone penetrometer (CPT) exploration and characterization.
The Vadose Zone Characterization System (VZCS)
The ability to obtain additional characterization data on contaminated plumes at new locations beneath tank farms is limited by poor access. The VZCS uses a CPT with gamma sensors to characterize gamma contamination in the vadose zone under tank farms. A truck-mounted VZCS can be driven into tank farms and located in any area the size of a parking space. Gamma contamination can be characterized to a depth of 150 ft. The VZCS has several sensors within a CPT. A magnetometer in the CPT tip reduces the probability of contacting subsurface utility or instrument lines during use. A screening module uses X-ray fluorescence (XRF) and gamma spectroscopy (GS) sensors to detect radioactive contaminants. A standard CPT tip module identifies soil stratigraphy. A soil moisture module enables the measurement of soil moisture content and soil resistivity, both important in determining soil stratigraphy and contaminant migration.
Slim-Hole Gamma Ray Log
Slim-hole gamma ray tools using sodium iodide (NaI) scintillation crystal detectors are best suited for high radioactivity environments. (A scintillator is a material that gives off light when a charged particle passes through it. Typically it is a form of plastic, produced with traces of certain elements that are readily excited by the passing charged particle and then rapidly decay, thereby producing light). At Lawrence Livermore National Laboratory (LLNL), Livermore, California, a slim-hole gamma ray drilling log detector was improved upon by doubling the scintillation crystal volume. This approach is of value in low radioactivity environments.

Limitations and Concerns

Spectral gamma probe
The use of the spectral gamma probe is currently limited to sites where a cone penetrometer can penetrate the subsurface to the desired depth. Its use normally restricted to about 150 feet. The spectral gamma probe generally does not peform well in geologic environments other than clays and sandy sediments. Sites that have radioactivity levels that span wide ranges could present problems for quantitative analyses. The NaI detector used in the present spectral gamma probe has a relatively high detection efficiency but has a relatively poor energy resolution, and its light output varies with temperature. Measurements made where high radiation levels are present need significant post-measurement corrections.

The Vadose Zone Characterization System (VZCS)
The probes cannot be used where the soil is laden with rocks and boulders because of the potential for probe or pipe breakage. Field maintenance is needed after CPT deployment. This includes assembly and disassembly, probe calibration, and repair, as needed. Field verification is needed.

Applicability

All of the technologies described detect gamma radiation in the subsurface environment.

Technology Development Status

All of the technologies described are in the demonstration phase of development. However, there are traditional laboratory methods that can analyze subsurface samples for gamma radiation.

Web Links

http://apps.em.doe.gov/ost/pubs/itsrs/itsr2364.pdf

http://apps.em.doe.gov/ost/pubs/itsrs/itsr2118.pdf

http://www.mgls.org/95Sym/Papers/Hill/index.html

http://www.frtr.gov/site/8_2_2.html

Other Resources and Demonstrations

See the descriptions of Surface Gamma Radiation Detectors, BetaScint^TM, Cone Pentrometer, SCAPS, and XRF.

See http://www.xrfcorp.com/technology/radiation_detection.html for a description of common radiation detection methods.

Radioactivity, or ionizing radiation, is the spontaneous disintegration of unstable atomic nuclei. Ionizing radiation can take the form of alpha particles, beta particles or gamma

For a list of other technologies that contain these properties click the 'SEARCH' button.

Go back to the... TECH CHART | TECH LIST | ABOUT PAGE | MAKE COMMENTS

DISCLAIMER

STATUS: The preceding technology description and links were last updated 10/2002.
If you believe any of the information is out of date, please let us know at cpeo@cpeo.org.

(AND) Match all words (OR) Match any words	(AND) Match all words (OR) Match any words	(AND) Match all words (OR) Match any words
Contaminant	Media	Technology
Fuel Organics/VOC Organics/SVOC Pest/Herbicides Metals Radionuclides Explosives-UXO Not Specific	Off-gas Ground Water Surface Water / Sed. Soil Landfill Materials Bldg. Surfaces Indoor Air/Soil Gas	Analytical/ACM In-Situ Treatment Removal Treatment/Destruct. Containment Mitigation