What Is Gamma Ray Spectrometry?

What Is Gamma-Ray Spectrometry?

Gamma ray spectrometry is the study of the energy spectra of gamma-ray sources, typically for the nuclear industry, astrophysics, and geochemical investigation.  Most radioactive sources produce gamma rays of varying intensities and energies.  When these gamma-ray emissions are detected and analyzed with a spectrometry system, a gamma-ray energy spectrum is produced.  
The equipment used in gamma-ray spectrometry includes an energy sensitive radiation detector such as  sodium iodine (NaI) crystals.  These detectors are passive materials that wait for a gamma interaction to occur within the detector volume, and then respond by producing a small flash of light, or a scintillation.  The intensity of the light is proportional to the energy deposited in the crystal by the gamma ray.  The detectors are joined to photomultipliers that convert the light into electrons and then amplify the electrical signal provided by those electrons.  After amplification and digitization, the pulse amplitudes are analyzed, and the output of the spectrometer is an energy spectrum of detected radiation.  Since individual radioactive isotopes emit specific gamma ray energies, gamma ray spectra can be used to diagnose the source of the radiation.
Natural sources of radiation derive from radio-isotopes synthesized during the creation of the solar system.  Because of their long half-lives, they still exist today.  Of these, potassium (K40), uranium (U238 and U235 and their daughters) and thorium (Th232  and their daughters) are the only radio-isotopes that produce high-energy gamma rays of sufficient intensity to be used for gamma ray mapping.
Gamma-ray spectrometry or radiometric surveying for mineral exploration measures the gamma-rays that are emitted from naturally occurring radioactive isotopes that are found in rocks and soils near the surface of the Earth.  The most abundant of these radioactive isotopes are potassium (K40), uranium (U238), and thorium (Th232).
The development of nuclear energy has resulted in the creation of artificial radio-isotopes.  For example, Cs137 is the main gamma-emitting fall-out product from nuclear explosions and accidents.
Radiation not originating from the Earth's surface is usually regarded as "background".  There are three main sources of background radiation: atmospheric radon, cosmic background, and instrument background.

Airborne Radiometric Surveys

Typically used in airborne radiometric surveying are RS-500 spectrometers manufactured by Radiation Solutions Inc.  These are recognized as the most advanced airborne spectrometer systems available, and include an on-board computer which allows real-time signal processing analysis, automatic gain control for individual crystals, multi-channel analysis and full spectrum recording.
These airborne spectrometers are installed inside fixed wing or rotary wing aircraft, and are flown over project areas to acquire radiometric data.  Meteorological conditions, topography of the area as well as the speed of the aircraft and the relative height of the sensor above ground all play important roles in the effective measurement of gamma ray levels within the survey area.  Choosing an experienced geophysical survey company to execute airborne radiometric surveys is paramount to ensuring the acquisition of precise and accurate radiometric data.  These experienced airborne geophysical survey companies have the experienced crews, aircraft, and geophysical equipment necessary to plan and execute different types of airborne surveys.
Radiometric surveys are often flown simultaneously with aeromagnetics and electromagnetics, providing a multi-parameter geophysical analysis of the survey area.  

Who Benefits from Gamma-Ray Spectrometry?

Mineral exploration companies, government agencies and engineering consultants are the major beneficiaries of gamma ray spectrometry surveys. Airborne radiometric surveys are a primary method of prospecting for economic mineral deposits such as uranium, porphyry copper and gold, and for lithologic mapping at surface.  Governments and environmental agencies also take advantage of this technology in order to identify the presence of radiation leaks from nuclear power plants.  

Specialists in Airborne Radiometric Surveys

Terraquest was established in 1984 and since then, our dedicated team has flown over 1,500 airborne geophysical surveys using both fixed wing and helicopter platforms.  Our professional crews provide significant experience having carried out airborne magnetic, gravity, gamma ray spectrometry, and electromagnetics on five continents.  Our quality data sets have been utilized in the exploration for base and precious metals, kimberlite, hydrocarbons, uranium, rare earth minerals and water. The company has performed exemplary surveys for both small and large exploration groups as well as many government agencies.  References can be provided upon request.    Visit www.terraquest.ca.


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