Crustal Geophysics and Geochemistry Science Center

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Properties - Radioactive

gamma ray spectrometer
Gamma ray spectrometer and the lead brick "tower" sample chamber. The scintillometer probe (orange cylinder) has been taken out of the sample chamber for this photo. The sample chamber door, lead blocks on the cart, is open to receive a sample.

Many rocks and minerals have radioactive properties due to their uranium, potassium and thorium content. PetLab is equipped with a gamma ray spectrometer (GRS) used to measure natural gamma radiation. The radiation spectrum is measured on 512 channels, ranging from ~100 to 3,000 keV. The scintillation probe contains a 76 x76 mm, thallium activated, sodium iodide crystal. The scintillation probe is housed in a lead "tower" sample chamber (5 cm thick) designed to shield the probe from ambient radiation. In addition to measuring the sample's gamma ray spectrum, the GRS spectrometer provides total count, percent potassium and equivalent uranium and thorium in parts per million (ppm). Count times can be varied from 1 second to 24 hours depending on sample properties. The PetLab GRS is mainly used as a screening tool; for more detailed gamma radiation analysis samples are sent to the USGS Reactor Facility.

Mineral Resources Program
Eastern Central GMEG Alaska Minerals Information Crustal Geophysics and Geochemistry Spatial Data