A Fast & Inexpensive Way to Analyze for Uranium and Radium in Soils by Gamma Spectroscopy


Spectra acquired on high resolution Germanium crystals are analyzed by standard software packages produced by Canberra (Genie), or Ortec (Gammavision).  We have both software products and both identify gamma peaks in the spectrum and associate them with the gamma lines from known radionuclides in the gamma library.  Spectra from natural sources that contain uranium, radium and other nuclides from the natural chains are difficult to analyze as the gamma peaks are heavily overlapped as shown above.  The photopeaks shown above are from an expanded section of the 90 keV peak complex from natural uranium in soils.  While the information on the uranium and radium concentrations in the soils is plainly there, the current software cannot deconvolute the overlapped peaks to provide the results.  So Radium and Uranium concentrations in soils are normally determined by putting a small quantity of the soil into solution by a pyrosulfate or NaOH fusion, and then separating the uranium and thorium by extraction chromatography and counting.  This is time consuming and expensive.

Recently, George Lasche and Bob Caldwell developed a new spectrum analysis package that takes a different approach to the analysis of a HPGE acquired gamma spectrum.  In their approach, an isotope, once identified in the spectrum, is stripped from the spectrum with all of its known gamma peaks.  This process continues interactively until all of the lines in the spectrum have been resolved and the residuals are structureless.  Then the spectrum is rebuilt and the contribution of each isotope in the overlapped peaks can be easily determined (see above).

Then, using soil specific efficiency curves at the soil density being analyzed, the concentrations of the uranium and radium in the sample can be quantified.  Testing we have been doing with known soil standards and intercomparisons with the separations lab on routine samples indicate excellent correlation for the new approach.  The minimum detectable activity for U and Ra is comparable to or below traditional methods if sufficient volumes of soil are analyzed. Please look back for papers and presentations being developed on this method for the RPSD 2016 meeting.

The end result is a fast, inexpensive measurement of isotopic uranium and radium in soils at a fraction of the time and cost required for traditional techniques.

This technique has been used for analysis of soils for NORM concentrations in several states, but has not been approved for analysis of drinking water or radiopharmaceuticals.