Dr. Robert Metzger of Radiation Safety Engineering, Inc. is pleased to be presenting 3 papers at next weeks ICRS-13 / RSPD-2016 joint conference in Paris, France.

Below are links to each of the 3 papers.

• VRF — Nuclear spectral analysis with non-linear full-spectrum nuclide shape fitting.

• Uranium, radium and thorium in soils with high-resolution gamma spectroscopy, MCNP-generated efficiencies, and VRF non-linear full-spectrum nuclide shape fitting.

• Shielding design of the Mayo Clinic Scottsdale cyclotron vault.

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.

A MCNP model of a PET/CT scanner
with a dosed patient in the scanner.

The vast majority of shield designs are performed by simple point kernel methods using the bulk attenuation properties of the shielding material and a known source term.  All of the NCRP manuals use this method. However, when the geometries are complex (see above), or the shields are layered, the point kernel techniques perform poorly and can result in significant overshielding at great cost for the construction,  or undershielding, requiring shielding retrofits, also at great cost.

For these complex designs, Monte Carlo (e.g. MCNP)or discreet ordinate (e.g. 3DANT or Mercurad) methods are preferable. While desirable, the implementation of these methods can be difficult.  The three dimensional geometry of the shielded room must be described to the code, and the run times for Monte Carlo methods can run days to weeks before the results converge.  Previously we have rented time on one of several supercomputers for these designs.

Recently, we have acquired two supercomputers from Thinkmate and Kingstar computers and have installed MCNP on them.    With the new installations of these dedicated supercomputers, we have been able to completely eliminate the computer charge for advanced designs and have reduced the time it takes to perform the analysis significantly.  This makes these approaches to shield designs far more affordable, and usable for smaller projects.

Areas where the Monte Carlo or discreet ordinate methods can contribute include facilities where:

• There is significant potential for streaming of radiation around barriers.
• Layered shields (e.g. Concrete over lead)
• Mixed field sources (e.g. protons, and photons)
• Multiple sources impacting a single area.
• Complex geometries where the source term is hard to define for point kernel methods.

Please call us for more information if these new capabilities could be of use to you.

We’re pleased to announce that the Journal of Radioanalytical and Nuclear Chemistry has published our article A Monte Carlo approach to food density corrections in gamma spectroscopy in their September, 2015 edition.

A PDF version of the article is available here and can also be found linked from our Papers page.  The article fully citeble and can also be found online by those with access to SpringerLink here.

Synthetic Precipitation Leaching Procedure (SPLP)

EPA Method 1312

This method measures the mobility of analytes present in soils, tailings, and wastes.  In our case, the test is used to measure the mobility of radionuclides in soils and wastes when leached with neutral pH water. The soil or other solid is placed in a specified container with a 20:1 volume of water at pH 4.2 or 5, and is agitated with a tumbler for 18 hours.  The solids are separated from the liquid by filtration, and the aqueous phase is analyzed for the radionuclides of interest.

All soils and most waters contain quantities of uranium, radium, and other natural radionuclides in varying concentrations.  For mill tailings and other sources that have the potential to increase the concentrations in groundwater, this test helps determine the mobility of the radionuclides in the test material.

The test normally takes two to three days for the leaching and separation.

Please contact us at (480) 897-9459 or (800) 477-9691 for pricing and any questions.