Using ORTEC GammaVision, Creating Libraries with Nuclide Navigator III

Using GammaVision
Creating Libraries with Nuclide Navigator III ― Simple and Quick!

GammaVision reads libraries of gamma-ray energies and yields created by Nuclide Navigator III in Microsoft Access format. The feature simplifies the creation of libraries, including parent-daughter nuclide relationships for True Coincidence Summing (TCS) corrections. The simple steps needed to create comprehensive parent-daughter libraries quickly for TCS calibrations and measurements are illustrated here. First a note about the True Coincidence Summing problem.

True Coincidence Summing Using GammaVision - Creating Libraries with Nuclide Navigator III
With radioactive decay, atomic nuclei transition from an excited state to a lower energy state. In many instances, gamma-radiation is released during this transition. The release of gamma rays results in a familiar gamma-ray spectrum. The transition is often a single gamma ray. But two or more gamma ray transitions could be involved¹. These multiple gamma rays from a single nuclide are said to be in cascade if they are emitted at roughly the same time ― and are thereby detected at the same time. In a typical gamma ray spectrum, the result is the gamma rays appear as a gamma peak of energy equal to the sum of the two energies. This phenomenon is known as True Coincident Summing (TCS) or Cascade Summing (CS). The summation of the energies results in losses from the two respective full-energy peaks and a new peak (a sum peak) that combines the two energies.

Cascade summing is highly geometry dependent (including a requirement to know the precise geometry of the detector and the source) and is distinguished from Random Summing² (RS). Errors resulting from TCS are particularly severe when sources are placed close to the detector ― where efficiency is the highest. In the past, the solution for cascade summing was simply to move the source far away from the detector ― resulting in large losses in efficiency and increased count times. Mathematical models have been used as well. However, these methods are limited by detector size and require a precise knowledge of the detector geometry, including the dead layer. Not so with the ORTEC approach!

The True Coincidence Correction
The true coincidence correction (TCC) is the correction necessary to account for all of the pulses removed from the full-energy peak due to cascade summing. This correction is a simple divisor of the net peak area, that is the net peak area is increased by the correction factor. The correction factor is detector and sample geometry dependent. The correction factor depends on the full-energy efficiency, that is the ability of the detector to detect the total energy of the gamma ray, and the total efficiency, that is the ability of the detector to detect any part of the gamma ray energy. The full-peak efficiency is determined in the efficiency calibration and the total efficiency is determined in the TCC part of Calibration Wizard.

Creating Libraries for TCC
Libraries for true coincidence corrections are accomplished using Nuclide Navigator Version III. Creating libraries for a TCC calibration is essentially the same as for any other purpose (the user creates a library that includes the certified nuclides of the calibration source). However, for coincidence summing corrections, the user must include not only information about the certified nuclides, but also comprehensive information about the daughter nuclides of the decay series and the decay path and intensity values of the parent/daughter relationships. Nuclide Navigator Version III simplifies this to a mouse click with the Copy Daughter Nuclides option. Simply choose the certified nuclides and check the Copy Daughter Nuclides option and Nuclide Navigator does the rest! The library can then be used by the Calibration Wizard in GammaVision to correct for cascade summing effects.

The following procedure illustrates the simple steps needed to create comprehensive libraries using Nuclide Navigator Version III.

Creating Libraries with ORTEC’s Nuclide Navigator Version III
Creating comprehensive libraries of gamma-ray energies and yields ― including parent-daughter relationships ― has just gotten simpler. The parent-daughter relationships must be included for calibrations with True Coincidence Summing corrections. Nuclide Navigator III streamlines this process by including the daughters for you. Once a library is created in may be used over and over again. The Nuclide Navigator software comes complete with several example libraries with Nuclear Power, Environmental Analysis, Waste Characterization and Activation Analysis.

Here’s how simple it is to create comprehensive libraries using Nuclide Navigator III.

Procedure

1. Open a Source Library.

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2. Open the Preferences dialog by selecting Options, then Copy/Report. Now click on the check box for the Copy Daughter Nuclides option to include all the daughter nuclides with each nuclide selection. You should verify that the All button is checked to transfer all the gamma rays for each nuclide. Then close the dialog with the upper right X.

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3. To copy your nuclides to your target library, type the symbol of the first nuclide in the Jump to Nuclide field and click Jump.

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4. The nuclide you selected will be in the lower right corner of the display. Right-click on the nuclide. In the popup menu, click on Copy Nuclide to Target Library.

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5. Now go to the top and enter the next nuclide and repeat. Repeat this procedure for each nuclide in your library.

Nuclide Navigator III automatically includes all parent/daughter and decay path information needed! And that’s all you need to do! The library is complete with all daughter nuclides in the decay chains of interest.

Notes:
1. Gilmore, G. & Hemingway, J. D. (1995). Practical Gamma-Ray Spectrometry, John Wiley and Sons, NY, NY.
2. Random summing, which is count rate dependent, is the statistical probability that two gamma rays from two or more discrete nuclei are detected at the same time.


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