In Situ Object Counting System Software
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Features
- No radioactive sources needed for accurate efficiency calibrations
- Works over a wide range of geometries
- Calibrations valid from zero distance out to 500 meters
- Calibrations valid from 50 keV to 7000 keV
- Calibrations accurate to within a few percent
- Calibrations accurate at any angle from detector, not just on centerline
- Eliminates the cost of purchasing radioactive standards, creating custom distributions, and radioactive waste disposal
- Results are available within a few seconds
- Operates with any size or type of Germanium detector which has been characterized by CANBERRA
- Ideal for in situ applications, where large and various sample types are often encountered
- Includes predefined geometry templates for ten common container shapes and sample distributions
- Includes library of common materials and tools to create new materials
- Works with cylindrical collimators with conical holes, and rectangular collimators with trapezoidal holes
- Includes predefined collimator entries for ISOCS Shield
- Custom templates can be provided to meet special application needs
- Sample size can be point-like, or up to 500 meters in size
- Easy to use fill-in-the blank operator interface
- Only a few physical sample parameters (e.g. Size, Distance from Detector, etc.) are needed to tailor a template to a sample
- Ability to vary assumed sample characteristics (e.g. Density, Container Wall Thickness, etc.) makes it ideal for What if...? analyses
- Easily launched from a desktop icon while running Genie 2000 Spectroscopy Assistant or PROcount
- Resulting calibrations may be stored, recalled, and used just like those generated by traditional calibration techniques
- Companion software to that is optimized for laboratory calibrations
Description
The ISOCS (In Situ Object Counting System) Calibration Software brings a new level of capabilities to Germanium gamma sample assay by eliminating the need for traditional calibration sources during the efficiency calibration process. By combining the detector characterization produced by the MCNP modeling code, mathematical geometry templates, and a few physical sample parameters, the ISOCS Calibration Software gives you the ability to produce accurate qualitative and quantitative gamma assays of most any sample type and size (Figure 1).
Figure 1
ISOCS Calibration Software is launched from the Desktop, used for Data Entry, and then generates the Genie 2000 Efficiency Curve.
In addition to saving money by eliminating the need to purchase (and later dispose of) many calibration sources, ISOCS Calibration also saves time. Instead of hours spent in traditional source preparation and long calibration counts, an ISOCS Calibration for a new geometry requires only a few seconds of computer calculations.
The secret to this capability is twofold:
1. The energy/efficiency/spatial response profile of the Ge detector has been characterized by CANBERRA with the well-known MCNP Monte Carlo modeling code.
2. Mathematical templates have been created for most of the sample geometries that will be encountered planar surfaces, rectangular boxes, barrels, pipes, etc.
To a basic geometry template, add the specifics for a given sample its size, density, distance from the detector, etc. and the ISOCS Calibration Software generates a custom efficiency calibration specifically tailored for that detector and sample. The remainder of this document will describe how this is done and how the various standard geometries templates are used.
The Assay and Calibration Process
To better understand how the ISOCS Calibration Software is used, it's necessary to look at the complete ISOCS sample assay process. In general terms, it's as follows:
- Count the sample. Use a detector which has been characterized by
CANBERRA, and the Model ISOXSHLD ISOCS Shield and Collimator System,
if required.
- Select the Geometry Template which best fits the sample type (such
as planar surface, rectangular box, cylinder, pipe, etc.).
- Measure the relevant physical sample parameters required by that
template (such as size, density, distance to the detector, etc.).
- Enter these parameters into the ISOCS Calibration Software and generate
an efficiency calibration for those conditions in 15 seconds, typically.
Examine/modify the shape of the resultant Genie 2000 calibration curve
and store it.
- Use this calibration for the analysis of the spectrum collected during the sample count in step 1, yielding a qualitative and quantitative assay of the sample.
The sample parameters recorded in step 3 are key elements to the process, for they allow the software to tailor the theoretical response of the detector for a given geometry to the specific sample being assayed. For maximum accuracy and flexibility, each template allows a wide variety of parameters to be specified.
In addition to the parameters mentioned in step 3, provisions are included for things like container wall thickness, the presence of absorbers between the source and detector, non-homogenous source location within a container, variable sample densities, and off-axis detector placement. In short, most any factor that can impact the assay may be measured and specified. If a parameter is not known, various values can be tried to determine what, if any, influence that parameter has on the results of the assay.
The Basic Geometries Included with ISOCS
The basic Geometry Templates included with the ISOCS Calibration Software can be seen in the following series of drawings. For each, the various physical parameters that may be varied are shown as numbered callouts.
Figure 2
Using the ISOCS System to assay a pipe.
In addition to these standard templates, custom templates can be defined by CANBERRA to meet special application needs. And for all templates, the presence or absence of a collimator can be specified and automatically accounted for.
The basic templates and their applications are as follows:
SIMPLE BOX A basic rectangular carton or waste shipping container, a truck filled will scrap iron, or even a small building.
COMPLEX BOX The same as the Simple Box, but with a more complex sample matrix. It includes the ability to distribute the contamination across as many as four (4) layers of material and/or to place an additional concentrated source anywhere in the container. Ideal for use in "What If?" analyses of non-uniform distribution in waste assay containers.
SIMPLE CYLINDER A basic barrel, tank, or drum. In an emergency, it could also be used for a quick whole body contamination count.
COMPLEX CYLINDER The same as the Simple Cylinder, but with a more complex sample matrix. It includes the ability to distribute the contamination across as many as four (4) layers of material and to place an additional concentrated source anywhere in the container. Ideal for use in "What If?" analyses of non-uniformity in barrels and drums.
PIPE A pipe, empty or full, including material that has plated out or built up on the inner walls, as shown in Figure 2.
CIRCULAR PLANE The end of a barrel or tank, the bottom of a bottle containing a sample, or a filter cartridge. This would also be used for in situ measurements of ground. The radioactivity can be distributed in any manner in up to ten layers of sources/ absorbers.
RECTANGULAR PLANE A floor, wall, or ceiling, or soil in situ. The template allows for surface contamination as well as up to ten layers of internal contamination behind an absorber such as paint, paneling, or a floor covering.
WELL OR MARINELLI BEAKER Used for well logging applications, or for standard Marinelli beakers.
SPHERE Internally contaminated spherical objects, like large pipe valves.
EXPONENTIAL CIRCULAR PLANE Similar to the Circular Plane, but here the radioactive source can be distributed to first increase in concentration and then decrease in concentration. Use this for fallout on soil, activation of concrete, analysis of resin beds, etc.
The Basic ISOCS Calibration Templates
Simple Box
Complex Box
Rectangular Plane
Simple Cylinder
Complex Cylinder
Circular Plane
Sphere
Pipe
Well or Marinelli Beaker
Exponential Circular Plane
NOTE: Templates for D&D applications are also available. These include external contamination on "I" or "H" beams, external contamination on "U" or "C" channels, external contamination on "L" angle beams, external contamination on the internal surfaces of a room, conical containers, and partially full horizontal cylinders or pipes. Custom templates are also available. Consult the factory for details.
Using the ISOCS Calibration Software
To illustrate how these templates and their related sample parameters are used, a typical ISOCS calibration will be described. It will be based upon the Simple Cylinder template, which would be the one most commonly used to assay material contained in drums.
The ISOCS calibration software is launched from a desktop icon.
Specifying the Detector and Collimator
The first step is to select the detector that is used for the count. Multiple detectors can be characterized and available for use. Then select the collimator that was used, if any. This provides the calibration software with appropriate mathematical models for these devices.
Selecting the Template
The next step is to select the source geometry template to be used, which is done from the menu shown in Figure 3. This menu will contain all of the standard templates that are included with ISOCS as well as any custom templates that may have been purchased.
Figure 3: Selecting the Geometry Template to be used.
Figure 4: The various types of parameters that can be
tailored to each calibration.
Parameter Input
The Parameter Input menu shown in Figure 4 is used to select the type of data to be entered. Note the last item, labeled Current Template View. Selecting it will always display a detailed drawing of the current template similar to the one shown in Figure 5, making it easy to see just which parameters are associated with the template being used.
Alternately, depressing the F2 key when in the screen to enter the parameters displays the same drawing.
Figure 5: The Simple Cylinder Geometry Definition.
Figure 6: Selecting the units for the physical measurement inputs.
Entering the Parameters
Selecting an item in the Parameter Input Menu will pop up a dialog box for use in entering the specified data.
In Figure 6, Dimension Units has been selected. The units to be used for length (sample dimensions), air temperature, sample density, and barometric pressure are selected here.
Figure 7: The Sample Parameter Input dialog.
Figure 7 shows the data entry screen for the source dimensions as well as the source-detector dimensions. Note that the title for the dialog box always identifies the currently selected template, and the contents of the dialog are always tailored to that template.
Figure 8: The ISOCS Materials Library Screen.
During the entry of source parameters, the material must be specified. The software performs absorption corrections for each of the object elements. The ISOCS software has a library of common materials that can be selected, as shown in Figure 8. Selection of the material also loads the default density, which can be edited if necessary. The program has all cross-sections of all the chemical elements stored in a library. This allows the user to easily create and add more materials, as necessary. Any material can be defined by atom fraction (chemical formula) or weight fraction.
Figure 9: The Collimator Parameters Input Dialog.
ISOCS supports both cylindrical shields with conical collimator entrance holes, and rectangular shields with trapezoidal entrance holes. The new collimator algorithm in the V3 release does not impair the accuracy of the overall calibration. Selecting the Circular Collimator Dimensions entry pops up the screen shown in Figure 9. The parameters are as shown in Figure 10. A similar drawing and input screen will appear if the rectangular collimator is selected.
To simplify the operation of the software, only a few of the parameters are mandatory; the others are needed only if you wish to have them used in the calculations. For example, the size of the sample is mandatory, but things like the size and type of any absorbers that may be located between the detector and the sample are only required when you wish to have them taken into account during the calibration process.
Figure 10: All templates can include a collimator to
reduce the field of view or minimize interferring radiation.
The Results
After entering the parameters and performing the calibration, the ISOCS results are converted in to an efficiency CAM file shown in Figure 1 which can be stored, retrieved, and used for sample assay in exactly the same manner as those produced by traditional "calibrated source" calibration.
Using ISOCS to Determine the Error Limits of an Assay
Another major benefit of the ISOCS Calibration is the ability to easily
determine the error limits of the results of an in situ
"What if...?" Errors
This classification covers questions such as "What if the container walls are thicker than we think?", "What if the container level is not as high as we think?", and "What if the material matrix is different than we assumed?"
To test the impact of these types of assumptions on the results, all that must be done is:
- Change the value of the parameter to be tested, such as Dimension 1.1 (container wall thickness) in Figures 5 and 7.
- Have a new efficiency curve generated.
- Re-analyze the sample spectrum using this new curve.
In a matter of a few seconds you'll see exactly what impact the new assumptions will have on the assay.
Non-homogeneity Errors
This class of error is essentially the same as a sampling error in a traditional "take some random samples and send them to a lab for analysis" method of doing waste assay. That is, if the activity in a container is not homogeneously distributed, how do you know that the assay of your samples (or the results a single ISOCS measurement) truly represent the contents of the container?
For the "sample and analyze" scenario, the only way to find out is to take a very large number of samples, and analyze the distribution.
Even then, the sampling results may not be correct for very non-uniform cases. If the sampling processes happened to completely miss a "hot spot", there is no evidence of the error, nor any measure of the bounds of the error. With in situ Gamma Spectroscopy, none of the sample is missed, but some of it may have a different efficiency.
With the ISOCS Ge/Shield/Software System, just perform a few more sample counts with the detector positioned at different locations about the sample. Analyze against the best assumption of the sample definition. Examine the results. For nuclides with multiple energy lines, if all show the same activity, then most likely the calibration is good. If all of the nuclide results from the various source-detector geometries agree, then most likely the calibration is good.
On the other hand, if the results are not the same, just modify the parameters in the source geometry template and reanalyze. This won't take long, and the existing acquisition spectra can be used. This can all be done on site, with none of the turn-around delays inherent in the "sample and analyze" approach.
Typical Results
Extensive testing and validation has been done on both the MCNP Detector Characterization and the ISOCS Calibration algorithms. The full MCNP method has been shown to be accurate to within 5% typically. ISOCS results have been compared to both full MCNP and to 119 different radioactive calibration sources. In general, ISOCS is accurate to within 4-5% at high energies and 7-11% at 1 s.d. for low energies. The full validation report showing the results of each of these tests is included with delivered software, and is available upon request to CANBERRA. A few of the comparisons are shown in Figure 11.
Figure 11: Extensive testing has shown that ISOCS and
traditional calibrations typically agree within a few percent.
Additional Information
Additional information on ISOCS, its hardware and software components, and its applications may be found in the following publications, all of which are available from CANBERRA:
Specification Sheets and Manuals
- Model ISOXSHLD ISOCS Shield System
- Model 1200 InSpector Portable Spectroscopy Workstation
- Model S500C/S502C/ S504C Genie 2000 Basic Spectroscopy Software
- Model S501C Genie 2000 Gamma Analysis Software
- Model S503C Genie 2000 PROcount Counting Procedure Software
- Model S573 ISOCS Efficiency Calibration Software Manual
- ISOCS Efficiency Calibration Validation and Internal Consistency Document, Part ICN9231205, Sept. 99 or later
Application Notes
- In Situ Gamma Spectroscopy with ISOCS, an In Situ>Object Counting System, CANBERRA Industries
Publications
- Ge Gamma Spectroscopy Characterization Tools for Contaminated Materials in Buildings, Boxes, and Dirt, Bronson, Frazier, CANBERRA Industries, ANS/ENS International Winter Meeting '96.
- ISOCS Mathematical Calibration Software for Germanium Gamma Spectroscopy of Small and Large Objects, Bronson, F., and Young, B., CANBERRA Industries, Atraskevich, V., Verdansky Institute of Geochemistry and Analytical Chemistry, American Nuclear Society Annual Meeting '97.
- Mathematical Calibration Of Ge Detectors, and the Instruments That Use Them, Bronson, F., and Young, B., CANBERRA Industries, NDA/NDE Waste Characterization Conference '97.
- Nuclear Instrumentation Tools for Lower Cost and Higher Reliability Decommissioning of Buildings and Grounds, Bronson, Frazier, CANBERRA Industries, TOPSEAL '96.
- Validation of the MCNP Monte Carlo Code for Germanium Detector Efficiency Calibrations, Bronson, Frazier and Wang, Ling, CANBERRA Industries, Waste Management '96.
- Optimum Size and Shape of Laboratory Samples for Gamma Spectroscopy With Various Size and Shape Ge Detectors, Bronson, F. CHP, Venkataraman, R. Ph.D., Young, B, Ph.D. , 44th Annual Conference on Bioassay, Analytical and Environmental Radiochemistry.
- Massemetric Efficiency Calibrations of Ge Detectors for Laboratory Applications, Bronson, F. CHP, Venkataraman, R. Ph.D., Young, B, Ph.D., 44th Annual Conference on Bioassay, Analytical and Environmental Radiochemistry.
- Mathematical Efficiency Calibration of Ge Detectors for Laboratory Sample Gamma Spectroscopy, Bronson, F., Venkataraman, R. Ph.D., Young, B, Ph.D. , 44th Annual Conference on Bioassay, Analytical and Environmental Radiochemistry.
- In Situ Applications Experiences Gained in the Use of ISOCS, A Laboratory-Quality Nuclide-Specific Field Gamma Radioassay System, Bronson, Frazier, Spectrum, '98 Conference.
- Validation of In Situ Object Counting System (ISOCS) Mathematical Efficiency Calibration Software, Venkataraman, R., Bronson, F., Atraskevich, V., Young, B. M., Field, M., Ninth Symposium on Radiation Measurements and Applications, '98.
- ISOCS (In Situ Object Counting System) Portable Gamma Spectroscopy Instrument, Booth, Leroy, CHP, (CP5) Research Reactor LSDP Project Report.
- ISOCS, A Laboratory Quality GE Gamma Spectroscopy System that you can Take to the Source for Immediate High Quality Results, Bronson, Frazier, CHP, Rapid Radioactivity Measurements in Emergency and Routine Situations Conference, '97.
System Requirements
To use the ISOCS Calibration Software, the following minimum system configuration is required:
Detector
Any Germanium detector type or size.
Model ISOXCAL to characterize a CANBERRA detector that on order; or ISOXCAL1 to characterize a previously ordered CANBERRA detector; or ISOXCAL2 to characterize a non-CANBERRA detector. The same characterization works for both ISOCS and LabSOCS software.
Shield
CANBERRA Model ISOXSHLD ISOCS Shield, or equivalent, if applicable.
Spectroscopy System
Any CANBERRA PC-based MCA system running the following software:
- CANBERRA Genie 2000 Basic Spectroscopy Software.
- Model S501C Genie 2000 Gamma Analysis Software.
The PC must be fully IBM compatible, have a math co-processor, and should be a 486DX or higher. For fast computations of large or collimated geometries, a high-end PC should be used.
Recommended options include:
- Model S503C Genie 2000 PROcount Counting Procedure Software.
- Model S505C Genie 2000 Quality Assurance Software.
- Model S506C Genie 2000 Interactive Peak Fit Software.
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| Models | ||
| ISOXCAL1: Calibration Existing CI Detector | ||
| ISOXCAL2: Calibration of Non-CI Detector | ||
| ISOXCAL: Calibration New Detector | ||
| ISOXVRFY: Calibration and Verification | ||
| S573C: ISOCS Efficiency Calibration Software | ||
| S573CS: ISOCS Efficiency Calibration Software Support - 1 Yr | ||