NORMALIZATION REPORT GAMMA RADIATION DETECTION SYSTEMS SANTA SUSANA FIELD LABORATORY AREA IV RADIOLOGICAL STUDY VENTURA COUNTY, CALIFORNIA

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1 NORMALIZATION REPORT GAMMA RADIATION DETECTION SYSTEMS SANTA SUSANA FIELD LABORATORY AREA IV RADIOLOGICAL STUDY VENTURA COUNTY, CALIFORNIA 1.0 INTRODUCTION Gamma detection systems scan the ground surface to detect gamma radiation anomalies as part of the Santa Susana Field Laboratory (SSFL) Area IV Radiological Study. These detection systems differ by the number and arrangement of detectors and their overall size and mobility. The systems are designed to provide as much scanning coverage as possible, given that the site terrain includes flat, sloped, steep sloped and rocky surfaces. Due to the highly varied terrain, one gamma detection system is not sufficient to obtain complete surface coverage. Figure 1 shows four ground scanning detection system configurations currently in use for the study. All feature large sodium iodide (NaI) detectors mounted beneath mobile platforms. Each configuration is best suited to operate in specific types of terrain and survey areas. The detection systems are: The enhanced radiation ground scanner (ERGS) II is an all terrain vehicle with an array of eight NaI detectors mounted on a telehandler (a telescoping forklift). Due to the size and weight of the detector array and the telehandler, the ERGS II mainly covers relatively open, flat or gently sloped terrain, however telescoping enables some access to relatively small steep areas. The mule mounted gamma scanner (MMGS) is two large NaI detectors placed on outriggers, separated by approximately 40 inches, which are saddle-mounted on a mule. The MMGS primarily covers sloped to steeped sloped terrain which may be rocky or unsuitable for the ERGS II to scan. The MMGS can cover biologically or culturally sensitive areas whereas the ERGS II and the TMGS may cause more soil disturbance. The track mounted gamma scanner (TMGS) is two large NaI mounted on a gasoline-powered platform which is propelled using two rubber tracks. The TMGS can scan level to steep sloped terrain, but may not be the best choice for highly-variable rocky surfaces. The wheel mounted gamma scanner (WMGS) is a hand-propelled three wheeled cart with a single large NaI detector. This detection system mainly covers smaller areas which cannot be accessed by the other systems. In Figure 1, the ERGS II is shown at the upper left, the MMGS is upper right, the TMGS is lower left, and the WMGS is lower right. Each system has a display to monitor in real time the scanning path and survey coverage, gamma data, global positioning system (GPS), and other information. An important consideration is that a balance must be struck between Santa Susana Field Laboratory Normalization Report 1 HydroGeoLogic, Inc. 6/1/2011

2 gamma detection sensitivity and the size, weight, and maneuverability of these detection system platforms in the field. The ERGS II is operated 15 inches above the ground surface with a maximum velocity of 2 feet per second. The MMGS outrigger frame allows for minor size adjustments to maintain a consistent scanning height when different mules are in service. The MMGS scans at a height of 35 inches with an optimal maximum velocity of 4 feet per second. The WMGS has a single detector mounted on a fixed-wheel cart at 12 inches height with a 2 foot per second maximal velocity. Figure 1 Photographs of various large NaI detection systems Figure 1 shows at the upper left an all-terrain vehicle mounted detection system called the ERGS II which contains eight detectors and a 48-inch by 16-inch active detector surface. The detector array is encased in a metal shield with lead and copper lining to reduce radiation from above and the sides and to maximize sensitivity to radiation from the ground. At the upper right, the MMGS has one detector on each side of a pack mule and MMGS scanning is guided by a mule handler. At the bottom left, the TMGS has two parallel detectors mounted on a flexible platform propelled by a gasoline powered engine. Lastly, at bottom right, the WMGS photograph shows a field computer, the GPS unit (at front), and a single downward-facing detector. The MMGS, TMGS, and WMGS are also shielded, but to a lesser degree than the ERGS II to reduce detection system weight for mobility in the field. Santa Susana Field Laboratory Normalization Report 2 HydroGeoLogic, Inc. 6/1/2011

3 The gamma radiation total count rate measurements from these systems vary widely due to the number of detectors and system configurations. The differences in count rates are observed even if each system scans the same parcel of ground. In order to integrate, map, and evaluate data collected from different detection systems on an equal basis, the gamma data must be normalized. The total gamma count rates trend: ERGS II is greater than TMGS, which is greater than MMGS, which is greater than WMGS. Each system is normalized to the ERGS II with the greatest detection sensitivity. The selection of a detection system to scan a particular survey section considers both a detection system s sensitivity and its ability to scan the terrain. In general, the most sensitive detection system that is capable of scanning the terrain will be selected. Spectral count rate data in the form of standardized regions of interest for identification of specific radionuclides are proportional to the total count rate trends in the absence of radionuclide contamination. This means the normalization factors determined with total count rates apply to the normalization of radionuclide regions of interest. The focus of this report is to describe the normalization process and document the findings. As each system is unique, the detection sensitivities will differ between configurations. That is the focus of the gamma scanning sensitivity report which is separate from this document. 2.0 METHODS The first step in normalizing data from the detection systems was to collect measurements for each system from the same plot of ground. This required selection of field gamma normalization areas. Next, the data was collected, processed, and summarized for analysis. Finally, through statistical analysis, a normalization ratio for each system was determined using the mean total count rates and standard deviation of each system. Mean total count rates were used to compute normalization factors. Standard deviations provide information to characterize each system. This report has been revised to normalize the TMGS which was developed subsequent to the development, field testing, and mobilization of the other detection systems. The data collection for the initial normalization report was conducted in November 2010 at the end of the 2010 dry season. The TMGS data was collected in the spring of 2011 at the end of the wet season. Total gamma count rates from scanning surface soils are influenced by a number of environmental factors which include surface soil moisture content. Increases in soil moisture correlate with a decrease in total count rates. 2.1 SELECT FIELD GAMMA NORMALIZATION AREAS The criteria for optimal survey areas included: Survey areas must be relatively flat, so that each detection system can access and scan the same parcel of ground entirely. The area or areas should be large enough to be representative of Subarea 5C. Santa Susana Field Laboratory Normalization Report 3 HydroGeoLogic, Inc. 6/1/2011

4 Data from the normalization survey areas should be approximately equal to the mean of the entire Subarea. During the physical assessment of the terrain in Subarea 5C, field staff noted particular locations which met the first criteria. As scanning was underway in Subarea 5C, the gamma data was evaluated to discern gamma radiation anomalies. During this evaluation process, a Subarea 5C mean of the total gamma count rate was calculated. Subarea 5C contained approximately 20 acres of survey area. Half an acre was deemed to be sufficient to represent the subarea, thus a half acre area was targeted for conducting normalization surveys. However, no areas in Subarea 5C were found with one contiguous half acre which had been cleared of vegetation for gamma scanning. Therefore, two areas were selected for normalization survey sites - one containing 0.34 acres and one containing 0.27 acres, totaling 0.61 acres. Figure 2 shows the selected normalization survey areas which were located in Subarea 5C, in Survey Sections SS-1 and SS-6. Both of these highlighted areas met the first two criteria for use as representative survey sites. Gamma data (total counts per second) is shown in Table 1. The ERGS II is the most sensitive detection system therefore the other systems will be normalized the ERGS II system. Table 1 is a comparison of the data measured in the two normalization survey sections, the summation of the normalization area data, and Subarea 5C. At the bottom of Table 1, the gamma count rate data have been divided by the mean count rate of Subarea 5C to compare the data from each area. Both of the normalization areas are less than 3 percent different from the Subarea 5C mean count rate. This is considered highly representative of the local area. For comparison, the ERGS II mean for Subarea 5C plus or minus one standard deviation about the mean is a range of 12, counts per second. The normalization survey area mean count rate data are well within this range of values. The maximum measurements collected by the ERGS II in Subarea 5C were 23,067 counts per second which is 80 percent greater than the Subarea 5C mean. Hence, the survey areas selected for normalization are acceptable and representative of the entire subarea. Santa Susana Field Laboratory Normalization Report 4 HydroGeoLogic, Inc. 6/1/2011

5 Figure 2 Normalization Survey Areas in Subarea 5C, SS-1 and SS-6 Each area was accessible by all of the detection systems and cleared of vegetation for scanning. The gamma data of these survey areas were inspected to ensure that both areas were free of anomalies and contained data which was representative of Subarea 5C. Table 1 ERGS II Fall 2010 Data Comparison of Normalization Areas and Subarea 5C Parameter SS-1 SS-6 Combined Total of 5C* Collection time (seconds): Mean count rate (cps): Standard deviation (cps): Mean of area/5c mean: 102.8% 101.0% 102.4% 100.0% Notes: *The gamma data collected with the ERGS II from Subarea 5C was summarized, evaluated, and then particular areas were excluded from calculation of the local Subarea 5C mean and standard deviation. These survey area data were excluded based on rigorous evaluation, and were essentially non-native surfaces, such as roadways, parking lots, and man-made drainages. Both asphalt and concrete often have gamma radiation signatures which significantly differ from soils, which is because of the source materials used in the asphalt or concrete construction. cps counts per second Santa Susana Field Laboratory Normalization Report 5 HydroGeoLogic, Inc. 6/1/2011

6 2.2 SURVEY DATA COLLECTION AND PROCESSING Gamma surveys were performed using the ERGS II, MMGS, TMGS, and WMGS to provide complete coverage of both normalization survey areas. During surveying, the detection systems typically scan in linear transects and must periodically turn 180 degrees at the boundary of the area so the survey area is completely covered. The turnaround data were eliminated during post-processing so that the normalization data from each detection system was compared for precisely the same survey areas. Figure 3 illustrates mapped coverage of the normalization areas using WMGS survey data as an example. Data post-processing removes or clips the turn-around data. Figure 3 WMGS map of data clipped to the normalization survey areas. 2.3 EVALUATE SURVEY AREA GAMMA DATA STATISTICS Table 2 shows calculated statistics for each scanning area using ArcGIS. These were tabulated for each normalization survey section, and combined for both sections. The table includes the collection time, minimum count rate, maximum count rate, mean count rate, and standard deviation data from each detection system. For the fall 2010 surveys, the ERGS II has the greatest count rates, the MMGS the next greatest, and the WMGS the least. Santa Susana Field Laboratory Normalization Report 6 HydroGeoLogic, Inc. 6/1/2011

7 Table 3 contains the spring 2011 data for the ERGS II and TMGS. The ERGS II data are repeated in Tables 2 and 3 because the soil moisture was expected to be significantly different between the end of the dry season (November 2010) and the end of the wet season (April-May, 2011). The ERGS II combined mean count rate data from these two different surveys differ by approximately 10 percent, with the end of the wet season having a lower mean total count rate (11,960 cps) than that of the end of the dry season (13,133 cps). This difference is consistent with the expected decrease in gamma count rate due to increased soil moisture. For the spring 2011 surveys, the ERGS II count rates greatly exceed those of the TMGS. Table 2 Gamma Count Data and Statistics of ERGS II, MMGS, and WMGS (Fall 2010) System Parameter SS-1 SS-6 Combined Collection Time (seconds): Minimum (cps): ERGS II Maximum (cps): Mean (cps): Standard Deviation (cps): Collection Time (seconds): Minimum (cps): MMGS Maximum (cps): Mean (cps): Standard Deviation (cps): Collection Time (seconds): Minimum (cps): WMGS Maximum (cps): Mean (cps): Standard Deviation (cps): Santa Susana Field Laboratory Normalization Report 7 HydroGeoLogic, Inc. 6/1/2011

8 Table 3 Gamma Count Data and Statistics of the ERGS II and TMGS (Spring 2011) System Parameter SS-1 SS-6 Combined ERGS II TMGS Collection Time (seconds): Minimum (cps): Maximum (cps): Mean (cps): Standard Deviation (cps): Collection Time (seconds): Minimum (cps): Maximum (cps): Mean (cps): Standard Deviation (cps): RESULTS AND DISCUSSION 3.1 CALCULATION AND APPLICATION OF NORMALIZATION FACTORS Table 4 contains the summarized raw gamma statistical data of each system, the normalization factors, and the application of the normalization factors to the gamma count rate data of each system. The normalization factors were calculated by dividing the mean count rate data of each detection system by the mean count rate of the ERGS II. The MMGS and WMGS were normalized to the fall 2010 ERGS II data whereas the TMGS was normalized to the spring 2011 ERGS II data. The resulting normalization factors are for the ERGS II, for the TMGS, for the MMGS, and for the WMGS. Prior to normalization, the raw data vary by up to a factor of six and one-half. By definition, after normalization the mean count rates are equal. Interestingly, the standard deviations of the different systems are highly similar which provides a fair degree of confidence that normalization will work well for gamma data collected sitewide. Additional confidence is provided by noting the minimum and maximum count rates among the detection systems. These data are remarkably consistent, especially considering that these systems scan at different heights. Santa Susana Field Laboratory Normalization Report 8 HydroGeoLogic, Inc. 6/1/2011

9 Table 4 Raw and Normalized Gamma Count Rate Data Collection Period Fall 2010 Spring 2011 Raw Data ERGS II MMGS WMGS ERGS II TMGS Minimum (cps): Maximum (cps): Mean (cps): Standard Deviation (cps): Normalization Factor Normalized Data ERGS II MMGS WMGS ERGS II TMGS Minimum (cps): Maximum (cps): Mean (cps): Standard Deviation (cps): VERIFICATION The purpose of normalization is to provide a means to combine gamma radiation data from all detection systems and compare those data on an equal basis. Assembling the data from different sources into one file and mapping those gamma count rates without normalization would be like comparing apples to oranges. The resulting merged data surface on the map would be very jagged with points of one detection system, interspersed with points of other systems. Once normalized, the resulting merged data surface appears as if all data could have been collected by one detection system. Figure 4 shows two gamma total count rate maps of a portion of Subarea 5C. The data shown in the top map has been normalized and that shown in the bottom map has not. The count rate scales are equivalent in both maps, with yellow representing the lowest gamma count rate data and indigo representing the highest data. Inspecting Figure 4, the normalized data appear as a relatively smooth and natural interpolated surface. For example, in the left central part of the bottom map (pre-normalization), a large disparity between contiguous surface areas is seen whereas in the top map (post-normalization) most of this disparity is eliminated and the map surface is contiguous. Another example is seen in the central right part of these maps. At bottom, there is a very high degree of contrast over gamma data depicting a road surface with turnouts. This particular data spans from the deepest indigo to the lightest yellow which shows data spans the entire range of count rates. Comparing the bottom map with the top, the data form an integrated representation of the scanned surface and the road and turnouts can be easily discerned. Santa Susana Field Laboratory Normalization Report 9 HydroGeoLogic, Inc. 6/1/2011

10 Figure 4 Top Figure: After data normalization Bottom Figure: Before data normalization One can clearly see the benefits of merging and normalizing the gamma data. Both the medial count rate data at left and the highest count rate data at central right (the road surface) benefit Santa Susana Field Laboratory Normalization Report 10 HydroGeoLogic, Inc. 6/1/2011

11 from normalization and permit an integrated assessment of mapped total gamma count rate data. 4.0 CONCLUSION All data collected during gamma scanning activities will be normalized using the normalization factors presented in this document. Only normalized data will be used to determine the presence of gamma radiation anomalies. Santa Susana Field Laboratory Normalization Report 11 HydroGeoLogic, Inc. 6/1/2011