ML26027A169
| ML26027A169 | |
| Person / Time | |
|---|---|
| Site: | Fort Calhoun  |
| Issue date: | 03/14/2024 |
| From: | John Clements, Davis L Energy Solutions, Omaha Public Power District |
| To: | Division of Decommissioning, Uranium Recovery and Waste Programs |
| Shared Package | |
| ML26027A165 | List: |
| References | |
| EPID L-2025-LLN-0012 FC-24-003, Rev 1 | |
| Download: ML26027A169 (0) | |
Text
Page 1 of 18 FC-24-003 Revision 1 Ludlum 44-10 Detector Sensitivity for Determining Scan MDCs on Concrete Surfaces Prepared By:
LJ Davis Date Prepared By:
John Clements Date Reviewed By:
Date Approved By:
Date L. J. Davis 3-14-24 3-14-24 Heath Downey 03-15-2024
Jason Q. Spaide Digitally signed by Jason Q.
Spaide Date: 2024.03.16 11:24:45 -05'00' Approved By:
Daniel Whisler Date 3/16/2024
Ludlum 44-10 Detector Sensitivity for Determining Scan MDCs on Concrete Surfaces FC-24-003 Revision 1 Page 2 of 31 1.0 PURPOSE The primary purpose of this TSD is to evaluate the sensitivity of the Ludlum Model 44-10, 2.0 x 2.0 NaI detector when used to scan the concrete surfaces of building structures as a function of background, scan speed, source dimensions and radionuclide mixture.
This evaluation assumes the use of Ludlum Model 4260-076 collimators. These collimators are constructed from 99% lead and 1% antimony and have a wall thickness of 0.23 inches.
2.0 TECHNICAL APPROACH The technical approach for establishing the MDC for gamma-emitting radionuclides utilizes the methodology and approach in MARSSIM Section 6.7.2.1 (NRC, 2000) and NUREG-1507 (Minimum Detectable Concentrations with Typical Radiation Survey Instruments for Various Contaminants and Field Conditions [NRC, 1998]) method for determining the scan MDC for gamma-emitting radionuclides.
The scan MDC was calculated for a collimated 2 x 2 NaI detector that is offset at 2, 6, and 12 inches from the concrete surface. The offset distance of the detector causes the field of view (FOV) to increase as the distance from the concrete surface increases. The three FOVs were evaluated with respect to a potential hot spot that would be measured by the detector.
The approach consisted of determining the following parameters:
x Radionuclide mixture and source activity (i.e., energy and yield of gamma emissions) x Density of source media and the physical size of source (i.e., areal dimensions of source) x Relative distribution of potentially impacted material (depth of elevated activity) x The source to detector probe geometry x Effect of the use of a collimator on the detector FOV x Ambient background radiation in the area to be surveyed.
x Scan rate (observation interval)
Ludlum 44-10 Detector Sensitivity for Determining Scan MDCs on Concrete Surfaces FC-24-003 Revision 1 Page 3 of 31 x Index of sensitivity x Efficiency of the surveyor 2.1 Detector Field of View (FOV) Evaluation The FOV for a collimated Ludlum Model 44-10 detector was empirically determined using a Cs-137 source. The source was moved in a 180-degree arc around the collimated detector. The center of the detector crystal was selected as the center of the detector. The detector net count rate was determined at 26 equally spaced increments. Each increment represented approximately 7.2 degrees. The results of these measurements are provided in Table 1 and graphically depicted in Figure 1.
In order to determine a reasonable FOV, the net count rates (net cpm) were evaluated for the arc locations to each side of the detector center point. The furthest arc locations exhibiting a count rate within 20% of the maximum (center point) value were considered the limits of the FOV, ensuring that a symmetrical distance was maintained on both sides. The arc degrees between these two points (115.2 and 72) is 43.2 degrees, which represents the angle a + b shown in Figure 2. It is assumed that this FOV angle will remain constant over the range of detector heights to be evaluated, and the FOV diameters can be calculated for varying detector heights via the geometric (tangent) calculations shown in Figure
- 2.
Table 1 Data from Field of View Determination Degrees Location CPM Net CPM Relative
Response
0 1
20200 17696 0.564 7.2 2
19700 17196 0.548 14.4 3
19300 16796 0.535 21.6 4
18200 15696 0.500 28.8 5
18500 15996 0.509 36 6
19000 16496 0.525 43.2 7
20600 18096 0.576 50.4 8
22900 20396 0.650
Ludlum 44-10 Detector Sensitivity for Determining Scan MDCs on Concrete Surfaces FC-24-003 Revision 1 Page 4 of 31 Degrees Location CPM Net CPM Relative
Response
57.6 9
25300 22796 0.726 64.8 10 27600 25096 0.799 72 11 29700 27196 0.866 79.2 12 31500 28996 0.924 86.4 13 32700 30196 0.962 93.6 14 33900 31396 1.000 100.8 15 32700 30196 0.962 108 16 31600 29096 0.927 115.2 17 29300 26796 0.853 122.4 18 26600 24096 0.767 129.6 19 25400 22896 0.729 136.8 20 22200 19696 0.627 144 21 21100 18596 0.592 151.2 22 20600 18096 0.576 158.4 23 20100 17596 0.560 165.6 24 20600 18096 0.576 172.8 25 21400 18896 0.602 180 26 21100 18596 0.592
Ludlum 44-10 Detector Sensitivity for Determining Scan MDCs on Concrete Surfaces FC-24-003 Revision 1 Page 5 of 31 Figure 1 Graph of Figure 1 Field of View Data Based on an analysis of the data, the detector FOV was determined to be 43.2 degrees. The detector FOV was then used to determine the diameter of the surface seen by the detector at different heights using the equations displayed in Figure 2.
Figure 2 Source Term Dimension Calculations 0
5000 10000 15000 20000 25000 30000 35000 0
10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 Degrees NetCPM
Ludlum 44-10 Detector Sensitivity for Determining Scan MDCs on Concrete Surfaces FC-24-003 Revision 1 Page 6 of 31 The resulting dimensions of the evaluated source surface diameters are shown in Table 2 below. These were then used as the source term dimensions in the MicroShield model.
Table 2 Field of View Dimensions Detector Distance (in.)
FOV Radius (in.)
FOV Diameter (in.)
2 0.79 1.58 6
2.38 4.75 12 4.75 9.50 2.2 Source Term Depth Determination The assumed depth of contamination was determined by the analysis of concrete cores collected during characterization efforts. These include the initial characterization performed in 2019 and documented in Chapter 2 of the LTP and the 2024 East Trench characterization performed in 2024 and documented in TSD 24-004 Summary of DCGLs, Remediation Strategy and Survey Methodology for the Auxiliary Building East Trenches.
The depth of contamination found during various characterization activities are shown in Tables 3 - 5 below. These results confirm that the majority of the contamination in concrete is contained in the top 0.5 of concrete. Values of 0.5 and 1.0 were subsequently used in the MicroShield modeling.
The depths of contamination within a survey unit must be assessed to determine if the use of Model 44-10 NaI detectors for scanning concrete surfaces is appropriate.
Table 3 2019 Characterization 6" Depth Samples 2019 Characterization 6" Samples Depth (inches)
% of Cs-137 Activity 0.0 - 0.5 92.40%
0.5 - 1.0 2.86%
1.0 - 1.5 1.46%
1.5 - 2.0 2.60%
2.0 - 4.0 0.34%
4.0 - 6.0 0.33%
Ludlum 44-10 Detector Sensitivity for Determining Scan MDCs on Concrete Surfaces FC-24-003 Revision 1 Page 7 of 31 Table 4 2019 1.5" Characterization Samples 2019 Characterization 1.5" Samples Depth (inches)
% of Cs-137 Activity 0.0 - 0.5 89.06%
0.5 - 1.0 7.43%
1.0 - 1.5 3.51%
Table 5 2024 989' East Trench Continuing Characterization Samples 2024 East Trench Continuing Characterization Samples Depth (inches)
% of Cs-137 Activity 0.0 - 0.5 99.95%
0.5 - 1.0 0.05%
2.3 Concrete Density Determination In order to develop a representative concrete density, the volume and mass of 0.5 pucks from 12 core samples were determined, and the density calculated.
As seen in Table 6, the average density was determined to be 2.54 g/cm3. This value was subsequently used in the MicroShield modeling.
Ludlum 44-10 Detector Sensitivity for Determining Scan MDCs on Concrete Surfaces FC-24-003 Revision 1 Page 8 of 31 Table 6 Core Sample Density Determination Data Sample ID Thickness (cm)
Radius (cm)
Weight (g)
Volume (cm3)
Density (g/cm3) 2002X-1-CJ-FCV2-001 1.1 2.15 46.1 15.97 2.89 2002X-1-CJ-FCV2-014 1.4 2.15 51.2 20.32 2.52 2002X-1-CJ-FCV3-001 1.3 2.15 48.6 18.87 2.58 2002X-1-CJ-FCV3-003 1.3 2.2 49.3 19.76 2.50 2002X-1-CJ-FCV3-008 1.3 2.1 44.1 18.00 2.45 2002X-1-CJ-FCV4-001 1.3 2.15 45.7 18.87 2.42 2002X-1-CJ-FCV4-003 1.2 2.15 45.3 17.42 2.60 2002X-1-CJ-FCV4-013 1.3 2.15 48.4 18.87 2.57 2002X-1-CJ-FCV4-014 1.3 2.15 49.0 18.87 2.60 2002X-1-CJ-FCV4-015 1.4 2.1 50.5 19.39 2.60 2002X-1-CJ-FCV4-017 1.4 2.15 46.2 20.32 2.27
Maximum 2.89
Minimum 2.27
Std. Dev.
0.15 Average 2.54 2.4 Detector Response Factor Determination The count-rate-to-exposure-rate ratio (CPMR) was determined as cpm per R/h using data in Table 6-3 of NUREG-1507, Rev. 1 for a Ludlum 44-10 NaI probe. For Cs-137, the CPMR associated with 662 keV was used, which correlated directly to a value of 900 cpm/R/h as provided in Table 6-3 of NUREG-1507. For Co-60, an energy specific CPMRj was calculated for each energy (j) output in MicroShield (i.e., at 693.8 keV, 1173.2 keV, and 1332.5 keV).
To determine the CPMRj at each energy, a plot was first generated using the CPMR values associated with a range of energies (662 keV to 3000 keV) from Table 6-3 of NUREG-1507 as shown in Figure 3 below:
Ludlum 44-10 Detector Sensitivity for Determining Scan MDCs on Concrete Surfaces FC-24-003 Revision 1 Page 9 of 31 Figure 3 CPMR Versus Energy A trendline (power fit in Excel) was fitted to the CPMR data, and the associated equation (as shown in Figure 3) was used to calculate the CPMRj at each respective energy as shown below:
Table 7 CPMR for Co-60 Energy Lines Co-60 energy (keV)
CPMRi (cpm/R/h) 693.8 818 1173.2 475 1332.5 417 Next, the exposure-rate-to-concentration ratio (ERC) values for Cs-137 and Co-60 were generated from MicroShield. In order to estimate the exposure rate of a hypothetical elevated area of contamination, MicroShield Version 8.03 was used to model a cylindrical volume of concrete at thicknesses of 0.5 and 1.0 inches, and the modeled area varied as the FOV corresponding to the heights (at 2, 6, and 12 inches above the concrete surface).
A separate series of MicroShield analyses were completed for both Co-60 and Cs-137, with the assumption that each respective radionuclide was 100% of that mixture. The Cs-137 or Co-60 concrete concentration used for each analysis was set to a value of 7.874E-11 Ci/cm3, which is the volumetric concentration associated with a 1 pCi/m2 activity concentration within a 0.5-inch layer of
Ludlum 44-10 Detector Sensitivity for Determining Scan MDCs on Concrete Surfaces FC-24-003 Revision 1 Page 10 of 31 concrete. The same concentration was also used for the 1-inch depth evaluations, which assumes the same uniform concentration is present for both depths. A concrete density of 2.54 g/cm3 was used, based on density samples of site concrete.
In accordance with the specified scanning heights, a dose point was established at 2, 6, and 12 inches above the source surface. Modeled exposure rates (in mR/hr, with buildup) were generated by MicroShield for the major gamma energies, which were then expressed as an ERC as R/h per pCi/m2. For Cs-137, the ERC associated with 662 keV was used. For Co-60, a summation of all ERCj values (for the three energies (j) of 693.8 keV, 1173.2 keV, and 1332.5 keV) was used, which was 5.429E-10 R/h per pCi/m2. A weighted CPMR was also developed for each of the three Co-60 energies, as shown in Table 8 below (and the Weighted CPMRj value is used for the Co-60 calculations). The ERCj values shown below are from the Co-60 MicroShield analysis associated with the 6-inch detector offset and a 0.5-inch thickness hot spot, though the weighted CPMRj value will be the same for all offset analyses.
Weighted CPMR =
Table 8 Co-60 CPMR, ERC and Weighted CPMR Co-60 Energy (keV)
CPMRj (cpm/R/h)
ERCj (R/h/pCi/m2)
Weighted CPMRj (cpm/R/h) 693.8 818 2.706E-11 4.075E-02 1173.2 475 2.583E-07 2.261E+02 1332.5 417 2.846E-07 2.184E+02 Co-60 Sum 5.429E-07 445 2.5 Weighted Efficiency for Multiple Radionuclides The MDC calculations for any specific radionuclide mixture fractions will be contained in a separate attachment to this TSD. Scan surveys that are outside of the specific parameters calculated for a particular mixture fraction are considered as qualitative and not quantitative.
2.6 Scan MDC Evaluation To calculate the Scan MDC, Equation 6.11 from NUREG-1507, Rev. 1 was used as follows.
Ludlum 44-10 Detector Sensitivity for Determining Scan MDCs on Concrete Surfaces FC-24-003 Revision 1 Page 11 of 31 Scan MDC =
Where:
MDCR = Minimum Detectable (net) Count Rate for an ideal observer (cpm) p = Surveyor Efficiency (unitless), used to address human factors (i.e., to address the reality of a non-ideal observer)
CPMR = Count-rate-to-exposure-rate ratio (cpm per R/h)
ERC = Exposure-rate-to-concentration ratio (R/h per pCi/m2)
The MDCR is calculated as follows.
MDCR =
=
Where:
si = minimum detectable number of net source counts in the observation interval (counts) d = the index of sensitivity (unitless) bi = background counts in the observation interval (counts) i = observational interval (in seconds), based on the scan speed and areal extent of the contamination (FOV)
For the MDCR calculation, d was set to 1.38 in accordance with Table 6-1 of NUREG-1507, Rev. 1. This value assumes that surveys will be performed to accept a true positive proportion of 0.95 and a false positive proportion of 0.60.
The observation interval was determined for each of the FOV sizes using the estimated average scan speed 0.25 m/s and the diameter of each hypothetical hot spot (FOV) modeled in MicroShield. The background counts in the observation interval (bi) were determined using the background value of 4500 cpm and the observation interval. Thiis background count rate is typical of the remaining concrete structures at FCS.
To complete the Scan MDC calculation, the surveyor efficiency (p) was set to 0.50 per MARSSIM recommendations, and the CPMR and ERC values were generated using Ludlum 44-10 probe data and MicroShield, as discussed in further detail below. The Scan MDC calculations for 100% Co-60 and 100% Cs-137 are provided in Table 9. This mixture fraction is calculated for the Auxiliary Building 989 East Trench survey unit. Other areas may have varying mix
Ludlum 44-10 Detector Sensitivity for Determining Scan MDCs on Concrete Surfaces FC-24-003 Revision 1 Page 12 of 31 fractions. The scan MDCs for other mix fractions can be calculated using the equation in Section 2.5.
Table 9 Scan MDCS at Various Concrete Depths, Detector Heights and Radionuclide Mixtures Source Height (Thickness)
- (in.)
Detector Height (in.)
Hot spot diameter (in.)
100% Cs-137 Scan MDC (pCi/m2) 100% Co-60 Scan MDC (pCi/m2) 0.5 2
1.58 2.40E+07 1.22E+07 0.5 6
4.75 1.19E+07 6.04E+06 0.5 12 9.50 8.29E+06 4.21E+06 1
2 1.58 1.46E+07 7.43E+06 1
6 4.75 6.61E+06 3.36E+06 1
12 9.50 4.33E+06 2.21E+06
Ludlum 44-10 Detector Sensitivity for Determining Scan MDCs on Concrete Surfaces FC-24-003 Revision 1 Page 13 of 31 3.0 REFERENCES 3.1 Multi-Agency Radiation Survey and Site Investigation Manual (MARSSIM),
NUREG-1575, Rev.1 August 2000 3.2 Minimum Detectable Concentrations with Typical Radiation Survey for Instruments for Various Contaminants and Field Conditions NUREG-1507, Rev. 1, August 2020.
3.3 Consolidated Decommissioning Guidance, Characterization, Survey, and Determination of Radiological Criteria, NUREG-1757, Vol. 2, Rev. 1.
3.4 Decommissioning Health Physics: A Handbook for MARSSIM Users, Second Edition, Abelquist, 2013.
3.5 Fort Calhoun Station Decommissioning Project License Termination Plan Revision 1, 2023.
3.6 TSD FC-24-004 Summary of DCGLs, Remediation Strategy and Survey Methodology for Auxiliary Building East Trenches, 2024.
4.0 ATTACHMENTS 4.1 Attachment 1: Scan MDC Calculations, Detector Response Determination, and MicroShield Reports for Various Nuclides and Distances
FC-24-003 Revision 1 Page 14 of 31 ATTACHMENT 1 SCAN MDC CALCULATIONS, DETECTOR RESPONSE DETERMINATION, AND MICROSHIELD REPORTS FOR VARIOUS NUCLIDES AND DISTANCES 1.0 SCAN MDC DETERMINATION FOR MIXTURES The Scan MDC development process described in Section 2.6 was used to establish a Scan MDC for concrete of 0.5-inch thickness and a mixture of 79% Cs-137 and 21%
Co-60. This approach can be used as an example to generate other mixture Scan MDCs, but the values here are considered specific to this mixture fraction and should not be considered representative of other mixtures.
A MicroShield evaluation was performed using a total concentration set to a value of 7.874E-11 Ci/cm3, which is the volumetric concentration associated with a 1 pCi/m2 activity concentration within a 0.5-inch layer of concrete. The fractional concentration was input to MicroShield as 6.220E-11 Ci/cm3 for the 79% Cs-137 fraction and 1.654E-11 Ci/cm3 for the 21% Co-60 fraction. A concrete density of 2.54 g/cm3 was used, based on density samples of site concrete.
The source modeled in MicroShield was a cylinder volume (with end shields) of 2.38-inch radius, which correlates to the FOV associated with a 6-inch detector height above the source. The MicroShield dose point was set to the 6-inch height above the source.
The resultant exposure rate (with buildup) was then used along with exposure rate fractions (ERFs) for the major Cs-137 and Co-60 energies to determine the Scan MDC, as described below.
The exposure rates from the major Cs-137 and Co-60 energies were summed, and the respective fractions were developed as shown in Table 1. The relative exposure rate contribution (fraction) of each radionuclide was determined by dividing the MicroShield exposure rate value for each radionuclide energy line by the total summed exposure rate. The resultant exposure rate fractions were summed for each radionuclide as radionuclide-specific ERFs. Table 1 - Development of Radionuclide Exposure Rate Fractions Radionuclide Energy (MeV)
Exposure Rate (R/h)
With Buildup Exposure Rate Fraction Radionuclide Exposure Rate Fraction (ERF)
Cs-137 0.6616 1.07E-07 4.84E-01 4.84E-01 Co-60 1.1732 5.43E-08 2.46E-01 5.16E-01 Co-60 1.3325 5.98E-08 2.71E-01 Totals 2.210E-07 1.00E+00 1.00E+00 The Scan MDC was developed using Equation 6.11 from NUREG-1507, Rev. 1 as follows, along with the exposure rate fractions described in Table 1. A description of the variables is provided in Section 2.6.
FC-24-003 Revision 1 Page 15 of 31 ATTACHMENT 1 SCAN MDC CALCULATIONS, DETECTOR RESPONSE DETERMINATION, AND MICROSHIELD REPORTS FOR VARIOUS NUCLIDES AND DISTANCES Scan MDC =
For the MDCR calculation, d was set to 1.38 in accordance with Table 6-1 of NUREG-1507, Rev. 1. This value assumes that surveys will be performed to accept a true positive proportion of 0.95 and a false positive proportion of 0.60. The observation interval was determined using the estimated average scan speed 0.25 m/s and the diameter of the hypothetical hot spot (i.e., a 4.75 inch [0.1207 m] diameter FOV) modeled in MicroShield. The background counts in the observation interval (bi) were determined using the background value of 4500 cpm and the calculated observation interval of 0.4827 s (source diameter/scan rate), where bi is 36.20 counts. The calculation of the MDCR is as follows.
MDCR =
=
MDCR = 1.38 36.20
/
. = 1032 cpm To address the mixture, the respective Cs-137 and Co-60 exposure rate fractions are used in the Scan MDC equation as follows:
Scan MDC =
In this equation, the exposure-rate-to-concentration ratio (ERC) is represented by the summed exposure rate for the combined mixture shown in Table 1 (2.210E-07 R/h).
Since a 1 pCi/m2 modeling assumption was used for the MicroShield input, the ERC can be expressed as 2.210E-07 R/h/pCi/m2. The Cs-137 and Co-60 radionuclide-specific CPMR values (described in Section 2.6) are multiplied times the respective Cs-137 and Co-60 exposure rate fractions (ERFs), as shown in Table 1. The surveyor efficiency (p) was set to 0.50 per MARSSIM recommendations. The calculation is as follows:
Scan MDC =
.. /. //. //
Scan MDC = 9.93E+06 pCi/m2
FC-24-003 Revision 1 Page 16 of 31 ATTACHMENT 1 SCAN MDC CALCULATIONS, DETECTOR RESPONSE DETERMINATION, AND MICROSHIELD REPORTS FOR VARIOUS NUCLIDES AND DISTANCES 2.0 DETECTOR RESPONSE FACTOR DETERMINATION FOR MIXTURES A discussion on the usage and development of the count-rate-to-exposure-rate ratio (CPMR) was provided in Section 2.4 in the context of a single radionuclide (Cs-137 or Co-60). A weighted CPMR can be developed for a mixture of radionuclides by using the exposure rate fractions to determine the relative response of each radionuclide in the mixture. An example below demonstrates the development of a weighted CPMR for the mixture of 79% Cs-137 and 21% Co-60.
A CPMR vs. Energy plot was first developed using the CPMR values associated with a range of energies from Table 6-3 of NUREG-1507. For this example, the energy range from 500 keV to 3000 keV was used (shown in Table 2), as these values will bound the major energies in Cs-137 and Co-60. Table 2 - Selected Energies and CPMR Values from NUREG-1507 Table 6-3 (2" x 2" Ludlum 44-10 detector)
Energy (keV)
CPMR (cpm/R/h) 500 1270 600 1010 662 900 800 710 1000 550 1500 350 2000 270 3000 190 The plot developed from the Table 2 values is shown below.
FC-24-003 Revision 1 Page 17 of 31 ATTACHMENT 1 SCAN MDC CALCULATIONS, DETECTOR RESPONSE DETERMINATION, AND MICROSHIELD REPORTS FOR VARIOUS NUCLIDES AND DISTANCES Figure 1 A trendline (power fit in Excel) was fit to the CPMR data, and the associated equation was used to calculate the CPMRj at each respective energy. The major energies associated with Cs-137 (661.6 keV) and Co-60 (1173.2 keV and 1332.5 keV) are used for the weighted CPMR calculation. The following power fit equation developed in Excel was used to determine the CPMRj for each respective radionuclide/energy.
CPMRj = 932505*(Energy in keV)-1.07 The ERCj values at each respective energy are used to develop the Weighted CPMR as follows (and previously presented in Section 2.4).
Weighted CPMR =
The results of the Weighted CPMR calculations for the 79% Cs-137 and 21% Co-60 mixture are shown as follows. The ERCj values were taken from the MicroShield reports associated with this mixture.
y=932505x1.07 R²=0.9963 0
200 400 600 800 1000 1200 1400 0
500 1000 1500 2000 2500 3000 3500 CPMRvs.Energy(BasedonNUREG1507Table63)
FC-24-003 Revision 1 Page 18 of 31 ATTACHMENT 1 SCAN MDC CALCULATIONS, DETECTOR RESPONSE DETERMINATION, AND MICROSHIELD REPORTS FOR VARIOUS NUCLIDES AND DISTANCES Table 3 Radionuclide Energy CPMRj ERCj Weighted CPMRj keV cpm/R/h R/h/pCi/m2 cpm/R/h Cs-137 661.6 895 1.069E-07 4.328E+02 Co-60 1173.2 485 5.426E-08 1.190E+02 Co-60 1332.5 423 5.979E-08 1.144E+02 ERCj Weighted CPMRj 2.210E-07 R/h/pCi/m2 666 cpm/R/h The calculated Weighted CPMRj was 666 cpm/R/h. Note that this value is specific to the 79% Cs-137 and 21% Co-60 mixture and should be recalculated for use with different mixture percentages.
The scan MDC for this mixture at 6 detector distance and assuming a 0.5 source thickness is 9.93E+06 pCi/m2.
FC-24-003 Revision 1 Page 19 of 31 ATTACHMENT 1 SCAN MDC CALCULATIONS, DETECTOR RESPONSE DETERMINATION, AND MICROSHIELD REPORTS FOR VARIOUS NUCLIDES AND DISTANCES
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FC-24-003 Revision 1 Page 31 of 31 ATTACHMENT 1 SCAN MDC CALCULATIONS, DETECTOR RESPONSE DETERMINATION, AND MICROSHIELD REPORTS FOR VARIOUS NUCLIDES AND DISTANCES