ML24214A070

Enclosure 19: Technical Basis Document, Instrument Efficiency Determination for Use in Minimum Detectable Concentration Calculations in Support of the Final Status Surveys at OCNGS Revision 0, February 14, 2024

ML24214A070
Person / Time
Site:	Oyster Creek
Issue date:	08/01/2024
From:	Erickson M Holtec Decommissioning International, Westinghouse
To:	Office of Nuclear Reactor Regulation
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Text

Instrument Efficiency Determination for Use in Minimum Detectable Concentration Calculations in Support of the Final Status Surveys at OCNGS Revision 0 Prepared by:

Westinghouse - Radiological Engineering Group 141 Longwater Drive Suite 113 Norwell, MA 02061

@Westinghouse

Author:

Martin C. Erickson Date Reviewer:

William Parish Date Approved:

Christopher C. Messier Date

Contents Executive Summary..................................................................................................................................... 3

1.0 INTRODUCTION

............................................................................................................................. 4 2.0 CALIBRATION SOURCES.............................................................................................................. 4 3.0 EFFICIENCY DETERMINATION.................................................................................................... 6 3.1 Alpha and Beta Instrument Efficiency (ei).......................................................................................... 6 4.0 Source to Detector Distance Considerations........................................................................................ 7 4.1 Methodology..................................................................................................................................... 8 4.2 Source (or surface) Efficiency (es) Determination............................................................................... 8 5.0 INSTRUMENT CONVERSION FACTOR (Ei) (INSTRUMENT EFFICIENCY FOR GAMMA SCANNING)..................................................................................................................................... 9 6.0 APPLYING EFFICIENCY CORRECTIONS BASED ON THE EFFECTS OF FIELD CONDITIONS FOR TOTAL EFFICIENCY.............................................................................................................. 9

7.0 CONCLUSION

............................................................................................................................... 10

8.0 REFERENCES

................................................................................................................................ 11 Table 2.1 OCNGS Nuclides and Major Radiations: Approximate Energies............................................................ 5 Table 3.1 Nominal Instrument Efficiencies (es)...................................................................................................... 7 Table 4.1 Source-to-Detector Distance Effects on Instrument Efficiencies for - Emitters.................................. 8 Table 4.2 Source Efficiencies as Listed in ISO 7503-1........................................................................................... 9 Table 5.1 Energy Response and Efficiency for Photon Emitting Isotopes............................................................... 9 ii

3 Executive Summary The minimum detectable concentration (MDC) of the field survey instrumentation is an important factor affecting the quality of the final status survey (FSS). The efficiency of an instrument inversely impacts the MDC value. The objective of this report is to determine the instrument and source efficiency values used to calculate MDC. Several factors were considered when determining these efficiencies and are discussed in the body of this report. Instrument efficiencies (ei), and source efficiencies (es), for alpha beta detection equipment under various field conditions, and instrument conversion factors (Ei), for gamma scanning detectors were determined and the results are provided herein.

4

1.0 INTRODUCTION

Before performing Final Status Surveys of building surfaces and land areas, the MDC must be calculated to establish the instrument sensitivity. The Oyster Creek Nuclear Generating Station (OCNGS) License Termination Plan (LTP) list the available instrumentation and nominal detection sensitivities; however, for the purposes of this basis document, efficiencies for the nominal 100 cm2 gas proportional/scintillation and the 2"x2" Nal (TI) detectors will be determined. Efficiencies for the other instrumentation listed in the LTP shall be determined on an as needed basis. The 100 cm2 scintillation probe, or the gas proportional probe will be used to perform building surface surveys (i.e., fixed point measurements). A 2"x2" NaI (TI) detector will be used to perform gamma surveys (i.e., surface scans) of portions of land areas and possibly supplemental structural scans at the sites. Although surface scans and fixed-point measurements can be performed using the same instrumentation, the calculated MDCs will be quite different. MDC is dependent on many factors and may include but is not limited to:

x Instrument Efficiency x

Background

x Integration Time x

Surface Type x

Source to Detector Geometry x

Source Efficiency A significant factor in determining an instrument MDC is the total efficiency, which is dependent on the instrument efficiency, the source efficiency and the type and energy of the radiation. MDC values are inversely affected by efficiency, as efficiencies increase, MDC values will decrease. Accounting for both the instrument and source components of the total efficiency provides for a more accurate assessment of surface activity.

2.0 CALIBRATION SOURCES For accurate measurement of surface activity, it is desirable that the field instrumentation be calibrated with source standards similar to the type and energy of the anticipated contamination. The nuclides listed in Table 2.1 illustrates the nuclides found in soil and building surface area DCGL results that are listed in the OCNGS LTP.

Instrument response varies with incident radiations and energies; therefore, instrumentation selection for field surveys must be modeled on the expected surface activity. For the purposes of this report, isotopes with max beta energies less than that of C-14 (0.158 MeV) will be considered difficult to detect (reference table 2.1). The detectability of radionuclides with max beta energies less than 0.158 MeV, utilizing

5 scintillation detectors, will be negligible at typical source to detector distances of approximately 0.5 inches. The source to detector distance of 1.27 cm (0.5 inches) is the distance to the detector with the recommended standoff. Tables 2.1 and 2.2 provide a summary of the LTP radionuclides and their detectability using Radiological Health Handbook data.

Table 2.1 OCNGS Nuclides and Major Radiations: Approximate Energies Nuclide Energy (Mev)

Emax (Mev)

Average E (Mev)

Photon Energy (Mev)

Detectable w/100cm2 Detector Detectable w/100cm2 Detector Detectable w/NaI 2x2 H-3 0.018 0.005 C-14 0.158 0.049 Mn-54 0.835 (100%)

9 Fe-55 N/A 0.0052 Co-60 0.314 0.094 1.173 (100%)

1.332 (100%)

9

9

Ni-63 0.066 0.017 Sr-90 0.544 2.245 (Y-90) 0.200 0.931 9

Nb-94 0.50 0.156 0.702 (100%)

0.871 (100%)

9

9

Tc-99 0.295 0.085 9

Sb-125 0.767 0.428 (30%)

0.600 (18%)

0.636 (11%)



9 Cs-137 1.167(5.4%)

0.512(95%)

0.195 0.662(85%)

Ba-1 37m X-Rays 9

9

Eu-152 1.840 0.288 0.122(37%) 0.245 (8%)

0.344(27%) 0.779(14%)

0.965(15%), 1.087(12%)

1.113(14%) 1.408(22%)

9

9

Eu-154 1.850(10%)

0.228 0.143(40%)

1.274(35%)

9

9

Np-237 4.800 0.070 0.035





Pu-238 5.50(72%)

5.46(28%)

0.099(8E-3%)

0.150(1 E-3%)

0.77(5E-5%)

9





Pu-239 5.16(88%)

5.11(11%)

0.039(0.007%)

0.052(0.20%)

0.129(0.005%)

9

Pu-240 5.17(73%)

5.12(27%)

9

Pu-241 4.90(0.0019%)

4.85(0.0003%)

0.021 0.005 0.145(1.6E-4%)

Am-241 5.49(85%)

5.44(13%)

0.060(36%)

0.101(0.04%)

9

Cm-243 6.06(6%)

5.99(6%)

5.79(73%)

5.74(11.5%)

0.209(4%)

0.228(12%)

0.278(14%)

9

Cm-244 5.8(76%)

5.76(24%)

9

NUREG-1507 and ISO 7503-1 provide guidance for selecting calibration sources and their use in determining total efficiency. It is common practice to calibrate instrument efficiency for a single beta

6 energy; however, the energy of this reference source should not be significantly greater than the beta energy of the lowest energy to be measured. Calibration sources should be selected that emit alpha or beta radiation with energies similar to those expected of the contaminant in the field.

Tc-99 (0.294MeV at 100%) and Th-230 (4.621 MeV at 23% and 4,687 MeV at 76%) have been selected as the beta and alpha calibration standards respectively, because their energies conservatively approximate the beta and alpha energies of the plant specific radionuclides most prevalent in the field.

3.0 EFFICIENCY DETERMINATION Typically, using the instrument 4 efficiency exclusively provides a good approximation of surface activity. Using these means for calculating the efficiency often results in an underestimate of activity levels in the field. Applying both the instrument 2 efficiency and the surface efficiency components to determine the total efficiency allows for a more accurate measurement due to consideration of the actual characteristics of the source surfaces. ISO 7503-1 recommends that the total surface activity be calculated using:





Where:

As is the total surface activity in dpm/cm2, Rs +B is the gross count rate of the measurement in cpm, RB is the background count rate in cpm, ei is the instrument or detector 2 efficiency, es is the efficiency of the source and W is the area of the detector window (cm2) (126 cm2 active for the 43-93/Scintillation detector) 3.1 Alpha and Beta Instrument Efficiency (ei)

Instrument efficiency (ei) reflects instrument characteristics and counting geometry, such as source construction, activity distribution, source area, particles incident on the detector per unit time and therefore source to detector geometry. Theoretically the maximum value of es is 1.0, assuming all the emissions from the source are 2 and that all emissions from the source are detected. The ISO 7503-1 methodology for determining the instrument efficiency is similar to the historical 4 approach; however, the detector response, in cpm, is divided by the 2 surface emission rate of the calibration source. The instrument efficiency is calculated by dividing the net count rate by the 2 surface emission rate (q2)

7 (Includes absorption in detector window, source detector geometry). The instrument efficiency is expressed in ISO 7503-1 by:





Where:

RS+B is the gross count rate of the measurement in cpm, RB is the background count rate in cpm, q2 is the 2 surface emission rate in reciprocal seconds Note that both the 2 surface emission rate and the source activity are usually stated on the certification sheet provided by the calibration source manufacturer and certified as National Institute of Standards and Technology (NIST) traceable. Table 3.1 depicts nominal instrument efficiencies that have been determined during calibration using the 2 surface emission rate of the source.

Table 3.1 Nominal Instrument Efficiencies (ei)

Source Emission Active Area of the Source (cm2)

Area of the Detector 100 cm2 Nominal Instrument Efficiency (ei) (Contact)

Tc-99 15.2 100 cm2 0.1203 Th-230 15.2 100 cm2 0.1393 4.0 Source to Detector Distance Considerations A major factor affecting instrument efficiency is source to detector distance. Consideration must be given to this distance when selecting accurate instrument efficiency. The distance from the source to the detector shall be as close as practicable to geometric conditions that exist in the field. A range of source to detector distances has been chosen, considering site specific survey conditions. In an effort to minimize the error associated with geometry, instrument efficiencies have been determined for source to detector distances representative of those survey distances expected in the field. The results shown in Table 4.1 illustrate the imposing reduction in detector response with increased distance from the source.

Typically, this source to detector distance will be 0.5 inches for fixed point measurements and 0.5 inches for scan surveys on flat surfaces, however they may differ for other surfaces. Table 4.1 makes provisions for the selection of source to detector distances for field survey conditions of up to 2.0 in. If surface conditions dictate the placement of the detector at distances greater than 2.0 in instrument efficiencies will be determined on an as needed basis.

8 4.1 Methodology The practical application of choosing the proper instrument efficiency may be determined by averaging the surface variation (peaks and valleys narrower than the length of the detector) and adding 0.5 inches, the spacing that should be maintained between the detector and the highest peaks of the surface. The source-to-detector distance was evaluated using a Ludlum 43-93 scintillation detector with a 1.2 mg/cm2 window for Tc-99 and Th-230. Five 1-minute measurements were made on contact and at distances of 0.5, 1, 1.5 and 2 inches. Measurement results are contained in Appendix B.

Select the source to detector distance from Table 4.1 that best reflects this pre-determined geometry.

Table 4.1 Source-to-Detector Distance Effects on Instrument Efficiencies for - Emitters Source to Detector Distance (in)

Instrument Efficiency (ei)

Tc-99 Distributed Th-230 Distributed Contact 1

1 0.5 0.849383 0.013418 1.0 0.597486 0.000716 1.5 0.468216 0.000301 2.0 0.356736 6.12E-05 4.2 Source (or surface) Efficiency (es) Determination Source efficiency (es), reflects the physical characteristics of the surface and any surface coatings. The source efficiency is the ratio between the number of particles emerging from surface and the total number of particles released within the source. The source efficiency accounts for attenuation and backscatter.

es is nominally 0.5 (no self-absorption/attenuation, no backscatter)- backscatter increases the value, self-absorption decreases the value. Source efficiencies may either be derived experimentally or simply selected from the guidance contained in ISO 7503-1. ISO 7503-1 takes a conservative approach by recommending the use of factors to correct for alpha and beta self-absorption/attenuation when determining surface activity. However, this approach may prove to be too conservative for radionuclides with max beta energies that are marginally lower than 0.400 MeV, such as Co-60 with a max of 0.314 MeV. In this situation, it may be more appropriate to determine the source efficiency by considering the energies of other beta emitting radionuclides. ISO 7503-1 source efficiencies are used as routine guidance and exceptions to those es efficiencies will be documented as appropriate to the specific measurement or survey. Using this approach, it is possible to determine weighted average source efficiency. For example, a source efficiency of 0.375 may be calculated based on a 50/50 mix of Co-60 and Cs-137. The source efficiencies for Co-60 and Cs-137 are 0.25 and 0.5 respectively, since the

9 radionuclide fraction for Co-60 and Cs-137 is 50% for each, the weighted average source efficiency for the mix may be calculated in the following manner:

(.25) (.5) +(.5) (.5) = 0.375 Table 4.2 Source Efficiencies as Listed in ISO 7503-1

< 0.400 MeVmax 0.400 MeVmax Beta Emitters es = 0.5 es = 0.5 Alpha Emitters es = 0.25 es = 0.5 5.0 INSTRUMENT CONVERSION FACTOR (Ei) (INSTRUMENT EFFICIENCY FOR GAMMA SCANNING)

Separate modeling analysis (Microshield) was conducted using the common gamma emitters with a concentration of 1.6 pCi/g of uniformly distributed contamination throughout the volume.

Microshield is a comprehensive photon/gamma ray shielding and dose assessment program, which is widely used throughout the radiological safety community. An activity concentration of 1 pCi/g for the nuclides was entered as the source term. The radial dimension of the cylindrical source was 28 cm, the depth was 15 cm, and the dose point above the surface was 10 cm with a soil density of 1.6 g/cm3. The instrument efficiency when scanning, Ei, is the product of the modeled exposure rate (Microshield) mRhr per 1/pCi/g and the energy response factor in cpm/mR/hr as derived from the energy response curve provided by Ludlum Instruments (Appendix A). Table 5.1 demonstrates the derived efficiencies for the major gamma emitting isotopes listed in Tables 2.1 and 2.2.

Table 5.1 Energy Response and Efficiency for Photon Emitting Isotopes Isotope Ei (cpm/pCi/g)

Mn-54 289 Co-60 478 Nb-94 546 Sb-125 320 Cs-137 238 Eu-152 413 Eu-154 387 When performing gamma scan measurements on soil surfaces the effective source to detector geometry is as close as is reasonably possible (less than 4 inches).

6.0 APPLYING EFFICIENCY CORRECTIONS BASED ON THE EFFECTS OF FIELD

10 CONDITIONS FOR TOTAL EFFICIENCY The total efficiency for any given condition can now be calculated from the product of the instrument efficiency ei and the source efficiency es.

etotal = ei x es The following example illustrates the process of determining total efficiency. For this example, we will assume the following:

x Surface activity readings need to be made in the OCNGS Reactor Building basement concrete surfaces using the 3002 and 43-93 scintillation detector.

x Data obtained from characterization results from the basin indicate the presence of beta emitters with energies greater than 0.400 MeV.

x The source (activity on the surface) to detector distance is 0.5-inch detector standoff.

x To calculate the total efficiency, etotal, refer to Table 4.1 "Source to Detector Distance Effects on Instrument Efficiencies for a - Emitters" to obtain the appropriate ei value.

x Contamination on all surfaces is distributed relative to the effective detector area.

x When performing fixed-point measurements with scintillation instrumentation the effective source-to-detector geometry is representative of the calibrated geometries listed in Table 4.1.

x Correction for pressure and temperature are not substantial.

In this example, the 2 value for ei is 0.1203 as depicted in Table 3.1 "Instrument Efficiencies". The source-to-detector correction for 0.5 inches is 0.849383 as depicted in Table 4.1 "Source to Detector Distance Effects on Instrument Efficiencies for a-Emitters". The es value of 0.5 is chosen refer to Table 4,2 "Source Efficiencies as listed in ISO 7503-1". Therefore, the total efficiency for this condition becomes = ei x es = 0.1203 x 0.849383 x 0.5 = 0.0511 or 5.11%.

7.0 CONCLUSION

Field conditions may significantly influence the usefulness of a survey instrument. When applying the instrument and source efficiencies in MDC calculations, field conditions must be considered. Tables have been constructed to assist in the selection of appropriate instrument and source efficiencies. Table 4,1 "Source to Detector Distance Effects on Instrument Efficiencies for a-Emitters" lists instrument efficiencies (ei) at various source to detector distances for alpha and beta emitters. The appropriate ei value should be applied, accounting for the field condition, i.e., the relation between the detector and the

11 surface to be measured.

Source efficiencies shall be selected from Table 4,2 "Source Efficiencies as listed in ISO 7503-1 ". This table lists conservative es values that correct for self-absorption and attenuation of surface activity. Table 5.1 "Energy Response and Efficiency for Photon Emitting Isotopes" lists Ei values that apply to scanning MDC calculations. The MicroshieldTM model code was used to determine instrument efficiency assuming contamination conditions and detector geometry cited in the section "MDCs for Gamma Scans of Land Areas" of the License Termination Plan.

Detector and source conditions equivalent to those modeled herein may directly apply to the results of this report.

8.0 REFERENCES

8.1 NUREG-1507, "Minimum Detectable Concentrations with Typical Radiation Survey Instruments for Various contaminants and Field Conditions," 1998 8.2 ISO 7503-1, "Evaluation of Surface Contamination - Part I: Beta Emitters and Alpha Emitters," 1988-08-01.

8.3 ISO 8769, "Reference Sources for the Calibration of Surface Contamination Monitors-Beta-emitters (maximum beta energy greater 0. 15MeV) and Alpha-emitters," 1988-06-15.

8.4 "Radiological Health Handbook," Revised Edition 1970.

12 Attachment A Microshield and Excel Forms

MicroShield LT 13.07 BHI Energy Results with Buildup: Dose Point No. 1 - (X = 0, Y = 25, Z = 0) cm Energy (MeV)

Activity (Photons/sec)

Energy Flux (MeV/cm2/sec)

Photon Flux (Photons/cm²/sec)

Exposure Rate (mR/hr)

Absorbed Dose Rate (mrad/hr)

Absorbed Dose Rate (mGy/hr) 6.938e-01 3.568e-01 2.586e-05 3.728e-05 4.993e-08 4.359e-08 4.359e-10 1.173e+00 2.187e+03 2.691e-01 2.294e-01 4.809e-04 4.198e-04 4.198e-06 1.333e+00 2.187e+03 3.070e-01 2.304e-01 5.327e-04 4.650e-04 4.650e-06 Total 4.375e+03 5.762e-01 4.598e-01 1.014e-03 8.849e-04 8.849e-06 Date Preparer Reviewer File Name Run Date Run Time C:\\Users\\marty.erickson\\Grove Engineering\\MicroShield\\Examples\\CaseFiles\\OC Co60.msd October 31, 2023 4:01:37 PM Project Info Case Title OCNGS 44-10 eff Co60£ Description OCNGS 44-10 eff for Co-60£ Geometry 8 - Cylinder Volume - End Shields Source Dimensions Height 15.0 cm (5.906 in)

Radius 28.0 cm (11.024 in)

Dose Points No. X Y

Z Air Gap

1. 1 0.0 cm (0 in) 25.0 cm (9.843 in) 0.0 cm (0 in) 10.0 cm (3.937 in)

Shields Shield Name Dimension Material Density (g/cm3)

Source 3.69e+04 cm³ Soil - Earth (Average US) 1.60122 Air Gap Air 0.00122 Source Input: Grouping Method - Actual Photon Energies Library: Grove Nuclide Ci Bq Ci/cm³ Bq/cm³ Co-60 5.9112e-008 2.1872e+003 1.6000e-006 5.9200e-002 Page 1 of 2 Case Summary of OCNGS 44-10 eff Co60 10/31/2023 file:///C:/Users/marty.erickson/Grove%20Engineering/MicroShield/html/OC%20Co60-1...

10/31/2023

'YY/...d;;__c__'tc,~

1/

~

~

X

' z

Buildup Buildup: The material reference is Source.

Mass Attenuation Library NIST Library Integration Parameters Radial 20 Circumferential 10 Y Direction (axial) 10 Page 2 of 2 Case Summary of OCNGS 44-10 eff Co60 10/31/2023 file:///C:/Users/marty.erickson/Grove%20Engineering/MicroShield/html/OC%20Co60-1...

14 Co-60 Total Ei Energy (MeV)

Energy (KeV)

Exposure Rate Mr/hr -1 pCi/g Energy Response cpm/Mr/hr Ei (cpm/pCi/g) 0.6938 684 4.99E-08 810,000 4.04E-02 1.173 1173 4.81E-04 496000 2.39E+02 1.333 1333 5.33E-04 450000 2.40E+02 Total 478

MicroShield LT 13.07 BHI Energy Results with Buildup: Dose Point No. 1 - (X = 0, Y = 25, Z = 0) cm Energy (MeV)

Activity (Photons/sec)

Energy Flux (MeV/cm2/sec)

Photon Flux (Photons/cm²/sec)

Exposure Rate (mR/hr)

Absorbed Dose Rate (mrad/hr)

Absorbed Dose Rate (mGy/hr) 4.470e-03 2.270e+01 5.969e-08 1.335e-05 4.092e-08 3.572e-08 3.572e-10 3.182e-02 4.528e+01 8.972e-06 2.820e-04 7.473e-08 6.524e-08 6.524e-10 3.219e-02 8.354e+01 1.739e-05 5.401e-04 1.399e-07 1.222e-07 1.222e-09 3.640e-02 3.040e+01 1.057e-05 2.903e-04 6.004e-08 5.242e-08 5.242e-10 6.616e-01 1.968e+03 1.361e-01 2.057e-01 2.638e-04 2.303e-04 2.303e-06 Total 2.150e+03 1.361e-01 2.068e-01 2.642e-04 2.306e-04 2.306e-06 Date Preparer Reviewer File Name Run Date Run Time C:\\Users\\marty.erickson\\Grove Engineering\\MicroShield\\Examples\\CaseFiles\\OC Cs137.msd November 1, 2023 2:14:43 PM Project Info Case Title OCNGS 4410 eff Cs137£ Description OCNGS 44-10 eff for Cs-137£ Geometry 8 - Cylinder Volume - End Shields Source Dimensions Height 15.0 cm (5.906 in)

Radius 28.0 cm (11.024 in)

Dose Points No. X Y

Z Air Gap

1. 1 0.0 cm (0 in) 25.0 cm (9.843 in) 0.0 cm (0 in) 10.0 cm (3.937 in)

Shields Shield Name Dimension Material Density (g/cm3)

Source 3.69e+04 cm³ Soil - Earth (Average US) 1.60122 Air Gap Air 0.00122 Page 1 of 2 Case Summary of OCNGS 4410 eff Cs137 11/1/2023 file:///C:/Users/marty.erickson/Grove%20Engineering/MicroShield/html/OC%20Cs137-11...

11/01/2023 7Y/..d;:._ c..~~

• /

~

__/

X

~ z

Source Input: Grouping Method - Actual Photon Energies Library: Grove Nuclide Ci Bq Ci/cm³ Bq/cm³ Ba-137m 5.9112e-008 2.1872e+003 1.6000e-006 5.9200e-002 Cs-137 5.9112e-008 2.1872e+003 1.6000e-006 5.9200e-002 Buildup Buildup: The material reference is Source.

Mass Attenuation Library NIST Library Integration Parameters Radial 20 Circumferential 10 Y Direction (axial) 10 Page 2 of 2 Case Summary of OCNGS 4410 eff Cs137 11/1/2023 file:///C:/Users/marty.erickson/Grove%20Engineering/MicroShield/html/OC%20Cs137-11...

16 Cs-137 Total Ei Energy (MeV)

Energy (KeV)

Exposure Rate Mr/hr -1 pCi/g Energy Response cpm/Mr/hr Ei (cpm/pCi/g) 0.0045 5

4.09E-08 0

0.0318 32 7.47E-08 0

0.0322 32 1.40E-07 0

0.0364 36 6.00E-08 0

0.6616 662 2.64E-04 900000 238 Total 238

MicroShield LT 13.07 BHI Energy Results with Buildup: Dose Point No. 1 - (X = 0, Y = 25, Z = 0) cm Energy (MeV)

Activity (Photons/sec)

Energy Flux (MeV/cm2/sec)

Photon Flux (Photons/cm²/sec)

Exposure Rate (mR/hr)

Absorbed Dose Rate (mrad/hr)

Absorbed Dose Rate (mGy/hr) 2.290e-03 1.451e-01 1.954e-10 8.533e-08 2.614e-10 2.282e-10 2.282e-12 1.737e-02 7.734e-01 1.253e-08 7.214e-07 6.765e-10 5.906e-10 5.906e-12 1.748e-02 1.482e+00 2.461e-08 1.408e-06 1.303e-09 1.138e-09 1.138e-11 1.960e-02 4.352e-01 1.151e-08 5.870e-07 4.247e-10 3.708e-10 3.708e-12 7.026e-01 2.187e+03 1.606e-01 2.285e-01 3.096e-04 2.703e-04 2.703e-06 8.711e-01 2.187e+03 1.991e-01 2.285e-01 3.747e-04 3.271e-04 3.271e-06 Total 4.377e+03 3.596e-01 4.571e-01 6.843e-04 5.974e-04 5.974e-06 Date Preparer Reviewer File Name Run Date Run Time C:\\Users\\marty.erickson\\Grove Engineering\\MicroShield\\Examples\\CaseFiles\\OC Nb94.msd November 1, 2023 2:28:46 PM Project Info Case Title OCNGS 4410 eff Nb94£ Description OCNGS 44-10 eff for 9b-94£ Geometry 8 - Cylinder Volume - End Shields Source Dimensions Height 15.0 cm (5.906 in)

Radius 28.0 cm (11.024 in)

Dose Points No. X Y

Z Air Gap

1. 1 0.0 cm (0 in) 25.0 cm (9.843 in) 0.0 cm (0 in) 10.0 cm (3.937 in)

Shields Shield Name Dimension Material Density (g/cm3)

Page 1 of 2 Case Summary of OCNGS 4410 eff Nb94 11/1/2023 file:///C:/Users/marty.erickson/Grove%20Engineering/MicroShield/html/OC%20Nb94-11...

11/01/2023

'?Y/d-c__~~

• , ~

X

' z

Source 3.69e+04 cm³ Soil - Earth (Average US) 1.60122 Air Gap Air 0.00122 Source Input: Grouping Method - Actual Photon Energies Library: Grove Nuclide Ci Bq Ci/cm³ Bq/cm³ Nb-94 5.9112e-008 2.1872e+003 1.6000e-006 5.9200e-002 Buildup Buildup: The material reference is Source.

Mass Attenuation Library NIST Library Integration Parameters Radial 20 Circumferential 10 Y Direction (axial) 10 Page 2 of 2 Case Summary of OCNGS 4410 eff Nb94 11/1/2023 file:///C:/Users/marty.erickson/Grove%20Engineering/MicroShield/html/OC%20Nb94-11...

II I

I I

II I

18 Nb-94 Total Ei Energy (MeV)

Energy (KeV)

Exposure Rate Mr/hr -1 pCi/g Energy

Response

cpm/Mr/hr Ei (cpm/pCi/g) 0.023 23 2.61E-10 0

0.0174 17 6.77E-10 0

0.0175 18 1.30E-09 0

0.0196 20 4.25E-10 0

0.7026 703 3.10E-04 846000 262 0.8711 871 3.75E-04 756000 284 Total 546

MicroShield LT 13.07 BHI Energy Results with Buildup: Dose Point No. 1 - (X = 0, Y = 25, Z = 0) cm Energy (MeV)

Activity (Photons/sec)

Energy Flux (MeV/cm2/sec)

Photon Flux (Photons/cm²/sec)

Exposure Rate (mR/hr)

Absorbed Dose Rate (mrad/hr)

Absorbed Dose Rate (mGy/hr) 1.500e-02 3.324e+02 2.932e-06 1.955e-04 2.515e-07 2.196e-07 2.196e-09 4.000e-02 1.294e+03 6.697e-04 1.674e-02 2.962e-06 2.586e-06 2.586e-08 5.000e-02 3.236e+02 4.267e-04 8.534e-03 1.137e-06 9.924e-07 9.924e-09 1.000e-01 6.219e+02 5.665e-03 5.665e-02 8.667e-06 7.567e-06 7.567e-08 2.000e-01 1.639e+02 3.578e-03 1.789e-02 6.315e-06 5.513e-06 5.513e-08 3.000e-01 5.914e+02 1.914e-02 6.378e-02 3.630e-05 3.169e-05 3.169e-07 4.000e-01 1.374e+02 5.855e-03 1.464e-02 1.141e-05 9.960e-06 9.960e-08 5.000e-01 1.234e+01 6.514e-04 1.303e-03 1.279e-06 1.116e-06 1.116e-08 6.000e-01 9.275e+01 5.828e-03 9.713e-03 1.138e-05 9.931e-06 9.931e-08 8.000e-01 3.894e+02 3.255e-02 4.069e-02 6.192e-05 5.405e-05 5.405e-07 1.000e+00 9.358e+02 9.784e-02 9.784e-02 1.803e-04 1.574e-04 1.574e-06 1.500e+00 5.074e+02 8.060e-02 5.374e-02 1.356e-04 1.184e-04 1.184e-06 Total 5.402e+03 2.528e-01 3.817e-01 4.576e-04 3.995e-04 3.995e-06 Date Preparer Reviewer File Name Run Date Run Time C:\\Users\\marty.erickson\\Grove Engineering\\MicroShield\\Examples\\CaseFiles\\OC Eu152.msd November 1, 2023 2:36:04 PM Project Info Case Title OCNGS 4410 eff Eu152£ Description OCNGS 44-10 eff for Eu-152£ Geometry 8 - Cylinder Volume - End Shields Source Dimensions Height 15.0 cm (5.906 in)

Radius 28.0 cm (11.024 in)

Dose Points No. X Y

Z Air Gap

1. 1 0.0 cm (0 in) 25.0 cm (9.843 in) 0.0 cm (0 in) 10.0 cm (3.937 in)

Page 1 of 2 Case Summary of OCNGS 4410 eff Eu152 11/1/2023 file:///C:/Users/marty.erickson/Grove%20Engineering/MicroShield/html/OC%20Eu152-11...

11/01/2023 7Y/d-- c__~~

Shields Shield Name Dimension Material Density (g/cm3)

Source 3.69e+04 cm³ Soil - Earth (Average US) 1.60122 Air Gap Air 0.00122 Source Input: Grouping Method - Standard Indices Number of Groups: 25 Lower Energy Cutoff: 0.015 Photons< 0.015: Included Library: Grove Nuclide Ci Bq Ci/cm³ Bq/cm³ Eu-152 5.9112e-008 2.1872e+003 1.6000e-006 5.9200e-002 Buildup Buildup: The material reference is Source.

Mass Attenuation Library NIST Library Integration Parameters Radial 20 Circumferential 10 Y Direction (axial) 10 Page 2 of 2 Case Summary of OCNGS 4410 eff Eu152 11/1/2023 file:///C:/Users/marty.erickson/Grove%20Engineering/MicroShield/html/OC%20Eu152-11...

~

- X

" z

20 Eu-152 Total Ei Energy (MeV)

Energy (KeV)

Exposure Rate Mr/hr -

1 pCi/g Energy

Response

cpm/Mr/hr Ei (cpm/pCi/g) 0.015 15 2.52E-07 0

0.04 40 2.96E-06 0

0.05 50 1.14E-06 0

0.1 100 8.67E-06 4680000 41 0.2 200 6.32E-06 3420000 22 0.3 300 3.63E-05 2610000 95 0.4 400 1.14E-05 2070000 24 0.5 500 1.28E-06 1575000 2

0.6 600 1.14E-05 1080000 12 0.8 800 6.19E-05 765000 47 1

1000 1.80E-04 630000 113 1.5 1500 1.36E-04 425000 58 Total 413

MicroShield LT 13.07 BHI Energy Results with Buildup: Dose Point No. 1 - (X = 0, Y = 25, Z = 0) cm Energy (MeV)

Activity (Photons/sec)

Energy Flux (MeV/cm2/sec)

Photon Flux (Photons/cm²/sec)

Exposure Rate (mR/hr)

Absorbed Dose Rate (mrad/hr)

Absorbed Dose Rate (mGy/hr) 1.500e-02 1.669e+02 1.473e-06 9.818e-05 1.263e-07 1.103e-07 1.103e-09 4.000e-02 4.451e+02 2.304e-04 5.759e-03 1.019e-06 8.894e-07 8.894e-09 5.000e-02 1.131e+02 1.491e-04 2.982e-03 3.972e-07 3.467e-07 3.467e-09 1.000e-01 8.850e+02 8.063e-03 8.063e-02 1.234e-05 1.077e-05 1.077e-07 2.000e-01 1.494e+02 3.261e-03 1.630e-02 5.755e-06 5.024e-06 5.024e-08 4.000e-01 1.560e+01 6.648e-04 1.662e-03 1.295e-06 1.131e-06 1.131e-08 5.000e-01 4.736e+00 2.500e-04 5.000e-04 4.908e-07 4.284e-07 4.284e-09 6.000e-01 1.764e+02 1.109e-02 1.848e-02 2.164e-05 1.889e-05 1.889e-07 8.000e-01 8.529e+02 7.130e-02 8.912e-02 1.356e-04 1.184e-04 1.184e-06 1.000e+00 6.728e+02 7.034e-02 7.034e-02 1.297e-04 1.132e-04 1.132e-06 1.500e+00 8.534e+02 1.356e-01 9.039e-02 2.281e-04 1.991e-04 1.991e-06 Total 4.335e+03 3.009e-01 3.763e-01 5.364e-04 4.683e-04 4.683e-06 Date Preparer Reviewer File Name Run Date Run Time C:\\Users\\marty.erickson\\Grove Engineering\\MicroShield\\Examples\\CaseFiles\\OC Eu154.msd November 1, 2023 2:42:04 PM Project Info Case Title OCNGS 4410 eff Eu154£ Description OCNGS 44-10 eff for Eu-154£ Geometry 8 - Cylinder Volume - End Shields Source Dimensions Height 15.0 cm (5.906 in)

Radius 28.0 cm (11.024 in)

Dose Points No. X Y

Z Air Gap

1. 1 0.0 cm (0 in) 25.0 cm (9.843 in) 0.0 cm (0 in) 10.0 cm (3.937 in)

Shields Page 1 of 2 Case Summary of OCNGS 4410 eff Eu154 11/2/2023 file:///C:/Users/marty.erickson/Grove%20Engineering/MicroShield/html/OC%20Eu154-11...

11/02/2023 7Y/..d;__c_~~

I I

I

Shield Name Dimension Material Density (g/cm3)

Source 3.69e+04 cm³ Soil - Earth (Average US) 1.60122 Air Gap Air 0.00122 Source Input: Grouping Method - Standard Indices Number of Groups: 25 Lower Energy Cutoff: 0.015 Photons< 0.015: Included Library: Grove Nuclide Ci Bq Ci/cm³ Bq/cm³ Eu-154 5.9112e-008 2.1872e+003 1.6000e-006 5.9200e-002 Buildup Buildup: The material reference is Source.

Mass Attenuation Library NIST Library Integration Parameters Radial 20 Circumferential 10 Y Direction (axial) 10 Page 2 of 2 Case Summary of OCNGS 4410 eff Eu154 11/2/2023 file:///C:/Users/marty.erickson/Grove%20Engineering/MicroShield/html/OC%20Eu154-11...

I I

I I

I

~

- X

" z

22 Eu-154 Total Ei Energy (MeV)

Energy (KeV)

Exposure Rate Mr/hr -1 pCi/g Energy Response cpm/Mr/hr Ei (cpm/pCi/g) 0.015 15 1.26E-07 0

0.04 40 1.02E-06 0

0.05 50 3.97E-07 0

0.1 100 1.23E-05 4680000 58 0.2 200 5.76E-06 3420000 20 0.4 400 1.30E-06 2070000 3

0.5 500 4.91E-07 1575000 1

0.6 600 2.16E-05 1080000 23 0.8 800 1.36E-04 765000 104 1

1000 1.30E-04 630000 82 1.5 1500 2.28E-04 425000 97 Total 387

MicroShield LT 13.07 BHI Energy Results with Buildup: Dose Point No. 1 - (X = 0, Y = 25, Z = 0) cm Energy (MeV)

Activity (Photons/sec)

Energy Flux (MeV/cm2/sec)

Photon Flux (Photons/cm²/sec)

Exposure Rate (mR/hr)

Absorbed Dose Rate (mrad/hr)

Absorbed Dose Rate (mGy/hr) 5.700e-04 8.097e+00 2.715e-09 4.763e-06 1.459e-08 1.274e-08 1.274e-10 5.405e-03 1.625e+02 5.166e-07 9.556e-05 2.928e-07 2.556e-07 2.556e-09 5.415e-03 3.218e+02 1.025e-06 1.892e-04 5.798e-07 5.062e-07 5.062e-09 5.950e-03 6.440e+01 2.254e-07 3.788e-05 1.161e-07 1.013e-07 1.013e-09 8.348e-01 2.187e+03 1.907e-01 2.285e-01 3.610e-04 3.151e-04 3.151e-06 Total 2.743e+03 1.908e-01 2.288e-01 3.620e-04 3.160e-04 3.160e-06 Date Preparer Reviewer File Name Run Date Run Time C:\\Users\\marty.erickson\\Grove Engineering\\MicroShield\\Examples\\CaseFiles\\OC Mn54.msd November 2, 2023 11:04:37 AM Project Info Case Title OCNGS 44-10 eff Mn54£ Description OCNGS 44-10 eff for Mn54£ Geometry 8 - Cylinder Volume - End Shields Source Dimensions Height 15.0 cm (5.906 in)

Radius 28.0 cm (11.024 in)

Dose Points No. X Y

Z Air Gap

1. 1 0.0 cm (0 in) 25.0 cm (9.843 in) 0.0 cm (0 in) 10.0 cm (3.937 in)

Shields Shield Name Dimension Material Density (g/cm3)

Source 3.69e+04 cm³ Soil - Earth (Average US) 1.60122 Air Gap Air 0.00122 Page 1 of 2 Case Summary of OCNGS 44-10 eff Mn54 11/2/2023 file:///C:/Users/marty.erickson/Grove%20Engineering/MicroShield/html/OC%20Mn54-11...

11/02/2023 7J//.d;;_ c_~~

-1~ __...,

X

' z

Source Input: Grouping Method - Actual Photon Energies Library: Grove Nuclide Ci Bq Ci/cm³ Bq/cm³ Mn-54 5.9112e-008 2.1872e+003 1.6000e-006 5.9200e-002 Buildup Buildup: The material reference is Source.

Mass Attenuation Library NIST Library Integration Parameters Radial 20 Circumferential 10 Y Direction (axial) 10 Page 2 of 2 Case Summary of OCNGS 44-10 eff Mn54 11/2/2023 file:///C:/Users/marty.erickson/Grove%20Engineering/MicroShield/html/OC%20Mn54-11...

24 Mn-54 Total Ei Energy (MeV)

Energy (KeV)

Exposure Rate Mr/hr -1 pCi/g Energy

Response

cpm/Mr/hr Ei (cpm/pCi/g) 5.70E-04 1

1.50E-08 0

5.41E-03 5

2.93E-07 0

5.41E-03 5

5.80E-07 0

5.95E-03 6

1.16E-07 0

8.35E-01 835 3.61E-04 800000 289 Total 289

MicroShield LT 13.07 BHI Energy Results with Buildup: Dose Point No. 1 - (X = 0, Y = 25, Z = 0) cm Energy (MeV)

Activity (Photons/sec)

Energy Flux (MeV/cm2/sec)

Photon Flux (Photons/cm²/sec)

Exposure Rate (mR/hr)

Absorbed Dose Rate (mrad/hr)

Absorbed Dose Rate (mGy/hr) 3.770e-03 1.082e+02 2.399e-07 6.364e-05 1.950e-07 1.702e-07 1.702e-09 2.720e-02 2.797e+02 2.875e-05 1.057e-03 3.827e-07 3.341e-07 3.341e-09 2.747e-02 5.219e+02 5.590e-05 2.035e-03 7.221e-07 6.304e-07 6.304e-09 3.100e-02 1.812e+02 3.220e-05 1.039e-03 2.895e-07 2.527e-07 2.527e-09 3.549e-02 9.109e+01 2.849e-05 8.028e-04 1.736e-07 1.515e-07 1.515e-09 1.170e-01 5.709e+00 6.666e-05 5.700e-04 1.037e-07 9.051e-08 9.051e-10 1.590e-01 1.525e+00 2.614e-05 1.644e-04 4.369e-08 3.814e-08 3.814e-10 1.726e-01 3.964e+00 7.431e-05 4.305e-04 1.267e-07 1.106e-07 1.106e-09 1.763e-01 1.508e+02 2.890e-03 1.639e-02 4.955e-06 4.326e-06 4.326e-08 2.041e-01 7.056e+00 1.572e-04 7.703e-04 2.788e-07 2.434e-07 2.434e-09 2.081e-01 5.318e+00 1.208e-04 5.806e-04 2.151e-07 1.878e-07 1.878e-09 2.279e-01 2.874e+00 7.141e-05 3.133e-04 1.295e-07 1.131e-07 1.131e-09 3.210e-01 9.122e+00 3.149e-04 9.808e-04 6.021e-07 5.257e-07 5.257e-09 3.804e-01 3.272e+01 1.328e-03 3.491e-03 2.579e-06 2.252e-06 2.252e-08 4.080e-01 3.977e+00 1.727e-04 4.233e-04 3.369e-07 2.941e-07 2.941e-09 4.279e-01 6.415e+02 2.916e-02 6.815e-02 5.703e-05 4.978e-05 4.978e-07 4.435e-01 6.607e+00 3.109e-04 7.010e-04 6.089e-07 5.316e-07 5.316e-09 4.634e-01 2.264e+02 1.111e-02 2.399e-02 2.180e-05 1.903e-05 1.903e-07 Page 1 of 3 Case Summary of OCNGS 44-10 eff Sb12 11/2/2023 file:///C:/Users/marty.erickson/Grove%20Engineering/MicroShield/html/OC%20Sb125-11...

6.006e-01 3.887e+02 2.445e-02 4.071e-02 4.772e-05 4.166e-05 4.166e-07 6.066e-01 1.098e+02 6.975e-03 1.150e-02 1.361e-05 1.188e-05 1.188e-07 6.359e-01 2.476e+02 1.647e-02 2.589e-02 3.202e-05 2.795e-05 2.795e-07 6.714e-01 3.964e+01 2.782e-03 4.143e-03 5.386e-06 4.702e-06 4.702e-08 Total 3.065e+03 9.663e-02 2.042e-01 1.893e-04 1.653e-04 1.653e-06 Date Preparer Reviewer File Name Run Date Run Time C:\\Users\\marty.erickson\\Grove Engineering\\MicroShield\\Examples\\CaseFiles\\OC Sb125.msd November 2, 2023 11:03:12 AM Project Info Case Title OCNGS 44-10 eff Sb12£ Description OCNGS 44-10 eff for Sb125£ Geometry 8 - Cylinder Volume - End Shields Source Dimensions Height 15.0 cm (5.906 in)

Radius 28.0 cm (11.024 in)

Dose Points No. X Y

Z Air Gap

1. 1 0.0 cm (0 in) 25.0 cm (9.843 in) 0.0 cm (0 in) 10.0 cm (3.937 in)

Shields Shield Name Dimension Material Density (g/cm3)

Source 3.69e+04 cm³ Soil - Earth (Average US) 1.60122 Air Gap Air 0.00122 Source Input: Grouping Method - Actual Photon Energies Library: Grove Nuclide Ci Bq Ci/cm³ Bq/cm³ Sb-125 5.9112e-008 2.1872e+003 1.6000e-006 5.9200e-002 Buildup Buildup: The material reference is Source.

Page 2 of 3 Case Summary of OCNGS 44-10 eff Sb12 11/2/2023 file:///C:/Users/marty.erickson/Grove%20Engineering/MicroShield/html/OC%20Sb125-11...

11/02/2023 7Y/4-_c_'C::J~

/

,.,.--, ~

- X

' z

Mass Attenuation Library NIST Library Integration Parameters Radial 20 Circumferential 10 Y Direction (axial) 10 Page 3 of 3 Case Summary of OCNGS 44-10 eff Sb12 11/2/2023 file:///C:/Users/marty.erickson/Grove%20Engineering/MicroShield/html/OC%20Sb125-11...

26 Sb-125 Total Ei Energy (MeV)

Energy (KeV)

Exposure Rate Mr/hr -1 pCi/g Energy Response cpm/Mr/hr Ei (cpm/pCi/g) 0.004 4

1.95E-07 0

0.027 27 3.83E-07 0

0.031 31 2.89E-07 0

0.035 35 1.74E-07 0

0.117 117 1.04E-07 0

0.159 159 4.37E-08 0

0.173 173 1.27E-07 0

0.176 176 4.96E-06 3000000 15 0.204 204 2.79E-07 0

0.208 208 2.15E-07 0

0.228 228 1.30E-07 0

0.321 321 6.02E-07 0

0.38 380 2.58E-06 2100000 5

0.408 408 3.37E-07 0

0.428 428 5.70E-05 2250000 128 0.443 443 6.09E-07 0

0.463 463 2.18E-05 1750000 38 0.601 601 4.77E-05 1750000 83 0.607 607 1.36E-05 1080000 15 0.636 636 3.20E-05 950000 30 0.671 671 5.39E-06 900000 5

Total 320

27 Appendix A Ludlum Response Curve

28 Energy Response for Ludlum Model 44-10 10 Co-57

""*2 I "ill, I

~

~ I "

c~

0.1 10 100 1000 10000 Comma,F.nori)* (l<oV) 28

29 Appendix B Tc-99 and Th-230 Source-to-Detector Distance Effects

30 Counts Counts Contact 875 Contact 43100 867 41800 829 42000 820 43000 825 42500 Mean 843.2 Mean 42480 0.5 in.

766 0.5 in.

386 752 447 683 544 674 734 706 739 Mean 716.2 Mean 570 1 in.

512 1 in.

24 507 24 469 44 526 29 505 31 Mean 503.8 Mean 30.4 1.5 in.

370 1.5 in.

14 417 15 376 10 393 13 418 12 Mean 394.8 Mean 12.8 2 in.

311 2 in.

4 306 6

307 1

305 1

275 1

Mean 300.8 Mean 2.6