Neutron Multiplicity Counting - PDF document

Manual Neutron Multiplicity Counting NATIONALLABORATORYAlamos thereof.Los Alamos National Laboratory strongly supports academic freedom and a Neutron Multiplicity CountingIssued:November 1998 NATIONALLABORATORYAlamos 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This document is intended to serve as a comprehensive applications guide to passivecounting, a new nondestructive assay (NDA) technique developed over theyears. the principles of multiplicity counter and mathematics. Existing counters in Department of (DOE) facilities are surveyed, andprocedures and defined. Current estimates of the expected given. Lastly, and procurement aresummarized. also includes a detailed collection of references on I.IntroductionA.Purpose of the Application Guide Photo of the Plutonium Scrap Multiplicity Counter, used B.Definition of Neutron Multiplicity Counting 0.10.30.4 The multiplicity distribution for spontaneous fission in C.Basic Principles of Neutron Multiplicity Countingeff2.521.68 .(1-1)/(2.521.68 ,(1-2)1.Spontaneous fission rateÐthe goal of the assay2.Induced fission, or sample self-multiplication, and its variation across the sample,3.The (4.Spatial variation in neutron detection efficiency,5.Energy spectrum effects on detection efficiency,6.Neutron capture in the sample, and7.The neutron die-away time in the detector. 1.For samples that meet the assumptions in the derivations, the assay is bias free2.If the sample does not meet the assumptions, the assay will be biased.3.There is no need for calibration with a series of physical standards, because there isD.Historical Reasons for Multiplicity Counting E.Areas of Application for Multiplicity Countinga.Improved materials accountability measurements,b.Verification measurements,c.Confirmatory measurements, andd.Excess weapons materials inspections. F.Advantages and Disadvantages of Multiplicity Counting1.The measurement accuracy for impure plutonium samples is much greater than for2.Information on sample self-multiplication and (3.Calibration for many material types does not require representative standards. Thus,4.The measurement time, typically 15Ð30 min., is still relatively short compared to5.If a multiplicity counter is used for conventional coincidence counting, one can use 1.The cost of a multiplicity counter is higher than the cost of a conventional2.The multiplicity counter will require somewhat more floor space and height than a3.The measurement time for good precision on triples, typically 15Ð30 min. or 1000 s, 4.For plutonium samples that do not meet the assumptions required by the analysis II.Multiplicity Counter Design PrinciplesA.Multiplicity Detector Design Goals1.spontaneous fission neutron energy spectrum,2.induced fissions, or self-multiplication, which may be variable3.the (4.spatial variation in neutron detection efficiency across the counterÕs sample cavity,5.potential changes in the neutron energy spectrum leaving the container6.neutron capture in the sample, and7.the neutron die-away time in the detector.1.Maximize the neutron detection efficiency to increase the detected triple coincidence2.Minimize deadtime losses in the counting electronics by substantially increasing the3.Minimize the detector die-away time, to decrease the background of accidental4.Minimize the effects of sample placement in the cavity, or variable plutonium 5.Minimize the effects of variations in the sampleÕs emitted neutron energy spectrum due6.Make the size of the assay chamber as large as needed for the containers to be assayed,7.Minimize the fabrication cost of the multiplicity counter. Sometimes this goal requiresB.Calculational Tools This is a Test GraphiteHelium-3 TubesAirJunction BoxSample Cavity is 20 cm x 41 cm and is Cadmium Lined 80 Tubes 92 cm Design schematic for the Plutonium Scrap Multiplicity Counter. In this crossthe tubes is filled with polyethylene. The graphite above and below the sample cavity scattersand reflects neutrons trying to exit the top and bottom of the cavity. The junction box containsthe Amptek preamp/ discriminators. The sample cavity is open to the air at atmospheric C.How Calculations Are UsedD.Examples of Figure of Merit Calculations 1000100101 0.20.40.81.01.21.41.8 240 Pu-effective Mass (g)Relative Assay Precision (%) Figure of Merit calculation of expected assay precision (RSD) vs 3002001000 0145 Alpha=0 Alpha=1 Alpha=3 Figure of Merit calculation of expected precision vs E.Examples of Energy Sensitivity Calculations 6543210 0.40.60.81.01.61.8 Neutron detection efficiency (relative to the efficiency at 2 MeV) vs neutron 0.70.80.91.1 Energy (MeV)Efficiency Relative to 2 MeVFig. 2.5. Neutron detection efficiency (relative to the efficiency at 2 MeV) vs neutronenergy for the In-Plant Multiplicity Counter and the Plutonium Scrap Multiplicity Counter Multiplicity counters achieve their flat energy response largely through the use of multipleof all four, as plotted in Figs. 2.4 and 2.5 above, is very nearly constant.6543210 0.00.10.20.30.40.5 Ring 1 Relative count rate responses for the four tube rings in the Pyrochemical A.Basic Differences between Multiplicity and Conventional CoincidenceB.Five-Ring Multiplicity Counter Schematic of the Five- C.Three-Ring Multiplicity CounterD.In-Plant (Pyrochemical) Multiplicity Counter GraphiteJunction Box80.6 cm106.7 cmSample Cavity is 24.1 cm x 37.5 cm and is Cadmium Lined 126 TubesTube Spacing is 1.59 cm Design schematic for the In-Plant (Pyrochemical) Multiplicity Counter.E.Plutonium Scrap Multiplicity Counter The PSMC uses 19 Amptek preamp/discriminator circuits. In the inner ring, there are threecontainers entirely within the flat portion of this efficiency profile. The first PSMC was fabricatedIndustries, Inc. F.ARIES Neutron Counter (ARNC) G.FB-Line Multiplicity Counter GraphiteHelium-3 TubesAir113 tubes Sample Cavity is 20cm x 41 cmand is Cadmium Lined92 cm 66cm Schematic diagram of the FBLNMC showing the 6543210 0.70.81.01.1 Pyrochemical Counter Energy (MeV)Efficiency Relative to 2 MeV MCNP calculations of the efficiency vs theH.Large Neutron Multiplicity Counters AA AA .. . ... ... JunctionBoxes A A . . . .. .. Support / Slide Rails A A Mechanical schematic for the Large Neutron Multiplicity Counter. The RFETS Large Neutron Multiplicity Counter.I.Shield Cell Drum Counter The Shield Cell Drum Neutron Counter, with multiplicity,J.High-Efficiency Neutron Counter (HENC) . Top view of the High Efficiency Neutron Counter developed by K.Plutonium Residues Multiplicity CounterL.Multiplicity Analysis with Conventional Counters IV.Multiplicity ElectronicsA.OverviewB.Thermal Neutron Detection and Die-Away Time neutron will be lost as it travels through the counter is nearly constant with time. Under these NtNe()(),(4-1)C.Thermal Neutron Detector Electronics Signal R C + TimeTube CasingCentral Wire Voltage Fig. 4.1. The neutron capture process in 3He tubes and the associated charge collection electronics.Typically, Amptek integrated circuits are used to amplify the tube output pulses, set the counting 3He TubesHigh VoltageAmptek Module Electronic layout with one Amptek channel processing the input signals from ORgatedeadtime--= .(4-2) Module 1 Module 2 Module N OUTPUT Electronic layout (simplified) of multiple Amptek modules connectedD.Derandomizer CircuitE.The Neutron Pulse Stream and Rossi- Distribution ,n) neutrons. The 01234567891011121314151617181920 01234567891011121314151617181920 01234567891011121314151617181920 01234567891011121314151617181920 A neutron pulse stream that contains both correlated (striped bars) and .(4-3) {{ Accidentals Gate Histogram of a Rossi-shown in Fig. 4.4. An actual measured distribution with exponential die-away time isF.Predelay Circuit InputPredelayShift RegisterUp - Down CounterStrobeR + A ScalerLong DelayA Scaler Conventional shift register circuit.G.Conventional Shift Register Basics and those collected in the A gate is the desired real signal R (or that fraction of R that lies within theand through the R+A gate. Figure 4.7 compares this process to an escalator. Every event that gets Counts pulses on EscalatorIncrements when pulse Ògets onÓ Comparison of the shift register circuit to an escalator. On EscalatorIn Accumulator0 On EscalatorIn Accumulator1Second neutron triggers accumulator 3 On Escalator O n Escalatorhird neutron A dd 2 to A ccumulatorFourth neutronAdd 3 to Accumulator Four Pulses Yield6 Coincidences Example of shift register operation as four neutron pulses pass Illustration of the total number of possible coincidence pairs between.(4-4)H.Multiplicity Shift Register Basics InputStrobePredelayShift RegisterUp-Down CounterSort by Number in CounterZeros ScalerOnes ScalerTwos Scaler Long Delay Multiplicity shift register circuit. 02680436029731130 181875306222207 217728311016603 3325270157224 45344922387 582313093 61237402 718342 8308 921 1000 triggers, because the singles scaler is situated at the output of the A scaler. The sum of all the I.Los Alamos MSR4/Canberra 2150 Multiplicity Shift RegisterJ.Los Alamos PSR/Aquila PSR-B Multiplicity Shift Registers. The singles K.Canberra JSR-14 Multiplicity Shift RegisterL.Los Alamos PATRM List Mode Module V.Multiplicity MathematicsA.OverviewB.The Spontaneous Fission Process 012345678 0.1 Spontaneous Fission of 240 Pu The spontaneous fission multiplicity distribution for Table 5.1.The spontaneous fission neutron yields of the plutonium isotopes and other related nuclides(from Ensslin 91a). AMultiplicity vInduced ThermalMultiplicity v Th901421.41 X 10yr�1 X 10'�6 X l02.141.9 U9214071.7 yr8 X 10'1.31.713.13 U921411.59 X l0yr1.2 X 101.762.4 U921422.45 X 10yr2.1 X l01.812.4 U921437.04 X 10yr3.5 X 101.862.41 U921442.34 X 10yr1.95 X 101.912.2 U921464.47 X 10yr8.20 X 102.012.3 Np931442.14 X 10yr1.0 X 102.052.70 Pu9414487.74 yr4.77 X 10'2.212.9 Pu941452.41 X 10yr5.48 X 10'2.162.88 Pu941466.56X 10yr1.16X 102.162.8 Pu9414714.35 yr(2.5 X 10)(5 X 10)2.252.8 Pu941483.76 X 10yr6.84 X 102.152.81 Am95146433.6 yr1.05 X 101.183.223.09 Cm96146163 days2.543.44 Cm9614818.1 yr1.35 X 102.723.46 Bk97152320 days3.403.7 Cf981542.646 yr3.7574.06 Spontaneous and induced fission multiplicity distributions. n)Pu s.f.Cm s.f.Cf s.f.Pu .025Pu 2 00.0540.0660.0680.0210.0150.0020.0110.006 10.2050.2320.2300.1470.1160.0260.0990.061 20.3800.3290.3340.3270.3000.1270.2750.227 30.2250.2510.2470.3270.3330.2730.3270.326 40.1080.1020.0990.1380.1840.3040.2050.259 50.0280.0180.0180.0370.0430.1850.0730.096 60.0020.0030.0030.0090.0660.0100.022 70.0010.0150.0010.003 80.0020.001 2.212.1562.1452.5402.7203.7572.8763.163 3.9573.8253.7945.1325.93911.9626.7488.240 5.5965.3365.3178.03610.10131.81212.58917.321 nnn .(5-1), is 2.156. From the C.Description of ( Table 5.3.Summary of alpha decay half-lives and yields of the plutonium isotopes and other relatednuclides (from Ensslin 91a). Aaaa Th1.41 X 10yr1.41 X 10yr4.1 X 10 U71.7 yr71.7yr8.0 X 10 U1.59 X 10yrl.59 X 10 yr3.5 X 104.824.8 U2.45 X 10yr2.45 X 10yr2.3 X 104.763.0 U7.04 X l0yr7.04 X l0 yr7.9 X 10 U2.34 X 10yr2.34 X 10 yr2.3 X 10 U4.47 X 10yr4.47 X 10 yr1.2 X 10 Np2.14 X 10yr2.14 X 10 yr2.6 X 10 Pu87.74 yr87.74 yr6.4 X 10 Pu2.41 X 10yr2.41 X 10 yr2.3 X 10 Pu6.56 X 10yr6.56 X 10 yr8.4 X 10 Pu14.35 yr5.90 X 10 yr9.4 X 104.891.3 Pu3.76 X 10yr3.76 X 10yr1.4 X 104.902.0 Am433.6 yr433.6 yr1.3 X 10 Cm163 days163 days Cm18.1 yr18.1 yr3.0 X 10 Bk320 days yr8.8 X 10 Cf2.646 yr2.731 yr1.9 X 10 materials that may be present, including oxygen, water, fluorine, etc. Whether the reaction can,n) reactions. Table 5.4.Reaction Q-values, threshold energies, and coulomb barriers for the low-Z elements thatundergo (a,n) reactions (from Ensslin 91a). NucleusNatural He100-18.9938.01.5 Li7.5-3.706.322.1 Li92.54.382.11.2 Be100+5.7002.610.8 B19.8+1.0603.25.9 B80.2+0.1603.25.0 C98.9-8.5111.343.7 C1.11+2.2203.77.2 N99.66.094.1 N0.4-6.428.134.1 099.815.24.7 00.04+0.5904.65.5 00.2-0.700.854.64.2 F100-1.952.365.12.9 Ne90.98.665.6 Ne0.3+2.5505.57.6 Ne8.8-0.480.575.54.5 Na100-2.963.496.01.8 Mg79.08.396.4 Mg10.0+2.6506.47.7 Mg11.0+0.0306.35.0 Al100-2.643.036.82.2 Si4.7-1.531.747.23.4 Si3 1-3.493.967.21.4 Cl24.24.298.31.0 If the total neutron emission rate due to (,n) reactions is N a ,n) neutrons to spontaneous fission neutrons bya=NaN NaFns .(5-2) +++++13400381141132026901020254169238239240241242241238240242fffffffff...(..) .(5-3) Thick target yields from the low-Z elements that can undergo ( Neutron Yield6 Alphas4.7 MeV (234U)Neutron Yield6 Alphas5.2 MeVAv. Neutronfor 5.2 MeV Li0.16 0.041.13 0.250.3 Be44 465 54.2 B12.4 0.617.5 0.42.9 C0.051 0.0020.078 0.0044.4 O0.040 0.0010.059 0.0021.9 F3.1 0.35.9 0.61.2 Na0.5 0.51.1 0.5 Mg0.42 0.030.89 0.022.7 A10.13 0.010.41 0.011.0 Si0.028 0.0020.076 0.0031.2 Cl0.0l 0.010.07 0.04 D.Definition of Sample Multiplication =the average number of neutrons created by induced fission,p =probability that a neutron will induce a fission =probability that a neutron will be captured without producing any =probability that a neutron will escape the sample (leakage If we neglect any neutron-producing reactions other than fission, then p + pThe multiplication factor k relates the number of neutrons in successive generations. If theeff, or just ÒkÓ for brevity. It isdefined as the ratio of the number of neutrons produced in one generation to the number eitheri. For allgenerations, the sum of the number of neutrons created per initial source neutron is the total. .(5-4) .(5-5) counting is the multiplication observed with the sample inside the counter rather than the M of theitself affects the coincidence response of the well counter. As the leakage multiplication M .(5-6) Table 5.6.Example of the change in the neutron multiplicitydistribution at M=1.04. n)Pu spontaneous fissionPu spont. fiss. +Pu induced fission:(M = 1.04) 00.0660.066 10.2320.227 20.3290.318 30.2510.242 40.1020.101 50.0180.025 60.0020.010 700.005 800.003 900.002 1000.001 2.1562.240 3.8254.712 5.33610.362 E.Assumptions in the Equations (3) It is assumed that ( i (a F.Definitions of the Multiplicity Distributions and Moments) =Distribution of neutrons emitted in a fission. If (D(n) =Distribution of detected neutrons. If the neutron detection efficiency e f(i) =Distribution of signal-triggered measured events, i.e., neutrons that are detected andg(i) =Distribution of fission-signal-triggered measured events, i.e., neutrons that would beb(i) =Distribution of randomly-triggered measured events, i.e., neutrons that are detected andr(i) =Distribution of correlated neutrons that are detected and counted following a signal trigger.s(i) = nnn,(5-7)nnnn()(),(5-8)nnnnn=--()()(),(5-9) ()!.(5-10)G.The Measured Foreground and Background Multiplicity Distributions Table 5.7 (same as Table 4.1) lists the multiplicity distribution for a real 60-g plutoniumTable 5.7.Neutron multiplicity distribution from a real 60-g 02680436029731130 181875306222207 217728311016603 3325270157224 45344922387 582313093 61237402 718342 8308 921 1000 1100 1200 Table 5.8.Neutron multiplicity distribution from a 3.8-kg plutonium metal sample measured in a multiplicitycounter with roughly 56% neutron detection efficiency. R+A A R+A AR+AA 01347503234258523377424182845457126 15548119874160824261832123318464414 21259469118155789251807348290147186 32088046427689521261250535534348203 4282866723471729427860883727749196 5332273913793082928587582483750164 6350769363737719829403541686251101 734113057340518483027484112425241 831095848291871023118999769353102 926937850238100633213004520354112 10223839981869904733855332655531 11179750501423376834575922535650 12140361741055127135399515225720 131070829676610303626129885830 14802171654691903718607145900 15591358238562633812914176011 1643081702691844399123136100 1731045531858200406022056210 1822160441273803414061226310 19156771386939742237746400 2011077855924814315449 217762743989554411228 22541207270021 01234567891011121314151617181920 1.00e+74.00e+7 Counts Counts in R+A Gate Multiplicity distribution for a 3.8-kg plutonium metal sample measured 012345 1.00e+62.00e+63.00e+64.00e+65.00e+6 Counts Counts in R + A Gate Multiplicity distribution for an AmLi random neutron source measured 0.00e+01.00e+7 MultiplicityCounts Counts in R + A Gate Multiplicity distribution for a large H.Extraction of the Correlated Multiplicity Distributions + Sbkg, where the fission trigger rate is F e n kkk=+-enen,(5-11)g(0) = r(0)b(0),g(1) = r(0)b(1) + r(1)b(0),g(2) = r(0)b(2) + r(1)b(1) + r(2)b(0), etc..(5-12) rbbkjk .(5-13)SinglesDoublesSSrSfb=-=-()()111Triples/2!))/2 .(5-17) = 1, = b = b - b = b - 3 b + 2 b .(5-18)SinglesDoubles Triples (b3-3b1b2+2b13)(5-21) I.The Emitted Fission Multiplicity Distribution ,(5-22) d ln=1 and 0 otherwise.With this definition of the emitted multiplicity distribution for actual samples, the first three ,(5-23) vMv, and (5-24) vMvvvvsisi22133133+--æèçöø÷+ìíïîïüýïþïnana()() .(5-25)J.The Detected Multiplicity Distribution DnP()()() .(5-26)nDn ,(5-27)knkeee .(5-28) e K.The Detected and Counted Multiplicity Distribution only a fraction of all coincidences can be detected. For a fission that occurs at t=0, the time tt + PD Simplified time distribution for signal-triggered events.pfsdstPDtPDG .(5-29)pnftppdttit()() .(5-30) nDnppdt()() .(5-31) : ririftfsdsdttPDtPDG()()() .(5-32) The second correlated moment r riiriftfsdsdttPDtPDG=-=()()()() .(5-33) ,(5-34) .(5-35) .(5-36) .(5-37)qfsds ,(5-38) qqdt .(5-39) derivation of r: nDnSdtqdsSdtqdsSGòòò .(5-40) sSG=-- .(5-41) sSG .(5-42) ejG .(5-43) t = -Gt = 0tt + G Simplified time distribution for random-triggered events. L.Analytical Definition of Singles, Doubles, and Triples SFMena,(5-44) FfM, and(5-45) FfMvvvsisii+--æèçöø÷+ìíïîïüýïþïenana2213313()().(5-46)F =spontaneous fission rate, 473 fission/s-g = effective e =neutron detection efficiency,M =neutron leakage multiplication, =(=doubles gate fraction,=triples gate fraction, =first, second, and third reduced moments of the =first, second, and third reduced moments of theeff2.521.68 .(5-47) M.Final Solution for Sample Mass, Multiplication, abMcMM+++=,(5-48) tsisi2332ennnn,(5-49) sisisisii-21331222332nnnnennnn, and(5-50) sisi2332ennnn.(5-51) MMS.(5-52) The second term in the numerator of Eq. 5-52 represents the effect of sample self-interrogation due240Pu-effective mass m240 is given by fissionssgm(/).(5-53) .(5-54)N.Final Solution for Sample Mass, Detector Efficiency, 240Pu-effective mass m240, sample (a : tss.(5-55) ,(5-56) .(5-57) VI.Multiplicity Counter Operating ProceduresA.Hardware Installation and SetupB.Overview of the NCC Code C.Software Installation and Setup1. 33 MHz 486 processor,4. 1.44 Mbytes Floppy Disk,6. Mouse, and7. Microsoft Windows 3.1, Windows 95, or Windows NT.D.Detector Parameter Setup of electronics that are available. In this case, these parameters are set directly on the electronicsTable 6.1.Example of detector parameter list for the Five- Shift Register Serial Port HV (V)1680 Deadtime Coefficient A0.12 x 10s 0.00 x 10s-2 Deadtime Coefficient C0 35.83 ns Detector Die-Away Times E.Detector Characterization: BackgroundF.Detector Characterization: Bias G.Detector Characterization: EfficiencyYYeln()/ ,(6-1) .(6-2)H.Detector Characterization: Die-Away Time and Gate Width .(6-3) .(6-4)I.Detector Characterization: Gate Fractions fDSdss=212n ,(6-6) e s1 s2 s3 J.Detector Characterization: Deadtime CoefficientsSSeand(6-7)DDe,(6-8) .(6-9) ,(6-10) ³=-+å1111112022()()()and(6-11) =-++³=-+å11212123033()() .(6-12) = 1, = -1, and = Rfibii=åa()()and(6-13)RfibiRbii-==ååba()()()maxmax .(6-14)TfSRcS .(6-15)K.Detector Characterization: Detectability Limit Bad ,(6-16)Pu by doubles counting. For 100 kg of waste,L.Measurement Control Features1.Background measurementsÑthe background values stored in the code should be2.Bias measurementsÑa bias run should be made at least once per day to ensure that the3.Precision measurementsÑthis option can be exercised relatively infrequently, such as4.Statistical and QA flagsÑthese tests monitor the data collected by the NCC code anda. A check-sum test is always applied to the multiplicity data to check for internalb. The accidentals/singles test (Eq. 4-4), with a usual limit of 4 c. The accidentals/singles test rate limit, which turns off the test at rates below 1000/s.d. The accidentals/singles test precision limit, which turns off the test if the accidentals e. The outlier test, which rejects runs that lie outside a limit, usually set to 3 f. The measurement control chi-squared limit, with a default value of 99%.g. The maximum number of allowed bad measurements, usually set to 10. For longh. DeclaredÑassay quality check limit, with a default value of 3 i. High voltage test limit, with a default value of 1%.M.Multiplicity Calibration Procedure 1.A series of californium sources can be used to determine the deadtime correction2.Using one of the californium sources of known yield, the dead-time-corrected 3.At this stage, one should correct for the difference in efficiency between californium standard, and adjusting the value of 4.Whenever possible, the three calibration coefficients should be adjusted for errorsa.Adjust b.Adjust c.Adjust in some consistent way, not yet defined, with one standard,5.It may be helpful to correct all multiplicity assays for shifts in the neutron energy6.For large metal samples, a correction for the nonuniform probability of fission in7.There is a final step that can be done at the end of a large measurement campaign ifa.Adjust only.b.Adjust e fdt. N.Additional Correction Factors : If samples are highly moderating, the neutron detection efficiencyhigh-energy neutrons (Fig. 2.6 or Fig. 7.9). Thus the ratio of Ring 1/Ring 3, 4, or 5 is a rough : Past measurements of large metal samples haveCFabMcM111=+-+-()().(6-17) O.Assay/Verification Sequence1.For each short run of 30 s or so,2.If there are additional runs, then for each run,3.When series of runs is done, using the cumulative distribution,4.For verification runs, compare with entered value5.Compute statistical errors from population of individual runs6.Report results and print out if requested7.Store all data in database and in an ASCII file. Do a run ( short time interval ~ 30s) consistency cumulative distribution from population of individual runs and store all data in database andASCII file. correctionCompute S, D,TSubtract BackgroundCalculate Assay ResultFor this run only For cumulative distribution No Yes The assay sequence used by the NCC Windows Code.P.Measurement Error Calculation n A.Factors That Affect Multiplicity Performance. Summary of past or expected multiplicity counter performance on various nuclear material aAssay Plutonium Metal2000 g Plutonium Oxide2000 g1000 g115000 s3000 s600 s0.8%Langner 91bKrick 92bLangner 93bStewart 95 Plutonium Scrap100 g 120 g300 g20-100 g100 g7-343000 s3600 sKrick 92bEnsslin 98Langner 98Langner P.C. Plutonium Waste1 g1 g151000 s1000 s2-5%Ensslin 95Ensslin 95 Plutonium Oxidein Excess1000 g1000 g1 - 101 - 81500 s1000 s5.0%bStewart 96Stewart 97(PC)Langner 96b 300 g1 - 21000 s1-2%1-3%Menlove 93 Large Drum1 - 4000 g1 - 4000 g1 - 67 - 506 - 12 h6 - 12 hRinard 97Rinard 97 Assay bias quoted without multiplication correction curve for metal. Assay precision based on counting statistics, gamma-ray isotopics, and scatter relative to calorimetry. Assay precision based on counting statistics and scatter relative to destructive analysis. 1.special nuclear material (SNM) mass,2.(3.available detector efficiency,4.sample self-multiplication,5.neutron energy spectrum effects,6.spatial distribution of fissile material,7.other matrix effects such as density, self-shielding, neutron poisons,8.available detector die-away time,9. available counting time/required precision,10.count rate/dead-time effects,11.container size and shape, and12.room background. B.Plutonium Metal 1 1 10 100 Coincidence a = 0 a = 1 a = 5 a = 20 a = 0 a = 1 a = 5 a = 20 240Pu mass (g) RSD (%) Example of the use of the Figure of Merit code to predict precision, Figure 7.2 compares conventional coincidence and multiplicity assays of eight plutoniumbias of -4.7% ± 20406080100120140160 Comparison of conventional coincidence and multiplicity assays 4003002001000 -40-2002040 (Assay-Reference)/Reference (%)240 Plutonium metal and oxide results using the In-Plant Pyrochemical Summary of plutonium metal and oxide results by coincidence and multiplicity techniques using the (Assay - Reference)/Reference (%) Conventional Assay1Multiplicity Assay1 Low Burn-Up Metal10-9.75.4 High Burn-Up Metal4-30.91.6-8.10.9 Metal Set 1 (Broken)5-3.31.3-9.05.6 Metal Set 2 (Unbroken)9-28.79.1-9.44.2 All Metal Samples14-21.7-9.34.6 Low Burn-Up Oxide1123.115.8-1.22.5 High Burn-Up Oxide345.66.40.32.0 All Oxide Samples4510.012.2-0.12.2 All Samples592.3-2.24.9 Plutonium metal buttons are dense, compact samples for which the theoretical point modeldoes not correctly describe the internal multiplication, so that corrections are required. ÒCompactÓ 0.071 (1 0.035 0.91.0 In-plant NMC at LLNL Compilation of plutonium metal data obtained Summary of plutonium metal and oxide results by multiplication-corrected, and both multiplication- Ratio Corrected1 Low Burn-Up Metal10-1.41.9-0.32.2 High Burn-Up Metal43.10.80.90.9 Metal Set 1 (Broken)5-0.11.01.30.9 Metal Set 2 (Unbroken)9-0.23.3-0.92.2 All Metal Samples14-0.12.70.02.0 Low Burn-Up Oxide11-1.61.9-1.42.0 High Burn-Up Oxide340.71.90.51.4 All Oxide Samples450.12.10.01.8 All Samples590.02.20.01.8 C.Plutonium Oxide 8.2% by Comparison of conventional coincidence and multiplicity assays of was Results for assay of 21 heterogeneous plutonium oxide inventory Assay effective 240Pu mass (g) 240Pu Mass: Multiplicity Analysis25020015010050 0 0 50100150 2 00 2 50Declared effective 240Pu mass (g) 1 . 024 * (d ec l are d mass ) Results for assay of 21 heterogeneous plutonium oxide inventoryD.Plutonium Scrap The relative standard deviation of the multiplicity assay for 1200-s measurements of 67 The measured ratio of Ring 1 to Ring 4 as a function ofE.Plutonium Residues 20 in Fig. 7.1. However, for plutonium samples 4.8%, butF.Plutonium Waste Estimated precision for neutron coincidence and 0.010.11102345678234556782345678Mass 240 Total Error in % Multiplicity Tunable Multiplicity Coincidence Comparison of the total error in tunable multiplicity with thePu by doubles counting. For 100 kg of waste, this isG.Verification of Plutonium Oxide in Excess Weapons Materials 0.83%. Twenty-eight of the measurements lie within the 3% limit set for bias defects, and 67 lie within the Physical Inventory Verification results for 69 items using single oxidesstacked oxidesmetal 0100200300400500600 Multiplicity assay results for single and -400-300-200-1000100 Assay Number (Randomized)(Declared - Assay) / Declared (%) Comparison of known- 4.17% (1 5.79% (1 -30-20-10010 Randomized Assay Number(Declared-LNMC)/Declared (%) Summary of initial PIV and later PIV measurement results forNeutron Multiplicity Counter (Langner 97b). (From LA-UR-97-2650)H.Mixed Uranium/Plutonium Oxide I.Mixed Uranium/Plutonium Inventory Verification in Large Drums30-, or 55-gal. drums. The SNM was in metal, oxide, scrap, scrub alloy, or other forms. For the J.Comments on Inventory Verification by Multiplicity Counting A.Summary of When to Apply Multiplicity Counting B.Sample Selection Criteria . Also, the throughout the assay chamber. A flat spatial profile is important because the is even more may be an may be required to get a low limit. may be required, which implies a large 3 . For high plutonium mass should be low to to minimize counting losses. The number of is used to reduce multiplication of of helps to is also important so to mitigate the change in neutron detection efficiency. The effect will will dampen the effect of thermal neutron capture in the poisons. on the sample well to increase the is used.C.Facility Selection Criteria around the well, such as the ARIES Neutron Counter can be used to assay samples near the glove-box line or in a separate NDA counting room. An at-line counter willFor either in-line or at-line applications, if the sample and/or the top end-plug are too heavy may be may be used, such as the Large of polyethylene , less 3 , and 3 . and nearly . Assay bias can also be minimized if one or two are . To determine assay bias, multiplicity counter results can be . The communications link is usedD.Multiplicity Counter Selection Criteria Table 8.1. Influence of sample and facility criteria on multiplicity counter selection. Sample and Facility CriteriaImportant Multiplicity Counter Feature Sample container sizeAssay chamber size Assay RSD/Count timeHigh detection efficiency High plutonium massLow counter die-away time ,n) rate High sample moderationFlat energy spectrum efficiency Neutron poisons in sampleCadmium-lined sample well Am content in sampleThick cadmium liner on sample well Irradiated samplesLead-lined sample well Unsealed process materialsIn-line counter design Canned, sealed samplesFree-standing, at-line counter design Heavy sample/end plugSample lifting mechanism Low sample entry neededFront-loading design High room backgroundExternal shield needed Weight/size constraintNo external shield Low assay bias requiredFlat spatial efficiency profile Facility system integrationSoftware communications link E.Commercially Available Multiplicity Equipment US: 303-430-8184F.Los Alamos Support Options Mark Pickrell,505-665-5098, mpickrell@lanl.govG.Typical Procurement CostsH.Routine Maintenance Requirements Abhold 98M. Arnone 92G. J. Arnone 96G. J. Arnone, ÒA New Pulse Arrival-Time Recording Module System,Ó 1996 IEEEBoehnel 75K. Boehnel, ÒDetermination of Plutonium in Nuclear Fuels Using the NeutronBoehnel 85K. Boehnel, ÒThe Effect of Multiplication on the Quantitative Determination ofBoldeman 85J. W. BondarL. Bondar, ÒTime Correlation Analyzer for Nondestructive Plutonium Assay,Ó noBondar 96L. Bondar, ÒPassive Neutron Assay of Plutonium by Multiplicity CounterBourret 94S. C. Bourret and M. S. Krick, ÒA Deadtime Reduction Circuit for ThermalBriesmeister 93J. F. Briesmeister, Ed., ÒMCNP - A General Purpose Monte Carlo Code forBrunson 97G. S. Brunson and G. J. Arnone, ÒApplications of a Versatile New Instrument Carrillo 98L. Annual INMM Meeting, July 26-30, 1998, Naples, Florida.Cifarelli 86D. M. Cifarelli and W. Hage, ÒModels for a Three Parameter Analysis of NeutronCrane 91T. W. Crane and M. P. Baker, Chapter 13, ÒNeutron Detectors,Ó in Passive , edited by T. D. Reilly, N. Ensslin, andDierckx 83Dierckx and Hage, Nuclear Science and Engineering 85, 1983.Dytlewski 90N. Dytlewski, N. Ensslin, and J. W. Boldeman, ÒA Neutron Multiplicity CounterDytlewski 91N. Dytlewski, ÒDead-time Corrections for Multiplicity Counters,Ó Dytlewski 93N. Dytlewski, M. S. Krick, and N. Ensslin, ÒMeasurement Variances in ThermalEnsslin 82N. Ensslin, T. L. Atwell, D. M. Leet, B. Erkkila, R. S. Marshall, A. Morgan, C.Ensslin 85N. Ensslin, ÒA Simple Self-Multiplication Correction for In-Plant Use,Ó Proc. 7thEnsslin 89N. Ensslin, ÒDevelopment of Neutron Multiplicity Counters for SafeguardsEnsslin 90aN. Ensslin, M. S. Krick, and N. Dytlewski, ÒAssay Variance as a Figure-of-MeritEnsslin 90bN. Ensslin, D. G. Langner, H. O. Menlove, M. C. Miller, and P. A. Russo,Ensslin 91aN. Ensslin, Chapter 11, ÒNeutron Origins,Ó in , edited by T. D. Reilly, N. Ensslin, and H. A. Smith, USEnsslin 91bN. Ensslin, Chapter 16, ÒPrinciples of Neutron Coincidence Counting,Ó in Passive , edited by T. D. Reilly, N. Ensslin, and Ensslin 91cN. Ensslin, M. S. Krick, D. G. Langner, and M. C. Miller, ÒActive NeutronEnsslin 92aN. Ensslin, M. S. Krick, D. G. Langner, and M. C. Miller, ÒActive NeutronEnsslin 92bN. Ensslin, M. S. Krick, D. G. Langner, D. W. Miller, and M. C. Miller,Ensslin 93N. Ensslin, M. S. Krick, W. C. Harker, M. C. Miller, R. D. McElroy, P. A.Ensslin 95N. Ensslin, M. S. Krick, and H. O. Menlove, ÒExpected Precision of NeutronEnsslin 96N. Ensslin, M. E. Abhold, and H. A. Smith, ÒResults from the First Waste andEnsslin 97N. Ensslin, A. Gavron, W. Harker, M. S. Krick, D. G. Langner, M. C. Miller,Ensslin 98N. Ensslin, L. A. Foster, W. C. Harker, M. S. Krick, and D. G. Langner,Gavron 74A. Gavron and Z. Fraenkel, ÒNeutron Correlations in Spontaneous Fission ofHage 85W. Hage and D. M. Cifarreli, ÒCorrelation Analysis with Neutron CountHalbig 91J. K. Halbig 94J. K. Harker 96W. C. Harker and M. S. Krick, ÒSoftware Users Manual Windows NCC,Ó HoldenN. E. Holden and M. S. Zucker, ÒNeutron Multiplicities for the TransplutoniumKrick 84M. S. Krick and J. E. Swansen, ÒNeutron Multiplicity and MultiplicationKrick 92aApplication Note on Passive Neutron Coincidence Counters (December 1992).Krick 92bM. S. Krick, D. G. Langner, D. W. Miller, J. R. Wachter, and S. S. Hildner,Krick 93M. S. Krick and W. C. Harker, ÒMultiplicity Neutron Coincidence Counting Krick 94aM. S. Krick 94bApplication Note on the Passive Neutron Multiplicity Counter (June 1994).Krick 96M. S. Krick, N. Ensslin, R. N. Ceo, and P. K. May, ÒAnalysis of Active NeutronKrick 97aM. S. Krick, ÒThermal Neutron Multiplicity Counting of Samples with Very LowKrick 97bM. S. Krick, D. G. Langner, and J. E. Stewart, ÒEnergy-Dependent Bias inKrick 98M. S. Krick, W. C. Harker, P. M. Rinard, T. R. Wenz, W. Lewis, P. Pham, andLangner 90D. G. Langner, N. Ensslin, and M. S. Krick, ÒPyrochemical Neutron MultiplicityLangner 91aD. G. Langner, N. Dytlewski, and M. S. Krick, ÒPyrochemical MultiplicityLangner 91bD. G. Langner 92D. G. Langner, M. S. Krick, and D. W. Miller, ÒThe Use of Ring Ratios toLangner 93aD. G. Langner and P. A. Russo, ÒGeometry-Based MultiplicationLangner 93bD. G. Langner 94D. G. Langner, M. S. Krick, and K. E. Kroncke, ÒA Large MultiplicityLangner 95D. G. Langner, M. S. Krick, and K. E. Kroncke, ÒThe Application ofLangner 96aD. G. Langner 96bD. G. Langner 97aD. G. Langner 97bD. G. Langner 97cD. G. Langner, M. R. Sweet, S. D. Salazar, and K. E. Kroncke, ÒFB- Langner 98D. G. McElroy 97R. McElroy, ÒCharacterization of the PRMC Unit 1 for MultiplicityMenlove 85H. O. Menlove 89H. O. Menlove 93H. O. Menlove 96H. O. Miller 96M. C. Miller 97M. C. Pickrell 96M. M. Pickrell, ÒDevelopment of a High-Efficiency Neutron Detector UsingPickrell 97aM. M. Pickrell and N. Ensslin, ÒApplication of Neutron Multiplicity Pickrell 97bM. M. Rinard 97P. M. Robba 83A. Robba, E. Dowdy, and H. Atwater, ÒNeutron MultiplicitySampson 93T. E. Sampson, T. L. Cremers, J. C. Martz, and W. R. Dvorzak, ÒAnSmith 91H. A. Smith and N. Ensslin, Chapter 23, ÒNDA Applications Guide,Ó in , edited by T. D. Reilly,Stewart 86J. E. Stewart, ÒA Hybrid Monte Carlo/Analytical Model of NeutronStewart 89J. E. Stewart, R. R. Ferran, and M. S. Krick, ÒMeasurement PerformanceStewart 91aJ. E. Stewart, et. al., ÒA Versatile Passive/Active Neutron CoincidenceStewart 91bJ. E. Stewart, Chapter 14, ÒPrinciples of Total Neutron Counting,Ó in , edited by T. D. Reilly,Stewart 93Application Note on the Passive/Active Neutron Coincidence Counter (AprilStewart 95J. E. Stewart, M. S. Krick, D. G. Langner, and T. D. Reilly, W. Theis, R. Stewart 96aJ. E. Stewart 96bJ. E. Stewart, S. C. Bourret, N. Ensslin, M. S. Krick, W. J. Hansen, andStewart 97J. E. Stewart, M. S. Krick, J. Xiao, R. J. Lemaire, and V. Fotin,Stewart 98J. E. Stewart, M. S. Krick, D. G. Langner, and T. R. Wenz, ÒNeutronTerrell 57J. Wachter 87J. R. Zucker 84M. S. Zucker and N. Holden, ÒParameters for Several Plutonium NuclidesZucker 86M. S. Zucker and N. Holden, ÒEnergy Dependence of the Neutron in Fast Neutron Induced Fission of Oak Ridge, TN37831.Springfield, VA22616. NATIONALLABORATORYAlamos Los Alamos, New Mexico 87545