Pseudocoincidence Techniques

Transcription

1 Pseudocoincidence Techniques Alfred Klett Berthold Technologies - Bad Wildbad Germany Air Monitoring Users Meeting AMUG Las Vegas/NV USA 3-6 May 2011

2 Overview Introduction Characteristics of Radioactive Chains Principles of Measurement Instruments Test & Calibration Applications AMUG 2011 Alfred Klett May 3,

3 Introduction In monitoring of man made airborne radioactivity concentrations MDAs are limited by the presence of natural activities Therefore efficient discrimination and subtraction techniques of natural contributions are required The natural occuring radionuclides exhibit specific characteristics, which allow to discriminate against man made radioactivity a few general facts physical facts are presented on the following slides AMUG 2011 Alfred Klett May 3,

4 Uranium-Radium decay chain 238 U α 234 Th β 234 Pa β 234 U α 230 Th α y 24 d 1.2 min y y 226 Ra α 222 Rn α 218 Po α 214 Pb β 214 Bi β 214 Po α 1600 y 3.8 d 3 min 27 min 20 min s 210 Pb β 210 Bi β 210 Po α 206 Pb 22 y 5 d 138 d stable AMUG 2011 Alfred Klett May 3,

5 Radon Progeny mobile gas Radon daughters pseudostable 222 Rn α 218 Po α 214 Pb β 214 Bi β 214 Po α 210 Pb 3.8 d 3 min 27 min 20 min s 22 y α-energies 6002 kev 7687 kev AMUG 2011 Alfred Klett May 3,

6 Uranium and Thorium Decay Chains AMUG 2011 Alfred Klett May 3,

7 The Pseudo-Coincidence Technique Detection of an alpha and a beta particle within a pseusocoincidence period of about 200 µs as a measure of the Radon and Thoron concentration Utilizing decays in the Uranium chain (Radon) 214 Bi 214 Po + beta 214 Po 210 Pb + alpha T 1/2 = 164 µs Utilizing decays in the Thorium chain (Thoron) 212 Bi 212 Po + beta 212 Po 208 Pb + alpha T 1/2 = 0.3 µs which are unique characteristics of these decays AMUG 2011 Alfred Klett May 3,

8 Examples of alpha-emitting nuclides Nuclide Half-live E α [kev] P α 235 U a U a Pu a Pu a Am a Po 180 s Po s AMUG 2011 Alfred Klett May 3,

9 Range of alphas in air 10 8 R [cm] Energy [MeV] AMUG 2011 Alfred Klett May 3,

10 Natural Radionuclides Identification alpha-energies of Radon and Thoron daughters E alpha > 6 MeV alpha-energies of artificial alpha-emitters E alpha < 6 MeV pseudo-coincident alpha-beta events in the Uranium and in the Thorium decay chains Long range alphas E alpha > 6 MeV are caused by natural bgrd Alpha-beta pseudo-coincidence events are proportional to natural background AMUG 2011 Alfred Klett May 3,

11 Detection with a gas filled detector Cosmic ray Guard detector α-long range α-short range β-particle pseudoco event α-particle Detector 2 Thin window 2 Detector 1 Thin window 1 Filter AMUG 2011 Alfred Klett May 3,

12 AMUG 2011 Alfred Klett May 3,

13 Pseudo-Coincidence: Electronic Circuit US Patent 3,546,457 AMUG 2011 Alfred Klett May 3,

14 Pseudo-Coincidence: Schematics US Patent 3,546,457 AMUG 2011 Alfred Klett May 3,

15 Air Monitor LB 150-DR for particulates Type Filter Detector Natural Bgrd Compensation Air flow MDA AMUG 2011 Alfred Klett May 3, 2011 Airborne particulates monitor Ø 200mm fixed filter Gas flow through proportional counter (Ø 200mm) with simultaneous alpha-, beta-measurement and with guard detector combined pseudocoincidence and alpha-range approx. 40 m³/h 100 mbq/m³ man made alphas (1h) 15

16 Applications for LB 150 DR (α-β) In facilities processing and storing radioactive waste In installation dealing with nuclear fuel and fissionable material In laboratories operating with hot cells In general research laboratories dealing with alpha emitting radioactive substances Well suited for stack monitoring at lowest detection limits available on the market Total release calculations day/week/month AMUG 2011 Alfred Klett May 3,

17 Gross Counting Rates LB150D 400 Berthold LB150D Alpha-Beta Particulates Monitor Gross Counting Rates [cps] alpha beta ps Time [h] Mean: cps Sigma: 66.5 cps Mean: 78.5 cps Sigma: 36.5 cps Mean: 36.8 cps Sigma: 17.2 cps AMUG 2011 Alfred Klett May 3,

18 Activities Ø200mm filter at 40m³/h flow Berthold LB150D Alpha-Beta Particulates Monitor Filter Activities [Bq] alpha beta Time [h] AMUG 2011 Alfred Klett May 3,

19 Ratios of Gross Counting Rates 7 Berthold LB150D Alpha-Beta Particulates Monitor Ratios of Counting Rates ratio beta/ps ratio alpha/ps ratio alpha/beta Time [h] AMUG 2011 Alfred Klett May 3,

20 Alpha-Beta Ratio 0,6 Berthold LB150D Alpha-Beta Particulates Monitor Alpha / Beta Ratio 0,5 Mean: 0.49 Sigma: , Time [h] AMUG 2011 Alfred Klett May 3,

21 Compensated Net Counting Rates Berthold LB150D Alpha-Beta Particulates Monitor Compensated Net Counting Rates [cps] Alpha compensated Beta compensated Time [h] AMUG 2011 Alfred Klett May 3,

22 Compensated Alpha-Counting Rate 10 Berthold LB150D Alpha-Beta Particulates Monitor Compensated Alpha Rate [cps] Mean: cps Sigma: 1.63 cps Time [h] AMUG 2011 Alfred Klett May 3,

23 Artificial Alpha-Activity 30 Berthold LB150D Alpha-Beta Particulates Monitor Artificial Alpha Activity [Bq] Mean: -1.0 Bq Sigma: 7.1 Bq Time [h] AMUG 2011 Alfred Klett May 3,

24 Detection Limits LB 150-DR Natural Activity Concentration MDA Man Made Activity Concentration Bq/m³ pci/m³ Bq/m³ pci/m³ AMUG 2011 Alfred Klett May 3,

25 Detection Requirements 1 DAC Activity Concentration Isotopes Particles Bq/m³ pci/m³ 238 Pu, 239 Pu, 240 Pu, 241 Am alpha U alpha Cm alpha mixed fission products beta DAC hrs = Annual Limit of Intake AMUG 2011 Alfred Klett May 3,

26 Timing Measurement alpha-beta Counts Time alpha pulse after beta [µs] W. Kraut et. al AMUG 2011 Alfred Klett May 3,

27 239 Pu Calibration at ICARE test bench in Saclay Institute Instrument Particulates Background Deposition of particulates AMUG 2011 Alfred Klett May 3, 2011 IPSN / CEA France LB 150R with dual alpha-detector AMAD diameter 0.4 µm and 4.0 µm labelled with 239 Pu known radon concentrations investigated with fluorescence labelled aerosols Datalogger Preamp./Discr. alpha-longrange alpha-shortrange Filter Flow Meter Detectors Pump Air In Exhaust 27

28 Results LB150R ICARE Calibration Results of calibration with 239 Pu AMAD Activity Reading relative response [µm] [Bq/m³] [Bq/m³] [%] ± ± ± ±10 AMUG 2011 Alfred Klett May 3,

29 MDA s LB150R determined at ICARE Detection limits for 239 Pu Radon Meas.Time Detection limit [Bq/m³] [min] [mbq/m³] AMUG 2011 Alfred Klett May 3,

30 LB 9128-ENV Moving Filter Monitor Beta monitor external γ-compensation β/α ratio Radon compensation Alpha-beta monitor external γ-compensation Pseudo-coincidence Radon compensation AMUG 2011 Alfred Klett May 3,

31 Technical Data LB 9128 Detector Detection Efficiency (typical) Shielding Background (typical) Gamma-sensitivity Radon Compensation Technique Ion implanted Silicon Detector area 600 mm², 300 µm depl. simultaneous alpha + beta Alpha: 20% for 241 Am Beta: 25% for 36 Cl Pb average thickness 30 mm Alpha: cps Beta: 0.2 cps < 0.4 cps at 1 µsv/h ( 137 Cs) Pseudocoincidence or Alpha/Beta Ratio AMUG 2011 Alfred Klett May 3,

32 Technical Data LB 9128 Measuring Range (at 20 Bq/m³ Radon level) Accuracy <15% Alpha: Bq/m³ Beta: Bq/m³ Maximum autonomous 8000 h operation period Response Time 1.33 h (10% - 90%) Temperature Range 0 C 40 C Dimensions Weight 553x600x959 mm³ (WxDxH) 120 kg AMUG 2011 Alfred Klett May 3,

33 Technical Data LB 9128 Nominal Air Flow 3 resp. 4 m³/h (pump type) Flow Meter 0 6 m³/h (<2%) Filter Schleicher Schüll No. 10 Glass fibre Recommended Filter speed 12.5 mm/h Selectable Filter speeds Suction Head Dusting Area Sampling tube connecting flange (2.5), 5, 10, 12.5, (15) mm/h Stainless Steel 625 mm² 25 mm AMUG 2011 Alfred Klett May 3,

34 Schematical Setup LB 9128 Air Inlet PLC Filter Advance Logic Heating Filter Speed v= 5/10/12.5/15mm/h Semi-Continuous LB Preamplifier Pulse Height Discriminate Detector DET. BIAS POWER AMP OUT SCA OUT ΔE OUT >E2 β α Bias LVPS Amp. Out Beta Tot. Alpha Tot. To Electronics Pump 4m³/h Encoder Dust Connection Area 25 x 25 mm² Si-Det. 600mm² BAI 9128 P DC Motor Glass Fiber Filter N 10 Filter Take Up Spool Filter Feed Spool Diff. Pressure Switch Δp Rota Meter Mass Flow Meter Range 0-18m³/h AMUG 2011 Alfred Klett May 3, To Electronics

35 Injection of 24 Na labelled aerosols AMUG 2011 Alfred Klett May 3,

36 Calibration LB 9128 with 24 Na Injection 70 Activity Concentration [Bq/m³] Injection Beta artificial Time [h] AMUG 2011 Alfred Klett May 3,

37 Radon Compensation LB ,8 0,6 0,4 0,2 0,0-0,2-0,4-0,6-0,8-1,0-1,2 BETA Bq/m³ RADON Bq/m³ : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : :00 BETA ARTPS BETA ARTBA RADON AMUG 2011 Alfred Klett May 3,

38 Detection limits LB 9128 at Radon activity concentration 7 Bq/m³ Measurement Alpha artificial Beta artifical Compensation Pseudocoincidence Pseudocoincidence MDA [mbq/m³] Beta artifical α-β ratio 240 AMUG 2011 Alfred Klett May 3,

39 Radon Compensation with semiconducting detectors we utilized for air monitors with semiconducting detectors since a long time pseudo-coincidence compensation or alpha-beta ratio compensation the pseudo-coincidence compensation factors had been consideraby higher than with gas operated detectors with a combined method using pseudo-coincidence and energy discrimination a major improvement was achieved the combined method records the following types of events high energy alphas exceeding 6 MeV Pseudo-coincident alpha and beta events AMUG 2011 Alfred Klett May 3,

40 Alpha Spectrum 241 p p Am p and Natural 1,2 1 Betaradiation Am-241 Radon and Thoron decay series Countrate (normalised) 0,8 0,6 0,4 Threshold 0, Energy (MeV) AMUG 2011 Alfred Klett May 3,

41 Alpha-channel measurements Bq/m³ Standard Instrument Modified Instrument MDA Modified Instr. MDA Standard Instr. 3 2 Tshort = 10 min Tlong = 30 min Energy Threshold: 6.5 MeV Min 1 2 Alpha Channel 3 AMUG 2011 Alfred Klett May 3,

42 Beta-channel measurements Bq/m³ Standard Instrument Modified Instrument MDA Modified Instr. MDA Standard Instr Tshort = 10 min Tlong = 30 min Energy Threshold: 6.5 MeV Min 5 10 Beta Channel 15 AMUG 2011 Alfred Klett May 3,

43 References 1) National Nuclear Data Center NNDC, Brookhaven National Laboratory based on ENSDF as of July 24, ) Klett A., Reuter W. and DeMey L., Dynamic Calibration of an Aerosol Monitor with Natural and Artificial α-emitters, IEEE Transactions on Nuclear Science, Vol. 44, No.3, pp , June ) Klett A., Erath W., DeMey L. and Nemecek P. Calibration Of An Alpha-Beta Moving Filter Particulates Monitor, IEEE Transactions on Nuclear Science, Vol. 49, No.4, pp , August ) Shevchenko S.V., Saltykov L.S. and Slusarenko L.I. About the effectiveness of the ABPD methods in air-borne alpha-activity monitoring Applied Radiation and Isotopes, Vol. 64, Issue 1, January 2006, ) Rotblat J., Application of the Coincidence Method to Testing the Lifetime and Level Scheme of Radium C, Nature, Vol. 144, Issue 3640, (1939) 6) Mattsson R., Paatero J., Hatakka J., Automatic Alpha/Beta Analyser for Air Filter Samples - Absolute Determination of Radon Progeny by Pseudo- Coincidence Techniques, Radiation Protection Dosimetry 63: (1996) AMUG 2011 Alfred Klett May 3,

44 References 7) German Patent / Deutsches Patent , Schaltung zum Bestimmen der Zahl von in Pseudokoinzidenz auftretenden Impulsen in einem Kernstrahlungsmessgerät, Laboratorium Berthold, ) United States Patent 3,546,457 Radiation Monitoring System Utilizing Pseudo-Coincidence Techniques, Rainer Kurz, Laboratorium Dr. Berthold, Wildbad, Germany, December 8, ) United States Patent 4,960,998, Method and apparatus for continuously determining gas-carried alpha-radioactivity. 10) Mattsson R., Paatero J., Hatakka J., Automatic Alpha/Beta Analyser for Air Filter Samples - Absolute Determination of Radon Progeny by Pseudo- Coincidence Techniques, Radiation Protection Dosimetry 63: (1996) 11) Kraut W., Natural Activity Counting by Pseudo-Coincidence Techniques: causes for the variability of the compensation factor once more revisited in detail, Conf. Proceedings 38th Annual Meeting German-Swiss-Austrian Radiation Protection Association, Dresden, Germany, Sep. 2006, Editors: Ettenhuber E., Giessing R., Beier E., Bayer A., AMUG 2011 Alfred Klett May 3,

45 References 12) Kraut W., Kuglstatter M., Vey D., Schwarz W., Filter Activity Analysis by Pseudo-Coincidence Techniques without Factor of Compensation, Conference Proceedings Annual Meeting German-Swiss-Austrian Radiation Protection Association, Borkum, Germany, Sep ) ANSI N42.17B Performance Specifications for Health Physics Instrumentation Occupational Arborne Radioactivity Monitoring Instrumentation (1989) 14) Standards for Measuring Airborne Radioactivity Letter to Journal of the Health Physics Society, Morgan Cox, Mark Hoover, Liliane Grivaud, Michelle Johnson, George Newton, Health Physics Journal 85 (2), , 2003 AMUG 2011 Alfred Klett May 3,