Practical Approaches using TDCR Measurements and Alpha/Beta Separation

Transcription

1 Practical Approaches using TDCR Measurements and Alpha/Beta Separation Jost Eikenberg, Maya Jäggi, Andreas Brand Division for Radiation Protection and Safety Paul Scherrer Institute, CH-5232 Villigen

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3 Overview / Topics TDCR standardization measurements with typical isotopes from the nuclear fuel cycle Presentation of a radiochemical method for simultaneous determination of 210 Pb and 226 Ra+ 228 Ra Simultaneous determination of 241 Pu (β-emitter) and 238 Pu, 239 Pu+ 240 Pu (-emitter) in nuclear materials

4 TDCR standardization measurements LSC measurements using pure β-emitting isotopes: 3 H, 63 Ni, 14 C, 36 Cl and 90 Sr/ 90 Y (isotopes in the order of increasing β-energy) Presentation of unquenched vs. quenched data

5 TDCR vs. Efficiency: all isotopes TDCR vs Efficiency: all nuclides, unquenched data rel. TDCR rel. efficiency

6 Tritium: 3 H (E max : 18.6 kev) TDCR vs Efficiency: H rel. TDCR rel. efficiency

7 63 Ni (E max : 65.9 kev) TDCR vs Efficiency: Ni rel. TDCR rel. efficiency

8 Radiocarbon: 14 C (E max : 156 kev) TDCR vs Efficiency: C rel. TDCR rel. efficiency

9 36 Cl: (E max : 709 kev) TDCR vs Efficiency: Cl rel. TDCR rel. efficiency

10 90 Sr/ 90 Y (E max : 546/2280 kev) TDCR vs Efficiency: Sr rel. TDCR rel. efficiency

11 Environmental application: determination of 228 Ra, 226 Ra and 210 Pb in aqueous samples using TDCR measurement technique and /β-separation

12 238 U-Series 235 U-Series 232 Th-Series U Pa Th Ac Ra Fr Rn At Po Bi Pb Tl 238 U 234 U 4.47x10 9 y β 2.45x10 5 y 234 Pa β Th 1.17min Th 24.1d 7.54x10 4 y Ra 1600y Rn 3.825d Po 214 Po 210 Po min β 214 Bi 19.9min 214 β Pb 26.8min 22.3y 1.6x10-4 s β 138.4d Bi 5.01d 210 β Pb 206 Pb stable 235 U 7.04x10 8 y Pa β 3.28x10 4 y 231 Th Th 1.06d 18.7d 227 β Ac y Ra 11.4d Rn 3.96s Po 1.8x10-3 s Pb 207 Pb 36.1min β 232 Th 228 Th 1.41x10 10 y β 1.91y 228 Ac β Ra 5.75y 6.13h Ra 3.66d Rn 55.6s Po 212 Po 211 Bi 212 Bi 2.14min stable 212 Pb 208 Pb 207 β 208 Tl Tl 4.77min 0.15s 66.3% β β 1.01h 10.6h 33.7% min β 3x10-7 s stable 8.784

13 Th-Ra relationship in the 232 Th and 238 U decay series : a 228 β: a 228 β: 613. h 228 Th Ra Ac Th + daugthers : a 224 β: d 220 : s 216 Th Ra Rn Po + daugthers : a 226 : a 222 : 3. 82d 218 Th Ra Rn Po + daughters

14 Continental water: relevant isotopes Alpha-emitter: U-238, U-234 Beta-emitter: Ra-228 (with fast ingrowing Ac-228) Alpha-emitter: Ra-226 (with Rn-222 prognies) Beta-emitter: Pb-210 (with ingrowing Bi-210) Alpha-emitter: Po-210

15 Schematic view of radioactive transformation 226 Ra (1600 y) 0.0 Z = 88 Z = γ Rn (3.82 d) 2 (4.5 %) 1 (95.5 %) Ra Rn+ He

16 relevant isotopes in continental water and their measurement methods at PSI radionuclide analytical technique 234 U, ( 235 U), 238 U U/TEVA separation, electrodeposition, -spectrometry 226 Ra, 228 Ra, 210 Pb filtration (RadDisc), OptiPhase Hisafe3 cocktail, LSC 210 Po spontaneous deposition on silver disc, -spectrometry

17 Relationship parent / daughter parent isotope half-life parent ingrowing daughter half-life daughter 210 Pb (β) 22.3 years 210 Bi (β) 6.02 days 226 Ra () 1602 years 222 Rn () 3.82 days 228 Ra (β) 5.76 years 228 Ac (β) 6.13 hours

18 Method implementation: low level determination of 210 Pb, 226 Ra+ 228 Ra in drinking water Filtration of the sample (2 liter) through 3 Empore RadDisc (Mn-oxide impregnated) membrane filters Elution of Pb with Diammonium Hydrogen Citrate Elution of Ra with alkaline Na-EDTA solution Measuring via LSC with optimized /βdiscrimination

19 Classical two photomultiplier LS electronic set-up

20 Pulse shape /β discrimination 1200 relative intensity beta-pulse alpha-pulse pulse decay time [ns]

21 Spill-over /β determination spillover [%] β in in β discriminator setting [ns]

22 The triple coincidence to double coincidence ratio (TDCR) counting technique PM R SAMPLE PM S PM T

23 Pulse Length Index (PLI) discrimination with HIDEX SL

24 -spectrum of 226 Ra with ingrowing daughters 2 h and 8 h after separation using HIDEX 300 SL LSC 140 Alpha

25 -spectrum of 226 Ra with ingrowing daughters obtained 6 days after separation 160 Alpha

26 β-spectrum of 214 Bi/ 214 Pb obtained 6 days after separation ( 226 Ra/ 222 Rn decay series products) 35 Beta

27 β-spectrum of 228 Ra with ingrowing 228 Ac 1 h and 8 h after separation using HIDEX 300 SL LSC 50 Beta

28 TDCR vs. Efficiency using high purity radionuclide standard solutions Pb Ra TDCR Ra TDCR = efficiency efficiency

29 long lived mother short lived daughter relationship λy A t A e xt yt y ( ) = x ( 0) ( e ) + Ay ( 0) e λ λ y λy λ Ay t Ax e x t λ e y t ( ) = ( 0) ( ) λ λ λ x λy << λy 1 λ λ y y x x x λ λ λyt A y ( t) = A x (0) (1 e λ t y )

30 LS-spectrum interference correction R Ac 228 r ε = ε A B Ac A B 228, cor ( Ra) rn, m RAc 228 rn ( Ac) A n = A Ra 228 = r ( 228 n, cor A ε Ra 228 Ra) A Ac B rn ( 228 = ε 228 Ac) B Ac 228

31 Comparison of measured 228 Ra and 228 Ac activities with calculated decay/ingrowth curves relative activity Ac ingrowth curve 228 Ra decay curve 228 Ac: measured data 228 Ra: measured data time after separation [h]

32 Comparison of measured 226 Ra and the progeny isotopes 222 Rn, 218 Po and 214 Po with calculated decay/ingrowth curves relative activity Rn+ 218 Po+ 214 Po ingrowth curve 226 Ra: measured data 222 Rn+ 218 Po+ 214 Po: measured data 226 Ra decay curve time after separation [d]

33 Comparison of measured 210 Pb and 210 Bi activities with calculated decay/ingrowth curves Pb decay curve relative activity Pb: measured data 210 Bi: measured data 210 Bi ingrowth curve time after separation [d]

34 Minimizing the interferences: 210 Pb 210 Pb: start counting not before 3 hours after separation because 226 Ra unsupported progeny products (i.e. 214 Pb/ 214 Po) have to decay prior to the measurement (βspectrum interferences)

35 Minimizing the interferences: 226 Ra 226 Ra: 224 Ra [(t 1/2 ) = 3.66 days] and its short lived progeny products should have been decayed prior to measurement, i.e. the sampled water should set aside for about 10 days before radiochemical separation (support from 228 Th has to be checked!). The same holds for 210 Pb (interference with 10 h half live decaying pure β-decaying 212 Pb)

36 Minimizing the interferences: 228 Ra The samples should be measured during the first 24 hours after chemical separation, i.e. when the ingrowth of the 226 Ra/ 222 Rn couple decay products (i.e. 214 Pb, 214 Bi) is not of large concern. These isotopes interfere strongly with the β-spectrum of 228 Ac, which has to be taken to correct the low energy spectrum of 228 Ra

37 lower limit of detection [mbq / L] = k1 ε V 2 * 0 A r s t m 228 Ra 210 Pb 226 Ra counting time [h]

38 LSC detection limits, 2 l aliquot, quantitative adsorption on RadDisc filter, counting time 6 h Ra-226: 3 mbq/liter Ra-228: 20 mbq/liter Pb-210: 15 mbq/liter

39 Field study: use of Ra-isotopes as natural tracers: isotopic signatures for determining mixing between waters from different source regions Nancy N Strasbourg Stuttgart Séléstat VOSGES Mulhouse Ill Colmar Rhine BLACK FOREST Belfort Basel Rhine France JURA Aare Zürich

40 Calculating mixing/exchange between river and ground water using 228 Ra/ 226 Ra and 87 Sr/ 86 Sr 87 Sr/ 86 Sr (atomic ratio) Strengbach river (pure granitic) other Vosges rivers (mainly granitic) river Ill and tributaries Rhine Valley groundwater river Rhine 27/2 27/ Ra/ 226 Ra (activity ratio)

41 C m M m PAUL SCHERRER INSTITUT TDCR blank correction For linear systems the general mass balance equation holds for mixtures of two components M 1 and M 2 with the concentrations C 1 und C 2 = C 1 M1 + C2 M 2 This relationship can be directly transferred to TDCR-measurements, i.e. the true or net-tdcr (TDCR n ) value has to be obtained via the brut-tdcr ( mixture ) (TDCR b ) and the TDCR-result of a blanc measurement (TDCR 0 ). r b with: with TDCR r It follows: b r n = b r = b TDCR b n r n r 0 = For pure β-emitter holds: A rn = ε = TDCR It results for the activity calculation n + r 0 TDCR 0 ( rb r0 ) TDCRn + r0 TDCR0 TDCRn ε n rb r0 ε n rb A = r TDCR b ( r ) b TDCR 0 r 0 2 n = r b TDCR b TDCR r b b r r 0 0 TDCR 0

42 Simultaneous determination of 241 Pu (βemitter) and 238 Pu, 239 Pu+ 240 Pu (emitter) in nuclear materials Application of extraction chromatography: adsorption onto BioRad 1X2 anion exchange resin Elution of the Pu-fraction using a HI/HCl acidic reduction solution Electrodeposition onto a stainless steel planchet, - spectrometric measurement Dissolution from the sample planchet, cocktail preparation /β-measurement via LSC

43 241 Am 243 Am 236 Pu 238 Pu 239 Pu 433 a Pu 241 Pu 7370 a Pu 2.8 a a a a 5.2 β 14.4 a a 4.9

44 Actinide analysis: 1-X2 / DGA sample solution separation + 3 MHNO 3 + yield spike isotopes + Na-nitrite: [Pu4+] + ascorbic acid [Fe2+] NO H + + e - = NO + H2 O Pu 3+ = Pu 4+ + e - 1-X2 resin Plutonium 9 M HCl 3 M HNO 3 5 M HCl Thorium 0.01 M HI + 9 M HCl U, Am, Cm DGA resin 2 M HNO 3 discard 0.25 M HNO M HCl Americium, Curium Uranium

45 redox reactions and equilibria reduction of Pu(vi) to Pu(iii) Pu + 2e 2Pu 2I I + 2e I + 2Pu I2 + 2Pu

46 -spectrum of U, Pu and Am (blue sample isotopes to be analyzed; red added spike isotopes) Am 241 Am 238 U 236 U 234 U 239 Pu 236 Pu 300 Impulse/Kanal Energie []

47 a/b-lsc with optimized /β separation (pulse index and energy), -spill in β < 1%, β-spill in < 0.1% 241 Pu β 238, 239, 240, 242 Pu

48 Conclusions TDCR measurement of non or weakly quenched samples yield sufficiently precise results for radionuclide analysis in the frame of decommissioning projects. Environmental application: LSC with optimized alpha/beta separation is a powerful tool to determine almost pure - emitting 226 Ra besides weak β-emitting 228 Ra Determination of Pu-isotopes in materials from the nuclear fuel cycle: optimized /β-separation yields precise results for measurement of pure beta emitting 241 Pu

49 Thank you for your attention