Comparison of the TDCR method and the CIEMAT/NIST method for the - PowerPoint PPT Presentation

Comparison of the TDCR method and the CIEMAT/NIST method for the activity determination of beta emitting nuclides Ole Nähle and Karsten Kossert Physikalisch-Technische Bundesanstalt (PTB), Braunschweig, Germany LSC 2010, Advances in Liquid Scintillation Spectrometry, Paris, 6-10 September 2010 Physikalisch-Technische Bundesanstalt

Motivation • CIEMAT/NIST and TDCR are based on the same free parameter model • A systematic comparison is difficult (different counters, different software, different parameters) • At PTB both methods are applied and the same software routines are used • Pure β -emitters should be a simple test Comparison of TDCR and CN for β emitters O. Nähle and K. Kossert

Free parameter model Basic assumptions: • Statistical distribution of emitted photoelectrons at the photo cathode of the PMT (e.g. Poisson distribution): ' − ' ( ) ( ) x m E m E e = ' ( , ( )) P x m E ! x with number of electrons x energy deposit in the scintillator E’ m ( E’ ) mean number of electrons • low PMT noise (coincidence circuit) • threshold adjustment (single electron peak) Comparison of TDCR and CN for β emitters O. Nähle and K. Kossert

Free parameter model Counting efficiency ' − ε = − = − ' ( ) 1 ( 0 , ( ) ) 1 m E pq P m E pq e with m ( E’ ) pq = EQ ( E )/( nM ) Q ( E ) non-linear response function of the scintillator 1 dE ∫ E = Q(E) + ⋅ 1 / 0 E k dE dx B is a free parameter (sometimes called “figure M of merit”); it corresponds to the average energy which is required to produce photoelectron 1/ M average number of photoelectrons per energy deposited in keV Comparison of TDCR and CN for β emitters O. Nähle and K. Kossert

Free parameter model electron spectrum S ( E ) E max ∫ − ε = − ( )/ ( )(1 ) EQ E M S E e dE 1 PMT: 1 0 E max ∫ − ε = − ( ) / 2 2 ( )( 1 ) EQ E M S E e dE 2 PMTs: 2 0 E max ∫ ε = − − ( ) / 3 3 ( )( 1 ) EQ E M S E e dE 3 PMTs: T 0 logical sum of double coincidences in a system with 3 PMTs: E max ∫ − − ε = − − − ( )/3 2 ( )/3 3 ( )(3(1 ) 2(1 ) ) EQ E M EQ E M S E e e dE D 0 Comparison of TDCR and CN for β emitters O. Nähle and K. Kossert

Free parameter model CIEMAT/NIST method (2 PMTs) : E max ∫ ε = − − ( ) / 2 2 ( )( 1 ) EQ E M S E e dE 2 0 The free parameter M is obtained from a measurement of a tracer radionuclide (e.g. 3 H) under same experimental conditions. Usually external quenching indicators are used for the efficiency transfer. Comparison of TDCR and CN for β emitters O. Nähle and K. Kossert

Free parameter model TDCR method (3 PMTs) : E max ∫ − ε = − ( ) / 3 3 ( )( 1 ) EQ E M S E e dE T 0 E = ∫ max ε − − − − − ( ) / 3 2 ( ) / 3 3 ( ) 3 (( 1 ) 2 ( 1 ) ) EQ E M EQ E M S E e e dE D 0 The free parameter is derived from the ratio of the experimental counting rates ε R = = T T TDCR ε R D D Comparison of TDCR and CN for β emitters O. Nähle and K. Kossert

Nuclides Radionuclides measured at PTB since 2002 using CIEMAT/NIST + … and CIEMAT/NIST + TDCR + … H-3 , Be-10, C-14, F-18 , Na-22, P-32 , P-33 , S-35 , Cl-36 , K-40, Ca-41, Ca-45 , Cr-51, Mn-54, Fe-55, Co-58, Fe-59, Co-60, Ni-63 , Cu-64, Zn-65, Ga-68, Ge-68/Ga-68, Se-79, Sr-85, Rb-87, Y-88, Sr-89 , Sr- 90/Y-90 , Nb-93m, Zr-95, Tc-99 , Cd-109, In-111, Sn- 113, Cd-113m , In-114m, I-123, Sb-124, I-124, Sb-125 , I-125, I-129, I-131 , Cs-134, Cs-137, Ce-139, Ce-141 , Pm-147 , Sm- 147 , Ho-166m, Lu-176, Lu-177 , Re-186, Ir-192, Tl- 204, Po-208, Pb-210, Ac-227, Th-228, U-233, Np- Comparison of TDCR and CN for β emitters O. Nähle and K. Kossert 237 Pu 238 Am 241 Pu 239 Pu 241 Cm 244

Experimental details • Sample composition: 15 mL Ultima Gold TM + 1 mL water, glass vials, quenching agent: nitromethane • Preparation by difference weighing of a pycnometer with traceable balances (typical mass of active solution: 30 mg) • Background sample was prepared with the same composition • Solutions were checked for impurities by means of gamma-ray spectrometry and long-term LS measurements Comparison of TDCR and CN for β emitters O. Nähle and K. Kossert

Detectors: CIEMAT/NIST Wallac 1414 PerkinElmer TriCarb 2800 Crucial points • Threshhold adjustments • Features of signal processing • Anti-coincidence detectors • Coincidence logic is not transparent Comparison of TDCR and CN for β emitters O. Nähle and K. Kossert

Detector: TDCR Crucial points • Threshhold adjustments by user • Coincidence and deadtime logic well known (MAC3) • No mass processing of samples Comparison of TDCR and CN for β emitters O. Nähle and K. Kossert

Nuclides and nuclear data (DDEP) Radio- Maximum Shape-factor Nature nuclide energy in keV function C ( W ) 32 P 1711 Allowed 1 33 P 249 Allowed 1 35 S 167 Allowed 1 45 Ca 256 Allowed 1 63 Ni 67 Allowed 1 1 st forbidden 89 Sr p 2 + q 2 1495 unique 1 st forbidden 90 Y p 2 + q 2 2280 unique 2 nd forbidden 99 Tc 0.54· p 2 + q 2 294 1 st forbidden 147 Pm 225 1+0.3/ W Comparison of TDCR and CN for β emitters O. Nähle and K. Kossert

Analysis 63 Ni 0.005 99 Tc 0.004 counts in arbitrary units 33 P 45 Ca 35 S 0.003 147 Pm 0.002 89 Sr 0.001 32 P 90 Y 0 0 200 400 600 800 1000 channel number Wallac counter with logarithmic amplification Comparison of TDCR and CN for β emitters O. Nähle and K. Kossert

Uncertainty budget 33 P u(a)/a in % Component CIEMAT/ TDCR NIST Statistics (6 samples; ≥ 8 repetitions per counter) 0.02 0.01 Weighing 0.08 0.08 Dead time 0.10 0.08 Background 0.03 0.03 Time of measurements (starting time and duration (life- 0.01 0.01 time)) Adsorption 0.05 0.05 Radionuclide impurities (none detected) 0.05 0.05 3 H activity/TDCR value and fit 0.07 0.02 Decay data (endpoint energy and beta shape-factor 0.06 0.03 function) Ionization quenching 0.20 0.17 Quenching indicator ( SQP ( E ), tSIE ) 0.01 -- Decay correction 0.13 0.10 Square root of the sum of quadratic components 0.30 0.24 Comparison of TDCR and CN for β emitters O. Nähle and K. Kossert

Analysis: Overall uncertainties TDCR CIEMAT/NIST Radionuclid E β ,max in e keV u(a)/a in % 90 Y 0.12 0.16 2280 32 P 0.23 0.25 1711 89 Sr 0.25 0.26 1495 99 Tc 0.27 0.45 294 45 Ca 0.25 0.27 256 33 P 0.24 0.30 249 147 Pm 0.35 0.35 225 35 S 0.33 0.29 167 63 Ni 0.97 0.58 67 Comparison of TDCR and CN for β emitters O. Nähle and K. Kossert

Analysis CIEMAT/ Unweighted TDCR Radio- kB in ( a TDCR - NIST mean activity nuclide cm/MeV a CN )/ a TDCR in % a mean in kBq/g a in kBq/g 0.0075 191.93 191.96 -0.02 191.95 90 Y 0.0110 191.95 191.95 0.00 191.95 0.0075 198.86 198.76 0.05 198.81 32 P 0.0110 198.88 198.75 0.07 198.82 0.0075 189.45 189.16 0.15 189.31 89 Sr 0.0110 189.49 189.14 0.18 189.32 0.0075 169.22 169.29 -0.04 169.26 99 Tc 0.0110 169.46 169.16 0.18 169.31 0.0075 182.65 182.45 0.11 182.55 45 Ca 0.0110 182.97 182.23 0.40 182.60 0.0075 243.40 243.55 -0.06 243.48 33 P 0.0110 243.81 243.08 0.30 243.45 0.0075 9.923 9.914 0.09 9.919 147 Pm 0.0110 9.948 9.899 0.49 9.924 0.0075 191.67 191.30 0.19 191.49 35 S 0.0110 192.23 190.94 0.67 191.59 0.0075 11.04 10.95 0.82 11.00 63 Ni 0.0110 11.14 10.91 2.06 11.03 Comparison of TDCR and CN for β emitters O. Nähle and K. Kossert

Analysis: kB-value Unweighted CIEMAT/ TDCR Radio- kB in ( a TDCR - a CN )/ a TDCR mean activity NIST nuclide cm/MeV in % a mean in a in kBq/g kBq/g 0.0075 189.45 189.16 0.15 189.31 89 Sr 0.0110 189.49 189.14 0.18 189.32 0.0075 11.04 10.95 0.82 11.00 63 Ni 0.0110 11.14 10.91 2.06 11.03 • A change in kB-value has inverse effect for TDCR and CIEMAT/NIST • Unweighted mean is robust against changes in kB • Applying both methods the model dependence can be reduced • Our analyses seem to favour kB =0.0075 cm/MeV Comparison of TDCR and CN for β emitters O. Nähle and K. Kossert

Analysis: shape-factor Radio- Maximum Shape-factor Nature Reference nuclide Energy in keV function C ( W ) Reich and 2 nd forbidden 99 Tc 0.54· p 2 + q 2 293.8(14) Schüpferling (1974) • Changing C(W) to 1: • TDCR result increases by 0.05% • CIEMAT/NIST increases by 0.95% • No compensation but clear indication that C(W) =1 is not a suitable shape factor for 99 Tc Comparison of TDCR and CN for β emitters O. Nähle and K. Kossert

Summary and Outlook • A combination of TDCR and CIEMAT increases the understanding of free parameter models • Systematic uncertainties may be identified and partly cancel out • Tests with the Hidex TDCR-system are promising • Extend investigation to electron capture nuclides • Establish sample changer with γ -detector Comparison of TDCR and CN for β emitters O. Nähle and K. Kossert

TDCR sample changer Light-tight housing γ -Detector Comparison of TDCR and CN for β emitters O. Nähle and K. Kossert

TDCR Sample changer Lead shield Optical chamber Sample depot Comparison of TDCR and CN for β emitters O. Nähle and K. Kossert

Sample changer Comparison of TDCR and CN for β emitters O. Nähle and K. Kossert

TDCR Physikalisch-Technische Bundesanstalt