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Physikalisch-Technische Bundesanstalt

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

• O. Nähle and K. Kossert

Comparison of TDCR and CN for β emitters

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

• O. Nähle and K. Kossert

Comparison of TDCR and CN for β emitters

Free parameter model

Basic assumptions:

• Statistical distribution of emitted photoelectrons at the photo cathode
• f the PMT (e.g. Poisson distribution):

with x number of electrons E’ energy deposit in the scintillator m(E’) mean number of electrons

• low PMT noise (coincidence circuit)
• threshold adjustment (single electron peak)

! ) ( )) ( , (

) ( ' '

'

x e E m E m x P

E m x −

=

• O. Nähle and K. Kossert

Comparison of TDCR and CN for β emitters

Free parameter model

Counting efficiency with m(E’)pq=EQ(E)/(nM) Q(E) non-linear response function of the scintillator M is a free parameter (sometimes called “figure

• f merit”); it corresponds to the average energy

which is required to produce photoelectron 1/M average number of photoelectrons per energy deposited in keV

pq E m

e pq E m P

) ( '

'

1 ) ) ( , ( 1

−

− = − = ε

∫

⋅ + =

E

dx dE k dE E Q(E)

B

/ 1 1

• O. Nähle and K. Kossert

Comparison of TDCR and CN for β emitters

Free parameter model

electron spectrum S(E) 1 PMT: 2 PMTs: 3 PMTs: logical sum of double coincidences in a system with 3 PMTs:

∫

−

− =

max

2 2 / ) ( 2

) 1 )( (

E M E EQ

dE e E S ε dE e E S

E M E EQ T

∫

−

− =

max

3 3 / ) (

) 1 )( ( ε

max

( )/3 2 ( )/3 3

( )(3(1 ) 2(1 ) )

E EQ E M EQ E M D

S E e e dE ε

− −

= − − −

∫

max

( )/ 1

( )(1 )

E EQ E M

S E e dE ε

−

= −

∫

• O. Nähle and K. Kossert

Comparison of TDCR and CN for β emitters

Free parameter model

CIEMAT/NIST method (2 PMTs):

The free parameter M is obtained from a measurement of a tracer radionuclide (e.g. 3H) under same experimental conditions. Usually external quenching indicators are used for the efficiency transfer.

∫

−

− =

max

2 2 / ) ( 2

) 1 )( (

E M E EQ

dE e E S ε

• O. Nähle and K. Kossert

Comparison of TDCR and CN for β emitters

Free parameter model

TDCR method (3 PMTs):

The free parameter is derived from the ratio of the experimental counting rates

dE e e E S

M E EQ M E EQ E D

) ) 1 ( 2 ) 1 (( 3 ) (

3 3 / ) ( 2 3 / ) (

max

− −

− − − = ∫ ε dE e E S

E M E EQ T

∫

−

− =

max

3 3 / ) (

) 1 )( ( ε

T T D D

R TDCR R ε ε = =

• O. Nähle and K. Kossert

Comparison of TDCR and CN for β emitters

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- 237 Pu 238 Am 241 Pu 239 Pu 241 Cm 244

• O. Nähle and K. Kossert

Comparison of TDCR and CN for β emitters

• Sample composition: 15 mL Ultima GoldTM + 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

Experimental details

• O. Nähle and K. Kossert

Comparison of TDCR and CN for β emitters

Detectors: CIEMAT/NIST

Wallac 1414 PerkinElmer TriCarb 2800 Crucial points

• Threshhold adjustments
• Features of signal processing
• Anti-coincidence detectors
• Coincidence logic is not transparent

• O. Nähle and K. Kossert

Comparison of TDCR and CN for β emitters

Detector: TDCR

Crucial points

• Threshhold adjustments by user
• Coincidence and deadtime logic well known

(MAC3)

• No mass processing of samples

• O. Nähle and K. Kossert

Comparison of TDCR and CN for β emitters

Nuclides and nuclear data (DDEP)

Radio- nuclide Maximum energy in keV Nature Shape-factor function C(W)

32P

1711 Allowed 1

33P

249 Allowed 1

35S

167 Allowed 1

45Ca

256 Allowed 1

63Ni

67 Allowed 1

89Sr

1495 1st forbidden unique p2+q2

90Y

2280 1st forbidden unique p2+q2

99Tc

294 2nd forbidden 0.54·p2+q2

147Pm

225 1st forbidden 1+0.3/W

• O. Nähle and K. Kossert

Comparison of TDCR and CN for β emitters

Analysis

Wallac counter with logarithmic amplification

0.001 0.002 0.003 0.004 0.005 200 400 600 800 1000

Ni

63

S

35

Pm

147

P

33

Ca

45

Tc

99

Sr

89

P

32

Y

90

channel number counts in arbitrary units

• O. Nähle and K. Kossert

Comparison of TDCR and CN for β emitters

Uncertainty budget 33P

Component u(a)/a in % CIEMAT/ NIST TDCR 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- time)) 0.01 0.01 Adsorption 0.05 0.05 Radionuclide impurities (none detected) 0.05 0.05

3H activity/TDCR value and fit

0.07 0.02 Decay data (endpoint energy and beta shape-factor function) 0.06 0.03 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

• O. Nähle and K. Kossert

Comparison of TDCR and CN for β emitters

Analysis: Overall uncertainties

Radionuclid e TDCR CIEMAT/NIST Eβ,max in keV u(a)/a in %

90Y

0.12 0.16 2280

32P

0.23 0.25 1711

89Sr

0.25 0.26 1495

99Tc

0.27 0.45 294

45Ca

0.25 0.27 256

33P

0.24 0.30 249

147Pm

0.35 0.35 225

35S

0.33 0.29 167

63Ni

0.97 0.58 67

• O. Nähle and K. Kossert

Comparison of TDCR and CN for β emitters

Analysis

Radio- nuclide kB in cm/MeV TDCR CIEMAT/ NIST (aTDCR- aCN)/aTDCR in % Unweighted mean activity amean in kBq/g a in kBq/g

90Y

0.0075 191.93 191.96

• 0.02

191.95 0.0110 191.95 191.95 0.00 191.95

32P

0.0075 198.86 198.76 0.05 198.81 0.0110 198.88 198.75 0.07 198.82

89Sr

0.0075 189.45 189.16 0.15 189.31 0.0110 189.49 189.14 0.18 189.32

99Tc

0.0075 169.22 169.29

• 0.04

169.26 0.0110 169.46 169.16 0.18 169.31

45Ca

0.0075 182.65 182.45 0.11 182.55 0.0110 182.97 182.23 0.40 182.60

33P

0.0075 243.40 243.55

• 0.06

243.48 0.0110 243.81 243.08 0.30 243.45

147Pm

0.0075 9.923 9.914 0.09 9.919 0.0110 9.948 9.899 0.49 9.924

35S

0.0075 191.67 191.30 0.19 191.49 0.0110 192.23 190.94 0.67 191.59

63Ni

0.0075 11.04 10.95 0.82 11.00 0.0110 11.14 10.91 2.06 11.03

• O. Nähle and K. Kossert

Comparison of TDCR and CN for β emitters

Analysis: kB-value

Radio- nuclide kB in cm/MeV TDCR CIEMAT/ NIST (aTDCR-aCN)/aTDCR in % Unweighted mean activity amean in kBq/g a in kBq/g

89Sr

0.0075 189.45 189.16 0.15 189.31 0.0110 189.49 189.14 0.18 189.32

63Ni

0.0075 11.04 10.95 0.82 11.00 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

• O. Nähle and K. Kossert

Comparison of TDCR and CN for β emitters

Analysis: shape-factor

• 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 99Tc

Radio- nuclide Maximum Energy in keV Nature Shape-factor function C(W) Reference

99Tc

293.8(14) 2nd forbidden 0.54·p2+q2

Reich and Schüpferling (1974)

• O. Nähle and K. Kossert

Comparison of TDCR and CN for β emitters

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

• O. Nähle and K. Kossert

Comparison of TDCR and CN for β emitters

TDCR sample changer

Light-tight housing γ-Detector

• O. Nähle and K. Kossert

Comparison of TDCR and CN for β emitters

TDCR Sample changer

Optical chamber Sample depot Lead shield

• O. Nähle and K. Kossert

Comparison of TDCR and CN for β emitters

Sample changer

Physikalisch-Technische Bundesanstalt

TDCR

Physikalisch-Technische Bundesanstalt

4π(LS)β−γ-Coincidence counting

+ Sample changer

Physikalisch-Technische Bundesanstalt

Outlook

• A sample changer will be established soon
• Versatile system including γ-channel (NaI or HPGe)
• TDCR and coincidence counting with high sample

statistics and repetitions

• Taking TDCR and coincidence data simultaniously

using FPGA-module

• O. Nähle and K. Kossert

Comparison of TDCR and CN for β emitters

Thank you for your attention