Comparison of the TDCR method and the CIEMAT/NIST method for ...

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 

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 

of the PMT (e.g. Poisson distribution): 

with 

P( 

x, 

m( 

E 

)) 

x number of electrons 

E’ energy deposit in the scintillator 

m(E’) mean number of electrons 

• low PMT noise (coincidence circuit) 

m( 

E 

• threshold adjustment (single electron peak) 

' 

= 

) e 

x! 

x −m( 

E 

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

' 

' 

)

Counting efficiency 

ε = 


' 

1− 

P( 

0, 

m( 

E ) pq) 

= 1− 

e 

−m( 

E 

with 

m(E’)pq=EQ(E)/(nM) 

Q(E) non-linear response function of the scintillator 

M is a free parameter (sometimes called “figure 

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 


' 

) pq 

1 

E dE 

Q(E) = 

E ∫0 1 + k ⋅ dE / dx 

B

ε 

electron spectrum S(E) 

1 PMT: 

2 PMTs: 

3 PMTs: 

ε 

ε 

ε 

1 

2 

= 

= 

E 

max 

E 


= − 

∫ 

0 

max 

∫ 

0 

E 

max 

T ∫ 

0 

−EQ( 

E)/ M 

SE ( )(1 e ) dE 

S( 

E)( 

1− 

e 

S( 

E)( 

1− 

−EQ( 

E) 

/ 2M 

logical sum of double coincidences in a system with 3 PMTs: 


e 

−EQ( 

E) 

/ 3 

M 

) 

) 

2 

3 

dE 

dE 

D = 

Emax 

∫ 

0 

−EQ( E)/3M2 −EQ( 

E)/3M3 SE ( )(3(1 −e) −2(1 −e) 

) dE

CIEMAT/NIST method (2 PMTs): 

ε 

2 

= 

E 

max 

∫ 

0 

S( 

E)( 

1− 

e 


−EQ( 

E) 

/ 2M 

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. 


) 

2 

dE

TDCR method (3 PMTs): 

ε 

ε 

D 

= 

E 

max 

T ∫ 

0 

E 

max 

= ∫ S( 

E) 

3(( 

1− 

e 

0 

S( 

E)( 

1− 

e 


−EQ( 

E) 

/ 3M 

) 

−EQ( 

E) 

/ 3M 

2( 

1 

− e 

−EQ( 

E) 

/ 3M 

) dE 

The free parameter is derived from the ratio of the experimental 

counting rates 

3 

dE 


) 

2 

− 

RT 

εT 

TDCR = = 

R ε 

D D 

) 

3

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- 


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 


Wallac 1414 

PerkinElmer TriCarb 

2800 

Crucial points 

• Threshhold adjustments 

• Features of signal processing 

• Anti-coincidence detectors 

Detectors: CIEMAT/NIST 

• Coincidence logic is not transparent 


Crucial points 

• Threshhold adjustments by user 

Detector: TDCR 

• Coincidence and deadtime logic well known 

(MAC3) 

• No mass processing of samples 


Nuclides and nuclear data (DDEP) 

Radionuclide 

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 147 Pm 225 1 st forbidden 1+0.3/W 


counts in arbitrary units 

0.005 

0.004 

0.003 

0.002 

0.001 

0 

63Ni 

35S 

147Pm 

99Tc 

33P 

45 

Wallac counter with logarithmic amplification 

Analysis 

0 200 400 600 800 1000 


Ca 

89Sr 

32P 

90 

channel number 

Y

Uncertainty budget 33 P 

u(a)/a in % 

Component 

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 (lifetime)) 

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 


Analysis: Overall uncertainties 

Radionuclid 

e 

TDCR CIEMAT/NIST E β,max in 

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 


Radionuclide 

90 Y 

32 P 

89 Sr 

99 Tc 

45 Ca 

33 P 

147 Pm 

35 S 

63 Ni 

kB in 

cm/MeV 


a in kBq/g 



(a TDCR - 

a CN )/a TDCR in % 

Analysis 

Unweighted 

mean activity 

a mean in kBq/g 

0.0075 191.93 191.96 -0.02 191.95 

0.0110 191.95 191.95 0.00 191.95 

0.0075 198.86 198.76 0.05 198.81 

0.0110 198.88 198.75 0.07 198.82 

0.0075 189.45 189.16 0.15 189.31 

0.0110 189.49 189.14 0.18 189.32 

0.0075 169.22 169.29 -0.04 169.26 

0.0110 169.46 169.16 0.18 169.31 

0.0075 182.65 182.45 0.11 182.55 

0.0110 182.97 182.23 0.40 182.60 

0.0075 243.40 243.55 -0.06 243.48 

0.0110 243.81 243.08 0.30 243.45 

0.0075 9.923 9.914 0.09 9.919 

0.0110 9.948 9.899 0.49 9.924 

0.0075 191.67 191.30 0.19 191.49 

0.0110 192.23 190.94 0.67 191.59 

0.0075 11.04 10.95 0.82 11.00 

0.0110 11.14 10.91 2.06 11.03 


Radionuclide 

89 Sr 

63 Ni 

kB in 

cm/MeV 


a in kBq/g 

Analysis: kB-value 



(a TDCR -a CN )/a TDCR 

in % 

Unweighted 

mean activity 

a mean in 

kBq/g 

0.0075 189.45 189.16 0.15 189.31 

0.0110 189.49 189.14 0.18 189.32 

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 


Radionuclide 

Maximum 

Energy in keV 

• Changing C(W) to 1: 

Analysis: shape-factor 

Nature 

• TDCR result increases by 0.05% 

• CIEMAT/NIST increases by 0.95% 

Shape-factor 

function C(W) 

99 Tc 293.8(14) 2 nd forbidden 0.54·p 2 +q 2 

Reference 

Reich and 

Schüpferling 

(1974) 

• No compensation but clear indication that C(W)=1 is not 

a suitable shape factor for 99 Tc 


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 


TDCR sample changer 

Light-tight housing 

γ-Detector 


Lead shield 

TDCR Sample changer 

Optical chamber Sample depot 


Sample changer 


Physikalisch-Technische Bundesanstalt 

TDCR

4π(LS)β−γ-Coincidence counting 

+ Sample 

changer 

Physikalisch-Technische Bundesanstalt

• A sample changer will be established soon 

Physikalisch-Technische Bundesanstalt 

Outlook 

• 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

Thank you for your attention

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