Institute of Nuclear and New Energy Technology(INET), Tsinghua University

A performance comparison of two kinds of liquid scintillation counters (LSCs)

from PerkinElmer, Inc.

Xiao-gui FENG 1), Guo-hua JIANG 2), Jian-hua HUANG 2), Jian-yu DU 3),

Qian-ge HE 1), Jian-chen WANG 1), Jing CHEN 1)

1) Institute of Nuclear and New Energy Technology, Collaborative Innovation Center ofAdvanced Nuclear Energy Technology, Tsinghua University, Beijing 100084, PR China

2) Analytical and Testing Center, Beijing Normal University, Beijing 100875, PR China

3) PerkinElmer, Beijing 100015, PR China

2

Outline

Introduction Experimental methods Results and discussion

Background count rate and counting efficiency α/β discrimination The instrument stability

Conclusions

Schematic diagram of lead shield and guard

Key features of Quantulus 1220

1 23 45

1,2: Guard PMT

3,4: Sample PMT

5: Sample

PMT: photomultiplier tubesAsymmetric lead shield

Liquid scintillation

guard

3

4

Key features of Quantulus GCT 6220

BGO (Bismuth-Germanium Oxide) Guard

GCT (Guard Compensation Technology) GCT is a mathematical method which determines the number of

environmental background events that were not blocked ordetected by the BGO guard, and then uses this information toreduce (in real time) sample background counts caused by theenvironment.

Quantulus1220

QuantulusGCT 6220

5

Three LSCs involved in this study

LSC ID Brand Model No. Serial No. Manufacture date

Installation site

LSC1 Quantulus GCT 6220 A622001 SGLO47150123 November 2015 Tsinghua University

LSC2 Quantulus 1220 1220-003 2200368 June 2005 Tsinghua University

LSC3 Quantulus 1220 1220-003 DG06118016 June 2011The Institute of

Crustal Dynamics

*The cooling unit in LSC2 was shut down because it was broken.

(*)

(18℃)

(18℃)

6

LSC1 and LSC2

Quantulus 1220(LSC2)

Quantulus GCT 6220(LSC1)

7

Samples and experiment plan Samples

Unquenched standards in 20mL glass vials: Blank, 3H, 14C Home-made samples in 20mL plastic vials (cocktail:10mL OptiPhase HiSafe 3)

3 blank samples: Blank1, Blank2, Blank3 2 samples of β-γ emitters: 60Co, 137Cs 1 pair of α or β emitters: 241Am, 90Sr/90Y

3 parts Part 1: background count rate and counting efficiency

Blank, 3H, 14C, Blank1, Blank2, Blank3, 60Co, 137Cs

Part 2: α/β discrimination

241Am, 90Sr/90Y

Part 3: instrument stability Blank, 3H, 14C

8

Counting conditions Assays of LSC1 (GCT=Off, -14.0, -12.4, -3.2, -2.6, -2.4, 0.1)

“CPM” assay “Alpha/Beta” assay

Protocols of LSC2 Protocol 1: H-3 or low energy beta counting Protocol 2: C-14 or high energy beta counting Protocol 3: Alpha/Beta counting (Guard active) Protocol 4: Alpha/Beta counting (Guard inactive)

Protocol of LSC3 Protocol 1: H-3 or low energy beta counting

“Optimize_GCT_Strength_Factors” assay

9

ROI (region of interest)

ROI is always selected as the whole spectrum(unless otherwise specified). 0-2000 keV for LSC1 channels 1-1024 for LSC2 and LSC3

10

Samples in glass vials

Condition

Blank 3H 14C

CR

(cpm)

SDCR

(cpm)

CR

(cpm)

SDCR

(cpm)

ε

(%)

CR

(cpm)

SDCR

(cpm)

ε

(%)

GCT

for LSC1

Off 16.02 0.88 107973.07 82.06 64.19 135776.48 424.00 95.52

-14.0 14.51 0.88 107971.65 82.03 64.19 135773.78 423.91 95.52

-12.4 13.52 0.85 107970.73 82.03 64.19 135770.82 423.82 95.52

-3.2 8.82 0.66 107965.60 82.35 64.19 135751.70 423.18 95.51

-2.6 8.54 0.64 107965.24 82.41 64.19 135750.19 423.12 95.51

-2.4 8.46 0.64 107965.13 82.44 64.19 135749.68 423.10 95.51

0.1 7.35 0.64 107963.65 82.82 64.19 135742.91 422.84 95.50

Protocol

for LSC2

1 13.18 0.39 107191.74 19.74 63.73 133970.98 221.09 94.25

2 4.88 0.32 47305.71 68.28 28.12 127703.37 156.04 89.84

CR: count rate; SDCR: the standard deviation of count rate; ε: counting efficiency

11

Samples in plastic vials

CR: count rate; SDCR: the standard deviation of count rate

Condition

Blank1 Blank2 Blank3

CR

(cpm)

SDCR

(cpm)

CR

(cpm)

SDCR

(cpm)

CR

(cpm)

SDCR

(cpm)

GCT

for LSC1

Off 10.56 0.12 10.70 0.33 10.84 0.71

-14.0 9.18 0.12 9.31 0.32 9.45 0.71

-12.4 8.29 0.06 8.43 0.34 8.56 0.71

-3.2 4.28 0.16 4.47 0.18 4.57 0.39

-2.6 4.08 0.18 4.26 0.14 4.33 0.37

-2.4 4.01 0.18 4.18 0.12 4.26 0.36

0.1 3.17 0.21 3.25 0.05 3.26 0.30

Protocol

for LSC2

1 3.67 0.20 3.51 0.29 3.73 0.07

2 2.02 0.17 2.06 0.21 2.11 0.04

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Samples of 60Co and 137Cs

CR: count rate; εR: relative counting efficiency

Condition

60Co 137Cs

CR

(cpm)

εR

(%)

CR

(cpm)

εR

(%)

GCT

for LSC1

Off 5912.67 47.66 4042.27 97.20

-14.0 5886.15 47.45 4032.79 96.98

-12.4 5864.02 47.27 4027.92 96.86

-3.2 5727.65 46.17 3997.88 96.14

-2.6 5717.37 46.09 3995.61 96.08

-2.4 5713.90 46.06 3994.84 96.06

0.1 5668.64 45.69 3984.83 95.82

Protocol

for LSC2

3 7809.39 62.95 4041.79 97.19

4 12405.66 100.00 4158.52 100.00

60Co:β/γ emitter

withcascade β-γ

radiation

137Cs:β/γ emitter

With nocascade β-γ

radiation

Guard inactive

Guard activeγ counting efficiency of guard:

LSC1

LSC2

54%

37%

13

Effect of quench on α/β discrimination

Fig. 1 The effect of quench on the optimum PSA

Fig. 2 The effect of quench on the misclassification at the optimum PSA

Composition of SimS：

HNO3 1.0mol/L

Na 18.3 g/L

Fe 6.0 g/L

Al 5.7 g/L

Ni 2.9 g/L

Nd 1.5g/L

SimS: Simulated Solution, the quenching agent represents the main composition of Chinese high level liquid waste.

Cross-over plot method: Optimum PSA, Misclassification

LSC2is

better

LSC1is

better

α: 241Am; β: 90Sr/90Y

PSA: pulse shape analysis

14

Effect of α/β discrimination on background count rate at the optimum PSA

CR: count rate; SDCR: the standard deviation of count rate

Condition

Blank1 Blank2 Blank3

CR

(cpm)

SDCR

(cpm)

CR

(cpm)

SDCR

(cpm)

CR

(cpm)

SDCR

(cpm)

β-MCA

GCT

for LSC1

Off 9.09 0.68 8.86 0.71 8.52 0.48

-14.0 7.71 0.68 7.48 0.72 7.14 0.50

-12.4 6.86 0.68 6.62 0.64 6.29 0.46

-3.2 3.37 0.44 3.38 0.46 2.91 0.33

-2.6 3.17 0.45 3.17 0.46 2.70 0.32

-2.4 3.10 0.45 3.09 0.46 2.63 0.32

0.1 2.30 0.51 2.22 0.48 1.84 0.26

LSC2: Protocol 3 3.26 0.15 3.20 0.21 3.21 0.17

α-MCA LSC1: all GCT 1.63 0.17 1.72 0.22 1.84 0.12

LSC2: Protocol 3 0.55 0.15 0.47 0.06 0.54 0.17

* The optimum PSA is 146 for LSC1 and 107 for LSC2.

MCA:multi-channel analyzer

15

Effect of α/β discrimination on counting efficiency near the optimum PSA

CR: count rate; εR: relative counting efficiency

Condition

241Am 90Sr/90Y

CR

(cpm)

εR

(%)

CR

(cpm)

εR

(%)

β-MCA

GCT

for LSC1

Off 248.60 84880.40 98.28

-14.0 244.13 84865.72 98.26

-12.4 241.53 84856.06 98.25

-3.2 227.16 84796.58 98.18

-2.6 226.37 84792.10 98.17

-2.4 226.11 84790.59 98.17

0.1 223.63 84770.86 98.15

LSC2: Protocol 3 139.36 86369.50 100.00

α-MCA LSC1: all GCT 81185.60 100.00 1512.80b

LSC2: Protocol 3 79964.78 98.50 1053.36b

The PSA is 150 for LSC1 and 110 for LSC2

Aging of PMTin LSC2

Bremsstrahlungfrom 90Sr/90Y

MCA:multi-channel analyzer

16

Results of stability test for the three LSCs

CR: count rate; RSDCR: observed relative standard deviation of CR;RSDpred: predicted relative standard deviation of CR; ε: counting efficiency

Condition Item Blank 3H 14C

LSC1: GCT=Off

CR (cpm) 16.54 104760.41 136006.99

RSDCR (%) 2.273 0.112 0.108

RSDpred (%) 2.245 0.125 0.125

ε (%) 63.97 95.69

LSC1: GCT=0.1

CR (cpm) 7.67 104750.68 135970.66

RSDCR (%) 3.381 0.112 0.108

RSDpred (%) 3.297 0.125 0.125

ε (%) 63.96 95.67

LSC2: Protocol 1

CR (cpm) 13.47 104196.92 134115.06

RSDCR (%) 3.503 0.139 0.114

RSDpred (%) 2.487 0.125 0.125

ε (%) 63.81 94.36

LSC3: Protocol 1

CR (cpm) 12.03 101578.24 135212.71

RSDCR (%) 3.104 0.112 0.116

RSDpred (%) 2.632 0.125 0.125

ε (%) 62.20 95.13

𝑅𝑅𝑅𝑅𝑅𝑅𝐶𝐶𝑅𝑅

𝑅𝑅𝑅𝑅𝑅𝑅𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝

2

1.026

1.052

1.983

1.390

Counting terminator

RSDpred

0.125%

χ2

𝑁𝑁 − 1

Best

Worst

χ2

𝑁𝑁 − 11

Reducedchi-square

17

Conclusions If proper GCT is applied, the background count rate in β-MCA for

Quantulus GCT 6220 can be lower than that for Quantulus 1220,but the background count rate in α-MCA for Quantulus GCT 6220is always higher.

For the counting efficiency, which LSC is higher depends not onlyon the LSC setting (including the aging of PMTs), but also on thedecay properties of the radionuclide to-be-determined.

The results of α/β discrimination vary with the quench level of thesamples: Quantulus GCT 6220 is better for high quenched samples,while Quantulus 1220 is better for low quenched samples.

It seems that Quantulus GCT 6220 exhibits better stability thanQuantulus 1220.

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References1. PerkinElmer (2002) Wallac 1220 Quantulus™ ultra low level liquid scintillation spectrometer(instrument manual, 1220-931-06)2. PerkinElmer (2015) QuantaSmart™ for the Tri-Carb® liquid scintillation analyzer (Models4810TR, 4910TR, 5110TR, and QuantulusTM GCT 6220) (reference manual, manual reordernumber 8860101 Rev. A)3. Zhao HP, Feng XG (2011) The influences of anticoincidence shield on liquid scintillation countrates for various kinds of radionuclides. J Nucl Radiochem 33(6):353-357 (in Chinese)4. Pujol L, Sanchez-Cabeza J-A (1997) Role of quenching on alpha-beta separation in liquidscintillation counting for several high capacity cocktails. Analyst 122: 383-3855. Pates JM, Cook GT, MacKenzie AB, Passo CJ (1998) Implications of beta energy and quenchlevel for alpha-beta liquid scintillation spectrometry calibration. Analyst 123: 2201-22076. Feng XG, He QG (2009) Simultaneous determination of 237Np, 238–240Pu and 241Am in HNO3solution by combining extraction, liquid scintillation counting, and α spectrometry. Nucl InstrumMethods Phys Res A 609: 165-17127. Feng XG, He QG, Wang JC, Chen J (2016) The effect of incidental radiations on thedetermination of α or β particles by liquid scintillation counting for low quenched samples. JRadioanal Nucl Chem 308: 67-798. Knoll GF (1999) radiation detection and measurement (3rd Edition). John Wiley & Sons, Inc.,New York/Chichester/Weinheim/Brisbane/Toronto/Singapore

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Decay scheme of 137Cs and 60Co

137mBa (2.552m)

137Cs

513.97 94.36

Eβ (keV) Iβ (%)

1175.63 5.64

137Ba

661.657 γ 84.99% ce 9.37%

100%

60Co

317.90 100

Eβ (keV) Iβ (%)

γ1 1173.20keV

60Ni

100%

γ2 1332.50keV

Decay scheme of 60CoDecay scheme of 137Cs

Ece = 624.218-661.644 keV, ΣIce = 9.37%

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Misclassification (MR)

SimS Volume =1.2mL，PSA=50

Am:α-MCA

Am:β-MCA

Sr/Y:α-MCA

Sr/Y:β-MCA

ROIPK𝑀𝑀𝑅𝑅α =R

G + R× 100%

𝑀𝑀𝑅𝑅β =B in ROIPK

Y + B× 100%

21

ROIPK for LSC1 and LSC2

ROIPK: the peak area of α emitter

Run No. SimS volume (mL) ROIPK for LSC1 (keV) ROIPK for LSC2 (channel)

1 0 220-400 650-800

2 0.1 170-350 625-775

3 0.2 140-300 610-760

4 0.4 120-270 590-745

5 0.8 85-220 550-710

6 1.2 70-190 450-700

7 1.6 25-180 350-690

22

Cross-over Plot

SimS Volume = 0mL SimS Volume = 1.2mL

23

Optimum PSA vs. regular quench index

Quantulus 1220 Quantulus GCT 6220

24

RSDCR and RSDpred

RSDCR: the observed relative standard deviation of CR (30 cycles)RSDpred: the predicted relative standard deviation from Poissondistribution which is used to describe the nuclear countingsystem:(1) for Blank, RSDpred = 1/(CR∙t)0.5 ∙ 100% (where counting time t

= 120 min);(2) for 3H and 14C, RSDpred is from counting terminator. The

terminator for LSC1 is “2 Sigma % = 0.25%”, implyingRSDpred = 0.125%. The terminator for LSC2 and LSC3 is“COUNTS = 640000”, therefore RSDpred =1/6400000.5 ∙ 100%= 0.125%.

25

Optimizing_GCT_Strength_Factors_Procedure-Rev_B.pdf

26

Optimizing_GCT_Strength_Factors_Procedure-Rev_B.pdf