1. Measuring Tritium in Water and Urine with Liquid Scintillation Counting
Kun-Ho Chung, Mun-Ja Kang
Korea Atomic Energy Research Institute
Nuclear Environment Safety Research Center
Page 1

2. Nuclear Decay Process-Radioactivity
Radionuclides ?
Nuclear Decay Process-Radioactivity
1. alpha (α) – emission of helium nucleus( 4He) composed of two protons and
two neutrons with a momogenic energy between 2-8 MeV
2. Beta (β) – electrons with either a positive (positron) or negative (negatron)
charge and emitted with a continuum of energy ( KeV)
3. Gamma (γ) – a high energy, short wavelength electromagnetic radiation,
originating in the nucleus of the atom
Page 2

3. Radioactivity Decay Law
Radionuclides ?
Radioactivity Decay Law
N = N0e-λt
N0 = number of atoms or activity (e.g. Bq) at staring time t0
N = number of atoms or activity after time interval t
 = decay constant or / t1/2
t1/2 = half-life of isotope
H-3 half-life has been accepted to be y = d, TU = Tritium Unit = Bq/kg (1 TU = 1 3H atoms per 10exp(18) H atoms)
Page 3

4. 1 Curie (1 Ci) = 2.22 x 1012 dpm 1 Bequerel (1 Bq) = 1 dps
Unit of radioactivity
1 Curie (1 Ci) = 2.22 x 1012 dpm
1 Bequerel (1 Bq) = 1 dps
1 Ci = 2.22 x 1012 dpm = 3.7 x 1010 dps
= 3.7 x 1010 Bq
= 37 GBq
1 mCi = 2.22 x 109 dpm = 3.7 x 107 dps
= 3.7 x 107 Bq
= 37 MBq
1 μCi = 2.22 x 106 dpm = 3.7 x 104 dps
= 3.7 x 104 Bq
= 37 KBq
H-3 half-life has been accepted to be y = d, TU = Tritium Unit = Bq/kg (1 TU = 1 3H atoms per 10exp(18) H atoms)
Page 4

5. Principals of LSC : Energy transfer process
Chemical
Quench
Color b hn
Page 5

6. Principals of LSC : Energy transfer process
Page 6

7. Principals of LSC : Energy transfer process
b-particle
Solvent molecule
Excited Scintillator
Emitted Photon P S b /
Illustration of the Collision Process
Page 7

8. Principals of LSC : Detector system of LSC (Quantulus 1220)
PMT
Liquid scintillator
LEAD(passive shield)
A/D CONVERTER
COINC. UNIT
SUMMING
AMPL .
MCA1
HALF1
TRIGGER
MCA SPLIT
INHIBIT
ANALOG
MCA2
HALF2
Page 8

9. Radionuclides ? Emax Number of beta particles Beta particle energy
Page 9

10. Both cosmogenic and man-made
Tritium
3H, Emax = 18.6 keV, half-life y
Both cosmogenic and man-made
Low energy – non hazardous, biological half-life 10 days
3H appears as part of water molecule as HTO
Drinking water limit 100 Bq/L
Measurable at this limit with any LSA in a reasonable time
Concentrations much smaller in environmental samples
Page 10

11. Weapons testing from 1954 to 1963
Tritium
Anthropogenic tritium is from atmospheric weapons testing and nuclear fuel cycle
Weapons testing from 1954 to 1963
Natural levels are now back to the levels of pre-atmospheric bomb tests
The present day activity in precipitation is approximately 2 Bq/L
Cosmic rays
14N(n,3H)12C
16O(n,3H)14O
2H(n,) 3H
Nuclear Tests
235U(n,f)3H
14N(n,3H)12C
16O(n,3H)14O
2H(n,) 3H
NPP
6Li(n,)3H
10B(n,2)3H
2H(n,) 3H
Page 11

12. Minimum Detectable Activity
Detection Limit
Minimum Detectable Activity
MDA = (4.65 sqrt(B*t)+ 2.71)/(E*V*t)
E = counting efficiency
V = sample volume
B = background count rate
t = counting time
An American National Standard on Performance Criteria for Bioassay, HPS N , Health Physics Society, McLean 1996, 112 p.
Page 12

13. Detection Limit vs. Counting Time
10 mL sample, 25 % counting efficiency, background 1 CPM
Page 13

14. Measurement of Tritium by LSC
Direct addition - mix with cocktail and measure (sample 10 mL)
less labor intensive
distillation or purification by Eichrom 3H column is needed to remove impurities from a low activity sample
Electrolytic enrichment (starting volume mL)
enrichment system required, no commercially made systems readily available
time consuming
Benzene synthesis (C6H6 contains 3 times as much 3H as H2O)
synthesis apparatus required, no commercially made synthesizers readily available
labor intensive, time consuming
carcinogenic end product
Page 14

15. typical 3H eff typical bkg detection limit
How do methods compare ?
typical 3H eff typical bkg detection limit
Direct counting 25 % 1.0 CPM 2.5 Bq/L
Benzene synthesis 60 % 1.2 CPM 0.37 Bq/L
Enrichment (20 x) 25 % 1.0 CPM 0.13 Bq/L
Direct counting and enrichment calculations are made for 10 mL water and 500 min counting time
20 mL benzene is equivalent to 30 mL water with 100 % yield.
Numbers are typical for Quantulus
Page 15

16. Distilled & Electrolytically Enriched Samples
Sample quench is constant for all samples, and no quench correction needed
Sample activity = Ao * (S-B)/(Std-B),
where Std, S, and B are reference, sample and blank count rates, respectively, Ao is reference standard activity and counting efficiency E = (Std-B)/Ao
Spectrum analysis software does the calculation based on raw spectra
When sample S and blank B count rates are low, the random noise signal & chemiluminescence is constant and low (typically 0.15 CPM in Quantulus) and subtracted in the above calculation
Page 16

17. Constant quench & EASY View software of Quantulus
Page 17

18. Internal standard method, ISO Standard 9698:1989(E)
Samples measured first as they are
Very small volume of known activity standard material added and recounted
Efficiency verified for each sample and activity calculated
Advantage:
Based on raw data, no quench curves needed
Works on any counter (performance is an issue)
Disadvantages:
Destroys samples, recounting not possible
Page 18

19. Counting with quench curves / Tri-Carb
Page 19

20. Measurement of Tritium by LSC
Cocktails for aqueous 3H samples
Ultima Gold LLT, high capacity, acceptance of mineral acids
Ultima Gold XR, high capacity, acceptance of mineral acids
OptiPhase HiSafe 3, multipurpose cocktail, lower water capacity than Ultima Gold’s
Cocktails are based on di-isopropyl-
naphthalene solvent, which has very low
vapor pressure and high flash point (148°C)
Page 20

21. Non-radioactive plastic vials for lowest activities
Ordinary polyethylene vials good with safe cocktails
super PE vial , 20 mL,
( PE vial, 20 mL)
Teflon coated polyethylene vials for classic cocktails
low diffusion PE vial, , 20 mL
( low diffusion PE vial, 20 mL)
Copper-teflon vials 15 and 20 mL, , (expensive, to be washed and reused, only for Quantulus)
Page 21

22. Standard reference material
Reference materials 3H counting
Conventional size standards for low level counting (20 mL glass vial)
3H standard (set of ten) ~3 x 104 DPM/vial
Internal Standards
3H water, ~2.5 x 106 DPM/g, 10 mL
Internal standard kits 3H W
3H for aqueous solvents, 40 capsules
‘Dead’ water needed for background correction
Page 22

23. Direct counting of 3H in urine samples: LSC source for 3H
add H-3 standard of 200 ml in vial: 3003 Bq/g
add Ultima Gold-LLT cocktail of 15~20 mL
add “dead” water: 5~0 mL
total volume in vial: 20 mL
counted by liquid scintillation counter
Page 23

24. Preparation of spiked urine samples with 3H standard
add H-3 standard of 200 ml in vial: 3003 Bq/g or 300 Bq/g
add Ultima Gold-LLT cocktail of 19 mL
add urine sample: 1 mL
total volume in vial: 20 mL
counted by liquid scintillation counter
Page 24

25. LSC quenching spectrum and curve for 3H
Page 25

26. What is the SQP(E)?
SQP(E)= 1%
99%
Page 26

27. Activity (Bq/L) = (Csamp- CBK) /60(100/E)(1/V)
Calculation
Activity (Bq/L) = (Csamp- CBK) /60(100/E)(1/V)
MDA (Bq/L) = { sqrt(CBK t)}/(60t)  (100/E)(1/V)
Csamp and CBK: count rate (cpm) of sample and background
E: % efficiency of H-3 in LSC
V: sample quantity (L)
t: counting time (min)
Page 27

28. Measuring 3H in Urine: urine sample spiked with 3H standard
Page 28

29. Measuring 3H in Urine: urine sample spiked with 3H standard
SQP(E)
LSC
efficiency
(%)
Spiked
activity (Bq/L)
Measured
Rel. deviation (%)
Spiked urine
sample 1
845.75
47.38
61,000
58,900
( cpm)
3.4
sample 2
845.98
47.41
620,000
617,400
(17562 cpm)
0.4
Page 29

30. MDA of the method for 3H in urine samples
Sample quantity: 1 mL
LSC efficiency: 47% (50~300 windows)
Count time: 30min
Back ground count rates: 5.83 cpm (50~300 windows)
MDA : Bq/L
Page 30

31. TR-LSC Application Note P10763:
Literature
TR-LSC Application Note P10763:
Time Resolved Liquid Scintillation Counting: (TR-LSC) for Environmental 3H Analysis
by Charles J. Passo, Jr. and Dr. Gordon Cook
PerkinElmer Life Sciences 2002
LSC Handbook of Environmental Liquid Scintillation Spectrometry, Packard 12/1994, PMC0387 (out of print)
Quantulus bibliography February 2006
46 references on LS measurements of 3H
Page 31

32. Homepage for more information and direct communication
Homepage for more information and direct communication