Performance Testing of Selected Liquid Scintillators

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Performance Testing of Selected Liquid
Scintillators

• Julian Dean
• Centre for Ionising Radiation Metrology, NPL

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Colloid (Emulsion) Counting

• Heterogeneous sample preparation technique
• Widely used by user community
• Wide range of commercial liquid scintillators
  commercially available
• Data provided often limited

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Aim of project

• To derive sample uptake/efficiency data for four
  specific liquid scintillators with a range of
  nuclides and matrices

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Scintillators

• Readysafe (Beckman Coulter)
• Ultima Gold AB (Packard)
• Uniscint BD (National Diagnostics)
• Unisolve 100 (NBS Biologicals)
• Frequently used in-house at NPL and found
  reliable

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Radionuclide standards
Radionuclide Calibration Laboratory Activity (Bq)
Tritium Amersham 1500
Sulphur-35 Amersham 150
Iron-55 NPL 6400
Strontium-90 NPL 450
Technetium-99 Amersham 1000
Plutonium-238 NPL 2000
Plutonium-239 NPL 2000
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Matrices
Radionuclide Matrices examined
Tritium Water
Sulphur-35 Water, 0.1 M HCl
Iron-55 HCl (0.1 M and 1 M)
Strontium-90 1 M HNO3, HCl (0.1 M and 1 M)
Technetium-99 NH4OH (0.01 M, 0.1 M and 0.5 M)
Plutonium-238 HNO3 (0.5 M, 1 M and 2 M)
Plutonium-239 HNO3 (0.5 M, 1 M and 2 M)
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Assessment of sample uptake

• Matrix added in 0.5 ml increments to scintillant
  (10 ml) until system became cloudy and/or
  unstable (ambient temperature)
• Each sample of scintillator taken from a single
  batch

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Sample preparation

• For each permutation of scintillant, radionuclide
  and sample matrix, samples were prepared at three
  volume levels 0.5 g, 1.5 g and the maximum
  uptake level
• In each case 0.1 g of standard solution added to
  vial and diluted with appropriate matrix
• All vials topped up to 18 g with liquid
  scintillator
• All samples prepared in triplicate
• Background samples prepared for each permutation

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Counting

• All samples counted on
• 1. Wallac Rackbeta 1219
• 2. Canberra Packard Tricarb
• Detection Efficiencies and Merit Values
  determined
• Merit Value Detection Efficiency x proportion
  of aqueous phase in vial (as percentages)

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Conclusions

• 1. Useful data generated for planning dilution
  checks and deriving approximate activity
  concentrations for some nuclides
• 2. No product universally superior to others but
  Ultima Gold is best overall for nuclides/matrices
  studied
• 3. Some uptake data conflict with manufacturers
  data
• 4. Similar detection efficiencies found for the
  two LS counters used

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Suggestions

• 1. Look at other scintillants, nuclides and
  matrices
• 2. Look at, e.g., temperature effects, count-rate
  stability, variations between batches
• 3. Pool user information into one database
• 4. Supplementary physical measurements (e.g.
  micellar size, formation)