1. Performance Testing of Selected Liquid Scintillators Julian Dean Centre for Ionising Radiation Metrology, NPL

2. Colloid (Emulsion) Counting Heterogeneous sample preparation technique Widely used by user community Wide range of commercial liquid scintillators commercially available Data provided often limited

3. Aim of project To derive sample uptake/efficiency data for four specific liquid scintillators with a range of nuclides and matrices

4. 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

5. Radionuclide standards RadionuclideCalibration Laboratory Activity (Bq) TritiumAmersham~ 1500 Sulphur-35Amersham~ 150 Iron-55NPL~ 6400 Strontium-90NPL~ 450 Technetium-99Amersham~ 1000 Plutonium-238NPL~ 2000 Plutonium-239NPL~ 2000

6. Matrices RadionuclideMatrices examined TritiumWater Sulphur-35Water, 0.1 M HCl Iron-55HCl (0.1 M and 1 M) Strontium-901 M HNO 3, HCl (0.1 M and 1 M) Technetium-99NH 4 OH (0.01 M, 0.1 M and 0.5 M) Plutonium-238HNO 3 (0.5 M, 1 M and 2 M) Plutonium-239HNO 3 (0.5 M, 1 M and 2 M)

7. 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

8. 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

9. 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)

15. 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

16. 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)