National Physical Laboratory

Minutes of the Sixth NMS LSUF Meeting

18th September 2007

National Physical Laboratory


Attendees:       Simon Jerome NPL (Chairman)
      Arzu Arinc NPL (Secretary)
         
      Eleanor Bakhshandeiar NPL
    Andrew Boschier Veterinary Laboratories Agency
      Pete Burgess NPL
      Darryl Campling UKAEA
      Hgun Ju Cha CHOL
      Kun Ho Chung KAERI
      John Davies Beta-Gamma Training
      Philip Doyle Amersham
      Alan DuSautoy NPL
      Ronald Edler PerkinElmer
      Chris Gilligan NPL
      Derek Hammond Health Protection Agency
      Chris Hardy Babcock Support Services Limited
      Phil Harrison PreClinical Insight
      Robert Huggett Zinsser Analytic
      Mum Ja Kang KAERI
      John Keightley NPL
      Dae-Ji Kim National Oceanography Centre
      David Lambert Veterinary Laboratories Agency
      Stephanie Long RPII
      Ann Mair UKAEA
      Dave Molino GE Healthcare
      Jenny Morris AWE
      Jung-Suk Oh National Oceanography Centre
      Andy Pearce NPL
      John Sephton NPL
      Graham Shephard Devonport Royal Dockyard
      Charlie Stewart UKAEA
      Marcel Schouwenburg TU Delft NCSV
      Simon Temple DPM Solutions Ltd
      James Thomson Febos
      Jill Walker RCD Lockinge
      Phil Warwick National Oceanography Centre
      Dave Wickenden BNG-Magnox (North)
         
Apologies:     Stephen Collins GE Healthcare
      Moira Mason British Energy
      James Riddick GE Healthcare
      Richard Starkey Servier Research and Development Ltd


1.  Chairman’s Welcome and Previous Minutes

  • Simon Jerome welcomed the members to the sixth meeting and explained briefly the aim of the forum.
  • The minutes of the fifth meeting were accepted as a true record.
  • Simon asked the participants if they would be happy to have User Forum meetings by user community rather than by technique for the new programme. In general, participants said they preferred the latter, with fora continuing to be run by technique.

2.  Invited talk: Waste Vacuum Pump Oil – Sample Preparation & Analysis – James Thomson, MERIDIAN

  • James began his talk by summarising the functions of vacuum oil, the various types of oil available, the additives and contaminants they contain and how the oil gets contaminated. He pointed out that the disposal of oil is extremely cost effective if one can prove that the oil is not contaminated.
  • James went through the various methods available for the analysis of oil samples:
    • Direct addition: Not recommended due to resulting chemiluminescence.
    • Freeze drying: Not recommended for 3H because any Organically Bound Tritium (OBT) will be missed; however, this method probably works with other nuclides.
    • Azeotropic distillation: As with freeze drying, OBT will be missed.
    • Oxidation:
      1. Using a sample oxidiser: This is a recommended method, but drawbacks are the limitation on the sample size (up to 100 ml) and the price of the original equipment (typically £38k).
      2. Using a RADDEC Pyrolyser: This method is also recommended, added to which the sample can be larger (up to 500 ml) and the price is more affordable (typically £20k).
    • Combustion: Also a recommended method uses a Parr Oxygen bomb; sample can be up to 5g and the initial outlay is in the range £2k to £3k.
  • James pointed out that, as a money-saving alternative, an oil-free pump could be used and he concluded his talk by recommending, from his personal experience, the oxidation method for analysing oil samples.

  • Following the talk, Simon Temple mentioned that oil analysis is a time consuming business and that the right balance needs to be found between the cost of disposing of contaminated oil and the cost required to certify oil as contamination-free.

3.  Invited talk: Red Shifted Liquid Scintillation. An opportunity to progress the technology?
     – Phil Harrison, PreClinical Insight

  • Phil began his talk by explaining the history behind the blue-shifted LSC, pointing out that it had been chosen to match the response of  Photomultiplier Tubes (PMTs). Phil is proposing instead to use a wavelength shifter which goes from the emission wavelength of solvent (~330 nm) to the red end of the spectrum (~ 600 nm).
  • Phil showed that red-shifted LS is less likely to be affected by colour quenching as the overlap between the scintillator emission spectrum and the quencher absorption spectrum is reduced.
  • PMTs with a wider spectral range (e.g. Hamamatsu, Newport Corporation) can detect at the red end of the spectrum, but the quantum efficiency is still lower than that observed for blue light (with about 10% compared with 30%). Charge Coupled Devices (CCDs) on the other hand have a quantum efficiency of 90% at the red end of the spectrum, but need cooling to reduce thermal noise.
  • The difficulty at the moment is finding fluors (wavelength shifters) that will absorb at 330nm and re-emit at 600 nm. Two different shifters might have to be used to achieve that big “jump” in wavelength.
  • Phil concluded that the two biggest advantages of red-shifted LSC are the minimisation (and possible elimination) of colour quenching and higher detection sensitivity.

  • Following the talk, a delegate commented about the fact that cooling the CCDs to – 80°C will cause a problem with the liquid scintillation cocktails, which are not designed to work at these temperatures. Phil replied that a thermal barrier is required between the CCDs and the sample changer, which he expects to be at a working temperature of about 10°C.
  • A participant asked if the CCDs suffered from degradation the same way that PMTs do. Phil answered that he didn’t expect the CCDs to degrade rapidly as they would be exposed to low light levels. He said he expected them to have a lifetime of 10 to 15 years.
  • Phil announced the commercialisation of a new scintillation counter for 2008 with 3 PMTs that will be used for measuring simultaneously triple and double coincidences making possible instant efficiency measurement. The counter will cost £30k.

4.  NPL talk: Updates to ISO Standards 9696, 9697 and 9698 – Simon Jerome

  • Simon started his talk by describing the work of Technical Committee 147, which deals with water quality.
  • Simon explained that the actual standards ISO 9696 (Water Quality - Measurement of gross α activity in non-saline water - thick source method) and ISO 9697 (Water Quality - Measurement of gross b activity in non-saline water) do not include the use of liquid scintillation counting.
  • The committee has agreed the preparation of a new standard for measuring gross α and ß activity concentration in non-saline water by Liquid Scintillation Counting.
  • Simon described the major points of the new standard: technique, suggested calibration standards, α/b discrimination method and activity loss.
  • Simon finished his talk by describing the changes to the ISO 9698 standard on 'Determination of tritium activity concentration by Liquid scintillation counting method'.

  • During the talk, a delegate raised the fact that the α/ß 'spill over' is quench dependent and was wondering if this had been taken into account. Simon replied that the quench levels would be assumed to be reproducible which would limit the need for such correction.
  • A participant enquired regarding the recommended sample volume for evaporation and commented that the evaporation of the sample would always leave a precipitate. Simon explained that the aim of the evaporation was to concentrate the sample solution (e.g. from 400 ml to 20 ml) without creating a precipitate.
  • A delegate commented on the possibility of using either DIN or PXE based cocktails as they both have a slow component allowing the α/ß discrimination method.
  • One delegate enquired as to the planned timescale for revision and preparation of new standards. Revisions to the existing standards should be complete by end of 2008 and the preparation of the new standard will take approximately 2 to 3 years.

5.  Invited talk: 3H speciation in bioshield concrete – Dae-Ji Kim, National Oceanography Centre Southampton

  • Dae-Ji started his talk by defining bioshield concrete and explaining where it is found and the possible methods of production of 3H in the concrete. Raddec PyrolyserTM combustion system was used to separate the 3H from the concrete.
  • The results show an exponentially increasing concentration of 3H with decreasing distance from the reactor core. Dae-Ji pointed out that the 3H recovery vs. the combustion time varies as a function of the distance between the concrete and the reactor. In this study, the concrete was separated into three regions varying in distance from the reactor: the inner region, the middle and the outer edge.
  • The results show that strongly bound 3H can be found in the inner region and loosely bound 3H can be found in the outer edge.
  • Dae-Ji concluded that high temperature and long combustion time are needed to liberate 3H from bioshield concrete.

  • Following the talk, one delegate enquired as to the sample size used for the analyses. Dae-Ji replied that it was about 0.5 mm.
  • Another participant enquired as to the mass of the sample used. This was around 1 g.
  • Simon Jerome commented that water is incorporated into concrete in two different ways, one of them making the water difficult to extract.

6.  Group discussion: Uncertainties in liquid scintillation counting – Facilitator - Pete Burgess

  • The aim of this session was to identify as many sources of uncertainty in liquid scintillation counting as possible and to identify the major contributors to the total measurement uncertainty.

    The list of uncertainties/errors identified by the delegates was organised and condensed to give the final summary below.

  • Counting statistics, background (e.g. from the vial, natural radioactivity, cosmic rays, electronic noise and shielding), sampling, mass, calibration standard, detection efficiency (this is affected by factors such as the cocktail, the reproducibility, the stability and the temperature), sample reproducibility, sample homogeneity, cocktail stability, chemical recovery (i.e yield determination), quench measurement, sample management, fingerprint/crosstalk, colour correction, nuclear data, time of day/correction to reference time, luminescence, dead-time correction, black box – coincidence time difference, operator error, traceability "of everything", taking the cocktail outside its useful range, enhanced chemiluminescence, sample storage (this is a particular problem with tritium owing to its mobility).

7.  Manufacturer's presentation:
     Determination of the 14C content in fuels containing bioethanol and other biogenic materials with liquid scintillation
     counting - Ronald Edler, PerkinElmer

  • Ronald explained the worldwide need for countries to introduce biogenic materials into fuel in order to limit the CO2 emissions from fossil sources. Unlike fossil fuels, biogenic fuel contains radioactive hydrogen and carbon (3H and 14C), which can be measured by liquid scintillation counting (LSC).
  • Ronald described the various methods available for counting 14C. The three standard methods are: LSC with CO2 trapping (the recommended cocktails being Carbo-Sorb E+ and Permafluor E+), accelerator mass spectrometry and LSC with benzene synthesis. A fourth method, which is non-standard, is the direct counting with LSC (the recommended cocktails being Ultima Gold F and OptiScint HiSafe). This last method is simple, fast, gives good accuracy and is low in cost.
  • Measurements of bioethanol concentration were carried out and good agreement was obtained between the actual values and the calculated values.
  • Ronald pointed out the problem with chemiluminescence due to the nature of the samples measured and the need for dark adaptation. He also mentioned the colour quenching problem for pure biodiesel arising from the yellow colour of the samples and how difficult it is to remove.

  • Following the talk, a participant suggested that Ronald try bleaching the biodiesel samples by leaving them under the UV light.

8.  Any Other Business


      Forthcoming events:

9. Date of Next Meeting

This is provisionally scheduled for Tuesday, 23rd September 2008.

Arzu Arinc

Secretary, LSUF

Last Updated: 25 Mar 2010
Created: 17 Apr 2007