28^th November 2006

National Physical Laboratory

 

Attendees:			Simon Jerome	NPL (Chairman)
			Arzu Arinc	NPL (Secretary)
			Nasser Baghini	Imperial College London
			Mike Barton	British Energy
			Pepita Bianchi	PerkinElmer
			Andrew Boschier	Veterinary Laboratories Agency
			Keith Bradshaw	AMEC-NNC
			Darryl Campling	UKAEA
			John Davies	PerkinElmer
			Maria Garcia- Miranda	NPL
			Chris Gilligan	NPL
			Arvic Harms	NPL
			Phil Harrison
			Robert Huggett	Zinsser Analytic
			Lena Johansson	NPL
			Kevin Kelleher	RPI
			Pieter Kwackman	RIVM
			Amanda Law	NPL
			Ian Mather	RCD Lockinge
			John McNamara	British Energy
			Andy Pearce	NPL
			Dave Rayner	NPL
			Franz Schönhofer
			Graham Shephard	Devon Royal Dockyard
			Richard Starkey	Servier Research & Development Ltd
			Simon Temple	DPM Solutions Ltd
			Dave Wickenden	AEAT
Apologies:			François Briot	PROCORAD
			George Ham	HPA
			David Lambert	Veterinary Laboratories Agency
			John Lavender	BAE Systems
			Dilys Wilding	HPA
			Selina Woods	NPL
			Paul Wright	RPA

1.  Chairman’s Welcome and Previous Minutes

• Simon Jerome welcomed the members to the fifth meeting and explained briefly the aim of the forum.
• The minutes of the fourth meeting were accepted as a true record.

2.  Invited talk: "LSC as a tool in analysing suspected packages" - Pieter Kwakman, RIVM, Netherlands

• Pieter began his talk by describing the routine liquid scintillation measurements carried out at RIVM. Tritium, ¹⁴C and ⁸⁹Sr/⁹⁰Sr are analysed in waste water and alpha/beta discrimination is used as a screening method. He explained that the spill-over observed when using alpha/beta discrimination for a given nuclide varied as a function of the Pulse Decay Discrimination (PDD) setting and the quench level.
• An overview of the protocol currently in place at RIVM for analysing suspect packages was given. A suspect package will first be checked for explosive content, and then the potential biological hazard will be eliminated by addition of 4% of glutaraldehyde. Although the action of glutaraldehyde is slow compared with other disinfectants, it was chosen because it does not create chemiluminescence in the vial. As a last stage, the vials are assayed for radioactive content using liquid scintillation counting.
• Pieter showed the effect of glutaraldehyde and calcium sulphate (CaSO₄) on the liquid scintillation spectrum for various nuclides and concluded his talk by encouraging the exchange of information within the participants of the forum.

• Following the talk, a comment was made about the need to extend this protocol to decommissioning work; in this area also, some of the samples may contain explosive materials, or may have biological hazards, as well as radioactive content.
• The need to hold practice exercises to improve communication and networking within the different laboratories was discussed.

3.  Invited talk: "Fluorescence based colour quench correction of Scintillation Proximity Assay" - Phil Harrison

• Phil started his talk by explaining the principles of Scintillation Proximity Assay (SPA). The technique uses microscopic beads in aqueous solution with attached nuclide-specific biological capture molecules. The emission of light can only happen if the capture molecule is bound to a labelled target molecule (e.g. ³H, ³⁵S or ¹²⁵I).
• The advantages of SPA compared with more traditional liquid scintillation methods are:

• samples are homogeneous;
• there is no need for prior chemical separation (ideal for biological samples);
• there is no chemical quench;
• assay and disposal costs are reduced.

• Phil described a multi-modality counter "Chameleon V", commercialised by Hidex Oy, which can be used either as a traditional liquid scintillation counter or for Scintillation Proximity Assay.
• Phil explained that in Scintillation Proximity Assay a Xenon flash light replaces the traditional external standard; therefore, the fluorescence intensity replaces the quench parameter. The Xenon flash light excites the beads, which then re-emit the light. If any coloured elements are present in the solution, the light is attenuated. This method gives a fast, accurate and reproducible value of the colour quench in the solution.

• Following the talk, a delegate queried the speed of the binding process between the target molecule and the capture molecule. Phil replied that, for biological samples, the kinetic of the reaction between the target and capture molecules could take from a few minutes to a couple of hours, and he added that the process was irreversible.
• Phil was asked the possibility of binding several molecules on one bead. He answered that it was possible to have more than one binding site per bead.

4.  NPL talk: "Status report to LSUF on formulation of Ionising Radiation Programme 2007-2010" - Dave Rayner

• Dave began his talk by describing the context of programme formulation. He described the services/activities that the National Measurement System (NMS) will fund and the ones that the customers will fund; for example, the NMS will fund the development of a new calibration service, but once the service is in place the customers concerned would bear the cost of the actual calibrations.
• He presented the formulation timetable and pointed out that the period from March to May 2007 would be the last opportunity to contribute to the programme before it was finalised.
• The consultation would be divided into six generic areas. The top ten specific needs identified in the 'Environment and Decommissioning' area were discussed.

• Following the talk, one delegate asked how the web responses were managed (for example, what would happen if more than one person from the same company replied). Dave replied that his team were noting any duplicate responses from different people working for the same organisation.
• A participant enquired if most companies were aware of the consultation. Dave replied that people had been informed via e-mail, that user forums were being used to spread information, and that questionnaires were available online. He added that the aim was not to get everyone to answer but to ensure that responses were received from a group of people representative of the user base.

5.  Invited talk: "Standard on assuring compliance of drinking water radioactivity" - Franz Schönhofer

• Franz began his talk by describing the aim of the European Union Council Directive on the quality of water intended for human consumption. The total indicative dose, which is calculated for one year assuming an average consumption of 2.2 L of water per day, should be kept below 0.1 mSv year^-1. This limit does not apply to mineral water and excludes the contribution of ³H, ⁴⁰K, and Radon and its decay products.
• Knowledge of the geographical locations of facilities which may contribute to public doses should be taken into consideration; for example, artificial radionuclides may arise near nuclear power plants, medical facilities, or the levels of natural-occurring radionuclides may be enhanced near, e.g., uranium mines. He pointed out that, although ²²⁶Ra and ²²⁸Ra were excluded from the calculation of the total indicative dose, they had the highest dose factors. However, some recommendations are available on the maximum levels of contaminants acceptable before action needs to be taken. Examples are 0.2 Bq L^-1 for ²¹⁰Pb and 0.1 Bq L^-1 for ²¹⁰Po.
• Another factor that needs to be taken into account is radiotoxicity, which is dependent on the age of person, the exposure pathway, and the physical and chemical state of the radionuclide. Data for ²²⁶Ra and ²²⁸Ra shows that the most vulnerable age group is 12-17 years old.
• Franz described various sample preparation and counting methods for the measurement of ²²²Rn, ²²⁶Ra and ²²⁸Ra by liquid scintillation counting. These included chemical separation with RadDisks, co-precipitation with radium sulphate, alpha/beta separation, and spectrum analysis.
• The talk ended with some examples of gross alpha/gross beta, ³H and ²²⁶Ra measurements carried out on 20 brands of Polish mineral water. The gross beta measurements revealed high levels of ⁴⁰K in some of the mineral waters. The levels of ³H varied between 1.5 and 3 Bq L^-1, which is below the recommended limit of 100 Bq L^-1; however, the presence of ³H can interfere with ²²⁸Ra measurements, for which the recommended limit for gross beta is less than 1 Bq L^-1.

• Following the talk, one delegate commented that the Environment Agency in the UK recommends distillation of ³H using sodium carbonate and asked Franz if he thought this was necessary. Franz replied that the use of the distillation process might discard some of the impurities and it was best to look at the whole spectrum.
• A discussion took place about the incoherence of the regulations regarding gross beta measurements. In the UK, it is permissible to subtract the ⁴⁰K contribution from a gross beta measurement; It is difficult to modify existing ISO standards to allow for new methods; A concentration of 0.8 Bq L-1 of ²²⁸Ra in water would lead to a dose far above the 0.1 mSv year^-1 recommendation; there is a need for correction for ingrowth of daughters which complicates the measurement process, which can be a problem when many samples have to be measured.

6.  NPL talk: "Standardisation of ²¹⁰Pb with liquid scintillation techniques" - Lena Johansson

• Lena started her talk by giving background information about ²¹⁰Pb: its decay chain, origin, applications, and ingrowth of its daughters as a function of time. She explained that measuring ²¹⁰Pb with the conventional method of coincidence counting was complicated and involved a large number of corrections, leading to a large final uncertainty. Cerenkov counting of ²¹⁰Bi (the decay product of ²¹⁰Pb) was used to standardise the ²¹⁰Pb.
• Firstly, ²¹⁰Bi was standardised using the CIEMAT/NIST efficiency tracing method. The standardised solution was then used to calibrate the liquid scintillation counter for Cerenkov counting. Finally, a ²¹⁰Pb solution was chemically separated from its daughters and was standardised by following the ingrowth with time of ²¹⁰Bi. The standardised activity of the ²¹⁰Pb solution was 529 kBq g^-1 ± 6 kBq g^-1 on 17th October 2005.
• Lena finished her talk by pointing out that ²¹⁰Pb standards were now available and could be purchased from NPL.

• Following the talk, one delegate asked if the ²¹⁰Po content of the ²¹⁰Pb solution had been checked. Lena answered that, as it had only been one year since the separation had been carried out, the ²¹⁰Po was still growing in the solution, but she added that an alpha spectrometry measurement had been carried out to calculate the percentage of ²¹⁰Po at the separation time.

7.  Manufacturers’ presentation:

     Dave Wickenden (WMT)

• Dave started his talk by explaining the various reactions leading to ³H and ¹⁴C production and subsequent contamination. He then explained the requirements necessary for the analysis of ³H and ¹⁴C: these included flexible design, control of combustion, minimum potential for memory effects, efficiency, cost effectiveness, capacity for handling large samples, and rapid sample throughput.
• A detailed description of how the WMT/Carbolite furnace functioned was given. Dave pointed out that the original design was 10 years old, but is continuously being improved (e.g. by fitting a new exhaust manifold). The typical combustion protocol and the various types of material analysed (e.g. terrestrial, marine, constructional, decorative and novel materials) were discussed. The sample recovery is about 94 % ± 3 % and the typical detection limits are 0.02 Bq g^-1 for ¹⁴C and 0.04 Bq g^-1 for ³H.
• Dave explained that interferences with volatile ⁹⁹Tc, ¹⁰⁶Ru and ³⁵S was possible, but he added that the use of alkaline distillation/silver catalyst resolved the problem.
• Dave ended his talk by listing the elements supplied with a Carbolite furnace. The actual price for a Carbolite Type 12/38/850 Dual Zone Tube furnace is about £6k.

• Following the talk, a participant asked Dave if he tried using a platinum catalyst rather than copper. He replied that he had not tried this method, but he thinks that copper is a good, robust catalyst that can be regenerated easily if attacked by acid.

8.  Any Other Business

• Andy Pearce gave a brief talk on Nuclear Decay Data. NPL recommends the use of data from the Decay Data Evaluation Project (DDEP). Andy pointed out that the nuclear data library Jeff 3.1 had replaced Jeff 2.2.
• Arvic Harms briefly announced the NPL Environmental Radioactivity Proficiency Test Exercise for 2007. He described the different types of samples which would be available and gave the provisional timetable for the exercise.

Arzu Arinc
Secretary, LSUF