5^th May 2004

National Physical Laboratory

Attendees:			Steven Judge	NPL (Chairman)
			Andrea Woodman	NPL (Secretary)
			Arzu Arinc	NPL
			Andrew Boschier	Veterinary Labs Agency
			Keith Bradshaw	NNC
			Darryl Campling	UKAEA
			Julian Dean	NPL
			Chris Gilligan	NPL
			Jason Goodwill	UKAEA
			Arvic Harms	NPL
			Nicol Henderson	National Diagnostics
			Robert Huggett	Zinsser Analytic
			Joseph Fatukasi	NPL
			David Lambert	Veterinary Labs Agency
			Olivia Marsden	NNC
			Moira Mason	British Energy
			John Mcnamara	British Energy
			Bob Russell	National Diagnostics
			Franz Schönhofer	Retired
			Jill Walker	RCD-Lockinge, Wantage
			Anna Williams	Amersham Plc, Cardiff
			Mike Woods	NPL
Apologies:			Matt Ashworth	DRPS
			Simon Jerome	NPL
			Lena Johansson	NPL
			Andy Pearce	NPL
			Larraine Young	NRPB

 

1. Chairman’s Welcome, Previous Minutes and Actions Arising

• Steven Judge welcomed members to the third meeting and then allowed each delegate to introduce themselves and describe briefly the kind of work they do.
• The minutes of the first meeting were accepted as a true record.
• Actions       A2.1: Questionnaires. Andrea Woodman reported that a few questionnaires had been returned, the main issues of which being that members wish to have an e-mail discussion group and are keen that a set of recommendations be produced on Minimum Detectable Activities.

A2.2: E-mail discussion group. Andrea Woodman explained that NPL do not currently have an e-mail discussion facility but that if members wish to start a discussion they should e-mail Andrea who will then forward it to the rest of the group.

A2.3: NPL Events Web page. Andrea Woodman confirmed that the date of this meeting had been put on the NPL Events web page (www.npl.co.uk/events).

A2.4: Limits of Detection. Steven Judge confirmed that this issue had been raised at the Low Level Radioactivity Measurements Techniques conference in Vienna recently and that a Good Practice Guide on MDAs has been proposed as part of the next NPL NMSPU programme.

2. Invited talk: "Update on Organically Bound Tritium Standard Project" – Arvic Harms

• Arvic began by summarising the presentation he gave in 2003 about the need for an organically bound tritium (OBT) standard and why it was decided that the OBT would be in the form of thymidine.
• Arvic went on to describe how the OBT was standardised, namely by Liquid Scintillation Counting using the standard addition method.
• The standard addition method assumed that no additional quenching occurred due to the addition of standardised tritiated water and that the counting efficiency for tritiated water is identical to that of tritiated thymidine. Studies indicated that these were viable assumptions.
• The separation of the OBT from the HTO by use of a desiccant was described and the final results displayed. The overall uncertainty in the standardisation was 1.6 %.
• The stability of the OBT was investigated and the self decomposition rate was found to be about 0.1 % per month when kept in storage at 4^oC.
• Finally it was announced that the OBT standard is made to order and that anyone interested should contact Arvic via radioactivity@npl.co.uk .
• Following the talk, Arvic was asked whether any preservatives were used. Arvic said that 10 % ethanol, as suggested by Amersham literature, was added to keep self decomposition down. The comment was made that perhaps a less volatile preservative could be found.
• The 1 % uncertainty in chemical form needed clarification and Arvic explained that this came from the separation of OBT from HTO. It was suggested that uncertainties be clearly detailed in certificates.
• The definition of OBT was discussed as it was uncertain whether tritium has to be bound to carbon to be classed as OBT rather than being labile. No conclusion was reached except to say that the Environment Agency definition does not specifically say it must be bound to carbon.

3. Invited talk: "Assay of Alpha Emitters by LSC" – Franz Schönhofer

• Franz was invited to give a talk as an expert in the field of liquid scintillation counting. Now retired, he has been involved in surveillance of nuclear installations in Austria, determining the environmental consequences of the Chernobyl incident and developing fast, simple but precise LSC measurement methods for ³H, ¹⁴C, ⁹⁰Sr, ²²²Rn, ²²⁶Ra, ²²⁸Ra etc.
• In his talk he described the use of liquid scintillation counting for a emitters and compared the spectra with those from b emitters. Much higher resolution is obtained with a emitters and they are 100 % efficient as any quench effect is negligible.
• Franz explained his method of counting ²²²Rn both in water and in air. For ²²²Rn in water, the solution is simply mixed with the cocktail and shaken, left for a few hours to reach equilibrium and then counted in a Quantulus. He found that Teflon coated vials were best. ²²²Rn in air is measured by use of charcoal which will absorb Radon when exposed to it. The charcoal is placed in a vial and after exposure the cocktail is added and left for the radon to diffuse out into the scintillant. The vial is then measured by LSC.
• He showed data describing measurements carried out across Austria for Radon and found that Radon levels are generally higher in buildings on the ground floor and during the colder seasons.
• Franz explained his involvement in the EU directive on the quality of drinking water. Water is passed through a filter which is then put into a vial with the LS cocktail and counted after an hour. He talked about the use of Rad disks, precipitation and the ingrowth of ²²²Rn.
• Franz commented that if anyone wishes to discuss LSC measurements with him he is very happy for them to contact him via franz.schoenhofer@chello.at.
• Following the talk there was a question about the efficiency of a emitters when there is also a g present, there was uncertainty about the detection of the g suppressing the a detection however measurements had never been found to be less than 100 %. Franz said that he too had always found 100 % efficiency and could not explain this. Steven Judge suggested we invite the instrument manufacturer to a future meeting. Action A3.1: Andrea Woodman and Steven Judge to contact Quantulus.
• Mike Woods and Julian Dean described a Radon measurement study carried out by NPL and comparisons between the track etch method (which can take 3 months) and the charcoal method (which takes only 1 week to get the result). It was found that preference in method depended on the laboratory doing the measurements and that quality of measurement depended largely on the quality of the laboratory involved. It was also reported that Northampton University has since carried out an in-depth analysis of weekly versus three monthly radon measurements and that a DEFRA report on the work is available (report no: DEFRA/RAS/03.006).

4. Invited talk: "⁹⁰Sr in Radioecology" – Franz Schönhofer

• Franz explained that ⁹⁰Sr is a pure b emitter with a 30 year half-life and is less radiotoxic than ²¹⁰Pb but comparable with ¹³¹I. The importance in measuring the ⁹⁰Sr in the environment is due to its chemical form. It is an earth alkali metal and will act in a similar way to calcium. This means that if ingested by the body it will be treated as calcium and therefore taken into the bone where it remains for a very long time. The daughter, ⁹⁰Y, has a much shorter half-life of 64 hours but has a high b end-point energy of 2.3 MeV which can affect the bone marrow.
• Both nuclides are pure b emitters and therefore relatively easy to measure. Franz compared conventional liquid scintillation counting with Cherenkov counting where there is an advantage of there being no interference from low energy nuclides such as ³H and ¹⁴C.
• Franz displayed graphs of the ⁹⁰Sr/g calcium level measured in Swiss milk, milk teeth and human vertebrae over a number of decades. The nuclear activity of the 1950’s and 1960’s was evident and there was a slight peak due to the Chernobyl accident. The levels are now gradually decreasing.
• Franz also described a project he was involved in to study ⁹⁰Sr levels in red deer antlers across Austria in order to indicate the impact of the Chernobyl incident on the environment and give an estimate of food contamination across the country over time. The antlers used were those collected by hunters and as such were well catalogued for date and location. As the deer sheds its antlers each year a lot of data could be obtained. The Quantulus counter was used and as it has a low background only small samples of 1g were needed from each antler. The results showed that higher precipitation did not necessarily mean higher ⁹⁰Sr levels. The factors which did influence the contamination included the soil pH, the concentration of calcium and stable strontium in the soil and how soon the ⁹⁰Sr gets into the animals through it’s diet i.e. directly when the ⁹⁰Sr is still on the surface or after time when the ⁹⁰Sr has been taken up through the roots.
• Following the talk, Franz was asked whether he preferred the Cherenkov or LS cocktail technique of measurement. He said in general the LS cocktail method was preferred although in the case of a nuclear accident the Cherenkov method may be more appropriate when the problem of interference from other nuclides would be greater.
• The comment was also made that strontium specific ion exchange columns are very good and give a high yield.

5. Invited talk: "National Diagnostics" – Bob Russell

• Bob described the history of National Diagnostics and their commitment to producing safe, biodegradable cocktails. He described the properties of their new cocktail for flow liquid scintillation counting along with some of their other products.
• It was also mentioned that the National Diagnostics catalogue includes a large section on the LSC technique and could prove very useful to technicians.
• Following the talk Bob was asked about the criteria for a cocktail to be considered biodegradable. Bob replied that 70 % disappears over a period of 7 days when fed to microbes. He did comment however that acceptance of biodegradable scintillants varies greatly with water boards across the UK.
• He was also asked about the compatibility of their cocktails with nuclides other than ³H and ¹⁴C. Generally if it will go into a solution and emulsify there should not be any problems.

6. Invited talk: "A Study of Options for LSC Waste Management" – Julian Dean

• Julian described a project which he is currently undertaking at NPL to examine disposal options for LS waste and to decide on the most appropriate for the radioactivity group at NPL.
• LSC waste at NPL is significant and currently disposal is very costly. He looked at the composition of the waste, the processing options such as use of demulsifiers or oxidation of organic compound, solidification and ion exchange and then the various routes it could take (such as being sent to a disposal company, being discharged directly as liquid waste or being consigned to Drigg as solid waste).
• The project is still in progress as a satisfactory method has yet to be found and it is likely that other processing options will be considered.
• One suggestion after the talk was to consider bioremediation and have a sewage tank on site- some Water Boards do allow organic waste into sewage so it could be feasible. There was then some discussion about the definition of organic solvent and the reluctance of local water boards to accept biodegradable scintillants.

7. Any Other Business

• Franz Schönhofer announced that he is on the board for the next LSC conference and will let those interested have information when it is available. It was suggested that a link to the information be put on the website. Action A3.2: Franz to let Andrea Woodman have relevant information.
• Anna Williams talked about problems she has had with Perkin Elmer regarding maintenance of instruments. Others agreed that they too had experienced problems with the service from Perkin Elmer. It was suggested that a letter of complaint be written to the company on behalf of the LS user’s community and also to invite a representative to a future meeting. There were suggestions that in the mean time users should try Lablogic or Edenglen for help with instruments. Action A3.3: Delegates to let Andrea Woodman have information about their problems with Perkin Elmer. Action A3.4: Andrea Woodman and Steven Judge to write to Perkin Elmer.
• Steven Judge presented the current status of the formulation of the next Ionising Radiation NMSPU programme at NPL. He announced that there were only a few days left for users to comment on the proposed projects.

8. Suggestions for next meeting which is likely to be held in April 2005

• Assay of waste water
• Nuclear Data
• Quantulus representative to discuss DOT software and a algorithms, the anti-coincidence system and software validation
• Total a,b counting
• Extended SIR system and MRA equivalence
• Analysis of oil for H3, C14
• LSC for surface contamination

9. Actions arising from the meeting

A3.1: Andrea Woodman and Steven Judge to contact Quantulus.

A3.2: Franz to let Andrea Woodman have relevant information about next LSC conference.

A3.3: Delegates to let Andrea Woodman have information about their problems with Perkin Elmer.

A3.4: Andrea Woodman and Steven Judge to write to Perkin Elmer.

Andrea Woodman

Secretary, LSUF