2^nd April 2003

National Physical Laboratory

Attendees:			Steven Judge	NPL (Chairman)
			Andrea Woodman	NPL (Secretary)
			Sarah Allinson	BNFL, Berkeley
			Matt Ashworth	DRPS, Alverstoke
			Bob Barber	Addenbrooke’s Hospital, Cambridge
			Andrew Boschier	Veterinary Labs Agency, Addlestone
			Keith Bradshaw	NIRAS, NNC Ltd, Warrington
			Darryl Campling	UKAEA, Abingdon
			Julian Dean	NPL
			Arvic Harms	NPL
			Robert Huggett	Zinsser Analytic
			Simon Jerome	NPL
			Lena Johansson	NPL
			Arthur Lally	Radiochemical Training Consultancy
			David Lambert	Veterinary Labs Agency, Addlestone
			John Mcnamara	British Energy, Hunterston B Power Station
			Kirsty Miller	UKAEA, Dounreay
			Bob Otlet	RCD-Lockinge, Wantage
			Andy Pearce	NPL
			Jock Thomson	PerkinElmer, Netherlands
			Mark Vincent	Amersham Plc, Cardiff
			Jill Walker	RCD-Lockinge, Wantage
			Anna Williams	Amersham Plc, Cardiff
			Mike Woods	NPL

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

1.1 Steven Judge welcomed members to the second meeting and introduced himself as the new LSUF Chairman.

1.2 Each member was asked to introduce him/herself and describe briefly the kind of work they do.

1.3 Steven gave an overview of what has been happening at NPL and the Centre for Acoustics and Ionising Radiation (CAIR) since the last meeting and he described the process of formulating the new 3 year programme which is due to start in October 2004. He invited anyone with ideas of what CAIR could usefully include in the new programme to contact him.

1.4 The minutes of the first meeting were accepted as a true record.

1.5 Actions

Action A1.1: Questionnaires. These will be handed out during the meeting.
Action A2.1: Members to complete questionnaire and send to Andrea Woodman, if not already done so.

Action A1.2: Report on saturation problems. Andy Pearce apologised for not being able to present anything at this meeting but would prepare something for a future meeting if still required.

Action A1.3: "Rapid Radiochemical Methods for Routine and Emergency Situations" conference proceedings. If anyone else would like a copy of these they should contact Simon Jerome, NPL.

Action A1.4: LSUF Web Page. The web page is up and running at http://www.npl.co.uk/lsuf/ and the minutes, terms of reference and presentations from the first meeting may be accessed from this page.

Action A1.5: E-mail discussion group. This is still required.
Action A2.2: Following advice from the IT department Andrea Woodman will arrange for a discussion group to be set up.

1.6 A comment was made that this meeting was not listed on the NPL Events web page.  It was however on the Ionising Radiation Diary page.
Action A2.3: Andrea Woodman to place the date of the next meeting, when known, on the Events page.

2. Invited talk: "Liquid Scintillation at NPL: Practical Applications" – Andy Pearce

2.1 Andy presented a talk on current work being done at NPL in the field of Liquid Scintillation Counting.

2.1.1 The talk described a project to determine the activity of P32 in the presence of longer lived impurities which were produced at the same time as the P32. Type A uncertainties of the order of 0.1 % were achieved.

2.1.2 A second project to determine the amount of P32 in neutron-activated thioacetamide discs was also described in which the P32 had to be assayed in a highly quenched solution, uncertainties of about 4 % were obtained for the activity concentration.

2.2 A suggestion was made following the presentation that Cherenkov might be an appropriate method for measuring P32.

3. Invited talk: "Organically Bound Tritium (OBT) Standard" – Arvic Harms

3.1 Arvic presented a talk describing the importance and difficulties involved in producing a standard of OBT which has a much higher accumulation factor in biota than HTO.

3.1.1 The chosen form for the OBT standard to be produced is thymidine as it is relevant to biological samples and is readily available in a tritiated form.

3.2 Discussion following the talk indicated that thymidine was an acceptable form however concerns were raised about its stability. Its most stable form changes by a few percent each year.

3.2.1 It was decided that effort should be made to characterise the instability as a function of time and to state transport and storage conditions as part of the certificate accompanying the standard.

3.2.2 A suggestion was made that a comparison exercise be made prior to the launch of the standard in order to compare the problems after transport and storage by the users.

4. Invited talk: "Sample preparation and Liquid Scintillation Counting" – Jock Thomson

4.1 Jock gave an in-depth talk explaining the composition of LSC cocktails and how they work. He also talked about the reasons for choosing between glass or plastic vials.

4.1.1 Jock then went on to describe the criteria for choosing the best cocktail for the users application.

4.1.2 He commented that once a vial is made up for counting, if the solution remains stable for 10 minutes then it will remain stable for months.

4.1.3 He urged users to contact manufacturers for advice when choosing cocktails in order to achieve the best results and reduce uncertainties.

5. Invited talk: "Quench and Quench curves" – Jock Thomson

5.1 Jock described the different types of quench and explained what a quench curve is and how it is used

5.1.1 Jock advised that quench standard curves use the full window however newer TriCarb counting systems can reset the data to optimised windows.

5.1.2 He also commented that there is sometimes a need to add quench in order to move the data onto the quench curve, otherwise extrapolation of the data to the quench curve can lead to bad uncertainties.

6. Invited talk: “Zinsser Analytic” – Robert Huggett

6.1 Robert presented a talk giving an overview of Zinsser Analytic and described some of the products they supply.

7. Invited talk: "Limits of detection and determination" – Simon Jerome

7.1 Simon presented a talk defining the limits of detection and determination and gave a number of formulae which have been devised by various parties to calculate these values. Discussion followed.

7.2 It was pointed out that the user must be certain the data has been accurately collected before starting to look at MDAs.

7.3 It was suggested that the standard deviation should be estimated then a coverage factor and that a Poisson distribution, which approximates to normal should be used rather than a Binomial.

7.4 Continuous method validation was said to be very important to monitor the consistency of standards and backgrounds.

7.5 It was considered important to establish a standard method in order to comply with UKAS, comparably bid for tenders and to accurately assess health physics problems. Therefore an international consensus is necessary provided the user community accept the outcome.
Action A2.4: Simon Jerome will raise this issue at the ICRM LLWG meeting to be held in October and report back at the next meeting.

8. Any Other Business

8.1 Alpha emitters are assumed to be 100 % efficient, concern was expressed that despite this intercomparisons show there to be a spread of a few percent between labs. Suggestions were to dilute the solution to avoid possible radiation damage to the scintillant and to use a Quantilus counter which gives less electrical noise. Comments were also made about the size of the vial i.e. scintillant volume affecting the efficiency.

8.1.1 A comment was made that when making alpha/beta separation measurements the alpha peak becomes a doublet after some time and no reason could be found for this. It was noted however that Teflon coated glass vials improve this situation.

8.2 The Low Level Radioactivity Measurements Techniques conference to be held in Vienna in October was advertised and more information can be obtained from Simon Jerome.

8.3 It was explained that minutes from this meeting would be e-mailed to members in future and put on the LSUF web page. However the minutes can still be sent by post on request.

8.4 All presentations made at this meeting will be put on the LSUF web page along with three further presentations supplied by Jock Thomson.

8.5 Any feedback on the format of this meeting would be welcomed along with suggestions for presentations at the next meeting.

9. Suggestions for next meeting which is likely to be held in April 2004

9.1 Update on OBT standard

9.2 Background quench curves for low level counting

9.3 Outcome of suggestion for international consensus for deriving limits of detection

9.4 Measurement of alpha emitters

9.5 Feedback from international conferences

10. Actions arising from the meeting

A2.1: Members to complete questionnaire and return to Andrea Woodman.

A2.2: Andrea Woodman to set up an e-mail discussion group.

A2.3: Andrea Woodman to put the date of the next meeting on the NPL Events web page.

A2.4. Simon Jerome to raise issue of limits of detection at the conference in Vienna

Andrea Woodman

Secretary, LSUF