Minutes of the First ASUF Meeting
14 April 1999
National Physical Laboratory
| Attendees: | David Anstee | Harwell Instruments (Canberra) | |
| Gary Bird | LGC | ||
| Keith Bradshaw | Southampton Oceanography Centre | ||
| Michaela Ciocanel | NPL | ||
| Martin Chandler | AWE Aldermaston | ||
| Matthew Curtis | Veterinary Laboratory Agency | ||
| Peter Danyluk | AWE Aldermaston | ||
| Jim Desmond | BNFL, Sellafield | ||
| Terry Gingell | DERA | ||
| George Ham | NRPB | ||
| Hilary Haywood | AWE Aldermaston | ||
| Peter Hodson | Veterinary Laboratory Agency | ||
| Janice Holding | DERA | ||
| Simon Jerome | NPL | ||
| Steven Judge | AEA Technology | ||
| Arthur Lally | RTC Ltd | ||
| Michael Loughlin | AWE Aldermaston | ||
| Ian McGregor | Rolls Royce | ||
| John Makepeace | NPL (Chairman) | ||
| Jon Martin | BNFL, Berkeley | ||
| Kelvin Reardon | LGC | ||
| Bill Rogerson | BNFL, Sellafield | ||
| Ann Ross | UKAEA, Dounreay | ||
| Martin Rushby | AWE Aldermaston | ||
| Bob Sharrock | URENCO | ||
| Robin Treadwell | AWE Aldermaston | ||
| Lee Vousden | DTI | ||
| Tony Ware | Environmental Energy Consultancy | ||
| Simon Woods | NPL (Secretary) | ||
| Alan Young | CEFAS |
1. Welcome and Chairman’s Opening Remarks
John Makepeace ( Section Head, Radioactivity Primary Standards, NPL) welcomed those present to the first meeting of the Alpha Spectrometry Users’ Forum (ASUF). The forum had been established in response to user requests for dedicated meetings where techniques and problems in a-spectrometry could be discussed. As such, this forum could be considered as a sister to the already established Gamma-Ray Spectrometry Users’ Forum (GSUF).
The forum is designed to facilitate the sharing of information between users. As such, the discussions at the ASUF meetings should be very much user led. NPL is funded to provide a Secretariat to the meetings (currently John Makepeace, Chairman, and Simon Woods, Secretary).
2. Draft Terms of Reference
The attached ASUF Terms of Reference were accepted nem com.
3. User Discussion
3.1 Limits of Detection
It was noted that the GSUF are also interested in this topic. There are 5 - 6 different formulations in use around the world which give different answers (e.g. ANSI (based on Currie), DIN (with an extra term)). Laboratories can set their own standards for accreditation purposes, but this leads to a confused situation.
Discussion ensued between the participants as to their own approaches, which were diverse and highlighted the subjectivity involved. The final consensus was that there is a need to standardise the approach to MDAs. A starting point would be to hold a survey of methods used, illustrated with reported detection limits for particular radionuclides. One of the NPL intercomparison exercises could be used for this purpose, and a decision then taken as how to progress.
Action 1.1: NPL (Simon Jerome/Julian Dean) to investigate incorporating a survey of MDA techniques into their intercomparison programme.
As an interim measure, laboratories should give the method used when reporting results or preparing data for tenders. It was however noted that problems often arose because the customer does not know what they are asking for.
Action 1.2: All to review their method of reporting MDAs
Those present associated with UKAS were asked if UKAS would make a recommendation. The answer was “No - UKAS compares principles not hard and fast facts”.
3.2 Sample Preparation
Discussions as to the benefits of “leaching” (using an acidic environment) versus those of “fusion” (using an alkaline environment) have been taking place for years. Leaching is the easier method, so laboratories tend to prefer it. Purists tend towards fusion whereby the whole sample is dissolved and is then chemically separated. However economics tend against this latter method e.g. provision of platinum dishes. Ideally, laboratories should try each method on each sample to see which gives the better results.
The forum noted that standards of measurement are not consistent; the ISO and BS committees have been disbanded. Whilst some people felt that there was a strong need for a British Standard on radiological methods, others felt it would be detrimental -one, specified, method may be precise, but is it accurate? An alternative way forward would be for UKAS to push for accredited laboratories rather than a standard method.
Poor understanding of the uncertainties involved is also a problem. A laboratory which underestimates its uncertainties may appear to be discrepant in any validating intercomparison when in fact they are not.
It was decided that, being a widespread problem, this topic should be tabled at the NPL Environmental Workshop with some of the bigger government customers, e.g. MAFF, EA, being invited to directly take part.
Action 1.3: NPL (Simon Jerome/Julian Dean) to include sample preparation in discussions at the Environmental Workshop.
3.3 Provision of Standards
Current availability of those required:
| 236Pu | High purity available from Nycomed-Amersham. | |
| 237Np | Being prepared by NPL. | |
| 242Pu | Available at required levels from both Nycomed-Amersham and NPL, though 241Pu contaminant levels were felt to be a problem. |
It was noted that unless there is co-operation at international levels, stocks of 242Pu will run out in the next few years. This matter should be raised at ICRM (PTB, May 2001).
Action 1.4: NPL (Simon Jerome) to raise 242Pu supply at the next ICRM Meeting (PTB, May 2001).
4. Invited talk
“The 1997 IAEA Intercomparison of Commercially Available PC-based Software for Alpha-particle Spectrometry” - Simon Woods, NPL
Four commercially available, PC-based analysis programs for alpha-particle spectrometry were compared using the 1997 IAEA test spectra. A systematic study of the analysis results was performed based on z-scores. The results indicate that the four programs leave room for substantial improvement.
Full details of this work may be found in Nucl. Instr. And Meth. A 428 (1999) 329 – 335 (2 papers).
5. Users Discussion Continued
5.1 Software Analysis
Most software packages are developed from gamma-ray spectrometry software and, as evinced by the preceding talk, is often not capable of doing what the user requires e.g. properly deconvoluting peaks. This is particularly evident in environmental alpha spectrometry. It was generally agreed that the manufacturers of the packages should talk to the users regarding what they want the systems to do.
It was agreed that the ASUF, through NPL, should arrange meetings with the main manufacturers (Harwell Instruments (Canberra) and EG&G), including their US personnel responsible for hardware and software development, and interested users.
Action 1.5: NPL (Simon Woods) to arrange discussion meetings between manufacturers and users.
5.2 Nuclear Data
It was noted that the alpha energies in the new Radiochemical Manual are based on those by Rytz, a reliable data source.
A desire to standardise on one data set was expressed. Simon Woods explained that this is not always feasible as the quality of data, even within a single data set, may vary greatly. Sometimes a better approach is to review all available data sources and make a qualified decision. Users should identify those nuclides which are causing problems and relay the information to Simon Woods.
Action 1.6: All to inform Simon Woods of problems encountered with decay data.
IAEA Technical Report Series no 261, “Decay Data of the Transactinium Nuclides”, is a good source of fully evaluated data to use.
5.3 Thorium Bioassay
Pu procedure - collect sample for 5 days, oxidise organics and separate with ion exchange.
However, with Th, how does one separate it from Pu as it doesn’t stay on the column, even though it should in theory. The answer is to use calcium phosphate rather than oxalate.
5.4 Prompt Air Sample Assay
A problem in Health Physics is the assay of Pu, U in the presence of Rn daughters, where, if the spectrum becomes degraded, peaks can overlap and interfere. It was suggested simply that the report should read “Pu and U in the presence of Rn daughters”.
5.5 Radiochemical Techniques
The question arose as to how to take samples. Sampling techniques tend to be unique to what is being sampled e.g. a pile of crushed concrete versus a field. It was felt that this should be governed by expertise rather than guidance.
6. Concluding Discussions
Generally the forum had highlighted the need for greater customer awareness. It was suggested that a document such as “Buying Analytical Services - How to Assess Quality” might be useful. Lee Vousden (NMSPU) commented that the VAM programme has been looking closely at this and would be the appropriate body to contact with requirements. Additionally, NPL will shortly be running a workshop on uncertainties which would be as appropriate for service purchasers as the users themselves.
The next ASUF would be arranged for approximately a year’s time, possibly to be consecutive with the NPL environmental intercomparison workshop. An invited talk by Simon Jerome (NPL)/Christian Hurtgen (SCK·CEN, Mol) was suggested.
Simon Woods
Secretary ASUF