Minutes of the 5th Meeting of the NMS Airborne Radioactivity Monitoring Users' Group
NPL – 8 November 2005
| Attendees: | |||
| Trevor Birkett | AWE | ||
| Derek Brazer | AWE | ||
| Chris Davies | URENCO | ||
| Julian Dean | NPL (Secretary) | ||
| Mike Dolan | AWE | ||
| James Forde-Johnston | Canberra-Harwell | ||
| Gavin Gillmore | Bradford University | ||
| James Grand | Berthold Technologies UK Ltd | ||
| Derek Hammond | NRPB | ||
| Victoria Howard | AMEC NNC Ltd | ||
| Michael Iwatschenko | Thermo Electron Corporation | ||
| Simon Jerome | NPL | ||
| Steven Judge | NPL (Chairman) | ||
| Alfred Klett | Berthold Technologies UK Ltd | ||
| Maria Marouli | NPL | ||
| Fred Martin | British Nuclear Group | ||
| Dick Morgan | Lab Impex Systems | ||
| Martin Oliver | Lab Impex Systems | ||
| Steve Phillips | MGP Instruments | ||
| Hilary Phillips | NPL | ||
| Stephen Phillips | Synodys | ||
| Max Pottinger | Thermo Electron Corporation | ||
| Gareth Price | AWE | ||
| Mark Rainbird | AWE | ||
| Chris Reeves | URENCO | ||
| Dale Robinson | British Nuclear Group | ||
| Debra Rook | British Nuclear Group | ||
| David Ryden | Canberra-Harwell | ||
| Bern Warr | GE Healthcare | ||
| Eliot Williams | UKAEA | ||
| John Simpson | RWE Nukem |
1. Chairman’s Welcome, Previous Minutes and Actions Arising
1.1 Steven Judge welcomed members and gave a short presentation by way of an introduction to the meeting. He then asked the members present to introduce themselves.
1.2 There were no corrections to be made to the previous minutes and they were agreed to be an accurate record of the 2004 meeting.
1.3 Previous Actions
A4.1: 'Secretary to change 210Pu to 210Po in section 4.4 of previous minutes.' This had been done.
A4.2: 'Anybody with information regarding self absorption factors to send them to Julian Dean.' Nothing had been received. The action still stands. Members should send any papers, reports or other documents to Julian Dean (Action 5.1).
A4.3: 'Any suggestions for a speaker on shrouded sampling probes to be given to Julian Dean.' None had been received. James Forde-Johnston said there was a possible speaker from the USA (Action 5.2).
A4.4: 'Julian Dean to set up a register of facilities.' A questionnaire was enclosed in the delegates' packs and delegates were asked to complete and return them to Julian Dean (Action 5.3).
A4.5: 'Members wishing to discuss uncertainties, or any other topic at a future meeting should contact Julian Dean.' Nothing had been received. The action still stands (Action 5.4).
A4.6: 'Secretary to complete list of frequently asked questions and answers with help from the rest of the group.' This had not been done. A request for members of a small working group was made and John Simpson and Peter Burgess volunteered to help(Action 5.5).
2. Invited talk: “The UK Tritium Users' Group and aspects of Tritium monitoring at AWE” – Gareth Price, AWE
2.1 The Tritium Users' Group (TUG) is a forum for the exchange of information on topics of common interest to the UK 'Tritium community'. It was proposed by AWE who suggested that a UK forum similar to the USA Tritium 'focus group' should be established. The first meeting of the TUG was held in June 2003 and further meetings have been held every few months since that time at various member sites. Some 18 organisations from across the UK nuclear industry are now represented at TUG meetings.
2.2 The scope of the TUG is wide, including all life-cycle stages of Tritium handling plant, Tritium metrology, waste disposal, training, and safety and regulatory matters.
2.3 AWE have both old and new Tritium processing facilities (the former now being in the decommissioning stage) as well as storage and test facilities. Tritium monitoring is carried out on stacks discharge, work areas and for health physics surveys (e.g. surface monitoring). A variety of detectors are used, such as flow-through ion chambers, gas proportional counters, liquid scintillation counters and particulate traps (for species such as Tritides). Gaseous emissions can be sampled for LSC using a commercial oxidiser/water-glycol trap collector. There are some maintenance issues with the gas PCs (used for surface monitoring) and LSC of smears is being considered as an alternative method. Stack discharges match observed peaks in monitoring data.
2.4 The use of different ion-chamber structures and materials was discussed. All suffer from Tritium hold-up. This is a particular problem with aluminium and also with steel but can be reduced by about an order of magnitude by gold plating. Much less hold-up is observed when 'virtual wall' chambers are used. These chambers are being evaluated and initial results are promising.
3. Invited talk: “Radon: Short- v long-term testing in homes in the UK” " - Gavin Gillmore, University of Bradford
3.1 Gavin described a recent DEFRA study which compared short- and long-term 222Rn monitoring methods for domestic measurements.
3.2 In each property under study, three types of integrating detectors were used ('track-etch', charcoal and electrets). At the same time, the 222Rn concentration was continuously monitored using a 'Rad 7' detector. The integrating detectors were deployed for measurement periods of one week, one month and three months. The EPA detector placement protocol was used, which specifies that there should be one detector in the main living area and another in a bedroom, and that specific limitations on their positioning must be observed. A rigorous Quality Control regime was employed to ensure detectors were protected from 222Rn before and after measurement, and that participating householders had complied with requirements.
3.3 Dwellings chosen (in Northampton) were checked for previous 222Rn measurements, local geology and 'householder suitability'. Types and ages of dwellings were recorded.
3.4 The results for charcoal detectors (plotted against data based on continuous monitoring) had a slope of 1.22 and it was suggested this may have been due to the use of too high an equilibrium factor by the manufacturers.
3.5 The relationship between indoor 222Rn levels and geology is complex. The British Geological Survey have produced Radon 'potential' maps for the UK.
3.6 'Seasonal Correction Factors' are used in the UK to convert the results of short-term measurements to the average concentration for a full year. It has been suggested that these factors may be geology dependent. The HPA use factors which assume that concentrations are high in winter and low in summer, but this pattern was not observed in the current study and it was suggested that new factors need to be derived for areas which clearly do not follow the model used by HPA.
3.7 The Radon Council takes the view that, when houses are being sold, properties in a given area should be tested at the time of conveyancing. Usually, 4 to 7 days is a sufficient measurement period, but longer measurements are required in borderline cases.
3.8 The majority of householders are curious about 222Rn but very few seek tests. Home Information Packs (HIPs) have increased demand for short-term measurements.
3.9 A principal conclusion of the project was that short-term measurement techniques for 222Rn in houses can be used effectively provided appropriate protocols are followed.
4. Invited talk: “NPL Good Practice Guide 82 - airborne radioactive particulate in the workplace” – Max Pottinger, Thermo Electron Corporation
4.1 Max gave a brief overview of the history and content of this guide, which is now almost complete. A consultation version of the guide had been available on the NPL website for about 6 weeks. A total of 31 copies had been requested and issued but no feedback had been received.
4.2 An appendix on reference sources has been prepared separately by David Ryden. The GPG Working Group had seen a draft and this would be discussed after the ARMUG meeting.
4.3 The aim was now to publish GPG 82 by February 2006. The appendix may be published separately.
5. Invited talk: “The development of a national standard for positron-in-air measurements” – Maria Marouli, NPL/Surrey University
5.1 Maria gave an introduction to this new NPL project, the objective of which is to develop a national standard, and a monitor calibration service, for measurements of positrons in gas.
5.2 Positron Emission Tomography (PET) is an imaging modality which is increasingly applied in medical diagnostics. It is based on the detection of annihilation quanta arising from a positron emitter artificially introduced into the body by injection or inhalation. Radionuclides commonly used in PET include 11C, 13N, 15O and18F, which have half-lives of less than 2 hours. They are produced using cyclotrons. There are 14 PET scanners installed in the UK at present with a further 8 planned for commissioning by 2010.
5.3 Sometimes the radionuclide is prepared in the gaseous phase. In this case, there is the possibility of accidental release of the gas to the environment, possibly as high as 4 GBq. It is a legal requirement that any such discharges be monitored, using a suitably calibrated instrument.
5.4 NPL maintains internal gas proportional counters for the standardisation of β-emitting gases (e.g. Tritium) and plans to model the response of these counters to positron emitters using Monte Carlo modelling (PENELOPE). The model will be validated and a positron-monitor calibration service will ultimately be set up, possibly involving a transfer instrument.
6. Invited talk: “Design, operation and calibration of a PET effluent stack monitor based on a coincidence technique” – Michael Iwatschenko, Thermo Electron Corporation
6.1 Thermo Electron have developed a coincidence technique for the measurement of positron-emitting gases in ducts and stacks. The technique uses large scintillation detectors positioned in-situ around a duct to monitor the annihilation photons emitted within the duct volume. The detectors can be positioned around existing ductwork and are linked to a PC with dedicated software.
6.2 The total coincidence count-rate is corrected for statistical coincidences and for the Compton scattering of natural-series γ-emitters and cosmic rays. Backgrounds are around 10 s-1 and Limits of Detection of < 1 kBq m-3 are achievable. Signal-to-noise ratios are 1 - 2 orders of magnitude lower than for integral γ measurements or positron measurements.
6.3 Calibration is carried out using point sources (e.g. 68Ge) positioned outside the duct volume. The calibration is independent of positron energy.
7. Invited talk: “Report on 2005 CIRMS conference” – Steven Judge, NPL
7.1 The Council on Ionising Radiation Measurement Standards (CIRMS) is an open non-profit-making organisation which advances and disseminates ionising radiation metrology. It holds an annual conference at the National Institute for Standards and Technology (NIST) in the USA which is attended by representatives of many stakeholder organisations including national measurement institutes.
7.2 Key trends identified at the 2005 meeting included (i) the increasing importance of uncertainty evaluation, (ii) advances in instrumentation resulting in more field use being possible, (iii) support for 'first responders' being a driver for developments in measurement technology, and (iv) 'personalised medicine' and 'clinical decision support' being major themes in pharmaceutical development.
7.3 Key topics covered included homeland security, surface contamination monitoring, medical applications of radionuclides and neutron metrology.
7.4 In the field of homeland security, measurements and treatments which would be required following a 'dirty-bomb' incident were covered. These could be improved by developments in areas such as biodosimetry, nuclear forensics and Monte Carlo modelling (e.g. to enhance portal-monitor resolution).
7.5 Recent developments in surface contamination metrology at NIST include investigations of P-factors, Monte Carlo simulations (giving activity per unit area) and the use of phosphor imagers to check source uniformity. Apparently, ISO8769 is ambiguous regarding uniformity of reference sources and ISO7503 is being re-written. The results of a short study of minimum detectable activities for different detectors and scanning speeds were presented.
7.6 In nuclear medicine, the use of radiopharmaceuticals and phophor imaging in pre-clinical studies is increasing, and new radioimmunotherapy products are being tested.
7.7 A novel approach to passive neutron dosimetry is being developed based on doped aluminium oxide crystals. Neutrons measurements are also being applied in the detection of explosives.
8. Any Other Business
8.1 A delegate asked if a Tritium monitoring Good Practice Guide was going to be produced. The chairman said that he would check to see if current NMS funding was available (see Action 5.6).
8.2 Another delegate asked when the minutes of this meeting would be available. The secretary said that the aim was to finalise the minutes by the end of the year.
8.3 The next meeting is likely to be held in November 2006 and members will be informed as soon as the date has been set.
9. Actions arising from this meeting
Action A5.1: Members should send any information on adsorption factors (e.g. papers, reports or other documents) to Julian Dean.
Action A5.2: Members should send any suggestions for a speaker on shrouded sampling probes to Julian Dean.
Action A5.3: Members are invited to complete the questionnaire enclosed in the delegates' packs and return to Julian Dean. Electronic copies will also be sent out.
Action A5.4: Members wishing to discuss uncertainties, or any other topic at a future meeting should contact Julian Dean.
Action A5.5: Secretary to complete list of frequently asked questions and answers with help from John Simpson and Peter Burgess.
Action A5.6: Chairman to check if NMS funding is available for a Tritium monitoring Good Practice Guide.
Julian Dean
Secretary, ARMUG
8th November 2005