Tuesday 25 September 2001
Scientific Museum, Bushy House, NPL

Agenda and Contents

Welcome and Introduction		David Thomas
Facilities and services of NPL Neutron Measurements Group		Vic Lewis
Current status of VIPER pulsed reactor and ASP accelerator at AWE, Aldermaston		Neville Bainbridge
The HMS Sultan neutron generator		Philip Beeley
The manganese bath for the absolute determination of emission rate of radionuclide neutron sources		Neil Roberts
SCK-CEN activities in the field of neutron dosimetry		Fillip Vanhavere
National Measurement System programme for Neutron Metrology		David Thomas
Application of passive neutron coincidence counting to measurement of nuclear materials		Anthony Towner, Adrian Tolchard
The determination of cosmic radiation fields in aircraft		Luke Hager
Aircrew dosimetry using TEPCs		Graeme Taylor
Calculated response characteristics for commonly used neutron survey meters		Rick Tanner
Preparation of RadFETs prior to neutron radiation		Chris Benson
Technology transfer, IRMF, good practice guides		Vic Lewis
Visits to the facilities of the NPL Neutron Metrology Group.
Members present and Apologies

Report of the Tenth Meeting of the Neutron Users' Club
National Physical Laboratory, Tuesday 25 September 2001

WELCOME AND INTRODUCTION

David Thomas welcomed the participants to NPL. The intention of these meetings was not only to disseminate information about research work undertaken at NPL but also for participants to talk about their facilities and programmes, and to discuss their problems and concerns.

The Neutron Users Club was run by NPL and funded under the National Measurement System (NMS). This was organised mainly in three-year programmes that were set up in response to the demands and views of the relevant UK user communities. The present NMS Ionising Radiation Metrology Programme began in October 1998. The next NMS Ionising Radiation Programme was due to start in a few days time on 1 October 2001. Some of the members present had contributed to its formulation.

FACILITIES and SERVICES of NPL NEUTRON METROLOGY GROUP Vic Lewis, NPL

Presentation (165 kB)

The NPL neutron facilities include two accelerators used for the production of monoenergetic neutron fields, a range of radionuclide neutron sources and a manganese sulphate bath facility for measuring radionuclide neutron source emission rates.

The 35 year old 3.5 MV Van de Graaff is used to produce neutron fields with energies from 8 keV to 6 MeV using various reactions, and from 13 to 20 MeV using the d+T reaction. All ISO-recommended neutron energies (from 27 keV to 19 MeV) can be obtained.  The neutron fluence rates produced using the ⁴⁵Sc(p,n) reaction are less than 8 cm^-2 s^-1 at 1 m (equivalent to 6 µSv hr^-1). Fields produced using the d+D reaction with neutron energies higher than 5 MeV are not clean due to competing reactions. Standards are restricted at lower energies to the range from 27 keV to 5.0 MeV, but the lowest energy for routine calibrations is 36 keV. In the higher energy range there are problems due to neutrons produced by reactions of the deuteron beam with contaminant oxygen, carbon and deposited deuterium in the tritium targets. The Van de Graaff is not used routinely for the d+T reaction.

The 150 kV SAMES accelerator is used to provide more intense neutron fields in the energy range from 14.1 to 14.7 MeV. Emission rates of up to 2 x 10⁹ s^-1 are produced, yielding fluence rates of about 2.5 x 10⁴ cm^-2 s^-1 at 1 m. It is intended to close down this facility because of the low demand for services and research, and to utilise the space for the replacement manganese bath facility when its building is demolished as part of the NPL rebuilding programme. The 14 MeV neutron  standards will be transferred to the ASP accelerator facility at AWE.

Thermal neutron fields are produced by moderating fast neutrons produced by the interaction of 2.8 MeV deuteron beams on two beryllium targets in a graphite pile. A servo-mechanism controlling the beam steering ensures a medium term stability of better than 0.4% for fluence rate. Thermal neutron fields of up to 3 x 10⁷ cm^-2s^-1 can be produced in a small central cavity. Routine irradiations and calibrations of radiation protection monitors are performed using a thermal beam extracted from the pile where fluence rates of up to 3.5 x 10⁴ cm^-2 s^-1 (1.1 mSv h^-1) are available. The fields are standardised using gold foil activation.

The UK standards are disseminated to customers through a range of measurement and irradiation services, all of which have been accredited by UKAS.

CURRENT STATUS of VIPER PULSED REACTOR and ASP ACCELERATOR at AWE, ALDERMASTON
Neville Bainbridge, AWE

VIPER Reactor

VIPER (Versatile Intermediate Pulsed Energy Reactor) was commissioned in 1967.  Its main purpose is to provide a hostile neutron environment in order to examine the response of materials in weapons components and military equipment.

The mechanism of VIPER allows the system to go super prompt critical by rapid insertion of additional fuel following the establishment of delayed critical conditions. A fast increase in neutron population ensues, inducing more fissions and so providing a corresponding rapid temperature increase. The reactor system has an inherent negative temperature coefficient of reactivity which, by virtue of fuel expansion and broader U-238 resonance capture cross-section (Doppler effect), arrests the neutron divergence bringing the system to sub-prompt critical conditions. The reactor then ejects part of its core to remove any further chain reaction in the system.

The peak power of the reactor is 20 GW which, although lasts for only a few hundred nanoseconds, is greater than the entire UK nuclear generating capacity.   The net effect of this prompt pulse is to produce about 3.5 x 10¹⁷ fissions and a burst of neutrons with a typical fission spectrum similar to that of a weapon burst.

VIPER thereby provides an assessment of material response within the warhead assembly under hostile conditions. These assessments have now started to include the effect of ageing in materials in the sense that response to neutron radiation may alter over the operational lifetime of the material. In addition, battlefield components also need to be demonstrated as radiation hardened. Such components include European Fighter & APC electronics, NBC detector equipment & other miscellaneous components. Criticality instrumentation is also tested on the reactor.

VIPER can also operate in steady state conditions up to a few hundred kW.  This allows neutron detector equipment to be tested at higher neutron intensities than normally encountered.

ASP Accelerator

The ASP (no known acronym) HV accelerator utilises the d+T reaction in order to produce 14 MeV neutrons.  A deuteron beam is accelerated to bombard a tritium-coated target to induce the fusion reaction, resulting in a near isotropic particle emission.  In addition, deuterium targets are employed, utilising the d+D reaction to produce 3 MeV neutrons.

Most work using the ASP facility is associated with neutron calibration for trigger mechanisms.  Also, neutron monitor overload tests are conveniently tested using the intense ASP field. It is intended that ASP will in the near future take over the national d+T neutron emission and fluence standards from NPL following the closure of the NPL SAMES accelerator.

ASP is also useful for evaluating component failures under accurate levels of neutron fluences (often used following any equipment failure in VIPER).  In addition, the facility is used for Fast Neutron Activation Analysis (FNAA) and studies of neutron transmission through special materials A useful by-product of the d+T reaction is the emission of an a-particle. This has allowed some unique studies to be performed on the penetration depth through selected materials. Alpha-particle emission is also used as a primary measurement of the neutron emission rate of the system.

The VIPER and ASP facilities are available for commercial work on all topics described above.

HMS SULTAN NEUTRON GENERATOR
Phil Beeley, DNST

Philip Beeley reported that, following the closure of the JASON reactor at Greenwich, DNST had been re-located from Greenwich to HMS Sultan, Gosport in October 1998. HMS Sultan is the naval school of air and marine engineering, providing support for requirements in the nuclear propulsion  programme. The department organised courses on nuclear reactor technology. One well-established course for MoD people involved in instrumentation was now open to the rest of the UK user community.

The number of students in the Department was increasing and involvement with other establishments was also increasing. The DNST had a collaboration with DSTL on personal dosimetry and was making increasing use of the NPL facilities for calibrations and research. There was a further collaboration with an American group on albedo dosimetry.

A G16 neutron generator from Sodern (France) had been installed and was being commissioned at HMS Sultan. This was a sealed tube unit producing 10⁸ neutron/s in continuous mode operation and 10¹¹ neutron/s in the pulsed mode, using the d+T reaction.The irradiation facilities at the new location also included a PANTAK X ray set and a ¹³⁷Cs/⁶⁰Co gamma-ray irradiation facility.

It has originally been intended to install the neutron generator in a graphite enclosure but this plan has been dropped and the reactor-grade graphite was now spare. A polyethylene cube had been used instead as the basis of the facility. This would provide a 14 MeV neutron beam, various irradiation fields and a facility for prompt-gamma activation analysis (in collaboration with Imperial College). The McBend code had been used to model the dose rates produced by the system. Further calculations using MCNP showed reasonable agreement with McBend (±5%) until boronated polyethylene was introduced.

The machine would be used for both teaching and research, and the programme would include activation analysis, fast and thermal neutron measurements, neutron instrumentation and time of flight measurements. It was expected that the cube would be finished in October; the generator would then be installed, tested and commissioned. It was hoped that authority to operate would be obtained in early 2002.

NPL MANGANESE BATH FACILITY Neil Roberts, NPL

Presentation (662 kB)

The NPL Manganese Sulphate Bath Facility provides the primary standard for total neutron emission rate. The output from sealed radionuclide neutron sources is measured and the calibrated sources are then used as transfer standards to calibrate dosemeters and the NPL long counters.  The Manganese Bath is therefore fundamental to the work of the NPL Neutron Metrology Group; most neutron measurements made at NPL are traceable to it.

The neutron source to be measured sits in an evacuated steel sphere at the centre of a 1 metre diameter tank containing manganese sulphate solution. The solution is activated by the reaction:

⁵⁵Mn + n ® ⁵⁶Mn ® ⁵⁶Fe + b ^- + g

The solution is pumped past two NaI detectors that count the g-photons from the decay of ⁵⁶Mn.  The half-life of ⁵⁶Mn is 2.579 hours and therefore the activity of the solution reaches saturation after about 24 hours.

At saturation the rate of activation equals the rate of decay, and, as activation is determined by the emission rate of the source, the count rate at saturation should enable the emission rate to be calculated. Only just over half of all neutrons are captured by manganese nuclei and  corrections have to be applied to compensate for those captured by other nuclei in the solution (hydrogen, oxygen, sulphur), by the source cavity sphere and source itself; and for those escaping from the boundaries of the tank.

 

Some of the corrections can be calculated only by modelling. Recently, the Monte Carlo code MCNP has been used in place of more basic in-house modelling codes.  It was found that the correction factors calculated with MCNP were higher by amounts ranging from 0.75% for a ²⁵²Cf X1 source to 1.23% for a ²⁴¹Am-Be X14 source.

There were two main reasons for the increase:

1. The in-house codes used an old set of cross-sections for the fast neutron reactions with oxygen and sulphur.  The ENDF/B-VI evaluation greatly increased the O(n,a) cross-section, particularly above 7 MeV.
2. The in-house codes underestimated the neutron fluence inside the source cavity, and did not include the source transfer rod in the calculations.

With satisfactory explanations for the discrepancies, and after successful validation results, MCNP modelling is now the preferred method.

The Manganese Bath can measure sources with emission rates from 2 x 10⁵ up to 2 x 10⁹ s^-1 which corresponds to 0.1 to 1000 µg ²⁵²Cf. The uncertainties range from 1.0% to 1.8% at the 2s level. The technique is absolute as the bath is calibrated using activated MnSO₄ solution that has been measured using the 4pb-g coincidence counting method. Smaller sources can be calibrated using the Moderator Detector that measures the source relative to one calibrated in the Bath.

In 2002, the Manganese Bath Facility will move into the building housing the Van de Graaff accelerator. The facility will occupy the area currently occupied by the SAMES accelerator facility. Operations such as source handling can be greatly improved as a result.  The facility is expected to be off-line for approximately 2 months in summer 2002 while the move takes place.

SCK-CEN ACTIVITIES in the FIELD of NEUTRON DOSIMETRY Fillip Vanhavere, SCK-CEN

Presentation (1.27 MB)

Fillip Vanhavere (Belgian Nuclear Research Centre) described the activities of SCK-CEN in the field of neutron dosimetry.

NATIONAL MEASUREMENT SYSTEM PROGRAMME David Thomas, NPL

Presentation (2.59 MB)

David Thomas described the various projects that will be undertaken by the CIRM Neutron Metrology Group (NMG) in the 2001-2004 National Measurement System (NMS) Ionising Radiation Programme. After describing the way in which the DTI NMS Policy Unit funds work at NPL, which is via three year contracts in the various metrology areas, he went through the neutron metrology projects within Theme 3 of the CIRM programme highlighting deliverables considered to be of most interest to neutron users.

Amongst the deliverables described in greater detail were:

• determination of typical ²⁵⁰Cf concentrations in ²⁵²Cf sources,
• provision of realistic neutron fields,
• validation of a simple technique for neutron measurements at hospital Linacs.

The third deliverable had strong links to work planned by the Belgian Nuclear Research Centre, SCK-CEN, as described in an earlier talk by Fillip Vanhavre. The realistic field deliverable, which would involve offering measurements on this facility to researchers in neutron dosimetry and spectrometry, had engendered considerable interest.

A description was given of the various international measurement comparisons currently underway. These exercises were important in ensuring that the standards offered at NPL are accurate and consistent with the standards of other national laboratories.

In addition to discussing the various deliverables, an overview was given of some of the services offered by the NMG and typical customers. Work on neutron spectrometry was being undertaken at NPL because of the importance of spectral data in understanding the extent of neutron dose measurement problems in workplace fields in the nuclear industry.

APPLICATION of PASSIVE NEUTRON COINCIDENCE COUNTING to MEASUREMENT of NUCLEAR MATERIALS
Adrian C Tolchard & Anthony C N Towner, AN Technology

The assay of nuclear materials is required for materials management and accountancy, criticality safety, process control, safeguards, security and waste management. Of the forms of nuclear decay, only neutrons can penetrate the walls of containers and high-density material. However, neutrons can be absorbed and moderated by soft (hydrogenous matrices). The even mass plutonium nuclides (²³⁸Pu, ²⁴⁰Pu and ²⁴²Pu) generate correlated neutrons from spontaneous fission events, random (single) neutrons from (a,n) reactions and a further source of correlated neutrons from induced fission events caused by primary neutrons.  Passive neutron coincidence counting discriminates correlated pairs of neutrons arising from the spontaneous fission of the even plutonium nuclides from random background (single) neutrons from (a,n) reactions and by so doing determines the mass of ²⁴⁰Pu_effective and, from the known isotopic content, the total plutonium mass.

In neutron counting of plutonium, thermal-neutron detectors (³He tubes embedded in a polyethylene moderator assembly) measure the neutron emissions from the Pu-bearing material. The resulting signals produced by the interaction of the neutrons with the gas consist of an event pulse train composed of time correlated neutrons from spontaneous fission and induced fission events and random (uncorrelated) neutrons from (a,n) reactions. 

In conventional passive neutron coincidence counting, the pulse train is input to a shift register, which counts the multiple neutron events during the characteristic neutron die-away time of the detector assembly when there is a high probability of detecting coincident events. This is achieved by opening an electronic gate with the first neutron pulse and counting subsequent pulses as neutron coincident events.  Following a delay of about 1 ms the shift register circuit samples the pulse train again and records any 'accidental' coincidences; the difference between these two registers is the coincidence count rate which is proportional to the plutonium spontaneous fission rate of the sample and hence to the ²⁴⁰Pu_effective mass.

In multiplicity counting, time correlation analysis determines the numbers of signal multiplets (the signal frequency distribution) in the detected neutron pulse train. From the moments of the neutron probability distribution it is possible to determine the number of neutron totals, the number of correlated neutron pairs and the number of correlated neutron triples in a pulse train.  The data analysis employs a point source model to perform a four-parameter analysis based on the frequency distribution to solve for:

1. spontaneous fission rate, F_s (and hence the ²⁴⁰Pu_effective mass),
2. detection probability, e,
3. (a,n) source term, S_a,
4. neutron multiplication, M

The following three analysis algorithms can be carried out:

1. FEM
   This algorithm determines F_s,e and M with an input of S_s or the Alpha ratio.
   
   For some types of samples of precisely known chemical composition (e.g. oxides and fluorides) this data may be obtained from the isotopic ratio.
2. FESA
   The analysis procedure determines F_s,e and S_awith an input of neutron multiplication, M.
3. SAFM
   In this algorithm the analysis determines the values of F_s, S_a and M with input of e, the detection probability.

Results were presented from in-plant measurements of plutonium oxide in 200 litre waste drums.  The data was analysed both in coincidence (two parameter) and multiplicity (four parameter) mode, the latter employing the FEM, FESA & SAFM algorithms described above.

DETERMINATION OF COSMIC RADIATION FIELDS IN AIRCRAFT
Luke Hager, NRPB

A recent EU safety directive made airlines responsible for monitoring radiation doses received by aircrew. NRPB had developed a passive dosimetry package for measuring cosmic radiation in aircraft. It comprised a 30 cm plastic box containing thirty six PADC neutron dosemeters at the centre surrounded by thirty TLD dosemeters. The former measured high LET radiation and the latter the low LET radiation. Two EPDs were also included to check on the number and duration of the flights. The package was put on board planes that flew at a cruising altitude of about 35,000 feet. At this altitude the cosmic radiation was about 50:50 protons and neutrons, the latter being produced by the interaction of the primary protons with the atmosphere.

The high-energy neutron response was characterised using facilities in Sweden, Belgium and Germany. Calibration was also carried out at CERN. Reasonable consistency (± 10%) had been achieved between the measurements carried out at the different centres. Good agreement had been obtained between the calculated and measured responses.

Measurements had been carried out at various latitudes. Normally, several return flights on the same route were necessary to obtain the required accuracy. The performance was satisfactory and further work was in progress.

AIRCRAFT DOSIMETRY USING TEPCs Graeme Taylor, NPL

Presentation (71 KB)

It is a surprising fact that the cosmic radiation doses received by aircrew are on a par with the radiation doses received by workers in the nuclear industry. Crew members flying predominantly long-haul flights may even approach an annual dose of 6 mSv. It is for this reason that a recent EU directive now requires airlines to assess the exposure their employees. Clearly the most cost-effective method of meeting this requirement is to calculate the route doses and there are several codes currently available that claim to do this. There are, however, significant differences between these codes, both in terms of how they work out the doses and in the results that they produce. Such discrepancies can be investigated by comparing calculations to measurements.

Although many dose measurements have been made on aircraft by a number of groups with a variety of instruments, comparing data from different flights is to some extent hampered by uncertainties in the response of individual instruments to cosmic radiation fields. Such problems can be alleviated by flying different systems on the same flights, enabling common points of reference to be made. Another solution is to perform as many flights as possible with the same instrument. This has the advantage of generating a self-consistent set of results that, regardless of uncertainties in calibration or correction factors, can be used to investigate the relative performance of software codes in their treatment of dose rate variations with such parameters as altitude, latitude and solar activity.

A collaborative partnership, between NPL, the Civil Aviation Authority, Virgin Atlantic Airways and the Mullard Space Science Laboratory has been engaged in just such a project for the past two years. To date measurements have been performed on over 100 flights to destinations in the USA, South Africa, mainland Europe and the Far East. The instrument used for these measurements is a tissue equivalent proportional counter, or TEPC. As its name suggests, the TEPC is made from tissue equivalent materials, resulting in it having a similar atomic composition to soft tissue. Consequently radiation interacts with the TEPC much as it would with living tissue, generating the same types of recoil particles with similar energy distributions. Furthermore, the sensitive volume of the TEPC simulates a microscopic volume of tissue smaller than a single cell, which means that the dose deposited by a recoil particle in the counter can be related to the LET of that particle. Given the relationship between radiation quality and LET, the TEPC can provide both a measure of the absorbed dose rate in tissue for a radiation field and a measure of that field’s radiation quality. In other words, it is capable of measuring the dose equivalent rate of that radiation field.

Given its design, it is not surprising that the TEPC has a good ambient dose equivalent response over a large range of neutron energies, from a few hundred keV up to 1000 MeV and beyond, making it an excellent instrument for cosmic ray dosimetry.

The collaborative project still has roughly two years to run, but already enough data has been gathered to show differences in the radiation quality between different routes (for example the London – Johannesburg route has a lower quality factor than any of the routes from London to northern hemisphere destinations). In addition, comparisons between measurements and the route dose predictions of the code CARI-6 show a discrepancy of roughly 20%, with the measurements being higher; the discrepancy also appears to be larger at higher latitudes. Conversely, preliminary tests carried out for a handful of flights indicate that the code EPCARD agrees with the measurements, although more work is required.

This project should help to shed light on the relative merits and limitations of available route dose software by providing a large, self-consistent database of measurements spanning a large range of flight altitudes, latitudes and solar activities. Given that air crew are now acknowledged to be exposed to radiation levels on a par with those seen in the nuclear industry, any information that reduces the uncertainty in their dose assessments is of benefit.

CALCULATED RESPONSE CHARACTERISTICS FOR COMMONLY USED NEUTRON SURVEY METERS Rick Tanner, NRPB

Presentation (368 KB)

Details of this presentation may be found in the above file.

PREPARATION of RadFETs PRIOR to USE with RADIATION

Chris Benson, University of Lancaster

Chris Benson described the structure and mechanism of RadFETs and the effect of incident radiation.  These were finding increasing use in medical dosimetry. The central element is a small (1 mm square) silicon diode with various leads attached. In order to assess the effect of neutron radiation it was necessary to look at the materials were present besides silicon. These include aluminium, oxygen and Kovar (nickel, cobalt, iron, manganese) in the substrates and tungsten, nickel and gold in the pins.

A number of problems with conventional semi-conductor packaging were identified. Non-standard microelectronics packaging was investigated in order to package the RadFETs differently. One of the main problems regarding the use of RadFETs with neutron radiation was find a way to manage without nickel in the connections. A more robust design was successfully achieved. This would be tested using the Consort Reactor.

TECHNOLOGY TRANSFER ACTIVITIES in the NMS PROGRAMME Vic Lewis, NPL

Presentation (146 KB)

The NMS Programme in Ionising Radiation Metrology has a wide-ranging technology transfer theme that supports user clubs and fora, organises national measurement comparisons, provides guidance documentation and runs workshops.

Eight user clubs are supported, with membership is open to all interested parties (details on the NPL website). These addressed specific areas except for the more general Ionising Radiations Metrology Forum. This meets bi-annually in May and November. Membership is free and open to any representatives of organisations involved in the metrology of ionising radiation and radioactivity. Details of IRMF, including the IRMF Catalogue of Calibration and Measurement Services available in the UK for Radiation Protection Instrumentation, could be found on the NPL Website.

One important IRMF activity is the organisation of comparisons of gamma-radiation monitoring, neutron area monitoring and surface contamination monitoring. The third neutron monitoring comparison had just begun.

NPL Measurement Good Practice Guides are produced by experts (NPL and others) in the subject concerned. They aim to encourage good practice and sometimes to act as codes of practice. Around forty have been or are being produced. Two have been produced in the IR area; draft versions of two more have been distributed as part of the consultation process and a further one is being written. These are written under the auspices of the IRMF except for one on Radiometric NDA. This covers a range of neutron detection techniques and is co-funded by industry and the regulator (HSE).

The Neutron User Club holds annual meetings at the end of September for two of the three years of each NMS programme. For the third year a workshop concentrating on a specific area would be held instead at the same time of year.

LABORATORY VISITS

Ten attendees visited the accelerator and irradiation facilities in the Chadwick Building (Building 47) after the meeting.

Members present

Philip Beeley		HMS Sultan, DNST, Gosport
Neville Bainbridge		AWE, Aldermaston
Jen Barnes		Saint-Gobain Crystals & Detectors UK Ltd, Reading
Chris Benson		University of Lancaster
Graeme Birch		SGS (Plastics), Wembley
Andy Corns		DSTL, Alverstoke
Bill Croydon		Siemens, Poole
Ian Dalton		BAE System Marine Ltd, Barrow-in-Furness
Dan Greenwood		HMS Sultan, DNST, Gosport
Luke Hager		National Radiological Protection Board, Chilton
Karl Hughes		BNFL, Sellafield
Shaun Hughes		AWE, Aldermaston
Bernard Hynes		AWE, Aldermaston
Richard Jenkins		BAE System Marine Ltd, Barrow-in-Furness
Malcolm Joyce		University of Lancaster
David Kilburn		BNFL, Sellafield
Scott Kinnear		BNFL, Sellafield
David Kestell		MRC, Harwell
David Locke		Southern Scientific Ltd, Worthing
Trevor Lowe		BAE System Marine Ltd, Barrow-in-Furness
Shaun Marriott		BAE System Marine Ltd, Barrow-in-Furness
Alex Pereira		Reeves Technologies, Loughborough
Robert Price		Clatterbridge Centre for Oncology, Merseyside
Roger Samworth		Reeves Technologies, Loughborough
Jon Silvie		BAE System Marine Ltd, Barrow-in-Furness
David Stevens		MRC, Harwell
Roger   Stokes		DSTL, Alverstoke
Rick Tanner		National Radiological Protection Board, Chilton
Adrian Tolchard		AN Technology, Wallingford
Anthony Towner		AN Technology,
Filip Vanhavere		SCK-CEN,
Andrew Williams		HMS Sultan, DNST, Gosport

Apologies had been received from:

Steve Allen		AWE, Aldermaston
M Armishaw		AEA Technology, Harwell
David Bartlett		National Radiological Protection Board, Chilton
Reg Bosley		AEA Technology, Harwell
Mark Brooker		AWE, Aldermaston
John Caunt		John Caunt Scientific, Oxford
Tim Daniels		National Radiological Protection Board, Chilton
John Harvey		Consultant
Bob Mason		Sherwood Nutec Consultancy, West Wickham
S Parry		Imperial College, Ascot
Ian Pearson		AEA Technology, Harwell
Tim Wilson		QINETIQ - Aquila
Lee Talbot		BNFL, Bradwell-on-Sea