Combined Alpha (4^th) and Gamma-Ray (6^th) Spectrometry Users’ Forum

Globe Room, Bushy House, NPL – 3 February 2004

Participants:		Ian Adsley	RWE Nukem
		Arzu Arinc	NPL
		Lois Armstrong	BNFL
		Nasser Baghini	Imperial College Reactor Centre
		Keith Bradshaw	NNC Ltd
		Sean Collins	NPL
		Chris Cooper	DRPS
		Matthew Curtis	VLA
		Lisa Davies	Capenhurst Urenco
		Tony Dell	VLA
		Tony Dix	BNFL
		Jim Fitzgerald	J F Computing
		Mike Froggatt	BNFL
		Lars-Erik De Geer	CTBTO
		Chris Gilligan	NPL
		Elizabeth Goadsby	DRPS
		George Ham	NRPB
		Nick Harmon	RWE NUKEM
		Arvic Harms	NPL
		Trevor Hatt	ORTEC
		Hilary Hayward	AWE
		John Hemmingway	University of Liverpool
		Peter Hodson	VLA
		Ed Holden	ORTEC
		Simon Jerome	NPL
		Lena Johansson	NPL
		Steven Judge	NPL (Chairman)
		Richard Lukey	VLA
		Desmond McMahon	NPL
		John McQuirk	BNFL
		Andy Pearce	NPL
		Louise Rayton	BNFL
		Bill Rogerson	BNFL
		Martin Rushby	AWE
		Ben Sanderson	BNFL
		Sarah Sheperd	Capenhurst Urenco
		Matthew Simpson	DSTL
		John Simpson	RWE NUKEM
		Robin Treadwell	AWE
		Pam Thompson	AWE
		Tim Twomey	ORTEC
		Stephanie Vallet	Canberra Harwell Ltd
		Sylvie Ward	Canberra Harwell Ltd
		Jon Wardle	AWE
		Nigel Watkins	NPL
		Denise Woods	NPL (Secretary)
		Mike Woods	IRMC Ltd
Apologies:		Chris Dale	NNC Ltd
		Will Evans	University Hospital Wales
		Phil Hurst	Nuclear Electric
		Elizabeth Jones	University Hospital Of Wales
		Bob Major	NNC Ltd
		Ian McGregor	Rolls Royce
		John McNamara	UKAEA
		Susan Parry	Imperial College Reactor Centre
		Paul Rabaiotti	University Hospital of Wales
		Ann Ross	UKAEA
		Graham Shephard	Devonport Royal Dockyard Ltd
		Tony Ware	Consultant
		Steve Waters	IRS Ltd
		David Weaver	University of Birmingham
		Dave Wickenden	AEA Technology

1. Welcome and Apologies for Absence

1.1 Steven Judge welcomed everyone to the forum. He paid tribute to Simon Woods and his work in the field of Nuclear Spectrometry and how, over the years he had published many papers. He said that Simon would be missed by many people, not just as a scientist but also as a friend.

1.2 Apologies for absence were given as above.

2. Approval of Minutes

1^st NSUF 3 December 2002
Approved nem com

3. Matters Arising

NSUF Action 1.1: NPL to report back on how the various guides were implemented during the installation of their new gamma spectrometry software.

This meeting.

4. User topics

4. 1 United Kingdom Nuclear Science Forum (UKNSF)
Desmond McMahon (NPL)

• The UKNSF is a national committee covering the measurement and evaluation of nuclear data such as decay data, fission yields and cross sections.
• The committee advises the UK representatives to the NEA Databank on the UK’s needs in this field and it also co-ordinates data evaluation and measurement work.
• Membership is open to all users, measurers and evaluators of nuclear data.
• The UKNSF is organised by NPL on behalf of the HSE.
• Further information is available on www.npl.co.uk/uknsf and a summary of the talk will be made available on the NSUF website

4.2 An update on TECDOC 619
Mike Woods (IRMC)

• An evaluation of half lives has been completed at NPL and published as an NPL report (CAIR 8). It can be downloaded from the NPL website (go to the publications section of www.npl.co.uk and search for ‘CAIR 8’).
• The values shown in CAIR 8 will be used in the revised version of TECDOC619, to be published by the IAEA Nuclear Data Section.
• Desmond MacMahon reported that work on the photon emission probabilities is well advanced and the document is expected to be published within months.
• Mike Woods thanked Sean Collins (NPL) for his valuable contribution to the work, collating and reviewing the published articles.
• Tim Twomey commented that if the half-life were 9 hours he could see why it is needed to be very accurate but not asked why was it necessary if the half-life is 1600 years? Mike Woods replied that the accuracy determines how long it is necessary before revalidating the source; normally it would be expected to have a shelf life of 15 years.
• Keith Bradshaw commented that very limited data are available for some of the obscure nuclides.
• Keith added that there had been discrepancies reported in the decay scheme of ^234mPa. Desmond McMahon replied that Alan Nichols (currently Head of the IAEA Nuclear Data Section) had carried out an evaluation of decay data for this radionuclide and the report had resolved the discrepancy.
• Keith Bradshaw raised the issue of the nuclear data given in the Radiochemical Manual (ed. Geoff Longworth, AEA Technology plc 1998, ISBN 0-7058-1768-7) – the interpretation of the uncertainties in the table was not clear. Mike Woods replied that the explanation of the uncertainties is given in the body of the text.
• Steven Judge asked the attendees of the Forum what uncertainties in nuclear data were required by users. The general response was that an uncertainty of better than 10% was needed for field measurements but, for instrument calibration, people were looking for an uncertainty better than 5%.
• Steven Judge added that there are links to nuclear data libraries on www.npl.co.uk/uknsf he urged everyone to always use uncertainties from recognised evaluations.

4.3 Correlated Uncertainties in Gamma Spectrometry
Andy Pearce (NPL)

• This presentation concerned the issue of taking into account correlations in gamma-ray spectrometry. A copy of the talk will be made available on the website.

5 The UKAEA Beach Monitoring Steering Group
Mike Woods (IRMC) on behalf of Joe Toole (UKAEA)

• A summary of this talk concerning the steps being taken to detect radioactive particles on the beach near Dounreay is available on the NSUF website.
• Mike added that everything relating to the beach monitoring was in the public domain and available on the UKAEA website if people wanted to look more into the matter.
• The aim of the monitoring was to detect particles up to a depth of 10cm. Desmond McMahon commented that 10 cm didn’t seem very deep to which Mike replied that this figure had been decided by SEPA after a risk assessment had been made. Ian Adsley added that they were always looking to make improvements. Desmond commented that there had been in the past some measurements with ¹³⁷Cs which demonstrated that it was possible to detect particles at a depth of 1 metre. Mike replied that one importanThe aim of the monitoring was to detect particles up to a depth of 10cm. Desmond McMahon commented that 10
• The detection efficiency of the instruments used have been calculated for both germanium and sodium iodide detectors as part of an EC contract and the reference to this work should be on the website.
• Ian Adsley commented that there was 1 particle found for every 10 million readings.
• Trevor Hatt asked what volume of sand needs to be removed to which Ian replied that once a particle had been found a tube would go down 15cm and this volume would be removed. Following the removal, their Health Physics staff would then use a monitor to confirm that the process had been successful.

6. Input to the NPL Programme Formulation process
Steven Judge (NPL)

• NPL is funded by the DTI to support the technical infrastructure to ensure that measurements of radioactivity are accurate and consistent. This presentation (copy on the website) asked for feedback from participants to guide NPL’s research programme over 2004-2007.
• Steven asked everyone to break into groups to consider 2 questions: -
  
  What are the key technical problems in nuclear spectrometry for your work?
  
  How can NPL make NSUF more useful for you?
  
  
• The replies would then be categorised into:-
  
  Topics for NSUF
  
  Topics for the NMS programme
  
  Topics for the working groups

The feedback from discussions groups was as follows

Issues for NMS programme

• High energy photon emitting standards (up to 3.5 MeV)
• Low energy photon emitting standards (8 – 50 keV)
• Low energy (1-2 MeV) alpha reference sources
• Mixed radionuclide volume sources with a soil matrix
• Ca-41 solution standards
• Provision of a mixed radionuclide solution for setting up coincidence summing correction software
• Mixed radionuclide solution including Pb-210
• Test spectra for benchmarking gamma- and alpha-spectrometers (including tests of minimum detectable activity calculations and identification of non-Gaussian shaped peaks)
• Good Practice Guide on gamma-ray spectrometry (including methods used to correct for sample density and composition)
• Nuclear decay data for heavy elements
• Nuclear decay data for natural series
• NPL to take a leadership role in relevant ISO/IEC committees
• Reference materials for site clearance should match Drigg/NIREX requirements

Issues for NSUF meetings

• Keynote speakers (e.g., applications of nuclear spectroscopy in space)
• Support for commercial software (particularly alpha spectra analysis)
• A better balance between gamma/alpha/mass spectrometry at meetings
• More notice of meetings

Other issues

Availability of Pu-242 and Pu-236 tracers is a priority

7. Manufacturer presentations

7. 1 Tim Twomey (Ortec)

• A summary of the talk on the portable nuclide identifier will be made available on the website.
• Tim Twomey pointed out that this was the first ever totally portable high purity germanium detector.
• The instrument was intended for use in homeland security; other detector systems could detect low levels of radioactivity activity but, because they could not identify the radionuclides, this gave rise to false alarms, which was a big problem. 90% of these false alarms were due to medical radionuclides.
• It was clear that using a germanium detector would improve the reliability of radionuclide identification and this was made possible by the use of the 1 watt Stirling cycle cooler. The Ortec digital electronics used now has a LFR noise filter. The portable nuclide identifier has been tailored for use at borders and for security forces dealing with possible radioactive contamination incidents.
• The specification was as follows:-
  
  50 x 30mm HPGe
  ‘Run for ever’ electrocooling system
  Battery operation > 3 hours
  Battery belt option
  Docking station – which contains a small Cs137 source
  Gamma line identification
  Measurement of gamma dose rate
  DC or AC power input
  Programmed to identify radionuclides recommended by the IAEA
• The question was asked as to how the device distinguishes between weapons grade plutonium and barium 133. Tim explained that by looking at the peaks that are not present in the barium 133 it is able to see the weapons grade plutonium. He added that because it works in real time it is faster and this makes it better for looking at material which is in shielding and also for looking at mixtures. Tim also added that there are neutron detectors in the pipeline.
• John Simpson asked what the price of a system would be to which Tim replied that depending on the model, around £32k.
• Lars De Geer asked how long did it take to cool; Tim replied that it took 8 hours from room temperature. The technology used for the electrocooling system was originally developed at Oxford University.
• Ian Adsley asked what the detection efficiency was. Tim explained that for a 50 x 30 mm detector it was 15% but that they are looking to produce a detector with a 40% efficiency.

7.2. Sylvie Ward (Canberra)

• A summary of the talk on GENIE 2000, the latest Canberra software for spectroscopy will be made available on the website.
• Sylvie added that software for cascade summing correction and LACE were available now.
• There was a library of nuclides which allows the calculation of the activity
• The Line Activity Consistency Evaluator (LACE) looks at 2 peaks from a radionuclide and checks that the calculated activity is the same for each peak.
• It is planned that the peaks will be labelled with the nuclides but this facility is not yet available.
• There is now enhanced copy plotting which gives more choices than previously
• Report generator improvement has led to more information being available
• For the data source information – it is now easier to find information.
• Sean Collins queried the reliance that could be put in the nuclear library used in the Canberra software as he had seen inconsistencies with TECDOC 619. Sylvie replied that it is possible to edit the library or make a new one if you wished.
• Keith Bradshaw enquired as to whether it had been tested with soils to which Sylvie replied that she would find out.

8. The Gamma Spectrometry Work of the CTBTO
Lars-Erik De Geer (CTBTO)

• A summary of the talk will be made available on the website.
• Lars explained that the work of the CTBTO was to monitor whether people were breaking the test ban treaty by testing nuclear weapons. There are 80 stations around the globe which use high sensitivity, high volume filter devices for radioactivity measurements. Other detection mechanisms (such as seismology) are also used. They are always trying to develop better systems.
• He stressed the importance of the CTBTO receiving the results from the laboratories within 4 days as they must not miss any events. They don’t analyse samples for all radionuclides, only those that are relevant to a nuclear weapon.
• The CTBTO have developed a software package VGSL – virtual gamma spec laboratory - which is a general purpose program, which includes cascade summing corrections.
• As 99.9% of spectra are generally from Pb-212, this is analysed automatically at first and then by the analysts. The Pb-212 spectrum is then removed from the spectrum. The Currie detection limit principle is then applied.
• Ian Adsley asked what peaks are normally left after the removal of the Pb-212, to which Lars answered Be-7. Keith Bradshaw then asked how sensitive the monitoring station equipment is, Lars replied that it could detect a 1kT atmospheric explosion which is 1/10 of the size of the bomb dropped at Hiroshima. Nasser Baghini asked where this could be detected, to which Lars replied worldwide.
• Lars explained that there were on average 100 seismic events every day and that the CTBTO provided the information relating to the activity measurements, but that it was up to the member states to decide whether there has been a bomb test. If a real event has happened there should be agreement between different measurement techniques.

9 Surveying and on-site assaying using gamma-ray measurement techniques
Ian Adsley (RWE NUKEM)

• A summary of this talk on methods to assay gamma emitting radionuclides on site will be made available on the website.
• Ian added that they use the GPS and that the positioning accuracy is dependent entirely on the price of the system. Digital maps are used and the contamination is plotted out on the map.
• There is a need for high resolution systems for LARCH where fission particles are being looked for.
• Physical and chemical techniques are used to separate the different nuclides.
• Different stripping techniques can be used.
• Large sodium iodide detectors are used in aerial spectrometry.
• There are problems when measuring radium-226 - if it is on the sand it blows away and the only way to measure it is by measuring the daughters which are below the surface.

10 Working Groups

• The working group for uncertainties in gamma spectrometry measurements needed to meet to finalise the document relating to these uncertainties, for which much of the work had been done.
• Steven Judge said that the next step was for a small group to meet and pull together all the information and publish the document. The members of that working group are:-
• Mike Woods (to chair)
  Richard Lukey
  Matt Simpson
  Robin Treadwell
  Mike Youngman
  NPL would provide a secretary (Sean Collins has taken on this role)
• The document will then be circulated for comment before being published.
• George Ham commented that after this document had been finished it would be useful to have a document relating to alpha spectrometry.

11 How QA was applied to the new gamma spectrometry software installation at NPL
Nigel Watkins (NPL)

• A summary of the talk will be made available on the website.
• This talk relates to the action 1.1 from the previous NSUF meeting.
• Nasser Baghini asked if there had been any improvements made at the same time to which Nigel replied that the algorithms used are identical to before and that they had not been looking for improvements, and as such it was not necessary to validate the software. An operational system which did the same job was all that was required.
• It was asked if the test spectra were available to users. Andy Pearce replied that it should be possible to put them on the website. He added that the spectra were compatible with Canberra and Ortec software.

10 Any Other Business

• Dave Wickenden (via email) asked how people approach problems with different densities. Keith Bradshaw replied that it was possible to validate using reference materials. Ian Adsley added that in Alan Nichols paper on Pa-234 there was a methodology that could be used. Ian offered to email the paper to Steven so that it could be put onto the NSUF website.
• Organically Bound Tritium standards – Steven Judge told everyone that Arvic Harms can now provide OBT samples at £750 per sample, further details are available from radioactivity@npl.co.uk
• Denise Woods gave timings for the environmental comparison exercise which was due to start.
• There was a request from George Ham that the form for registration for the next NSUF should be sent out earlier.
• Keith Bradshaw commented that the NPL website needed to be kept up to date
• John Hemmingway commented that he thought the talk by Lars De Geer was very good and that it would be good if there could be a non-UK talk each year.

12 Date of Next Meeting

Provisionally Thursday 26th May 2005

Denise Woods
Secretary, NSUF