Combined Alpha (6^th) and Gamma-ray (8^th) Spectrometry User’s Forum

Module 16, Lecture Theatre, NPL – 23 May 2006

Participants:		Simon Jerome	NPL (Chair)
		Arzu Arinc	NPL (Secretary)
		Ian Adsley	RWE NUKEM
		Dirk Arnold	PTB
		Duncan Aston	High Technology Sources Limited
		Nasser Baghini	Imperial College Reactor Centre
		David Baker	NIRAS
		Keith Bradshaw	NNC Ltd
		Pete Burgess	NPL
		Nichola Chapman	Imperial College Reactor Centre
		David Coles	CEFAS
		Matthew Curtis	VLA
		Chris Dale	AMEC
		Peter Danyluk	AWE
		Ashley Davies	AWE
		Julian Dean	NPL
		Tony Dell	VLA
		Tony Dix	British Nuclear Group
		Julie Eccles	UKAS
		Gerhard Fritz	Canberra Harwell Ltd
		Joel Gasparro	IRMM
		Chris Gilligan	NPL
		Gordon Gilmore	NTS
		Paul Griffiths	BIL Solutions
		Anniken Hagen	Algeta Asa
		George Ham	HPA
		Mathew Harker	AWE
		Arvic Harms	NPL
		Trevor Hatt	AMTEC
		Ed Holden	Ametek
		Gareth Johnson	AWE
		Andrew King	AWE
		Piers de Lavison	NPL
		Cindy Lawes	British Nuclear Group
		Philip Leaney	DSTL
		John Locke	Serco Assurance
		Richard Lukey	VLA
		Clive Lythgoe	British Nuclear Group
		Desmond MacMahon	Retired
		Maria Marouli	NPL/University of Surrey
		Olivia Marsden	AWE
		Robert McKeag	Centronic
		John McQuirk	British Nuclear Group
		Timothy Miller	AWE
		Margaret Moore	AWE
		Scott Moreland	ORTEC
		Susan Parry	Imperial College Reactor Centre
		Andy Pearce	NPL
		Dave Rayner	NPL
		Jeff Ruddle	UKAS
		Ben Sanderson	BIL Solutions
		Sarah Shepherd	URENCO (Capenhurst) Ltd
		John Simpson	NUKEM
		Mathew Simpson	DSTL
		Paul Smedley	CEFAS
		Ben Taylor	CEFAS
		Pamela Thompson	AWE
		Robin Treadwell	AWE
		John Wardle	AWE
		Claire Watt	AWE
		David Watt	Canberra Harwell Ltd
		Bill Westall	British Nuclear Group
Apologies:		John Caunt	John Caunt Scientific Ltd
		Sean Collins	NPL
		James Grand	Berthold Technologies (UK) Ltd
		Elizabeth Jones	University Hospital of Wales
		Steven Judge	NPL
		Vicki Ritherdone	Scientifics Ltd
		Nathan Thomas	AWE
		Stephanie Vallet-Thomas	Canberra Harwell Ltd
		Richard Wilson	Westlakes Scientific Consulting
		Mike Youngman	HPA

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

• Simon Jerome introduced himself and welcomed members to the fourth meeting.
• The minutes of the third meeting were accepted as a true record.
• Actions:

A1.1: Piers de Lavison to put Alan Nichols' paper 'Decay of Th-234 and Daughter Pa-234m in Secular Equilibrium' onto the NSUF website. Done.

A2.1: Piers de Lavison to put a link on the website to the guidance for industry paper Q2B Validation of Analytical Procedures: Methodology. Done.

2. Invited talk: 'Gamma assay measurement techniques for nuclear decommissioning' - Ian Adsley, Nukem

• Ian began his talk by listing the various 'parties' interested in nuclear decommissioning. A description of the requirements, the drivers and the difficulties encountered in the "real world" of nuclear decommissioning was given.
• He pointed out that the only technique applicable to field measurement was gamma spectrometry. He added that the Dawson method, which consists on measuring the dose rate, was still in common use but that it implied the assumption of the fingerprint.
• Some examples of decommissioning work were discussed, such as an aerial survey of 137Cs contamination, a site survey and a gamma radiation profile. Illustrations of measurements in various frequently-used geometries (such as buckets, drums and bags) were displayed.
• Ian concluded his talk with two examples: the description of the measurement of 241Pu via the ingrowth of the daughter nuclide 241Am and the decommissioning work on 100 submarine reactor fuel cores.

• Following the talk, Julian Dean mentioned that NPL was planning on running a comparison based on a 200 litre drum containing a low-density matrix spiked with g-emitting nuclides at around 0.4 Bq/g. The drum should be ready for circulation in October or November of this year; if people are interested in participating they should contact Julian Dean.
• Pete Burgess asked Ian Adsley if when he was presenting this as a measurement technique to customers, they were asking him to give them confidence on the method. Ian replied that he always opted for the simplest solution possible and tried to keep people as much involved as possible.

3. Invited talk: 'Mass spectrometry and its role at the Sellafield site' - Clive Lythgoe, British Nuclear Group

• Clive Lythgoe began his talk by describing the Sellafield site and then described the work of the mass spectrometry group in more detail. He showed illustrations of various mass spectrometers and explained that routine measurements were done on Plutonium and Uranium samples. Other samples, such as Gadolinium, Neodymium, Lutetium and Erbium were analysed in a non-routine manner, and that Zirconium was under investigation at the moment.
• The main plants within Sellafield where the samples originated from were named and the various purposes of the measurements were discussed, these being Accountancy/Safeguards, Plant control and Product Specification.
• Clive explained briefly the analytical technique used in mass spectrometry. Single and double tracers, large scale and small scale dried spikes are the various types of tracers employed. Clive described in more details the large scale dried spike analysis. He mentioned that the measurement time for this type of analysis was about 3 days, this included the collection and transfer of the sample, the homogenisation, chemical separation, analysis and reporting of the results.
• Clive finished his talk by enouncing the disadvantages of TIMS and he highlighted the fact that Multi Collector ICP-MS (MC-ICP-MS) was the way forward for quicker and simpler measurements.

• Following the talk, a question was raised - where is the dilution process occurring? Clive replied that the spiking of the samples is done in the highly active cells, and then the samples are diluted and transferred by automatic pneumatic transfer across the site. The samples arrive in a cell where they are placed in a shielded container and taken into a fume hood.
• A participant asked about the maintenance of the apparatus and how easy it is to obtain suitably qualified engineers. Clive answered that this is carried out by a company named Analytik, which is specialised in TIMS instruments and has classified workers.
• The matter of the significance of the contamination of the apparatus for decommissioning was raised as an issue. Clive gave as an example the recent decommissioning of a single collector mass spectrometer that was used for 24 years for analysing Pu and U samples. He said that the most active part was the source itself and that even the flight tube contained very little activity. There was not really an issue with contamination.
• A participant asked what the sensitivity of the MC-ICP-MS was. Clive said that with a solution at 100 ppb, one could achieve a precision better than 0.05%.
• Simon Jerome enquired about the cost of adding a "nuclear box" at the end of the MC-ICP-MS. Clive explained that it cost about £210k-250k, but he added that a major part of the cost had been the design of the system as this was the first time it had been done. The cost had now come down to £100k-120k.

4. Invited talk: 'Determination of Pu isotopic ratios in low activity samples by alpha-particle and L X-ray spectrometry' - Dirk Arnold, PTB, Germany

• Dirk began his talk by explaining that the deconvolution of ²³⁹Pu and ²⁴⁰Pu was complicated when using alpha spectrometry, therefore there was a need for L X-ray spectrometry.
• The method is based on the difference of X-ray emission probabilities for ²³⁹Pu and ²⁴⁰Pu. It requires a simultaneous measurement with an alpha spectrometer and a calibrated X-ray detector. The alpha and X-ray spectrometers used at PTB, and an example of spectrum for the 239Pu calibration source, were illustrated.
• The results of measurements on synthetic sources were shown. The deviation between known and calculated activities is very small (=1%). The only exception is for small ratios of ²³⁹Pu where the deviation is more significant (~ 7%).
• Dirk pointed out that to reduce the uncertainty on the activity ratio one needed to reduce the uncertainty on the background. Therefore the measurements are carried out underground in the Asse salt mine at ~500 meters below surface. A reduction in the background by a factor of ten has been observed.
• Some measurements of environmental samples arising from various places in Europe were discussed.
• Dirk concluded his talk by highlighting the fact that this technique was simple, cheaper and more accurate for ²³⁸Pu (although less so for ²³⁹Pu and ²⁴⁰Pu) than mass spectrometry, and the same source can be used with both detectors.

• Following the talk, a participant asked how long one needed to measure for. Dirk replied that the length of the measurement was function of the activity of the source. A source containing a few mBq requires a measurement time of weeks, whereas a source of a few Bq can be measured in one day.
• A question was raised regarding the origin of the pure ²³⁸Pu and ²³⁹Pu sources. Dirk answered that PTB had old stocks obtained from Harwell and that it was possible to get some sources from Geel (IRMM).

5. NPL talk: 'Formulation begins for the next NMS IR programme' - Dave Rayner

• Dave Rayner began his talk by explaining in detail the timetable for the formulation process for the 2007 - 2010 NMS Ionising Radiation programme. He pointed out that there would be a user consultation process between June and October this year, and that this would be the time when users could most influence the content of the final programme.
• The consultation methods to be employed, and the main changes arising from a recent review of the National Measurement System (NMS) programmes, were described.
• A non-exhaustive list of the markets where the NMS IR is expected to have an impact was given, these included nuclear decommissioning, nuclear as an energy source, nuclear submarines, homeland security, emergency planning for 'dirty bomb' attacks, space, cancer therapy, imaging and sterilisation.
• Dave pointed out the importance of having the participants' input on the technological changes that will affect them and the market they are interested in and how the Ionising Radiation programme can react to these changes.
• Dave finished his talk by highlighting the importance of getting involved in the consultation process in order to give personal views.

• Following the talk, a participant asked if some information on the consultation was available on the NPL website. Dave explained that the consultation was at a very early stage and that this will happen in the next couple of weeks.
• A question was raised about the availability of Dave's talk on the NSUF website. Dave confirmed that the talk will go on the NSUF website.

6. Invited talk: 'Gamma-ray spectrometry of radionuclides with cascading gamma-rays' - Joël Gasparro, IRMM, Belgium

• Joël Gasparro started his talk by describing HADES the underground laboratory where IRMM operates 5 ultra low background HPGe-detectors.
• Some examples of nuclides (⁶⁰Co, ¹⁰⁶Ru, ¹³³Ba) were given where summing effects were affecting the results either by count loss 'summing out' or by count addition 'summing in'.
• There are five possible ways of dealing with summing effects: not applying any corrections, using a standard to calibrate for the same radionuclide in the same geometry, using correction tables, calculating correction factors by using photopeak and total efficiencies, and finally, using the Monte Carlo method.
• Joël pointed out that by not correcting for summing with a point source measured directly on the top of a planar detector, one could overestimate the efficiency by up to 60%.
• The use of correction tables is an easy, fast and reliable method if the detector and geometry used are similar to the ones in the tables. The possible corrections for the differences are difficult.
• The calculation of correction factors by using photopeak and total efficiency is easy and accurate for simple decay schemes but intractable for radionuclides with complex decay schemes.
• Joël described briefly the principles of Monte Carlo simulation and gave a list of the main Monte Carlo simulation codes. He showed the effects on the efficiency of various parameters such as tilting of crystal, rounded edges, dead layer thicknesses of detector, and distance from crystal to window.
• Joël concluded his talk by explaining that the "best method" varies as a function of one's needs. The chosen method should be a function of the need for quantitative analysis, the frequency of measurement of the samples, and the accuracy required. For example, for routine measurements, a standard with similar geometry is ideal, whereas for samples with a range of geometries, Monte Carlo can be more appropriate.

• Following the talk, a question was raised regarding how UKAS perceives the use of theoretical methods. Julie Eccles replied that if it was demonstrated that the method is reliable then it was not an issue.
• A participant asked if the summing was corrected accurately with the Gamma Vision software. Joël replied that he was not familiar with this software. Dirk Arnold commented that Gamma Vision performed well if one used the same geometry and the same composition of the sample, but didn't allow these parameters to be changed. Gerhard Fritz (Canberra Harwell Ltd) added that the Genie software allowed for changes in the density, composition and geometry of the samples and was giving pretty precise results.
• Ian Adsley enquired how quickly the summing effect was dropping when the source was moved away from the top of the detector. Gerhard Fritz replied that at 2 or 3 cm from the detector the effect of the cascade summing was less than 5%. Richard Lukey added that at 15 cm the effect was less than 1%.

7. Invited talk: 'Accreditation standards update: ISO 17025:2005, ISO Guide 43:1997 and ISO Guide 34:2004' - Jeff Ruddle, UKAS

• Jeff Ruddle began his talk by explaining that the ISO 17025 was updated to be compatible with ISO 9001-2000. He then described the main changes affecting the ISO standard and went through the new and amended closes.
• Jeff pointed out that all the organisations had to be accredited to the new version of the ISO 17025:2005 by the end of May 2007.
• The bases and working progress for the new ISO Guide 43 (Proficiency Test Providers) were explained in detail. These included the need for assessment of providers, background, first steps, creation of a steering group, assessment criteria, identification and training of staff, guidance document PT1, accreditation organisations and feedback.
• Similarly work on the ISO guide 34 (Reference Material Producers) was described, which included why producers should be assessed, background, first steps, steering group, assessment process and teams, current status of pilot programme, assessment findings and future plans.
• Jeff ended his talk by giving the names of the organisations accredited as Proficiency Testing Providers and/or Reference Material Producers.

8. Invited talk: 'Remote gamma imaging of high dose environments' - Paul Griffiths, BIL Solutions

• Paul Griffiths began his talk by describing the main features and typical applications of the RadScan®:800. He pointed out that the primary function was to provide colour contour maps showing the spread and intensity of radiation over an area.
• Pictures of the various components of the RadScan®:800 were displayed and the performances of the three collimation angles available were discussed, these being 4° (standard angle), 3° and 2°. The scanning is done by small increments for a set length of time. A gamma spectrum, containing up to three Regions Of Interest (ROI), is formed at each position and saved in the database. If required, extra ROI can be analysed after data collection.
• Paul explained that at the start of the measurement one will see a picture of the area to analyse and after measurement, a radiometric overlay image would be added onto it. The colour range varies from blue for low activity areas to red for high activity areas.
• Three case studies involving RadScan®:800 imaging were discussed. The first case was the clean-up of 137Cs contamination, the second was a blockage detection and the third was advanced ALARP planning.
• Paul finished his talk by summarising the positive impacts of the RadScan®:800 on the work environment, such as increased levels of safety, identification of blockages and leaks in process plant, and help in planning decommissioning strategies.

• Following the talk, Paul was asked how they chose the detector size. He replied that the aim was to have a detector that was light enough for one individual to be able to assemble alone. He added that the actual detector head weighed 24 kg.
• A question was raised regarding the possibility of interchanging the detection crystal. Paul answered that he didn't know if the crystal used was of a conventional size but he added that if the physical size of both crystals was similar, the exchange should be possible.
• Paul was asked for the reason for the high collimation. He replied that it was to improve the spatial resolution and to reduce the contribution to the background from the scattered photons.
• A participant asked the cost of the RadScan®:800. Paul answered that it was about £130k.

9. Manufacture presentations: λ-spectrometry analysis software

9.1 Gerhard Fritz (Canberra-Harwell)

• Gerhard gave the outline of his talk. He then described the new features and enhancements of the g-spectrometry analysis software Genie 2000 V3.1 such as multi-language installation, USB dongle support, ISOCS/LabSOCS as an analysis engine, interactive analysis and additional isotopes for cascade summing corrections.
• The new electrical cooling for germanium detectors Cryo-CycleTM and Cryo-PulseTM 5 were presented. Gerhard explained that Cryo-CycleTM combines an electromechanical cryocooler and a liquid nitrogen Dewar. The cryocooler condenses the boil-off gas from the Dewar. It can be used on existing detectors, has low noise and reduces the refill of the liquid nitrogen to once a year. The Cryo-PulseTM 5 is liquid nitrogen free and is composed of a sealed compressor and a coldhead. It is reliable, low on power consumption and has a fast cool down time.
• Gerhard finished his talk by describing CARTOGRAM, a new gamma camera that takes an optical picture of an object and overlays it to a picture of the activity distribution. Typical applications are waste treatment and nuclear decommissioning.

• Following the talk, a participant asked if the original Genie algorithms were reviewed and checked to see if they were correct as he thought the function fitted to the peak area was unrealistic. Gerhard replied that the fit was function of the square root of the energy. The participant commented that this was not what was written in the manual and that he believed there was a mistake in the formula.
• A question was asked regarding the Cryo-PulseTM 5 - how long will it take for the detector to warm up if the mains power goes off? Gerhard replied that it takes 30 minutes and added that the unit is equipped to go back in a cooling down cycle when the power comes back.
• A question was raised regarding the power consumption for the Cryo-CycleTM. Gerhard replied that it uses 300 Watts.
• Dirk Arnold commented that in the past there was a limitation in the efficiency calibration to a minimum of 45 keV and enquired if there was any progress made to go lower in energy. Gerhard replied that the mathematical efficiency calculation still didn't go below 45 keV, but he added that Canberra was investigating the possibility of developing a model that will go as low as 5 keV. Dirk then asked how the X-rays below 45 keV where dealt with. Gerhard replied that the software did not cover them at the moment.
• A participant asked if the Cryo-PulseTM 5 consumed 5 Watts only. Gerhard answered that the cooling part was using 5 to 10 Watts and that the rest of the unit consumed about 50 to 60 Watts.

9.2 Scott Moreland (Ortec/Ametek)

• Scott introduced himself to the participants and enounced the aim of his talk. The purposes of the GammaVision software were given, these being hardware control, spectrum display, spectrum analysis and network support.
• Some of the features were described in detail, such as interactive analysis, calibration wizard, absorption correction, zero dead time and True Coincidence Correction (TCC). The absorption correction is available for any number of materials and can correct for internal or external absorption. The zero dead time feature, also called Loss Free Counting (LFC), corrects the spectrum - not the counting time - for dead time losses. True coincidence correction depends on the detector and the detector-source geometry. Ortec uses the cascade summing correction of Blaauw and holds the exclusive worldwide license for it.
• Scott ended his talk by highlighting the fact that users' feedback is a vital part of the future product development process and that the participants are encouraged to give their feedback to Ortec.
• Following the talk, a GammaVision user commented on a couple of "bugs" he had observed. Background subtraction does not include the uncertainty on the background; a proper weighted mean is not applied when a nuclide emits a multitude of gammas (thus giving greater weight to the smaller peaks); and although 8 detectors can be controlled at the same time, only one job can be set up. Scott replied that most of these issues were being resolved at the moment. Ortec is working on the total propagated uncertainty where the background uncertainty will be included. Scott mentioned as well that the user manual was being revised. He insisted on the fact that it was crucial to report any bugs observed to Ortec.
• A participant asked how well the True Coincidence Correction worked. Scott answered that he was not aware of instances where the software was not performing correctly but part of the validation process was on going.
• A question was raised about the possibility of taking account of the ingrowth of the daughter products for some nuclides. Scott said that he would look into that issue.
• A participant asked if the GammaVision software presented was Version 6 or a newer version. Scott replied that it was a new release but not a new version.
• A question was raised regarding whether standards of radioactivity were used during the validation process, or if the process consisted of checking the algorithms. Scott answered that it was mainly achieved by control of the algorithms.
• A participant asked if the attenuation feature of GammaVision that allowed for an absorber to be taken into account also allowed for the correction of absorption within the sample and how it was done. Scott replied that he wasn't completely sure and that the new manual should give all the details.
• Scott was asked the origin of the nuclear data source that was used in the GammaVision libraries. He replied that there were 3 different libraries available and that one could use any recognised nuclear database they wished to. Desmond MacMahon pointed out that at the last NSUF meeting he presented a talk on the nuclear decay data recommended by NPL. He commented that BIPM endorsed the use of Decay Data Evaluation Project (DDEP) data when possible.

10. Any Other Business

• Richard Lukey enquired about the publication of the updated TecDoc 619. Action 1.1: Arzu Arinc to contact IAEA (Alan Nichols) to ask for an update on the publication of TecDoc 619.
• Keith Bradshaw asked if there was any update regarding the gamma spectrometry uncertainties working group and if a publication was imminent. Action 1.2: Simon Jerome will collate all of the previous papers and restart the working group.
• A participant pointed out the use of different MDAs in different organisations and the lack of consistency throughout the UK. Dirk Arnold mentioned the existence of an ISO standard ISO 11929 on detection limits and decision thresholds. Joël Gasparro pointed out that for decision threshold there were two formulas, one for approximate solution and one for exact solution and that the latter contained a mistake. Action 1.3: Simon Jerome to collate the relevant information and for this to be discussed at the next meeting.

Forthcoming events

• Airborne Radioactivity Monitoring Users' Group
  NPL, 7th November 2006
  Contact: Julian Dean
• Ionising Radiation Metrology Forum
  NPL, 15th November 2006
  Contact: Dagmara Tyler
• Fifth Liquid Scintillation Users' Forum
  NPL, 28th November 2006
  Contact: Arzu Arinc

11. Date of the Next Meeting

Provisionally Tuesday 22^nd of May 2007.

Arzu Arinc

Secretary, NSUF