Minutes of the 5^th Nuclear Spectrometry Users’ Forum

Module 16, Lecture Theatre, NPL – 22 May 2007

Participants:		Simon Jerome	NPL (Chairperson - morning)
		John Keightley	NPL (Chairperson - afternoon)
		Arzu Arinc	NPL (Secretary)
		Peter Bode	Delft University
		Keith Bradshaw	NNC Ltd
		Adrian Clacher	NIRAS
		Matthew Curtis	VLA
		Pippa Crosby	Consultant (Project Services?)
		Tony Dell	VLA
		Alma Eslava-Gomez	Scientifics Ltd
		Maria Garcia-Miranda	NPL
		Terry Gingell	DSTL
		George Ham	HPA – RPB
		Matt Harker	AWE
		Trevor Hatt	AMETEK
		Michael John	British Nuclear Group
		Pamela Jones	URENCO (Capenhurst) Ltd
		Céline Lefèvre	Canberra UK Ltd
		John Lightfoot	BIL Solutions
		Richard Lukey	VLA
		Ann Mair	UKAEA
		Olivia Marsden	AWE
		Robert McKeag	Centronic
		Margaret Moore	AWE
		Jenny Morris	AWE
		Susan Parry	Imperial College at Silwood Par
		Clare Payne	AMETEK
		Andy Pearce	NPL
		Ian Pearman	NUKEM
		Lorna Proctor	RWE
		Martin Rushby	Canberra UK Ltd
		Jeff Ruddle	UKAS
		Sarah Sheperd	URENCO (Capenhurst) Ltd
		Lucy Sims	CEFAS
		Lindis Skipperud	Norwegian University of Life Sciences
		Paul Smedley	CEFASTL
		Charlie Stewart	UKAEA
		Jenny Swan	UKAEA
		David Thomas	NPL
		Simon Waldren	AWE
		Selina Woods	NPL
		Mike Youngman	HPA - RPB
Apologies:		Ian Adsley	Ian Adsley RWE NUKEM
		Nasser Baghini	Imperial College Reactor Centre
		Paul Curtis	Imperial College
		Luc Debaerdemaeker	Canberra Harwell Ltd
		Julie Eccles	UKAS
		Ian McGregor	Rolls Royce
		John McNamara	British Energy
		John Simpson	RWE NUKEM
		Mathew Simpson	DSTL
		Stéphanie Vallet-Thomas	Canberra UK Ltd
		Tony Ware	Compuserve

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

• Simon Jerome introduced himself, welcomed members to the fifth meeting and briefly summarised the day’s agenda.
• The minutes of the fourth meeting were accepted as a true record.
• Actions arising from the fourth meeting had been

A1.1: Update on TecDoc 619. No paper published yet but the data are accessible by clicking this link.

A1.2: Gamma-spectrometry uncertainties working group. Simon Jerome proposed the publication of a Good Practice Guide for the next programme.

A1.3: Minimum detectable activities. Simon Jerome proposed the publication of a Good Practice Guide for next programme.

2.  Invited talk:  The ²¹⁰Po Poisoning Incident in London, November 2006 – the work of the HPA radiochemistry team
     – George Ham, HPA

• George started his talk by describing the timing of the main events from the first suspicions of ²¹⁰Po poisoning to the initiation of the urine sampling programme. Urine samples were chosen over faecal samples for practical reasons. The reporting level was 30 mBq per sample which corresponded to a minimum detectable dose of 0.3 mSv (20 days after intake and assuming 100% intake by inhalation).
• George explained the various aspects of the work: Validation of method used, Quality Assurance, analytical procedure, triage of people with high exposure risk, organisation of collection of the samples, analysis of samples, dose assessment, reporting, disposal of samples and laboratory issues.
  
  
• Following the talk, a participant enquired about the ease of getting hold of ²⁰⁹Po tracer radionuclide. George replied that luckily they had just ordered two bottles of standard, so he had plenty in stock. But, he mentioned having difficulty in getting silver discs.

3.  Invited talk: Isotope-ratios for source identification, measured with AMS and ICP-MS – Lindis Skipperud, Norwegian
     University of Life Sciences

• Lindis began her talk by explaining that the determination of the isotope ratios for Uranium and Plutonium allows the identification of the origin of the contamination (e.g. nuclear fuel for civil reactors, weapons production, global weapons fallout).
• Measurements at the Techa River in Russia, contaminated by several releases of radioactive waste, suggested that 25% of the Pu contamination comes from weapon production operations and 75% from civil sources.
• Lindis gave various examples of Uranium and Plutonium measurements and concluded that ICP-MS used with traditional a-spectrometry was a good tool to determine isotope ratios and Accelerator Mass Spectrometry (AMS) was a powerful method for low activity concentrations.
  
  
• Following the talk, a delegate enquired about the influence of the Chernobyl fall out on the results from the Techa River. Lindis replied that she didn’t think that the fallouts would have contaminated this area but even if they did they wouldn’t be detected because of the activity levels.
• A participant enquired how low one can measure with AMS. Lindis replied that it is of the order of a femtogram of Plutonium.

4.  NPL talk: Water Analysis – SCA, BS and ISO – Simon Jerome

• Simon apologised for changing the topic of his talk with little warning. He explained that quite a few of the laboratories taking part in the iodine comparison had not been able to submit results due to their involvement with the ²¹⁰Po measurements.
• Simon described the various standards groups working on water analysis. The Standing Committee of Analysts (SCA) provides authoritative guidance on methods of sampling and analysis. Their primary duty is to develop and publish analytical methods. Simon gave the list of the current ‘Blue Books’ dealing with radioactivity measurement and described the current activities of the working group.
• BSI EH/3 is a committee on water quality and is responsible for UK input on ISO TC147 and CEN/TC230. The current activities of the ISO TC147 Working Group 9 (Radiological Measurements) were described.
  
  
• Following the talk, a participant asked Simon to explain who the SCA were. He replied that the organisation SCA falls under the Environment Agency and is a group of experts who are there to provide independent guidance and advice.

 5.  Invited talk: Lanthanum halide detectors, a new step in scintillation spectrometry – Peter Bode, Delft University
      (awaiting Permission to Publish)

• Peter began his talk by introducing the University of Delft and its organisation. He continued by explaining the basics about scintillators (i.e. definition, functioning, required characteristics).
• Peter went through the major properties of the newly discovered LaBr₃ scintillators doped with Ce; these included:
  • Stability
  • High density and high atomic number
  • Ease of production
  • Good energy resolution
  • Fast time resolution
  • High scintillation yield
  • Better linearity than NaI detectors
    
    
• Following the talk, a participant enquired the price of BrilLanCe^TM detector. Peter replied that a 3”x 3” detector was about 10,000 Euros. He added that these detectors required a different type of Photomultiplier Tubes than the NaI detectors.
• Peter was asked the reason why the LaBr₃:CE³⁺ detector was chosen for space exploration. He answered that the energy resolution was much better than for a NaI detector.
• A delegate enquired the robustness of the detector (i.e. resistance to physical damage). Peter commented that the robustness of the new detector was similar to that of NaI detectors.

6.  Invited talk: Requirements of ISO/IEC 17025:2005 and Accreditation – Jeff Ruddle, UKAS

• Jeff Ruddle started his talk by defining the method validation as described in ISO 17025:2005. He continued by explaining the criteria to be considered to declare a method "fit for purpose".
• Jeff went through the accreditation requirements necessary for validation of a non-standard method (e.g. robustness, reproducibility, traceability, linearity and matrix effects).
• He pointed out the need for a validation plan and records of all the validation measurements. He also added that the use of standards whenever available was recommended; another recommended option is participation in proficiency test exercises.
  
  
• Jeff ended his talk by giving references to publications on method validation and by pointing out the availability of a training course at LGC on the subject.

7.  NPL talk: Neutron Spectrometry – David Thomas

• David started his talk by explaining the reasons for making neutron spectrum measurements. Various area survey devices and personal dosimeters respond differently as a function of the neutron energy – which can vary from 10^-3 eV to 10⁷ eV. It is therefore important to know which type of neutrons one is measuring to make sure the appropriate device is employed.
• David explained that ³He sandwich spectrometers and ³He proportional counters can be used for laboratory measurements of neutrons, but unfortunately are no good for field measurements. The efficiency of these devices to thermal neutron is so high that the pile-up events will swamp the energy region of interest.
• One of the most important reactions in neutron spectrometry is (n,p) scattering, which is when a neutron collides with a hydrogen and transfers some energy to the recoil proton. The amount of energy transferred is a function of the scattering angle θ. When θ=0° then the energy of the neutron is completely transferred to the proton. The detection efficiency is very low if one only restricts the angle to θ=0°, but measuring without angle restriction implies that the spectrum obtained is complicated and needs "unfolding".
• David described the characteristics of the two most common types of proton recoil spectrometers, the hydrogen-filled proportional counter and the scintillator spectrometer. He added that these counters were high resolution and could be used for field measurements but only covered 11% of the total dose equivalent spectrum.
• Bonner spheres, which are balls of polyethylene with a thermal neutron detector at the centre, can be used to cover the whole energy region. The size of the Bonner sphere determines the type of neutron it will respond to, with the bigger spheres for the higher energy neutrons and the smaller spheres for the lower energies.
• David concluded his talk by showing a comparison exercise, which confirmed that the Bonner spheres are appropriate for measuring dose equivalent accurately.
  
  
• Following the talk, a participant asked David if he had tried to digitalise the output from the counter to separate the pile-up events from the real events. He replied that the pile-ups were completely swamping the region of interest and the true events were only a fraction of the counts. He tried using Cadmium to cut out all the thermal neutron below 0.5 eV but low energy neutrons were still being detected in large numbers. David said that his feeling was that the digitalisation process would represent lots of work and would not necessary give successful results.
• A delegate enquired about the neutron dose outside nuclear facilities. David replied that it was just about possible to detect the neutrons with the Bonner spheres, but the dose was negligible.

8.  Commercial talk: Application of extraction chromatography to the determination of radionuclides in soil and
      biological samples – Steffen Happel, Eichrom

• Steffen began his talk by describing the characteristics of the new extraction chromatography DGA resin. This resin is especially suited for Am extraction with better recovery results than those obtained with TRU resins.
• The flowcharts for the preconcentration of Am and Pu from 100 g of soil followed by the separation of Am and Pu from the preconcentrate were shown. The results obtained with this rapid method were good with a recovery of 50-60% for ²⁴³Am and 40-65% for ²⁴²Pu. The FWHM obtained was 73 keV for ²⁴³Am and 62 keV for ²⁴²Pu.
• In order to analyse soil samples and animal tissue, various methods including co-precipitation, use of TEVA/TRU/DGA and Diphonix resins, complete dissolution, leaching and ashing of the samples were described.
• Steffen ended his talk by giving the detailed procedures and expected recoveries for the:
  • Analysis of Pu, Np, U, Am and Sr from urine and faecal samples.
  • Analysis of Pu and Am in food and milk samples
  • Analysis of Pb and Po in milk, crop and animal sample

9.  Any Other Business

• A manufacturers exhibition was held in the reception during the afternoon break. The following manufacturers were represented: AMETEK, Canberra, NIRAS, NUKEM and Project Services Ltd.
• The NPL-recommended Nuclear Decay Data has been published as NPL Report IR 6 and will shortly be available on the "NPL Reports & Papers" page of the NPL website.

Forthcoming events

• The next PROCORAD meeting will be held at NPL from 18-20 June 2008; see http://www.procorad.org/ for more details.
• NPL will be holding the next meeting of the Ionising Radiation Metrology Forum (IRMF) on 21st May 2008. Please contact radioactivity@npl.co.uk for further information.
• NPL will be holding the Seventh Liquid Scintillation Users' Forum (LSUF) on the 23rd September 2008. Please contact Arzu Arinc for further information.

11. Date of Next Meeting

This is scheduled for Tuesday, 17th June 2008.

Arzu Arinc

Secretary, NSUF