Wednesday 28^th May 2008
National Physical Laboratory

Present:

Chairman:		Pete Burgess		National Physical Laboratory
Secretary:		Lawrence Jones		National Physical Laboratory
		Duncan Aston		High Technology Sources
		Nasser Baghini		Imperial College Reactor Centre
		Bhaswar Baral		Centronic Ltd
		John Bennett		DSTL
		Ray Chegwin		NPL
		Ludovic Chevallereau		Serco Assurance
		Alan Clare		Sellafield Ltd
		Rob Corby		Magnox Electric
		Robin Crosse		Thermo Fisher Scientific
		Bill Croydon		Radiation Watch Ltd
		Tim Daniels		Health Protection Agency, Radiation Protection Division
		Paul Deacon-Smith		Medical Physics Directorate, St Thomas’s Hospital
		Julian Dean		NPL
		Denise Delahunty		Regional Rad. Physics & Protection Service
		Geoff Druce		AWE
		David Fletcher		AWE
		James Forde-Johnston		Canberra UK Ltd
		Penny Giorgio		RPA - Surrey University
		Rikki Glover		LabImpex
		James Grand		Berthold Technologies (UK) Ltd
		Chris Hill		Thermo Fisher Scientific
		Michael Hodgson		Thermo Fisher Scientific
		Ed Holden		Berthold Technologies (UK) Ltd
		Steve Hutchins		AWE
		Michael Iwatschenko		Thermo Electron Corporation
		Richard Jenkins		BAE Systems Ltd
		Sami Kafala		Imperial College
		Clare Lee		NPL
		John Locke		Serco Assurance
		Will MacIvor		Johnson Controls
		Andrew Main		Johnson Controls
		Shaun Marriott		BAE Systems Ltd
		Ray McConnell		BIL Solutions
		Kyle Millar		Defence Equipment & Support
		Roy Mooney		MPA
		Ross Morgan		Thermo Fisher Scientific
		Robert Newiss		Nukem
		Steve Newton		VT Nuclear Services
		James Parkin		Lab Impex Systems Ltd
		Nigel Pearce		UKAS
		Mike Renouf		British Nuclear Group Sellafield Ltd
		Tony Richards		Retired
		Geraint Roberts		Health Protection Agency, Radiation Protection Division
		Jon Silvie		BAE Systems Ltd
		Keith Simmons		Defence Equipment & Support
		John Simpson		Retired
		Jeffrey Slade		AWE
		Karen Southall		HPA
		Simon Threadingham		DSTL
		Nick Troughton		JFIMS
		Jonathon Wardle		AWE
		David Williams		Magnox Hinckley A
		Michael Woods		IRMC

On behalf of NPL, Pete Burgess welcomed delegates to the 35th meeting of the IRMF.

35.1  Neutron Monitoring Comparison

Graeme Taylor reported on the ongoing neutron monitoring comparison. The monitors had been returned from BAE Systems and measurements were to be made at NPL before they were to be shipped onwards for further measurements. So far two companies had participated. AWE, HPA and NUKEM had yet to participate.

35.2  Surface Contamination Monitoring Comparison

Pete Burgess gave a brief follow up to the surface contamination monitoring comparison. The emission rates and spectra of the sources used were being investigated. Pete stated that work may continue with his new employers, Nuvia.

35.3  Calibration of Surface Contamination Monitors Comparison

Mike Woods presented the final report of the calibration of surface contamination monitors comparison. The comparison had involved UKAS accredited laboratories making measurements with a BP19 and an AP5. Comparisons had also been made of snapshot readings versus eye averaging. One conclusion of the exercise had been that manufacturers' type test data were not reliable: Chris Hill (Thermo Fisher) and Mike Renouf (Sellafield) disagreed with this.

View Mike Woods' presentation here

35.4  Diagnostic X-ray Comparison

Denise Delahunty presented results from the medical diagnostic X-ray comparison exercise, which had included 17 participants from hospitals and standards laboratories. The results had identified a difference between those traceable to NPL and to PTB: potential reasons for this were to be investigated. Also, the results obtained using solid state detectors from a particular manufacturer had been consistently discrepant, Denise was going to write to the manufacturer concerned to inform them of the results.

View Denise Delahunty’s presentation here

35.5  Test adapters based on natural Lutetium

Michael Iwatshencko (Thermo Fischer GmbH) gave an interesting presentation on the use of Lutetium test adapters as a possibility to replace traditional check sources. He listed the disadvantages of conventional check sources before describing new ceramic adapters containing naturally occurring ¹⁷⁶Lu. The benefits of ¹⁷⁶Lu included the ability to manufacture scratch resistant adapters of uniform and consistent emission rate.

In response to John Simpson’s question about how much the adapters cost compared to traditional check sources, Michael said that they were cheaper than traditional check sources, there would be no disposal costs and no replacement costs as there was no depreciation in source activity.

Mike Woods asked about any chemical toxicity and Michael Iwatshencko said there was none. When asked if Thermo Fisher Scientific would put a working life on the sources, Michael told Keith Simmons that they would not. Denise Delahunty asked if Thermo Fisher Scientific could make large area sources, but at that time the maximum for individual sources was 2" diameter.

View Michael Iwatschencko’s presentation here

35.6  Review of GPG14

Pete Burgess (NPL) apologised for not having circulated a draft of GPG14 before Christmas. A draft had been prepared and some of the main changes had been the definition of the 2π efficiency for contamination calibrations and the addition of specific guidance for dual probes. A .pdf format was ready to be circulated and Pete requested that comments were returned as quickly as possible for prompt publication.

A discussion, following a statement from Mike Woods that the timescale for the revision had been too long, concluded that the Good Practice Guide should only be revalidated periodically and the next full review should take place when a major change in the legislation occurs.

35.7  Manufacture of electroplated sources

Chris Gilligan gave an interesting presentation on the source preparation capabilities and facilities at NPL. He described the manufacture of bespoke electrodeposited sources of ²³⁹Pu for use with the IonSens monitor for Eliot Williams (UKAEA).

View Chris Gilligan’s presentation here

35.8  Overview of the IonSens monitor

IonSes Monitor 

It had been planned that Eliot would describe the use of these ²³⁹Pu sources to demonstrate the suitable performance of the instrument for clearance monitoring of pipes that had carried Mox fuel.  However, Eliot had been unable to attend the meeting so, Pete Burgess (formerly of UKAEA) gave an overview of the IonSens as he’d been involved in its development. The purpose of the sources had been to test the IonSens unit for possible use monitoring scrap from a Mox fuel production line which was being decommissioned. The Belgian regulator had set a very tight target of 0.04 Bq cm-² over 300 cm², (12 Bq in total) and it had been impossible to do this economically by probe. There was also a large amount to clear. The IonSens was attractive as large quantities (tens of kgs) of cleaned material could be monitored in a few minutes. Previous type testing had not worked to such a tight target. The sources were placed with the test scrap and the instrument response determined. The unit with the case open and a test load is pictured right.

35.9  Comparison of true and apparent activities on air filters

Julian Dean presented two new projects to be undertaken by NPL. The first was to focus on measurement of alpha-contaminated air filters to determine ratios of true to apparent activity. The second project was to measure the effects on monitor response of adsorption of activity into porous surfaces and attenuating layers over non-porous surfaces. Julian asked members to contact him with preferences of instruments and radionuclides to be included in the projects, filter types, surfaces and attenuating materials of interest. David Williams and Bill Croydon said that Magnox and Siemens respectively might be able to supply air filters.

View Julian Dean's presentation here

35.10  Production of calibration sources for beta in air monitors

Sean Collins (NPL) gave an interesting presentation on problems he had encountered when transferring a Surface Emission Rate calibration of ⁹⁰Sr from a windowless proportional counter to a windowed proportional counter. Sources of the same apparent construction had yielded a range of calibration factors for the windowed counter. However, Sean had found that an appropriate factor could be derived from the source spectra collected.

View Sean Collins' presentation here

35.11  Problems with bets in air monitor test sources

It had been planned that Paul Blinco (JCI) would follow on from Sean's on to describe problems with beta in air monitor test sources and the associated consequences, but unfortunately, he was unable to attend the meeting. Therefore, Pete Burgess presented an overview of the issues on his behalf. The problem had been that the construction of a test source could have a major influence on its performance. Paul had determined the ratio of the indicated count rate to the NPL value of the surface emission rate and had found out that that ratio had a range of a factor of 2 when measured for a variety of constructions for the same nuclide and source diameter. This was due to the collimating effect of any thick cover over a beta source, which meant that more of the beta particles were emitted in the forward direction than should have been. This resulted in too high a proportion of the particles striking the detector of an activity in air monitor, giving too high an apparent efficiency. This was a long standing problem, identified by David Ryden in the mid 90s. An advice note had been issued on the subject but it was clear that some of the covered sources were still in use. The practical implication was that instruments calibrated with such sources would underestimate true activity on a filter card. The best solution was to replace the sources but an alternative was to use a real activity in air monitor as a transfer standard. The monitor should be calibrated with "good" sources, confirmed to be in specification and linear with emission rate, and then used to determine the effective emission rate from the poorer quality sources. These poorer quality sources could then be used to test other instruments of the same construction.

35.12  PID on/off phantom ratios

Karen Southall (HPA) gave a presentation concerning the calibration of Personal Integrating Dosemeters. She explained that in theory, dosemeters should be calibrated on phantom, but this was impractical when large numbers were to be tested, generally free in air. Karen had measured on/off Phantom ratios of a variety of instruments which could then be used to correct for the lack of backscatter from a phantom.

35.13  BSI/ISOIEC update

Tony Richards gave a presentation updating delegates on the standards being developed by the ISO Technical Committee 85 Working Group 17.

View Tony Richards' presentation here

35.14  Linearity and temperature characteristics of bubble detectors

Lawrence Jones presented the findings of an investigation into the use of bubble detectors that had shown sensitivity to gamma-rays. Measured sensitivities of the low sensitivity detectors were significantly higher than those provided by manufacturers. The measurements had been made in order to validate the detectors as a viable means for making neutron dose measurements in and around medical Linacs.

View Lawrence Jones’ presentation here

35.15  Any other business

• Keith Simmons informed the meeting that he had received permission from the authors to publish JSP425, the MOD's minimum calibration standard for radiation protection instrumentation: the next step was to obtain security branch clearance. The second part of the document provided calibration protocols for general instruments. It would be made clear that the protocols were appropriate for the MOD use of these instruments only, and so were not necessarily suitable elsewhere. Mike Woods said he would try to combine the calibration data from UKAS labs with those from JSP425 in order to make them available publicly.
  
  
• Pete Burgess told the members about a document he had been involved in writing about exit monitoring of personnel. The document was aimed at QPs and RPAs and included the methodology for choosing appropriate alarm levels. Pete was to visit a nuclear industry group shortly for a second review of the document and it was hoped that it might be published as an NPL Good Practice Guide in the future.
  
  
• Next IRMF meeting to be held on Wednesday, 26th November 2008.

Lawrence Jones

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