Wednesday 3 November 1999
National Physical Laboratory

Present:

Chairman: Dr J B Hunt, National Physical Laboratory
Secretary: Dr V E Lewis, National Physical Laboratory

There were 32 other members present from 18 establishments including:

AEA Technology (Amersham)			AEA Technology (Harwell)
AEA Technology (Winfrith)			BAE Systems (Barrow-in-Furness)
BNFL (Sellafield)			BNFL Magnox (Berkeley)
DERA Rad. Prot. Service (Alverstoke)			DNST (HMS Sultan, Gosport)
DRaStaC (Aldermaston)			Johnson Controls (Dounreay)
Kingston University (Kingston)			National Physical Laboratory
National Rad. Prot. Board (Chilton)			NE Technology (Beenham)
Northern Ireland Rad. Prot. Service (Belfast)			Rad. Prot. Service (Leeds)
Reg. Rad. Physics Prot. Service (Edgbaston)			UKAS (Feltham)

A further 17 members, including some from a further nine establishments, had sent apologies.

MAIN AGENDA ITEMS

Intercomparison of calibrations of gamma-ray dose-rate monitors

Duncan McClure (NRPB) described the four monitors used and the rationale for their choice. Vic Lewis (NPL) showed the timetable for the measurements which had begun in July 1998 and ended in July 1999. Summaries of the results were discussed.

Farmer and 600 cc ionisation chamber: Results (¹³⁷Cs only) were mostly within ± 5% band.

The standard deviation was 2.5%.
The sets of values were generally constant with air kerma rate as expected.
The uncertainties in kerma rates reported by participants ranged from 2% to 10%.

Mini 6-90/MC20: Results showed a dead time effect due to kerma rate.

The standard deviation at 300 mGy h^-1 was 2.9% for ¹³⁷Cs results.
The spread was similar for the calibrations with ⁶⁰Co, but for fewer participants.
The spread was larger for the calibrations with ²⁴¹Am where there were inconsistencies.

Mini 900D: Results were not in such good agreement.

The larger spreads for ¹³⁷Cs were possibly due to problems in reading the meter needle.
The standard deviation at the medium rates was 4.0%.
There was a larger spread for the ²⁴¹Am and ⁶⁰Co results.

Mini 6-80/MC71: Results were similar to those for the Mini 6-90 but at lower air kerma rates.

The standard deviation for ¹³⁷Cs results at 5 mGy h^-1 was 2.5%.
The ²⁴¹Am results, corrected for kerma rate effects were in reasonable agreement.
The three results reported for ²²⁶Ra were consistent when corrected for kerma rate.

Full details have been published in: NPL Report CIRM 32.

Intercomparison of calibrations of surface contamination monitoring

Clare Scott (NPL) reported a delay in starting the participants’ measurements. It was planned to use the Berthold LB122, Mini EP15 and DP6 instruments.

Fifteen laboratories had expressed interest in taking part. Each laboratory would have two weeks to perform their measurements.

Intercomparison of calibrations of neutron area survey monitors

Vic Lewis (NPL) reported that five laboratories were participating in the current exercise; namely DRaStaC , AEA Technology (Harwell), NRPB, VSEL and NPL. The measurements involved calibrations of the Harwell 0949 and Studsvik 2202D monitors in fields produced by ²⁴¹Am-Be and ²⁵²Cf sources. The measurements had started in September 1998 and were completed a year later. The workshop had been held in early October.

It was hoped to have the results analysed shortly and the final report produced in early 2000.

Good Practice Guide on Practical Radiation Monitoring

Alan Edwards (DRaStaC) reported that this guide was intended to fill the gap between the calibration good practice guide and the ability of people in the field to use an instrument. In order to get input from people who make routine measurements, a workshop had been held at NPL in July with some fifty delegates, invited from all areas of health physics monitoring.

The user would be lead through the main steps for making measurements. There would be six sections on -

• definition of the problem - assessing the aim of the monitoring;
• information gathering - available records, history of facility, etc,
• selecting instruments;
• monitoring strategies - training for surveyors, plan of work;
• monitoring techniques - how to get readings and what to record;
• interpretation - expressing data as meaningful radiation quantities.

All the details would be included in the annex.

The target date for first draft was February 2000. Completion was expected November 2000.

Good Practice Guide on Installed instrumentation

Max Pottinger (BNFL Magnox, Berkeley) reported that the Steering Group had agreed a provisional title, namely, The Examination, Testing and Calibration of Installed Radiological Protection Instrumentation and Air Monitoring Equipment. The guide would cover installed gamma monitors and installed contamination monitors. The inclusion of air monitoring was tentative; it may be necessary to make this the subject of a further guide instead. Tritium-in-air monitors would not be included.

The Steering Group had looked at the instrumentation to be covered in the above three areas. Routine function checks, annual/periodic tests and before-first-use tests would be looked at. An appropriate way of referring to related information in GPG 14 would be considered. The meeting gave its views on the inclusion of appropriate items in the gamma monitor and contamination monitor annual checks and before first use tests.

Completion was not expected before 2001.

OTHER ITEMS

Working Party on NIS 0825

Vic Lewis (NPL) reported that recent progress on drafting the examples of uncertainty budgets had been very slow. Some four of the five or six examples had been completed. He could not say when the revised document would be complete.

Type testing

Peter Burgess (NRPB) asked if members were happy with non-UK type testing data.

A discussion on the purpose, scope and practicalities of type testing followed.

NMS Programme for Ionising Radiation

Julian Hunt (NPL) gave a brief update on the present situation. A brochure had been produced last year outlining the programme; anyone wishing to obtain a copy should contact the Secretary. Formulation of the next three-year programme (starting October 2001) would begin in April 2000. The next IRMF meeting would be an ideal time for members to say what they would like to see included in the next programme.

Investigation of P-factors

Peter Burgess (NRPB) commented that the small range of values used for alpha particles and soft beta P-factors did not make sense. He demonstrated this with an example of a-particles emitted in a substrate, penetrating the surface layer and entering a detector through a thin window. This did not apply to hard betas and gamma-rays, for which P-factors had some use in deriving activities.

Members expressed concern over the current situation. It was suggested that advice on where P-factors can be used should be put into the Good Practice Guide on Practical Radiation Monitoring. It might be necessary to warn that the approach should not be used for alpha-monitoring.

Good Practice Guide 14

Clare Scott (NPL) reported that about 250 copies in total were now in circulation. The feedback had invariably been positive.

IRMF Catalogue of Calibration Facilities

The Secretary reported that all entries in the IRMF catalogue had been put on the IRMF Website. The WWW version would be kept up to date, incorporating any changes or additions received.

A paper version had been produced as NPL Report CIRM 25 (March 1999).

Accreditation

Roger Worrall (UKAS) stated that ISO17025, currently due out in early 2000, would gradually replace the UKAS publication M10 as the standard against which laboratories would be assessed. There were some changes of a minor nature.

Resignation of Chairman

This was the last IRMF meeting for the Chairman, Julian Hunt, who had been involved with the Forum since it began in 1991. Julian has moved to another area in NPL.

Next Meeting

It was agreed that the next meeting will take place on Wednesday 24 May 2000.

Vic Lewis

Secretary, IRMF

Centre for Ionising Radiation Metrology, NPL (vic.lewis@npl.co.uk)

The above report is a summary of the minutes of the meeting. These have been sent to all members attending the meeting and those who had previously expressed an interest in attending IRMF meetings.

Anyone with an interest in the metrology of ionising radiation who wishes to attend or learn more about IRMF meetings and activities should contact the Secretary.

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