IAEA-TECDOC-1599 Quality Control Procedures Applied to Nuclear Instruments Proceedings of a Technical Meeting Vienna, 23–24 August 2007 September 2008 IAEA-TECDOC-1599 Quality Control Procedures Applied to Nuclear Instruments Proceedings of a Technical Meeting Vienna, 23–24 August 2007 November 2008 The originating Section of this publication in the IAEA was: Physics Section International Atomic Energy Agency Wagramer Strasse 5 P.O. Box 100 A-1400 Vienna, Austria QUALITY CONTROL PROCEDURES APPLIED TO NUCLEAR INSTRUMENTS IAEA, VIENNA, 2008 IAEA-TECDOC-1599 ISBN 978–92–0–108308–1 ISSN 1011–4289 © IAEA, 2008 Printed by the IAEA in Austria November 2008 FOREWORD Quality Control (QC), test procedures for Nuclear Instrumentation are important for assurance of proper and safe operation of the instruments, especially with regard to equipment related to radiological safety, human health and national safety. Correct measurements of radiation parameters must be ensured, i.e., accurate measurement of the number of radioactive events, counting times and in some cases accurate measurements of the radiation energy and occuring time of the nuclear events. There are several kinds of testing on nuclear instruments, for example, type-testing done by suppliers, acceptance testing made by the end users, Quality Control tests after repair and Quality Assurance/Quality Controls tests made by end-users. All of these tests are based in many cases on practical guidelines or on the experience of the own specialist, the available standards on this topic also need to be adapted to specific instruments. The IAEA has provided nuclear instruments and supported the operational maintenance efforts of the Member States. Although Nuclear Instrumentation is continuously upgraded, some older or aged instruments are still in use and in good working condition. Some of these instruments may not, however, meet modern requirements for the end-user therefore, Member States, mostly those with emerging economies, modernize/refurbish such instruments to meet the end-user demands. As a result, new instrumentation which is not commercially available, or modernized/refurbished instruments, need to be tested or verified with QC procedures to meet national or international certification requirements. A technical meeting on QC procedures applied to nuclear instruments was organized in Vienna from 23 to 24 August 2007. Existing and required QC test procedures necessary for the verification of operation and measurement of the main characteristics of nuclear instruments was the focus of discussion at this meeting. Presentations made at the technical meeting provided valuable information, new proposals, and technical opinions which have been compiled and summarized in this publication and should be useful for technical staff dealing with QC test procedures for maintenance, repair, design and modernization/refurbishment of nuclear instruments. Nine experts in this field as well as users of nuclear instruments presented their latest results; discussions held during the meeting and following the presentations included many technical comments. This publication is a culmination of the interactions and presentations which occurred during the meeting. The IAEA thanks all the participants for their active involvement in the meeting. Special thanks are given to F. J. Ramirez for serving as rapporteur during the meeting, and for his assistance in the report’s preparation. The IAEA officers responsible for this publication were H. Kaufmann and F. Mulhauser of the Division of Physical and Chemical Sciences. EDITORIAL NOTE This publication has been prepared from the original material as submitted by the authors. The views expressed do not necessarily reflect those of the IAEA, the governments of the nominating Member States or the nominating organizations. The use of particular designations of countries or territories does not imply any judgement by the publisher, the IAEA, as to the legal status of such countries or territories, of their authorities and institutions or of the delimitation of their boundaries. The mention of names of specific companies or products (whether or not indicated as registered) does not imply any intention to infringe proprietary rights, nor should it be construed as an endorsement or recommendation on the part of the IAEA. The authors are responsible for having obtained the necessary permission for the IAEA to reproduce, translate or use material from sources already protected by copyrights. CONTENTS 1. SUMMARY......................................................................................................................1 1.1. Introduction................................................................................................................1 1.2. International standards for nuclear instrumentation..................................................2 1.3. Special test procedures for newly developed instruments.........................................3 1.4. QC test procedures for manufacturing of detectors...................................................3 1.5. QC test procedures for troubleshooting of tld readers...............................................4 1.6. QC test procedures for radiation detectors and associated counting systems............4 1.6.1. QC test procedures for radiation detectors.....................................................5 1.6.2. QC test procedures for radiation survey monitors.........................................5 1.6.3. QC test procedures for nuclear counting systems..........................................6 1.7. Future/further needs of the Member States................................................................6 1.8. Conclusions................................................................................................................6 PRESENTATIONS International standards and quality control procedures applied to nuclear instruments..........11 P. Urbański Quality assurance plan for gas filled detector manufacturing..................................................17 C. G. Hofer, M. E. Miller, S.I. Thorp, I. Martínez A fault tree for common problems with TLD readers..............................................................21 M. López Rodríguez QC test on radiation detectors and the associated nuclear counting systems...........................27 F.J. Ramírez-Jiménez, L. Mondragón-Contreras, P. Cruz-Estrada Quality control tests for radiation survey instruments.............................................................35 S.L.C. Mdoe, Y.Y Sungit Quality control test for nuclear counting systems....................................................................43 R. Engels and H. Kaufmann Quality control of nuclear ADC’s with a new FPGA based pulser.........................................53 P.P. Vaidya, M. Vinod, T.S. Ananthakrishnan, P.K. Mukhopadhyay ABBREVIATIONS AND ACRONYMS................................................................................57 LIST OF PARTICIPANTS......................................................................................................59 1. SUMMARY 1.1. INTRODUCTION Nuclear instruments (NI) are the fundamental tools for deriving benefits from any application of nuclear science and technology. They are widely used in areas such as environmental monitoring, industry, human health, and nuclear research; therefore, the user profile can vary from academic researchers, healthcare professionals, industrial technologists, and environmental scientists to radiation protection and reactor personnel. The International Atomic Energy Agency (IAEA) assists the Member States in the acquisition, maintenance, repair, modification and refurbishment of nuclear instruments. In this respect, Member States have an interest in building up their capacity for self-reliance and sustainable activities. Practical expertise and transfer of knowledge are pre-requisites for progress towards these objectives. There are several kinds of testing on nuclear instruments, for example, type-testing done by suppliers to ensure that equipment meets design criteria and functionality, it is similar to the acceptance testing that must be made at the reception of the equipment by the end users. In many Member State laboratories, Quality Control (QC) tests after repair are needed to guarantee that the instrument keeps its original characteristics. Quality Assurance (QA)/QC tests are done by end-users, for example, medical physicists in the field of human health to ensure clinical fitness of instrumentation. In many cases, electronic engineers need to make these measurements in order to guarantee the accuracy and precision of the obtained results. QC procedures are a key aspect in the operation of instruments and in the reliability of the data obtained. These procedures are particularly important as several national institutes have modernized/refurbished their nuclear instruments to meet current end-user demands like automatic control, data acquisition, and evaluation towards the traceability of data. Modernizations such as these highlight a growing demand for proper and suitable QC procedures for testing as well as relevant test instructions. In these proceedings some examples of the different kinds of testing are addressed as samples of the real work made in the field in order to figure out the complexity of the activities of the Nuclear Instrumentation specialists. Improper operation of nuclear instruments can lead to inaccuracy of a whole nuclear system, a condition which can be identified through proper test procedures. There are test procedures both for specific sections of radiation measuring systems and also for complete systems in order to verify that items meet their specified requirements or technical specifications. Test procedures are therefore important for quality control as they enhance the reliability of the operation of instruments and of the data obtained. The refurbishment of nuclear instruments deals with typical nuclear sections like the single- channel analyser (SCA), the multi-channel analyser (MCA) and counting systems. These basic sections are encountered in any equipment for environmental radiation monitoring, nuclear applications in human health, nuclear research and nuclear technology based industrial applications. The refurbishment/modernization of equipment improves the quality of the measurements and, in many cases, allows the continuation of vital activities that would otherwise be stopped due to the unavailability of proper high cost instruments. Refurbishment or modernization is commonly performed by using microprocessors and microcontrollers. As a result it is sometimes necessary to design new test procedures for the verification and validation of the operation of the modified instrument in order to assure the overall quality of the “new equipment”. 1 The objective of the Technical Meeting is to present results achieved in the area of QC procedures, tests and test instructions for Nuclear Instrumentation applied in environmental monitoring, industry, human health, and nuclear research. These results relate to current activities and future trends in the field of QA/QC procedures and their validation procedures. Further procedures on control software as utilized in Multi Channel Analyzers (MCA) and nuclear counting systems (in environmental monitoring, nuclear spectroscopy, industrial applications, etc.) were discussed. The meeting intended to address and collate existing procedures for future applications of QA/QC. This publication reflects the priority needs of Member States in the field of QA/QC procedures, tests and their test instructions, and makes suggestions as to how to respond to these needs. The emphasis of the document is on the current status of activities. QC validation procedures, test procedures/instructions and education and training leading to self- sustainability are also covered. It is foreseen that this document will be published by the IAEA. Member States will gain knowledge necessary to increase their QC performance capacity for nuclear instruments and to improve quality control capability for maintenance, repair, modernization and/or refurbishment of nuclear instruments as well as for data evaluation. Selected documents, presentations and the related software packages created for the Technical Meeting (TM) are available on CD. 1.2. INTERNATIONAL STANDARDS FOR NUCLEAR INSTRUMENTATION International standards play an important role in QC management. Many basic QC procedures are contained within the international standards. Nuclear instruments must meet not only general requirements included in these QC standards, but also strict rules related to ionisation radiation. The results of a survey of international standards related to Nuclear Instrumentation and QC tests conducted by the Institute of Nuclear Chemistry and Technology, Poland, were presented in Paper 1. From among 39’336 active international standards published by such organizations as: International Standards Organization (ISO); International Electrotechnical Commission (IEC); European Committee for Standardization (CEN); and European Committee for Electrotechnical Standardization (CENELEC), only 582 are devoted to nuclear subjects. It is sometimes difficult to find an appropriate standard for a particular instrument. This is due to the fact that standards are issued by different organizations and often a multifunctional approach is used in classification. In order to facilitate this search, the list of all 582 standards devoted to Nuclear Instrumentation was arranged according to the International Classification for Standards (ICS) and presented. A list of several test procedure standards for radiation detectors was presented in Paper 4. H. Kaufmann, IAEA, pointed out that quality control testing and standards applicable to NI are not well digested by the Member States. A good starting point to improve this situation is to clearly identify which standards are available. In some cases the standards are not updated (Paper 4) or the new revisions appear after a very long time. For example, the D 7282 – 06 ASTM standards entitled “Standard Practice for Set-up, Calibration, and Quality Control of Instruments Used for Radioactive Measurements” only appeared in July 2007. The information included in this standard was presented during the meeting. This procedure deals with commonly used nuclear counting instruments: alpha spectrometers, gamma spectrometers, gas proportional counters and liquid scintillation counters. 2 1.3. SPECIAL TEST PROCEDURES FOR NEWLY DEVELOPED INSTRUMENTS Special test procedures may need to be designed to verify and validate the operation of newly developed NIs and refurbished or modernized equipment. Failure or poor performance of dedicated nuclear instruments such as personal radiation detection systems or safety related systems can lead to critical errors. Quality control of front-end electronics in NI needs to be considered in both modernized and refurbished NIs as well as in newly designed ones. Procedures to test homogeneity of detectors as well as linearity tests for the amplifier(s) and Analog to Digital Converters (ADC) must be performed. As examples of special test procedures needed for newly developed instruments, the case of a nuclear ADC is presented. The Electronics Division, BARC, India, is designing a precision and sliding pulse generator for quality control of nuclear ADCs (Paper 7). The pulse generator is based on 16 bit Digital to Analog Converter (DAC) and Field Programmable Gate Array (FPGA) technology. For full-scale pulse amplitude of 10 V, a minimum step size of almost 150 µV can be obtained using 16-bit DACs. To reduce the step size further down to almost 10 µV, an interpolation method is employed. Use of mechanical switches and potentiometers on the front panel has been avoided to achieve increased reliability. Parameters such as operational mode (precision/sliding), pulse amplitude, frequency, pulse duration, sweep period, etc. are entered via keypads and shown on a LCD display. The pulse amplitude can be varied from 0 V to 10 V and the frequency from 1 Hz to 300 kHz. The pulse width can be changed from 1 µs to 1 ms in sliding mode and sweep period can be set from 5 to 1000 s. The pulser has a stable output in the precision mode and is suitable for measuring the drift and temperature coefficient of nuclear ADCs. It can also be used for testing the differential DNL, and integral nonlinearity (INL) of these ADCs. It is expected that the pulser would be suitable for measurement of differential nonlinearity by ramped amplitude method without getting spurious values due to correlation effects. Procedures for performing these measurements have been described. The values of DNL and INL can be found from the acquired histogram of the ADC output using a software program. A prototype keypad with programmable precision and sliding pulser giving flat-top output has been constructed. Preliminary tests have shown good integral linearity and temperature stability of the output. A plan for using this pulser to test the functionality and performance of nuclear ADCs at the design stage was presented. Some of these tests can be used for QA purposes by users of nuclear ADCs. For measurement of INL and DNL, the method given in the IAEA-TECDOC-363 was followed. 1.4. QC TEST PROCEDURES FOR MANUFACTURING OF DETECTORS The Instrumentation and Control Department of Comisión Nacional de Energía Atómica, Argentina, has developed a set of QC test procedures in the frame of the Instrumentation and Control QA system. This is designed to ensure that manufactured detectors work properly before they are delivered to end users (Paper 2). These procedures are part of the manufacturing work plan for a project providing several types of gas filled detectors to the Argentine company INVAP, who is responsible for installing them in the reactor they have built for the Australian Nuclear Science and Technology Organisation (ANSTO). 3