1 Quality Assurance of Radiation Protection Monitoring Instruments in India S.M. Tripathi*, Liji Daniel, Suresh Rao and D.N. Sharma Radiation Safety Systems Division, Bhabha Atomic Research Centre Mumbai-400085, India Abstract. Bhabha Atomic Research Centre (BARC) is the National Metrology Institute (NMI) for developing, maintaining and disseminating standards for ionizing radiation in India. Radiation Safety Systems Division (RSSD) of BARC has the requisite infrastructure in the form of experts, trained manpower, laboratories, equipments and facilities for providing calibration services to users and ascertaining traceability to international standards. It periodically participates in various international inter-comparisons. RSSD maintains reference radiation fields that are required for calibrating Radiation Protection Monitoring Instruments that form the backbone of the radiation monitoring programme for harnessing the benefits of nuclear energy and ionizing radiations. These instruments are type-tested and periodically calibrated at standard reference radiation fields to ensure their healthy working condition and fitness for their intended use. This paper describes the details of the standardization procedures adopted for reference radiation fields and infrastructure established and maintained at RSSD, BARC in accordance with the recommendations of ISO-4037. The paper describes the various tests that are carried out for radiation protection monitoring instrument to study the variation of the calibration factor with influencing quantities like linearity of response, energy response, angular dependence and overload characteristics. The results of these tests for typical instruments are also discussed. The present work also describes various types of indigenously developed radiation protection monitoring instruments and their performance characteristics. Adaptability of these instruments for the implementation of operational quantities are discussed briefly. It also dwells on the IAEA Quality Audit for radiation protection level calibrations, which RSSD has been participating since 2001. Our results of the quality audit are well within the acceptance limit (±7%) set by IAEA for the participating laboratories. KEYWORDS: Metrology, traceability, quality assurance, quality audit, radiation monitors, type testing 1. Introduction The quality of a radiation protection program depends on the quality of the radiation measurements made by the radiation protection monitoring instruments. Mostly the quality is unknown and is merely evaluated on the basis of the calibration. If these instruments are not calibrated then the decisions based on these instruments will be misleading. Quality assurance involves the methods used to ensure that the dosimetric measurements are correct and traceable to national standards. Radiation Standards Section of Radiation Safety Systems Division, Bhabha Atomic Research Centre, Mumbai maintains the national standards for ionising radiation in India. It is the apex laboratory to develop, maintain and disseminate standards for ionising radiation measurements. This paper describes the methods adopted for quality assurance of radiation protection monitoring instruments in India based on the recommendations of ISO-4037. 2. Reference standard for protection level calibration A 100.9 cc cylindrical graphite walled ion chamber is maintained as a reference standard for the calibration of protection level radiation monitoring instruments [1]. The sensitivity of this ion chamber was calculated and experimentally established according to the procedures for the dosimetry of X and gamma reference radiation specified in ISO 4037-2 [2]. Various parameters like saturation characteristics, linearity of response, energy response, polarity effect, short-term stability and long-term stability were studied to establish it as a reference standard. The output current of the ion chamber is measured using a sensitive digital picoammeter (UNIDOS, PTW make). The reference radiation fields maintained at BARC have been standardized using the 100.9 cc reference standard ion chamber. The overall uncertainty in the standardization of the radiation field with reference standard has been evaluated to be within ± 5% using the GUM method, recommended by ISO [3]. Recently
