Development of a windowless multi-wire proportional chamber (MWPC) counting system for measuring extended-area beta source

A windowless MWPC counting system has been developed to measure surface emission rate of extended-area sources. A new anode and guard plane design gives better electric-field uniformity in the (250×200)mm² sensitive volume relative to a previous-generation MWPC at KRISS, which has been used as a national standard with uncertainty <1%. The conditions of stable operation for the new MWPC system were studied, and the uncertainty was estimated with an extended-area ³⁶Cl source. The relative combined standard uncertainty was evaluated to be 0.23%, a 50% improvement over the previous-generation MWPC counting system.

A primary standard for the measurement of alpha and beta particle surface emission rate from large area reference sources

A large area windowless gas flow multi wire proportional counting system for the calibration of large area reference sources has been developed as a primary standard at Bhabha Atomic Research Centre (BARC). The counting system consists of a multi wire proportional counter (MWPC), vacuum system, gas flow system and pulse processing units. The MWPC detector assembly consists of a vacuum tight aluminum enclosure, multi wire grid and sliding source tray. Various detector characteristics like operating characteristics curve, Fe-55 spectrum for beta discriminator threshold setting and dead time of the measurement system were studied and determined in order to achieve an optimized detection capability. The surface emission rates of different source strengths were measured and their relative combined standard uncertainties were determined. Large Area Sources Comparison Exercise (LASCE) was organized by International Committee on Radionuclide Metrology (ICRM) working group and coordinated by National Institute for Ionising Radiation Metrology (ENEA), Italy, to demonstrate equivalence of surface emission rate measurements at the international platform. BARC participated in the programme and the results of LASCE are also discussed in this paper.