Measurement of beta surface emission rate from an extended area 36Cl source using a multiwire proportional counter

We have developed, as a national standard, a windowless multiwire proportional counting (MWPC) system for gross measurements of α- and β-emitting radionuclides at an uncertainty level below 1%. Various detector characteristics have been studied and several working parameters of the system have been determined in order to achieve an optimized detection capability. The detector is commissioned through an international comparison of the β emission rate from an extended area 36Cl source. Correction for the dead time loss is made by the non-extendable dead time method. A linear extrapolation of pulse height spectrum is employed to correct for the loss in the detection efficiency due to discriminating against the events formed from a small number of original ion pairs. The surface emission rate was measured to be 1.84×103 counts/s with the relative combined standard uncertainty of 0.46%. The measured uncertainty indicates that the constructed MWPC is capable of serving as a national standard.