探索电离室测量的新安培计溯源路线
Exploring a new ammeter traceability route for ionisation chamber measurements
摘要：
我们比较了商品安培计和自制的积分静电计在读取小于100 pA的电离室电流时的性能。积分静电计用未知电流对电容器充电，并测量由此产生的电压变化率，而安培计使用高值电阻作为放大器的反馈元件，将电流转换为电压。两个系统的噪声性能非常相似，平均时间小于1000秒。这两个系统都使用具有百万分之一（ppm）精度的参考电流源进行校准，揭示了静电计指示电流的460ppm的误差，来源不明。该误差完全在放射性核素校准的不确定度预算内，但远大于电容、电压和时间的可追溯校准中的单个不确定度。电离室电流中的噪声远大于两种仪器的本底噪声，测试提供了强有力的迹象，表明过量噪声源自用于为电离室供电的高压源。
英文摘要：
We compared the performance of a commercial ammeter and a home-made integrating electrometer in reading ionisation chamber currents less than 100 pA. The integrating electrometer charges a capacitor with the unknown current and measures the resulting rate of change of voltage, whereas the ammeter uses a high-value resistor as the feedback element to an amplifier which converts current to voltage. The noise performance of both systems was very similar for averaging times less than 1000 seconds. Both systems were calibrated using a reference current source with 1 part per million (ppm) accuracy, revealing an error of 460 ppm in the electrometer indicated current, of unknown origin. This error is well within the uncertainty budget for radionuclide calibrations, but much larger than the individual uncertainties in the traceable calibrations of capacitance, voltage and time. The noise in the ionisation chamber current was much larger than the noise floor of both instruments, with tests providing strong indication that the excess noise originated in the high voltage source used for energising the chamber.
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