AMS radiocarbon measurement with high accuracy

A project of 14C trace on deep water in South China Sea requires an accuracy of AMS radiocarbon measurement better than 2.5‰, which is higher than the accuracy for routine measurements of the NEC compact AMS system at Peking University. A series of modifications have enhanced the stability of the AMS system, minimizing fractionation effects and improving the accuracy and quality control of measurements. The ripple of terminal voltage has been reduced from 100 V to less than 50 V. The variation of beam currents from different samples is within 20% and a special tool is designed for proper installation of sample wheels. Measurements on standards and secondary samples demonstrate an improvement in accuracy to <2.5‰.