The organic scintillator NE102A has been used to detect low energy X-rays (6-11 keV) in coincidence measurements of K-shell ionization probabilities. For 500 keV protons on Cu a timing resolution of better than 5 ns has been achieved. The influence of delayed light emission upon detection efficiency has been investigated. It has been found that 25% of the detected pulses are due to delayed light emission if the level of energy discrimination is set slightly above electronic noise. The efficiency of NE102A for undelayed detection of low energy X-rays has been determined by two independent methods.