The fuel areal density &rgr;Rmeasurement of imploded plastic hollow shell targets by use of a neutron activation technique is reported. Silicon was doped as an activatable tracer into a hollow shell of tritium‐contained deuterated polymer(CDTSi). This target was imploded by 0.53 &mgr;m Nd:glass laser light and the induced radioactivity of28Al was measured with a &bgr;‐&ggr; coincidence counting system. The collection efficiency was calibrated by the use of radioactive tracer24Na and was verified by comparing the estimated &rgr;Rwith that simultaneously measured by a knock‐on method.