AbstractThermoluminescence (TL) has been observed in γ‐irradiated extended‐chain crystals of polyethylene above room temperature. The TL curve, which exhibits four peaks at 50, 90, 120, and 140°C, is different from that given by folded‐chain crystals, in both shape and intensity. In particular, a shape, strong glow peak is observed at 140°C, corresponding to the melting temperature of the extended chain crystals. These results are discussed in relation to independent measurements by differential scanning calorimetry and electron spin r