Abstract Irradiation of Harshaw TLD-100 chips by a thermal neutron fluence of about 10 16 n cm −2 in a reactor has caused an increase of their thermoluminescence output by a factor of about 8000 times. The increase is more or less proportional to the thermal neutron fluence, at least up to 10 16 n th cm −2. The irradiated TLDs are stable in their thermoluminescence output. As the glow curves before and after irradiation are similar, the original number of luminescence centres seems to have been increased by this irradiation. As a result, these TLD's are much more sensitive than even the most sensitive TLD presently available in the market.