The LET factors RＬＥＴ(RＬＥＴ≈005) of neutron response for LiF(Mg,Cu,P)TLD have been determined experimentally due to the existing LET effects of the response for LiFTLD to neutron absorbed dose.Based on the data,one experimental method to define the photon fluence in various n+γ mixed fields in the fast neutron reactor with coupled 6LiF7LiFTL detectors has been checked.The experimental results show that the ratios of the TL due to the effect of neutrons in 7LiF(Mg,Cu,P)to the total TL due to the combined effects of the γrays and neutrons are between 81% and 17.1%.In order to reduce the effect caused by the uncertainty of the neutron spectra and improve the accuracy of the measurement for the photon fluence,we propose a new LiFTLD,in which there are 50% 6LiF and 50% 7LiF.It is coupled with a 6LiFTLD to measure the photon fluence in the n+γ mixed fields.