Comparison of Equivalent Doses Obtained with Various post-IR IRSL Dating Protocols of K-Feldspar

Five dating protocols with post-infrared infrared (IR) stimulated luminescence signals (i.e. pIRIR) were performed on the K-feldspar of loess samples. Two of them were the single-aliquot regenerative-dose protocol (SAR) with two-step pIRIR stimulation, with the first IR stimulation at 50°C or 200°C and the second at 290°C (pIR₅₀IR₂₉₀, pIR₂₀₀IR₂₉₀). Two of them were the SAR protocols with five-step or six-step IR stimulation at multiple elevated temperatures to 250°C or 300°C (MET-pIRIR₂₅₀, MET-pIRIR₃₀₀). The final one was the multiple-aliquot regenerative-dose (MAR) protocol with the MET-pIRIR₃₀₀ signal, together with a 500°C heat treatment administered before the test dose (‘MAR with heat’). The results show that when the equivalent dose (D_e) of the sample was less than 500 Gy, all of the protocols gave consistent results; however, when D_e exceeded 750 Gy, all of the SAR protocols underestimated D_e. The pIR₅₀IR₂₉₀ signal had the highest degree of underestimation, while the pIR₂₀₀IR₂₉₀, MET-pIRIR₂₅₀ and MET-pIRIR₃₀₀ signals had similar D_e values and similar degrees of underestimation. Possible reasons for the SAR D_e underestimation are discussed. We suggest that only the ‘MAR with heat’ protocol is suitable for samples with D_e exceeding 750 Gy.