The electron spin resonance (ESR) detects unpaired electrons, which are trapped and stabilized at lattice defects and impurities in substances. The number of trapped electrons is increased by natural and artificial irradiation of ionizing radiation. In a magnetic field, the unpaired electrons are raised to the excited state by absorbing the microwave energy. The absorbed energy is equivalent to the number of trapped electrons and thus to the radiation dose accumulated over the observed period.

The JEOL FA-100 X-band electron spin resonance (ESR) spectrometer was installed at LIAG, equipped with a variable temperature controller (ES-DVT4) for low-temperature measurements from the room temperature to 103 K. An in-house device for sample irradiation using a Varian VF-50J X-ray tube with the maximum energy of 50 kV and an integrated heating element (100—600°C) has been developed for artificial irradiations and preheats for samples within quartz glass tubes (Oppermann & Tsukamoto, 2015). This device is used to conduct single aliquot equivalent dose (D_e) measurements (Tsukamoto et al., 2015; 2017). An ESR age is derived by dividing the D_e by the environmental dose rate for the sample.

The new BRUKER ELEXSYS E500 X-Band ESR Spectrometer can measure samples at temperatures down to -263,15°C (10K) by helium-cooling.

Since ESR dating method was introduced to earth sciences in the mid-1970s, it has been applied to a wide range of substances. Calcium carbonate such as mollusc shells, corals or speleothems as well as tooth enamel were successfully dated. Another datable material is quartz. We are currently focusing on the quartz ESR dating for dating sediments, because ESR has a great potential to extend the age range of the luminescence dating. We are also developing the method of ESR thermochronology (King et al., 2016) using quartz to investigate mountain uplift/erosion and fault activity.