K-band ESR spectra of calcite stalagmites from southeast and south Brazil

Samples of calcite stalagmites from Caverna Santana (São Paulo State) and Caverna Botuvera (Santa Catarina State), southeastern and southern Brazil, respectively, were studied by electron spin resonance (ESR). The more common microwave frequency (X-Band, 9.5 GHz) as well as higher frequency K-band, 24 GHz were employed for the determination of the age of the samples. Even after extensive signal averaging, the dosimetric signal is not very well defined in the X-band (9.5 GHz). Using the K-band spectrometer it was possible to clearly identify the 6 hyperfine lines of Mn2+ and other paramagnetic centers in the g=2 region: SO2− and CO2− radicals. The use of high microwave frequency gives better S/N and spectral resolution making the identification of the dosimetric signal easier. The total dose (TD) or equivalent dose (ED) deposited in the samples was 2.3±0.3 Gy and 1.7±0.4 Gy for Caverna Botuvera samples and 2.6±0.7 Gy for the sample of Caverna Santana, giving an age of 2.9±0.7 ky, 2.1±0.8 ky and 3±1 ky, respectively. These first results are compatible with U/Th analysis. Due to the low S/N precision, measurements were possible only with the use of secondary standard composed on Mn2+ lines, naturally present in this sample.