PULSED AND CW-ESR STUDIES OF CO2- IN CACO3 IRRADIATED BY HE+ AND GAMMA-RAYS FOR ESR DATING

Orthorhombic CO2- produced by gamma- and He+-irradiation in aragonite has been measured by electron spin resonance (ESR). An alpha/gamma> effectiveness ratio in producing defects, k-value, of 0.0027+/-0.0011 was obtained from the growth curve. Pulsed ESR provided the spin-spin relaxation times, T-2=1.25+/-0.04 mu s for orthorhombic CO2- in gamma-irradiated modern coral and T-2=1.58+/-0.02 mu s in nonirradiated fossil shell. The signal of the isotropic CO2- is found to be almost removed in the field sweep electron spin echo (ESE) spectrum, and the selective detection of orthorhombic CO2- becomes possible. ESR dating and dosimetry can be performed for impurity-included carbonates whose spectra are superposed using the ESE technique.