760
K. Komaguchi et al. / Spectrochimica Acta Part A 66 (2007) 754–760
4. Conclusions
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The ESR and ENDOR study revealed that 6Li enriched
lithium formate monohydrate, 6LiOOCH·H2O, is a promis-
ing material applicable to high-sensitive ESR dosimetry. The
decrease in line width by a factor of 0.61 (0.92 mT) compared
with that of ordinary LiOOCH·H2O (1.5 mT) was attained by
the 6Li enrichment: the signal intensity was seven to eight times
stronger than the alanine under the optimized spectrometer set-
tings for each sample, and the intensity linearly increased with
the absorbed dose in the low dose range from around 0.1 Gy.
On the other hand, the deuteration of crystallization water little
affected the signal intensity. By the accompanying enhance-
ment of the ESR intensity and resolution, we evaluated accurate
−
ESR parameters of the CO2 radical anion, formed in irradi-
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ENDOR observations revealed that at least four different Li
−
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−
theoretical DFT calculations, the CO2 radicals are located
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Acknowledgements
We thank Professor S. Yamanaka and Dr. H. Fukuoka for
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Instruments. This work was supported in part by the grant from
STINT (the Swedish Foundation for International Cooperation
in Research and Higher Education) and Wenner-Gren founda-
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6
Appendix A
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6Li2CO3 was synthesized as the starting material for the syn-
6
6
thesis of LiOOCH·H2O through the reaction of LiCl (2.1 g)
6
with excess amount of Na2CO3 (∼12 g) in water. Li2CO3 is
less soluble in water on increasing temperature, contrary to
NaCl as the by-product, which is more soluble with tempera-
ture, so that the mixture solution was warmed up to near 100 ◦C
6
to separate Li2CO3 crystals from the solution by filtration.
6
After giving twice rinses with hot water, the Li2CO3 crys-
tals were mixed with an excess amount of HCOOH in distilled
water, and then anhydrous 6LiOOCH crystals were obtained by
evaporation of the water together with HCOOH and CO2 as by-
products at 160 ◦C. Finally, the LiOOCH·H2O crystals were
6
recrystallized from water by keeping it in a desiccator at room
temperature.