For an EPR spectral intensity standard useful for human biophysical dosimetry, the following are the requirements: 1) A solid standard which is non-hygroscopic 2) Should have an EPR spectrum which can be measured at room temperature. 3) The spectrum should be non-overlapping with the radiation-induced signals from teeth. 4) The standard sample should be easily prepared and standardized. Several groups have tried to develop such an EPR spectral intensity standard with the above mentioned properties but did not succeed. We have developed successfully a standard which complies with the criteria described above. In brief, we grew single crystals of the diamagnetic compound, 4-hydroxy 2,2,6,6 tetramethyl piperidine by slow evaporation. During crystal growth, we doped the paramagnetic molecule, 4-hydroxy 2,2,6,6 tetramethyl piperidine-1-oxyl, which has significant structural similarity with the host molecule. We obtained crystals using several concentrations of the dopant to arrive at an EPR spectrum with intensity in the range of the radiation-induced signals in the teeth.
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