Study on the EPR/dosimetric properties of some substituted alanines

Polycrystalline phenyl-alanine and perdeuterated l-αα-alanine (l-αα-alanine-d4) were studied as potential high-energy radiation-sensitive materials (RSM) for solid state/EPR dosimetry. It was found that phenyl-alanine exhibits a linear dose response in the dose region 0.1–17 kGy. However, phenyl-alanine is about 10 times less sensitive to γγ-irradiation than standard l-αα-alanine irradiated at the same doses. Moreover, the EPR response from phenyl-alanine is unstable and, independent of the absorbed dose, decreases by about 50% within 20 days after irradiation upon storage at room temperature. γγ-irradiated polycrystalline perdeuterated l-αα-alanine (CD3CD(NH2)COOH) has not previously been studied at room temperature by EPR spectroscopy. The first part of the present analysis was with respect to the structure of the EPR spectrum. By spectrum simulations, the presence of at least two radiation induced free radicals, R1=CH3C
• (H)COOH and R2=H3N+−C
• (CH3)COO−, was confirmed very clearly. Both these radicals were suggested previously from EPR and ENDOR studies of standard alanine crystals. The further investigations into the potential use of alanine-d4 as RSM, after choosing optimal EPR spectrometer settings parameters for this purpose, show that it is ca. two times more sensitive than standard l-αα-alanine.