Sammendrag
The amino acid L-α-alanine is the most commonly used material for solidstate
electron paramagnetic resonance (EPR) dosimetry, due to the formation of highly
stable radicals upon irradiation, with yields proportional to the radiation dose. Two
major alanine radical components designated R1 and R2 have previously been uniquely
characterized from EPR and electron−nuclear double resonance (ENDOR) studies as
well as from quantum chemical calculations. There is also convincing experimental
evidence of a third minor radical component R3, and a tentative radical structure has
been suggested, even though no well-defined spectral signature has been observed
experimentally. In the present study, temperature dependent EPR spectra of X-ray
irradiated polycrystalline alanine were analyzed using five multivariate methods in further
attempts to understand the composite nature of the alanine dosimeter EPR spectrum.
Principal component analysis (PCA), maximum likelihood common factor analysis
(MLCFA), independent component analysis (ICA), self-modeling mixture analysis
(SMA), and multivariate curve resolution (MCR) were used to extract pure radical
spectra and their fractional contributions from the experimental EPR spectra. All methods yielded spectral estimates resembling
the established R1 spectrum. Furthermore, SMA and MCR consistently predicted both the established R2 spectrum and the
shape of the R3 spectrum. The predicted shape of the R3 spectrum corresponded well with the proposed tentative spectrum
derived from spectrum simulations. Thus, results from two independent multivariate data analysis techniques strongly support
the previous evidence that three radicals are indeed present in irradiated alanine samples.
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