Electron spin resonance studies of electron irradiated peptides. A single crystal of N-acetylglycine at 77 K.
Free radicals formed in single crystals of N-acetylglycine, irradiated and observed at 77 K, have been studied using ESR spectroscopy. Two different radical species were found. One radical (called ...
ESR study of L-alanine-1-13C irradiated at low temperatures.
The ESR spectra of l‐alanine‐1‐13C, x irradiated at low temperatures (T < 150°K), have been examined. The spectra have been interpreted in terms of a carboxyl radical similar to those postulated for other irradiated organic acids. From the values of the 13C hyperfine tensor it has been confirmed that the unpaired electron is essentially a 22pπ‐type electron located primarily on the carboxyl carbon and that this spin density interacts with the α proton. From the magnitude of the isotropic 13C hyperfine splitting it is found that the RCO2− structure is bent about 8° from planarity. The stable room‐temperature fragment in irradiated l‐alanine‐1‐13C exhibits essentially isotropic 13C splittings of 12.8 G.
Long term response stability of a well-type ionization chamber used in calibration of high dose rate brachytherapy sources
Well-type ionization chamber is often used to measure strength of brachytherapy sources. This study aims to check long term response stability of High Dose Rate (HDR)-1000 Plus well-type ionization chamber in terms of reference air kerma rate (RAKR) of a reference 137Cs brachytherapy source and recommend an optimum frequency of recalibration. An HDR-1000 Plus well-type ionization chamber, a reference 137Cs brachytherapy source (CDCSJ5), and a MAX-4000 electrometer were used in this study. The HDR-1000 Plus well-type chamber was calibrated in terms of reference air kerma rate by the Standards Laboratory of the International Atomic Energy Agency (IAEA), Vienna. The response of the chamber was verified at regular intervals over a period of eight years using the reference 137Cs source. All required correction factors were applied in the calculation of the RAKR of the 137Cs source. This study reveals that the response of the HDR-1000 Plus well-type chamber was well within ±0.5% for about three years after calibration/recalibration. However, it shows deviations larger than ±0.5% after three years of calibration/recalibration and the maximum variation in response of the chamber during an eight year period was 1.71%. The optimum frequency of recalibration of a high dose rate well-type chamber should be three years.