Marc F. Desrosiers

CURRENT STATUS OF THE EPR METHOD TO DETECT IRRADIATED FOOD

This review gives a brief outline of the principles of the EPR detection method for irradiated foods by food type. For each food type, the scope, limitations and status of the method are given. The extensive reference list aims to include all which define the method, as well as some rarely cited works of historical importance.

Advancements in accuracy of the alanine dosimetry system. Part 2. The influence of the irradiation temperature

Abstract Systematic measurements of the temperature coefficient for alanine electron paramagnetic resonance (EPR) response have been performed for irradiation in the temperature range (10–50)°C and in the absorbed dose range (1–100) kGy at the dose rate 9.5 kGy/h. During the 60 Co -ray irradiation, - l -alanine dosimeters were kept in a sealed aluminum holder that provided an effective heat exchange with the temperature-controlled environment. The time between the irradiation and signal measurements was standardized, and a reference sample fixed in the resonant cavity was used to correct the signals for small variations in the spectrometer sensitivity. The temperature coefficient for each dose was determined from approximately 30 experimental points processed by the weighted least-squares technique after the necessary statistical tests were done. The temperature coefficients thus determined were considerably lower than previously reported. The dose dependence of the temperature coefficient features a minimum at (20–30) kGy (about 0.135%/K) with higher values at 1 kGy (0.17%/K) and at 100 kGy ((0.175–0.19) %/K). With the exception of very high doses, no significant distinction was found between the temperature coefficients of Bruker and NIST dosimeters, which differ in shape and binder content.

Advancements in accuracy of the alanine dosimetry system. Part 1. The effects of environmental humidity

A one-year study of the EPR signal of g-irradiated ( 60 Co) L-a-alanine with simultaneous monitoring of the cavity Q-factor was undertaken. The widespread opinion that the EPR signal remains absolutely stable under normal laboratory storage conditions is inaccurate. At 0% humidity, the signal can be regarded as stable within 21% of its initial value for 6 months for 1 and 10 kGy doses, but for only 3 months for 100 kGy. When stored at the same relative humidity values up to 60%, the fading rates for dosimeters irradiated to 1 and 10 kGy are similar, whereas signals of dosimeters irradiated to 100 kGy fade considerably faster for all humidities. The rates of fading increase with the relative humidity, especially above 60% R. H. Environmental humidity also deteriorates the accuracy of alanine dosimetry by changing the resonant cavity Q-factor. This is particularly important when irradiated alanine dosimeters are used as instrument calibration standards. Short-term changes in alanine EPR signal amplitudes were recorded upon removal of the irradiated dosimeters from their storage environments. The importance of an in situ standard to correct for measurement errors due to environmental eAects is demonstrated. # 2000 Elsevier Science Ltd. All rights reserved.

Estimation of the absorbed dose in radiation-processed food--2. Test of the EPR response function by an exponential fitting analysis.

The use of electron paramagnetic resonance spectroscopy to accurately evaluate the absorbed dose to radiation-processed bones (and thus meats) is examined. Additive re-irradiation of the bone produces a reproducible dose response function which can be used to evaluate the initial dose by back-extrapolation. It was found that an exponential fit (vs linear or polynomial) to the data provides improved accuracy of the estimated dose. These data as well as the protocol for the additive dose method are presented.

Critical evaluation of the sugar-EPR dosimetry system

Abstract Sugar has received much attention as an emergency dosimeter for the general populace. This study was undertaken to clarify several conflicts in the literature. Here we report on the spectral characteristics of common ‘cane’ sugar and sucrose, the lower limit of detection for cane sugar, and the influence of absorbed dose on the study of time-dependent EPR signal intensity changes.

Examination of gamma-irradiated fruits and vegetables by electron spin resonance spectroscopy

Abstract The ESR spectra of the seeds, pits, shells, and skins of a variety of irradiated fruits and vegetables were measured. All spectra, control and irradiated, contained a single resonance with a g-factor of 2.00. Additional resonances due to Mn2+ were observed for the drupelets of blackberries and red raspberries. An unusual radiation-induced radical was observed for irradiated mango seed; however, the signal decayed completely within a few days. It was concluded that only in a few specialized cases could the ESR resonances observed be suitable for postirradiation monitoring or dosimetry.

Mechanically-induced generation of radicals in tooth enamel

Mechanical instrumentation of enamel leads to the formation of long-lived free radicals that can be conveniently measured by electron paramagnetic resonance (EPR) spectroscopy. Powdered enamel tissue exhibited EPR signals remarkably similar to the radicals formed by ionizing radiation. The observations described below lead to the conclusion that physical stress will induce a free-radical formation in dental tissues. These observations have significance for other areas of study such as dosimetry and archeological dating.

Complex time dependence of the EPR signal of irradiated L-α-alanine☆

Abstract Measurements of the EPR signal amplitude of γ-irradiated L-α-alanine with use of an adjacent reference sample have revealed variations in the signal intensity within hours and days after irradiation. The character of the time dependence of the amplitude varies with dose and the amplitude changes reach 1–1.5%. This observation favors the hypothesis that irradiated alanine contains several paramagnetic centers. Usefulness of adjacent reference samples in alanine dosimetry is also demonstrated.

Uncertainties in alanine dosimetry in the therapeutic dose range

A method for evaluating the overall uncertainty of alanine EPR transfer dosimetry in the therapeutic dose range is described. The method uses experimental data on EPR signal reproducibility from replicate dosimeters irradiated to low doses (1-5 Gy), estimates of Type B uncertainties, and Monte Carlo simulations of heteroscedastic orthogonal linear regression. A Bruker ECS106 spectrometer and Bruker alanine dosimeters have been used for this evaluation. The results demonstrate that alanine dosimetry can be used for transfer dosimetry in that range with the overall uncertainty 1.5-4% (1sigma) depending on the dose, the number of replicate dosimeters. and the duration of the calibration session (the session should not exceed one working day).

Advancements in accuracy of the alanine EPR dosimetry system: Part III: Usefulness of an adjacent reference sample

Abstract High stability of the radiation-induced radicals in alanine and the high reproducibility of alanine response to radiation make it possible to determine radiation doses accurately with Electron Paramagnetic Resonance (EPR) spectral analysis. Small uncontrollable variations of the EPR spectrometer sensitivity, however, can significantly deteriorate the accuracy of the method. The errors due to these variations can be eliminated or markedly decreased if an adjacent reference sample (such as a synthetic ruby crystal) is permanently present in the cavity, and if ratios of the alanine and ruby signal amplitudes are used throughout the dosimetric session instead of the absolute alanine amplitudes. This paper addresses methodological aspects of using such adjacent reference samples in alanine dosimetry and provides illustrations of the usefulness of this technique.