Radiation-induced Electron Paramagnetic Resonance Signals Research Articles

Identification and dose assessment of irradiated cumin by EPR spectrometry

The use of electron paramagnetic resonance spectroscopy to accurately distinguish irradiated from unirradiated cumin and assess the absorbed dose to radiation-processed cumin is examined. The results were successful for identifying both irradiated and unirradiated cumin. Additive reirradiation of the cumin produces a reproducible dose response function, which can be used to assess the initial dose by back-extrapolation. Third-degree polynomial and exponential functions were used to fit the EPR signal/dose curves. It was found that the 3rd degree polynomial function provides satisfactory results without correction for decay of free radicals. The exponential fit to the data cannot be used without correction of decay of free radicals. The stability of the radiation-induced EPR signal of irradiated cumin was studied over a storage period of 6 months. The additive reirradiation of some samples was carried out at different storage times (10, 20 and 30 days) after initial irradiation.

Elimination of the background signal in tooth enamel samples for EPR-dosimetry by means of physical–chemical treatment

A method of elimination of the background EPR signal in tooth enamel is proposed. This method implies treatment of enamel powder by highly active reduction reagent hydrazine with subsequent washing out by ethanol-water solution. Such treatment results in reducing both the native background signal (which is assumed to be originated by the organic component) and the mechanical induced EPR signal in enamel. Testing of the efficiency of hydrazine treatment is made for different sizes of enamel powder. It is shown that the optimal results are obtained for a powder fraction of about 100–200μm. The radiation-induced EPR signal in enamel is practically not changed after treatment by hydrazine.

In vivo EPR dosimetry of accidental exposures to radiation: experimental results indicating the feasibility of practical use in human subjects

Low frequency electron paramagnetic resonance (EPR) provides the potential advantage of making accurate and sensitive measurements of absorbed radiation dose in teeth in situ, i.e. without removing the teeth from the potential victim. The potential limiting factors for making such measurements are: (1) whether low frequency EPR is sufficiently sensitive to detect radiation-induced signal in human teeth; (2) whether sufficient sensitivity can be maintained under in vivo conditions. In this manuscript, we summarize results indicating that this approach is feasible. Using 1.2 GHz EPR spectroscopy, we found that the lower limit for these measurements in isolated human teeth is 0.2 Gy or lower. Measurements of radiation-induced EPR signals in the teeth of living rats were achieved with sufficient sensitivity to indicate that, when taking into consideration the larger mass of human teeth, similar measurements in human teeth in situ would provide sensitivity in the dose range for potential accidental exposures. We estimate that the current lower limit for detecting radiation doses in human teeth in situ (in vivo) is 0.5–1.0 Gy; this would be sufficient for determining if a person has been exposed to potentially life threatening doses of ionizing radiation. The limiting factor for sensitivity appears to be background signals rather than signal/noise, and there are feasible means to overcome this problem and further increase sensitivity. The additional instrumental developments required to make an effective in vivo EPR dosimetric spectrometer for the measurements in teeth in human subjects in situ, seem quite achievable.

EPR detection of foods preserved with ionizing radiation

The applicability of the epr technique for the detection of dried vegetables, mushrooms, some spices, flavour additives and some condiments preserved with ionizing radiation is discussed. The epr signals recorded after exposure to gamma rays and to beams of 10 MeV electrons from linac are stable, intense and specific enough as compared with those observed with nonirradiated samples and could be used for the detection of irradiation. However, stability of radiation induced epr signals produced in these foods depends on storage condition. No differences in shapes (spectral parameters) and intensities of the epr spectra recorded with samples exposed to the same doses of gamma rays ( 60Co) and 10 MeV electrons were observed

Aspects of detection of irradiated foods by EPR spectroscopy

Some methodological aspects important for the detection of irradiated foods by the EPR spectroscopy are discussed. These are: specificity and stability of the EPR signals produced by ionizing radiation in foods, complexity of radiation induced EPR signals and their detection at different doses, the dose dependence of the intensities of the EPR signals involved. The importance of the native EPR signals observed in foods for the detection of irradiation and the role of quantitative measurements in the development of detection methods are shown.

EPR Dosimetry of Cortical Bone and Tooth Enamel Irradiated with X and Gamma Rays: Study of Energy Dependence

Previous investigators have reported that the radiation-induced EPR signal intensity in compact or cortical bone increases up to a factor of two with decreasing photon energy for a given absorbed dose. If the EPR signal intensity was dependent on energy, it could limit the application of EPR spectrometry and the additive reirradiation method to obtain dose estimates. We have recently shown that errors in the assumptions governing conversion of measured exposure to absorbed dose can lead to similar "apparent" energy-dependence results. We hypothesized that these previous results were due to errors in the estimated dose in bone, rather than the effects of energy dependence per se. To test this hypothesis we studied human adult cortical bone from male and female donors ranging in age from 23 to 95 years, and bovine tooth enamel, using 34 and 138 keV average energy X-ray beams and 137Cs (662 keV) and 60Co (1250 keV) gamma rays. In a femur from a 47-year-old male (subject 1), there was a difference of borderline significance at the alpha = 0.05 level in the mean radiation-induced hydroxyapatite signal intensities as a function of photon energy. No other statistically significant differences in EPR signal intensity as a function of photon energy were observed in this subject, or in the tibia from a 23-year-old male (subject 2) and the femur from a 75-year-old female (subject 3). However, there was a trend toward a decrease (12-15%) in signal intensity at the lowest energy compared with the highest energy in subjects 1 and 3. Further analysis of the data from subject 1 revealed that this trend, which is in the opposite direction of previous reports but is consistent with theory, is statistically significant. There were no effects of energy dependence in the tooth samples.

Applications of EPR spectroscopy to radiation treated materials in medicine, dosimetry, and agriculture

Survey is given of the EPR studies on irradiated bone mineral referred to transplantology, physiology, pathology, dosimetry and to the detection of irradiated food. Stability, dose-dependency and nature of radiation-induced EPR signal in bone mineral (hydroxyapatite) are discussed. Paramagnetic centers produced by radiation as “labels” as applied to biomedical experiments and dosimetry are evaluated. Results on the detection of irradiated fruits, vegetables, and other dry food products are presented.

Electron Paramagnetic Resonance of Radiation Damage in a Lunar Rock

ALTHOUGH lunar material has been exposed to radiations from indigenous radioactive atoms, solar wind protons and cosmic ray particles for a very long time, no electron paramagnetic resonance (EPR) signals attributable to natural radiation damage had been observed in the returned Apollo 11 and 12 samples1–3. We report here evidence for the presence of radiation induced EPR signals in one of the lunar samples (12021–42) we have examined.