Effect of absorbed dose and storage length on electron paramagnetic resonance (EPR) signal strength in irradiated alfalfa seeds

摘要

A kind of alfalfa seeds was irradiated by 1, 2, 3, 4 and 5 kGy at a dose rate of 6.288 kGy·h-1 in a self-shielded irradiator of 137Cs gamma rays. The EPR spectra, which were measured subsequently between 0.3401 and 0.3501 T, showed that there was a direct proportional relationship between the EPR signal strength of free radi- cals produced by gamma irradiation in the alfalfa seeds and absorbed dose. The first derivative EPR spectra of the al- falfa seeds were very clear and easy to identify. However, the EPR signal strength of the peak-to-peak amplitude de- creased rapidly and most of them decayed beyond 50% within 3 days after the seeds were irradiated. It tended to sta- bilize after half a month since the seeds were irradiated. The differences of the EPR signal strength between the irra- diated and unirradiated alfalfa seeds still remained. All seeds were stored at ambient temperature for more than 3 months. Therefore, using EPR spectrometry technique to measure free radicals in alfalfa seeds as a means to deter- mine whether the seeds have been irradiated or not is feasible, relatively fast and simple.