| Nuclear technology, atomic reactor and radioisotope had been widely developedand applied in recent years. It brought enormous economic benefits with hugeradioactive waste, and most of the waste were discharged into the sea. The first nuclearpower plant in Fukushima happened to be a serious nuclear leakage accident resultedfrom Japanese Earthquake in March2011. Especially after low-level fission product ofatomic reactor were discharged into the sea, radioactivity in surrounding seas had beenrapidly increased. The absorption and enrichment of radioactive nuclide in marineorganism would effect on quality security of aquatic products, which was directlyrelated to consumer’s physical health. Nuclear pollution was a factor can’t be ignored inall of the factors related to quality security of aquatic products. The paper summarizedand analyzed the methods to detect radio nuclide at home and abroad. Of which, themost popular methods including physical method and radiochemical analysis methodwere introduced, especially of cesium and strontium. The differences of the twomethods in detect mechanism, pretreatment process, sensitivity were compared, whichwould be of great importance not only to choose the proper test method according todifferent samples, but also establish a rapid and simple method for nuclide detection.We established a new physical method to detect radioactive nuclide in aquatic productsby using High Purity Germanium gamma spectrometer, and optimized the key detectionconditions. The method was applied to monitor nuclear pollution situation in Shandongimport and export in order to estimate the influence of Fukushima nuclear accident on aquatic products security in our country. The main contents were introduced as follows.1. According to the character of fission product, the method to detect nuclearpollution situation in aquatic products included two parts: physical method andradiochemical analysis method. The physical method was based on the ray which wasemitted by radioactive nuclide in order to a qualitative and quantitative analysis. Theradiochemical analysis method detected samples after enrichment and separation ofradionuclide, of which, there were three methods: precipitation, ion exchange, solventextraction. The conclusion was: the former had a simple pretreatment processing, highsecurity and high cost; the later one had a high sensitivity, complicated to operate,harm to operators, producing radioactive liquid waste which is difficult to deal with.2. High Purity Germanium(HPGe) gamma spectrometer took advantage of highpurity Germanium detection to detect gamma-ray emitted from radioactive nuclide, thendetermine the kinds and specific activity values. The physical method detection stepswere as follows: samples were processed with washing, air-dry, taking the edible partsand drying, crushing and filling, then test with HPGe gamma spectrometer. The dryingtime and temperature were decided by different samples; weigh the sample box beforeand after filling to record quality of the sample; the sample box should keep clear andsealed; the detection time was6-8h; saving the map in time. We used LaboratorySourceless Calibration Software (LabSOCS) to scale the machine, Genie-2000toanalysis the map to get the kind and specific activity value of the samples.3. Qualitative and quantitive analysis were using HPGe gamma spectrometer bydetecting gamma-ray which radiated by radio nuclide, sample thickness was animportant factor to detection effiency of HPGe gamma spectrometer, the experienceshowed that:75mm was the best sample thickness with the quality was300±20g; HPGegamma spectrometer was expensive, so optimizing detection time would be of greatimportance, the experience showed that: The optimum detection time was6-8h.4. The method established in2was applied to monitor the nuclear pollution situation in Shandong import and export aquatic products, the results showed: thedetection rate of positive samples was13.4%, the radionuclide were134Cs、137Cs and110mAg, the relevance ratio were6.92%、9.04%and4.34%, respectively. It wasimportant to note that the positive samples of134Cs also were that of137Cs, but theresults between137Cs and110mAg were completely independent except one codfishsample. The specific activity concentrated on1.0-9.9Bq/Kg,83%、91%'81%ofpositive samples, respectively. But the value of110mAg is higher than the other two, ofwhich, the specific value were up to13%, the highest value of the three nuclides were9.9,16.1and17.2Bq/Kg, which were under the limit standard in all over the world.From the time distribution, the months which presented higher detection rate wereMarch-May, July. The time was coincided with the anniversary of the JapaneseEarthquake, when the radioactive nuclide in marine organism reached the dynamicbalance. From the species distribution, the positive samples of134Cs and137Cs weremackerel, cod and hilsa herring with the percent of78%, at the same time, the positivespecies of110mAg were squid, which percent reached up to94%. |
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