According to the ‘Regulations on the Delivery of Low and Medium Level Radioactive Waste’, Notification No. 2021-26 of the Nuclear Safety and Security Commission, a history of radioactive waste and a total amount of radioactivity in a drum are mandatory. At this time, the inventory of radionuclides that make up more than 95% of the total radioactivity contained in the waste drum should be identified, including the radioactivity of H-3, C-14, Fe-55, Co-58, Co-60, Ni-59, Ni-63, Sr- 90, Nb-94, Tc-99, I-129, Cs-137, Ce-144, and total alpha. Among nuclides to be identified, gamma-emitting nuclides are usually analyzed with a gamma ray spectrometer such as HPGe. When a specific gamma-ray is measured with a detector, several types of peaks generated by recombination or scattering of electrons are simultaneously detected in addition to the corresponding gamma-ray in gamma-ray spectroscopy. Among them, the full energy peak efficiency (FEPE) with the total gamma energy is used for equipment calibration. However, this total energy peak efficiency may not be accurately measured due to the coincidence summing effect. There are two types of coincidence summing: Random and True. The random coincidence summing occurs when two or more gamma particles emitted from multiple nuclides are simultaneously absorbed within the dead time of the detector, and this effect becomes stronger as the counting rate increases. The true coincidence summing is caused by simultaneous absorption of gamma particles emitted by two or more consecutive energy levels transitioning from single nuclide within the dead time of the detector. This effect is independent of the counting rate but affected by the geometry and absolute efficiency of the detector. The FEPE decreases and the peak count of region where the energy of gamma particles is combined increases when the coincidence summing occurs. At the Radioactive Waste Chemical Analysis Center, KAERI, samples with a dead time of 5% or more are diluted and re-measured in order to reduce the random coincidence summing when evaluating the gamma nuclide inventory of radioactive waste. In addition, a certain distance is placed between the sample and the detector during measurement to reduce the true coincidence summing. In this study, we evaluate the coincidence summing effect in our apparatus for the measurement of radioactive waste samples.

Substrate affinity and insecticide sensitivity of acetylcholinesterase (AChE) from Daphnia magna S., Bombyx mori L., Musca domestica L., Myzus persicae S., Anguilla anguilla L., Cyprinus carpio L., Oryzias latipes T.&S., Homo sapiens L., Bos taurus L. were tested. The Km values of M. domestica AChE to acetylthiocholine (ATCh), propionylthiocholine (PTCh), butyrylthiocholine (BTCh) were 57.3 μM, 13.4 μM and 85.9 μM respectively, which were lower than those of A. anguilla, C. carpio, O. latipes, H. sapiens and B. taurus. In nontarget organisms, the I50 values of AChE to fenitroxon and DDVP were 1.5×10-6 M~7.8×10-5 M and 2.4×10-6 M~1.1×10-4 M respectively, thus they have lower sensitivity compared with M. domestica. The I50 value of M. persicae AChE to pirimicarb was 1.3×10-8 M, which was higher sensitivity compared with other test animals except D. magna. The I50 values of D. magna AChE to fenitroxon, DDVP, carbaryl, eserine, pirimicarb were 5.2×10-10 M~2.1×10-8 M, which were higher sensitivity compared with the other test animals used for this study. cDNA of Daphnia magna AChE precursor was sequenced and compared with those of Musca domestica, Drosophila melanogaster and Torpedo californica.