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The yields of 85Krm, 87Kr and 88Kr of neutron-induced fission of 239Pu are important nuclear parameters. They have a moderate half-life, are β- decay and emission γ-rays with a certain probability, so it is appropriate to use γ-ray spectrum method to determine their yield. At present, there are few experimental data with large deviation abroad and no experimental results have been reported in China. The yield measurements of 85Krm, 87Kr and 88Kr of thermal-neutron-induced fission of 239Pu were carried out based on the irradiation of plutonium target by Xi’an Pulsed Reactor rabbit system. The purified plutonium solution was then titrated and dried to prepare the silica-encapsulated plutonium target. Three kinds of measurement experiments were designed: γ-ray nondestructive method for the relative yield of 88Kr and 99Mo, gas-solid separation method for 85Krm, 87Kr and 88Kr and γ-ray nondestructive method for the relative yield of 85Krm, 87Kr and 88Kr. After the target irradiation and cooling, the fission products were measured by the above-mentioned methods. The efficiency of the three kinds of experimental samples was calibrated by the equivalent efficiency curve method. The plan source of organic glass package was used to equate the efficiency calibration of quartz tube source, and the plan source of stainless steel package with the same thickness and material as the measuring source was used to equate the efficiency calibration of 50 mL gas source. By Monte Carlo simulation, the suitable equivalent position was selected, and the efficiency value was fine corrected (less than 0.8%). The uranium target was prepared in the same way of plutonium target. The relative yields of 85Krm, 87Kr and 88Kr of 235U fission induced by thermal neutron measured by gas-solid separation after irradiation are consistent with the recommended values of the evaluation database, which indicates that the release rates of 85Krm, 87Kr and 88Kr in the plutonium target are the same. After modified by the influence of non-primary neutron field and non-primary isotope, the fission yields of 85Krm, 87Kr and 88Kr were obtained based on the measured relative yield with reference product 99Mo and the yield of 99Mo given by ENDF/BⅧ.0 evaluation database. The measured yields are (0.559±0.020)%, (0.992±0.034)% and (1.264±0.037)%, respectively, which are consistent with the evaluation value of the database and the uncertainty is significantly reduced compared with other literature value. In this paper, the retrieval and deduction methods of γ-ray energy peak interference ratio in measurement are universal, but the uncertainty of theoretical yield may be added. The experimental method in this paper can also provide reference for the measurement of fission product yield at different neutron energy points.

The measurement of (n,2n) reaction cross section induced by fast neutron plays an important role in nuclear reaction mechanism research and nuclear technology applications. Experiments have been carried out over the last several decades. However, most experiments focused on solid samples including 89Y, 151Eu, 203Tl, 232Tl and so on, and there are few reported results about gaseous samples such as xenon and krypton. The 78Kr(n,2n)77Kr reaction cross section was poorly studied, and this work aimed to measure the cross section induced by 148 MeV neutron. The measurement was performed by the activation method, and the experiment was carried out at the Cockcroft Walton Accelerator of China Institute of Atomic Energy (CIAE). A cell made of PMMA was used as the gas container, and the 78Kr gas (enriched to 995% abundance) was injected into the cell using a syringe. The mass of 78Kr gas sample was determined by weighing method. Quasi monoenergetic neutron beams with a yield of about 3×1010 s-1 were produced via the T(d, n)4He reaction (Q=17.6 MeV). The ion beam current was about 250 μA, and the average energy of D+ particles was about 300 keV. The neutron flux determination was accomplished by attaching two 93Nb foils (same diameter as the cell and thickness of 50 μm) with purity of 9999% to the upstream and downstream faces of the cell. The sample was placed at 0° angel relative to the incident D+ beam direction and centered about the TTi target at a distance of about 10 cm, where the neutron flux was 2×107 cm-2·s-1. After irradiation, the activities of 77Kr and 92Nbm were measured by offline gammaray spectrometric technique using a precalibrated HPGe detector on the surface of the detector end cap due to their low activity. To obtain detection efficiencies, another irradiation experiment was carried out individually to produce 77Kr and 92Nbm with high activities, which were used to measure the count rate ratio of the characteristic γray at a distance of 25 cm and on the surface. The efficiencies at the position of 25 cm were obtained by interpolating the efficiency curve which was pre-calibrated using various standard γ sources. Besides, Monte Carlo codes were written to calculate correction factors caused by geometry difference and neutron flux difference. As a result, the cross section was determined to be (464±19) mb, and was compared with the literature data and evaluations. The result of this work is much higher than that of previously reported. The result is helpful to the analysis and evaluation of 78Kr(n,2n)77Kr reaction cross section.

In the spectral mean cross section measurements of 197Au(n,2n)196Au and 45Sc(n,2n)44Scm, the activation products 196Au and 44Scm have low activity and shorter halflife, but the activation products 198Au and 46Sc from neutron capture reactions of 197Au(n,g) and 45Sc(n,g) have strong activity and longer halflife, which results in poor signaltonoise ratio of gammaray characteristic peaks, and increases the measuring uncertainty of 196Au and 44Scm activity. In order to accurately measure 196Au and 44Scm, a radioactive activity measuring device based on anticoincidence principle was developed. The main techniques used were as follows: Firstly, liquid flash measurement system has been used to detect the betaray emitted by the decay of 198Au and 46Sc, basing on the anticoincidence principle, the betaray would be used to suppress Compton background caused by gammarays emitted by the two nuclides above; Secondly, a portable antiCompton spectrometer has been constructed using a ring sodium iodide crystal, and the Compton background caused by the decay of 198Au and 46Sc has been further suppressed by the anti-Compton principle. Thirdly, a thin layer of lead shield has been placed between the radioactive source distributed evenly in the liquid scintillation and a wellshaped high purity germanium (HPGe) crystal to absorb the Xrays emitted by the decay of the 196Au, as results, the coincidence between the Xrays and the characteristic gammarays emitted by 196Au in the HPGe crystal reduces significantly, and the detection efficiency of this measurement device for 196Au increases too. By using the digital spectrometer, the liquid flash measurement system and the antiCompton spectrometer integrated into one, the anticoincidence effect could be superimposed and good experimental results were obtained. For 198Au and 46Sc, the anticoincidence inhibition ratio is 871% and 869% respectively. The detection efficiency for 44Scm is 313%. After increasing the shielding layer, the detection efficiency for 196Au increases greatly, from 5.5% when the shielding layer is not available up to 11.9%. Under the condition of strong isotope interference (198Au or 46Sc of 02 MBq), the minimum detectable activity (MDA) of 24 h detecting to 196Au is less than 07 Bq, and to 44Scm is less than 03 Bq. Applying the double anticoincidence measuring device established in this paper to the activity measurement of 196Au and 44Scm could effectively reduce the uncertainty of 197Au(n,2n)196Au and 45Sc(n,2n)44Scm average crosssection measurement.

Cleft palate only (CPO) is one of the most common craniofacial birth defects. Environmental factors can induce cleft palate by affecting epigenetic modifications such as DNA methylation, histone acetylation, and non-coding RNA. However, there are few reports focusing on the RNA modifications. In this study, all-trans retinoic acid (atRA) was used to simulate environmental factors to induce a C57BL/6J fetal mouse cleft palate model. Techniques such as dot blotting and immunofluorescence were used to find the changes in m6A modification when cleft palate occurs. RNA-seq and KEGG analysis were used to screen for significantly differentially expressed pathways downstream. Primary mouse embryonic palate mesenchymal (MEPM) cells were successfully isolated and used for in vitro experimental verification. We found that an increased m6A methylation level was correlated with suppressed cell proliferation in the palatine process mesenchyme of cleft palate mice. This change is due to the abnormally high expression of m6A methyltransferase METTL14. When using siRNAs and the m6A methyltransferase complex inhibitor SAH to interfere with the expression or function of METTL14, the teratogenic effect of atRA on primary cells was partially alleviated. In conclusion, METTL14 regulates palatal mesenchymal cell proliferation and cycle-related protein expression relies on m6A methylation modification, affecting the occurrence of cleft palate. [ABSTRACT FROM AUTHOR]

Background: Microvascular decompression (MVD) has become widely accepted for hemifacial spasm (HFS). The significance of facial nerve notch (FNN) for the outcome after MVD is still unknown.Objective: To investigate the correlative analysis between the FNN at the root exit zone (REZ) and the curative effect of MVD for HFS.Method: A prospective study was performed, which included 232 patients with Cohen score ≥2 who had undergone MVD. The patients were divided into two groups: the group with facial nerve notch (FNN) and the group without FNN, according to whether there is FNN caused by the offending vessels during the MVD operation. All the patients were followed up for 24 months.Results: The group with FNN caused by offending vessels at the REZ area was confirmed in 119 patients, of which 117 patients were immediately cured and two patients received partial relief on the 1st day of postoperation. The group without FNN at the REZ area was confirmed in 113 patients, of which 43 patients were immediately completely cured while 70 patients were not immediately completely cured after MVD operation. After 24 months of follow-up, 119 patients with FNN were all completely cured, 71 patients without FNN were completely cured, and 42 patients without FNN were not completely cured. Multivariate logistic regression analysis shows that compared with without FNN group, the FNN group had statistical significance for the clinical results both on the-1st -day (P < 0.01) and 2 years of follow-up (P < 0.05) after MVD operation.Conclusions: FNN is an important reference factor to evaluate both the short-term and long-term curative effect of microvascular decompression for hemifacial spasm. The postoperative effect of patients with FNN is much better than that of patients without FNN. [ABSTRACT FROM AUTHOR]

Byline: Jianfeng. Liang, Zhuangli. Guo, Li. Zhang, Yanbing. Yu Aims: To study the clinical manifestations, illness-related factors and microsurgical management of adolescent-onset idiopathic hemifacial spasm. Materials and Methods: Of the [...]