Measurement of the ^(232)Th(n,f)cross section in the 1-200 MeV range at the CSNS Back-n

The ^(232)Th(n,f)cross section is very important in basic nuclear physics and applications based on the Th/U fuel cycle.Using the time-of-flight method and a multi-cell fast-fission ionization chamber,a novel measurement of the^(232)Th(n,f)cross sec-tion relative to^(235)U in the 1–200 MeV range was performed at the China Spallation Neutron Source Back-n white neutron source(Back-n).The fission event-neutron energy spectra of^(232)Th and^(235)U fission cells were measured in the single-bunch mode.Corrected 232Th/235U fission cross-sectional ratios were obtained,and the measurement uncertainties were 2.5–3.7%for energies in the 2–20 MeV range and 3.6–6.2%for energies in the 20–200 MeV range.The^(232)Th(n,f)cross section was obtained by introducing the standard cross section of^(235)U(n,f).The results were compared with those of previous theoreti-cal calculations,measurements,and evaluations.The measured 232Th fission cross section agreed with the main evaluation results in terms of the experimental uncertainty,and 232Th fission resonances were observed in the 1–3 MeV range.The present results provide^(232)Th(n,f)cross-sectional data for the evaluation and design of Th/U cycle nuclear systems.

Back-n white neutron source at CSNS and its applications

Back-streaming neutrons from the spallation target of the China Spallation Neutron Source(CSNS)that emit through the incoming proton channel were exploited to build a white neutron beam facility(the so-called Back-n white neutron source),which was completed in March 2018.The Back-n neutron beam is very intense,at approximately 29107 n/cm2/s at 55 m from the target,and has a nominal proton beam with a power of 100 kW in the CSNS-I phase and a kinetic energy of 1.6 GeV and a thick tungsten target in multiple slices with modest moderation from the cooling water through the slices.In addition,the excellent energy spectrum spanning from 0.5 eV to 200 MeV,and a good time resolution related tothe time-of-flight measurements make it a typical white neutron source for nuclear data measurements;its overall performance is among that of the best white neutron sources in the world.Equipped with advanced spectrometers,detectors,and application utilities,the Back-n facility can serve wide applications,with a focus on neutron-induced cross-sectional measurements.This article presents an overview of the neutron beam characteristics,the experimental setups,and the ongoing applications at Backn.

Measurement of the neutron total cross section of carbon at the Back-n white neutron beam of CSNS

To verify the performance of the neutron total cross-sectional spectrometer, the neutron total cross section of carbon is initially measured in the energy range of 1 eV to 20 MeV using the time-of-flight method. The measurement is performed at the Back-n white neutron source with a 76-m time-of-flight path using the China Spallation Neutron Source. A multilayer fast fission chamber with 235U and 238U is employed as the neutron detector. The diameter and thickness of the natural graphite sample are 70 mm and 40 mm, respectively. Signal waveforms are collected using a data acquisition system. Off-line data processing was used to obtain the neutron time-of-flight spectra and transmissions. The uncertainty of the counting statistics is generally approximately 3% for each bin in the energy range of 1–20 MeV. It is determined that the results for the neutron total cross section of carbon obtained using ^235U cells are in good agreement with the results obtained using 238U cells within limits of statistical uncertainty. Moreover, the measured total cross sections show good agreement with the broadening evaluated data.

吉西他滨对人舌鳞癌Tca8113细胞的放射增敏作用及其机制研究

目的研究吉西他滨(GEM)对人舌鳞癌Tca8113细胞的放射增敏作用及其相关机制。方法用不同浓度GEM处理人舌鳞癌Tca8113细胞24 h,测定细胞存活率并确定后续实验浓度。对Tca8113细胞进行单独放疗或联合GEM处理,MTT法测定细胞存活率;平板克隆形成实验研究各组细胞集落形成的能力;流式细胞术验证Tca8113细胞对放射的敏感性变化。Western blotting检测Bcl-2、Bax、 Cleaved Caspase-3及Cleaved Caspase-9蛋白的表达。结果不同浓度GEM作用时的细胞存活率比较,经方差分析,差异有统计学意义(P<0.05)。与0.00μmol/L组比较,GEM浓度为0.01、0.02、0.03、0.10及1.00μmol/L时细胞存活率降低(P<0.05)。照射剂量为4 Gy时,与单纯放疗组比较,GEM联合放疗组细胞存活率降低(P<0.05)。克隆形成实验显示,GEM联合放疗组集落形成能力最弱(P<0.05);流式细胞术进一步证实,GEM联合放疗组较单纯放疗组凋亡率升高(P <0.05)。GEM联合放疗组Tca8113细胞凋亡高于其他各组,且Tca8113细胞中Bax、Cleaved Caspase-3及Cleaved Caspase-9蛋白表达水平高于其他组(P<0.05);而Bcl-2蛋白表达则低于其他各组(P<0.05)。结论 GEM对舌鳞癌Tca8113细胞的增殖有抑制作用,联合放射治疗能有效提高放射敏感性;两者可能具有协同抗肿瘤作用。

Multi-core-shell-structured LiFePO_(4)@Na_(3)V_(2)(PO_(4))_(3)@C composite for enhanced low-temperature performance of lithium-ion batteries

In this work,a multi-core-shell-structured LiFePO_(4)@Na_(3) V_(2)(PO_(4))_(3)@C(LFP@NVP@C) composite was successfully designed and prepared to address inferior low-temperature performance of LiFePO_(4) cathode for lithium-ion batteries.Transmission electron microscopy(TEM) confirms the inner NVP and outer carbon layers coexisted on the surface of LFP particle.When evaluated at low-temperature operation,LFP@NVP@C composite exhibits an evidently enhanced electrochemical performance in term of higher capacity and lower polarization,compared with LFP@C.Even at-10℃ with 0.5 C,LFP@NVP@C delivers a discharge capacity of ca.96.9 mAh-g^(-1) and discharge voltage of ca.3.3 V,which is attributed to the beneficial contribution of NVP coating.NAS ICON-structured NVP with an open framework for readily insertion/desertion of Li+ will effectively reduce the polarization for the electrochemical reactions of the designed LFP@NVP@C composite.