Photonuclear production of nuclear isomers using bremsstrahlung induced by laser-wakefield electrons

In this study,we theoretically investigate the feasibility of using laser-wakefield accelerated(LWFA)electrons for the photonuclear measurement of nuclear isomers according to the characteristics of the electrons obtained from LWFA experiments conducted at the Compact Laser-Plasma Accelerator(CLAPA)laboratory.The experiments at the CLAPA show that a stable electron beam with an energy of 78-135 MeV and a charge of 300-600 pC can be obtained.The bremsstrahlung spectra were simulated using Geant4,which suggests that a bremsstrahlung source with a peak intensity of 10^(19) photons/s can be generated.Theoretical calculations of isomer production cross sections from the photonuclear reactions on six target nuclei,^(197)Au,^(180)Hf,^(159)Tb,^(115)In,^(103)Rh,and ^(90)Zr,were performed and compared with the available experimental data in EXFOR,which suggest that further experiments are required for a series of photonuclear reaction channels.Flux-averaged cross sections and isomer ratios(IR)resulting from such bremsstrahlung sources are theoretically deduced.The results suggest that IR measurements can be used to constrain nuclear components,such asγstrength function and optical model potential.In addition,the detection of the decay characteristics was evaluated with Geant4 simulations.The use of the LWFA electron beam and its bremsstrahlung for photonuclear studies involving nuclear isomers is anticipated.

Measurements of ^(nat) Cd(γ,x)reaction cross sections and isomer ratio of ^(1,5m.g)Cd with the bremsstrahlung end-point energies of 50 and 60 MeV

The flux-weighted average cross sections ^(nat) Cd(γ,xn)^(115g,m,111m,109,107,105,104)Cd and ^(nat) Cd(γ,x)^113g,112,111g,110m)Ag reactions were measured at the bremsstrahlung end-point energies of 50 and 60 MeV.The activa tion and off-line y-ray spectrometric technique was carried out using the 100 MeV electron linear accelerator at the Pohang Accelerator Laboratory,Korea.The ^(nat)lCd(γ,xn) reaction cross sections as a function of photon energy were theoretically calculated using the TALYS-1.95 and the EMPIRE-3.2 Malta codes.Then,the flux-weighted average cross sections were obtained from the theoretical values of mono-energetic photons.These values were compared with the flux-weighted values from the present study and were found to be in general agreement.The measured experimental reaction cross-sections and integral yields were described for cadmium and silver isotopes in the ^(nat)Cd(γ,xn)^(115g,m,111m,109,107,105,104) and ^(nat)Cd(γ,x)^(113g,112.111g,110m)Ag reactions.The isomeric yield ratio(IR) of ^(115g.m)Cd in the ^(nat)Cd(γ,xn) reaction was determined for the two bremsstrahlung end-point energies.The measured isomeric yield ratios of ^(115g,m)Cd in the ^(nat)Cd(γ,xn) reaction were also compared with the theoretical values of the nuclear model codes and previously published literature data of the ^(116)Cd(γ,x) and ^116(γ,2n) reactions.It was found that the IR value increases with increasing projectile energy,which demonstrates the characteristic of excitation energy.However,the higher IR value of ^(115g.m)Cd in the ^(116)Cd(n,2n)reaction compared to that in the ^(116)Cd(γ,x)reaction indicates the role of compound nuclear spin alongside excitation energy.

Systematics of Isomeric Cross Section Ratio for(n,t)Reaction at 14.6 MeV

On the basis of Hauser-Feshbach theory and some approximations,parametrized formulae of isomeric cross section ratio including two adjustableparameters for(n,t)reaction at 14.6MeV are derived.By fitting these formulae to theavailable measured data,parameters are obtained and the systematic behaviour of theisomeric cross section ratio are studied.The isomeric cross section ratio predicted by thepresent work is in good agreement with the limited measured data.

响应面法优化高顺式虾青素的制备工艺研究

天然存在的虾青素多为全反式构型,但顺式构型的虾青素具有更好的生物活性且更易被人体选择性吸收。为研究高顺式虾青素的制备工艺,该实验采用微波加热法对虾青素进行虾青素异构化,以全反式虾青素为原料,乙酸乙酯为溶剂,虾青素顺式占比为评价指标,采用单因素及响应面试验优化了虾青素异构化。得出制备高顺式虾青素最佳条件为:催化剂为异硫氰酸甲酯60 mg/mL,虾青素溶液质量浓度1.5 mg/mL,微波温度69℃,微波功率600 W,微波时间22 min。最佳条件下虾青素总顺式占比为49.34%,该研究有利于提高虾青素顺式比例,为虾青素用于功能性食品打下理论基础。

一种MTW结构分子筛的合成及其二甲苯异构化反应性能

采用类似五元环中间体结构的烷基吡咯烷为模板剂,通过动态水热法在不同碱度比和硅铝比条件下合成了一种具有MTW拓扑结构的分子筛(LMTW),通过XRD、N_(2)吸附-脱附、SEM、Py-FTIR和电子晶体学等方法对分子筛的结构进行表征。以该分子筛为酸性组分,负载铂制备了转化型二甲苯异构化双功能催化剂(Pt/LMTW),使用微型活塞流反应器对催化剂的反应性能进行评价,并与Pt/REI-430催化剂的性能进行比较。实验结果表明,合成的LMTW分子筛具有和MTW分子筛一致的特征峰及相似的晶胞参数,合成过程中的碱度比和硅铝比会影响分子筛的孔道结构、比表面积及酸性等。与Pt/REI-430催化剂相比,制备的Pt/LMTW催化剂用于二甲苯异构化反应具有优异的性能。

A Proposed Stereochemical Mechanism for the Improved Preparation of Maleic Anhydride Cycloadduct of CLA

The fatty acid derivatives, prepared from renewable natural oils, can be used as highly promising and potential substitutes for petrochemicals. The study of process improvement and stereochemical mechanism for preparing these derivatives would be beneficial for their industrial production. Conjugated linoleic acid (CLA) containing 9cis-11trans (9c, 11t) and 10trans-12cis (10t, 12c) isomers was prepared from Salicornia herbacea seed oil. Maleic anhydride cycloadduct of CLA (MAC) was prepared by an improved process, and it was characterized by FTIR, 1H and 13C NMR, etc. A new method to calculate conformers-ratio of CLA or MAC was also developed. Furthermore, the stereochemical mechanism for the improved preparation of MAC was proposed primarily by the calculation method above. The following observations were made: 1) The yield of MAC could reach as high as 96.7% under mild reaction conditions and with an easy and efficient product separation;2) The trans-trans CLA in the s-cis conformation acted as a predominant reactant to Diels-Alder [4 + 2] cycloaddition of maleic anhydride, which was the main reaction occurred simultaneously with catalytic configurational isomerizations of CLA in one step;3) From all studied CLA conformers, the most stable conformation was the s-trans conformation of trans-trans CLA, while the s-cis conformation of trans-trans CLA had the most favorable structural parameters for cyclohexenyl ring formation;4) Four MAC conformers derived from 9c, 11t- and 10t, 12c-CLA, were obtained as final main products that were determined to be cis-cycloadducts;5) The endo/exo ratios of the cis- cycloadducts derived from 9c, 11t- and 10t, 12c-CLA, were 2.14:1 and 1.99:1, respectively;and 6) The results obtained from the calculation method above were in excellent accordance with those from our experiments.

Measurement of^(134)Xe(n,2n)^(133m),gXe reaction cross sections in 14‑MeV region with detailed uncertainty quantification

A lead-shielded HPGe detector and offlineγ-ray spectra of the residual product were used to measure the cross section(CS)and ratios of isomeric CS(σm/σg)in^(134)Xe(n,2n)^(133m),gXe reactions at different energies(13.5 MeV,13.8 MeV,14.1 MeV,14.4 MeV,14.8 MeV)relative to the^(93)Nb(n,2n)^(92)mNb reaction CS.The target was high-purity natural Xe gas under high pressure.The T(d,n)4He reaction produces neutrons.TALYS code(version 1.95)for nuclear reactions was used for calculations,with default parameters and nuclear level density models.The uncertainties in the measured CS data were thoroughly analyzed using the covariance analysis method.The results were compared with theoretical values,evaluation data,and previous experimental findings.CS data of the 134Xe(n,2n)133mXe and 134Xe(n,2n)133gXe reactions and the corresponding isomeric CS ratios at 13.5 MeV,13.8 MeV,and 14.1 MeV neutron energies are reported for the first time.This research advances our knowledge of pre-equilibrium emission in the(n,2n)reaction channel by resolving inconsistencies in the Xe data.

异构多星编队的脉冲构型保持控制方法

近地轨道的双星编队通常设计具有自稳定性的编队构型参数初值,通过保持编队构型参数形成长期稳定的相对周期运动。针对编队中卫星数量增多产生的相对运动耦合问题,提出了基于Hill坐标和三角函数公式的多星相对运动分析方法。基于SAR载荷测量基线定义,结合多星编队构型参数的相对运动特性,提出了编队构型参数的设计方法,能够实现多星编队的最大有效基线组合。通过分析J_2项摄动和大气阻力摄动的长期影响,研究了异构多星编队的相对运动衍化规律,提出了主从形式的脉冲偏置控制,能够有效保持针对异构多星编队设计的编队构型。通过面质比异构的四星编队控制仿真,验证了脉冲偏置控制形式下异构多星编队构型保持控制方法的有效性。

EU⁃1分子筛的合成及其在正己烷异构化反应中的催化性能

在不同硅铝比(n SiO_(2)/n Al2O_(3))的合成凝胶(含纯硅凝胶)中引入晶种,合成了纯相的EU‐1分子筛。研究了铝源、模板剂和晶种添加量对EU‐1分子筛的结晶度、形貌尺寸等的影响;重点研究了不同硅铝比对样品结晶度、晶粒尺寸、酸性、比表面积和孔容等的影响。将合成结果绘制成了纯相EU‐1分子筛的合成条件三元图,从三元图可看出,晶种法可显著扩大纯相EU‐1分子筛的合成区域。将Pt/H‐EU‐1用于正己烷异构化反应,结果表明,该催化剂具有优异的正己烷异构化活性及稳定性,对异构烷烃有较高的选择性。

蛾类昆虫性信息素生物合成的研究进展

综述了各种不同化学结构类型的蛾类雌性信息素生物合成途径。此外还叙述了特定比例的性信息素成分在雌蛾体内产生的机理以及某些蛾类中信息素生物合成酶类与物种进化间的关系。

一代树状碳硅烷液晶的光化学研究——端基含12个4-丁氧基偶氮苯介晶基元

研究了新的含12个丁氧基偶氮苯介晶基元的一代树状碳硅烷液晶D1及偶氮苯介晶基元化合物M5在氯仿、四氢呋喃、N,N-二甲基甲酰胺、乙醇和苯等溶剂中的量子产率、反-顺光异构化、光回复异构、反/顺异构组分比、热回复异构及活化能.D1和M5的光致变色速率常数为10^(-1)s^(-1),而含同一偶氮基元的光致变色液晶聚硅氧烷的光致变色速率常数为10^(-8)s^(-1),因此,液晶树状物D1的光响应速度比后者快10~7倍.

二代光致变色液晶树枝状碳硅烷的光化学研究——端基含36个丁氧基偶氮苯介晶基元

研究了新的含 3 6个丁氧基偶氮苯介晶基元的二代光致变色液晶树枝状碳硅烷 (D2 )在氯仿、四氢呋喃溶液中的光强 ,吸收光强 ,摩尔消光系数 ,最大吸收波长 ,量子产率 ,活化能 ,异构转换率 ,光回复异构化反应平衡常数 ,反 -顺光异构化反应速率常数 ,光回复异构化正

Y型沸石硅铝比对1-己烯异构化性能的影响

在FCC条件下,采用1-己烯为原料,对不同晶胞常数(硅铝比)的Y型沸石在脉冲微反装置上进行评价,以考察Y型沸石硅铝比对1-己烯异构化性能的影响。结果表明,晶胞常数为2.428～2.431nm的Y型沸石具有良好的异构烷烃选择性。

硅铝比对镁碱沸石催化剂催化正丁烯异构化性能的影响

采用水热合成法,通过改变投料配比,在硅铝比分别为20,40,60,80,100,120时合成了镁碱沸石,经挤条成型后制得催化剂。采用XRD、低温N2吸附-脱附、SEM、NH3-TPD和吡啶吸附FTIR等方法对合成的镁碱沸石进行了表征,并在固定床反应器上以正丁烯骨架异构化制异丁烯为探针反应评价了催化剂的性能。表征结果显示,硅铝比对镁碱沸石的比表面积和孔体积的影响较小,对相对结晶度、晶粒粒径和酸性等影响较大,硅铝比为60~80时合成的镁碱沸石具有最高的相对结晶度、较大的晶粒尺寸、适宜的酸量及L/B酸的比值。反应结果表明,硅铝比为60~80时合成的镁碱沸石催化剂的正丁烯骨架异构化活性和稳定性最好,异丁烯收率较高且副产物丙烯收率较低。

端基含4个丁氧基偶氮苯介晶基元光致变色液晶树状物的光化学研究

研究了新化合物含 4个丁氧基偶氮苯介晶基元的零代 (D0 )光致变色液晶树状物在氯仿和四氢呋喃中的吸收光强、最大吸收波长、摩尔消光系数、量子产率、活化能、异构转换率、反 -顺光异构化反应速率常数、热回复异构化反应速率常数、光回复异构化反应平衡常数及速率常数 .D0的光致变色反应速率常数为 10 -1s-1,而含偶氮基元液晶聚硅氧烷的光致变色反应速率常数为 10 -8s-1,因此液晶树状物D0的光响应速度比后者快 10 7倍 .

^(197)Bi 高自旋同质异能态寿命的确定

介绍了用在不同符合时间窗条件下布居和退激同质异能态的γ跃迁之间的符合强度比确定布居较弱的高自旋同质异能态寿命的方法。并用这种方法成功地确定了１９７Ｂｉ的４个同质异能态的寿命。

14．5MeV（n，2n）反应同质异能态截面比的系统学

在实验数据的基础上，使用Ｈａｕｓｅｒ－Ｆｅｓｈｂａｃｈ理论，在一定的假定和近似下进行了１４．５ＭｅＶ（ｎ，２ｎ）反应同质异能态截面比的系统学研究。在３５≤Ａ≤２０９、０≤Ｊ＿ｍ≤１６、０≤Ｊ＿ｇ≤８范围内，通过获得的系统学参数，可以很好地预言无实验数据核素的１４．５ＭｅＶ（ｎ，２ｎ）反应同质异能态截面比。

E_p<3 GeV能区质子反应同质异能态截面比的系统学

提出了Ep<3GeV能区质子反应同质异能态截面比的半经验公式。该公式仅含有 1个系统学参数 ,适应于产物核质量数 4 4≤A≤ 197、同质异能态自旋 0 5≤Jm≤ 9.5和基态自旋 0 5≤Jg≤7的质子反应。该半经验公式很好地再现了已有实验数据 ,能较好地预言无实验数据的同质异能态截面比或同质异能态截面。

芳烃装置乙苯积累的原因分析及对策

针对芳烃装置二甲苯系统在加工外购混苯生产过程中出现的乙苯积累问题,依据C8芳烃异构化反应的机理、热力学及动力学的论述,分析乙苯积累的原因,找出解决乙苯积累的对策,为指导芳烃装置的正常生产提供理论依据。

不同硅/铝比La/ZSM-5分子筛对催化裂化轻汽油异构化/芳构化性能的影响

分别以硅/铝摩尔比为40、200、300、400的ZSM-5分子筛为载体,以金属镧为活性组分,制备一系列催化裂化(FCC)轻汽油异构化/芳构化催化剂,通过X射线衍射(XRD)、N_(2)吸附-脱附、^(27)Al MAS NMR、氨气程序升温脱附(NH_(3)-TPD)、吡啶红外吸附(Py-FTIR)、扫描电镜(SEM)等手段对其进行表征。以FCC轻汽油为原料,研究了La/ZSM-5分子筛硅/铝摩尔比变化对异构化/芳构化反应性能的影响。结果表明:随着ZSM-5硅/铝摩尔比的增加,其酸强度逐渐降低,B酸与L酸酸量比值减小,芳烃产率呈现先增加后减少的趋势;当硅/铝摩尔比为200时,Bronsted(B)酸与Lewis(L)酸酸量比值最低,FCC轻汽油异构化/芳构化性能最高;在反应温度380℃、压力1.0 MPa、氢/油体积比100和体积空速1.0 h^(-1)的条件下,La/ZSM-5-200分子筛催化剂作用下异构化/芳构化产品与反应原料相比,烯烃体积分数降低32.81百分点,异构烷烃体积分数增加18.24百分点,芳烃体积分数增加到5.97%,辛烷值降低5.38个单位,达成以芳构/异构反应为主的大幅度降烯烃的目标,为京Ⅵ(B)汽油标准的实施提供了技术支持。