Background Simulation of a Fission Fragment Chamber in the Experiment of ^(209)Bi(e,e’K^+)^(209)_ ΛPb

An experiment for measuring the hyperon-related fission rate was carried out with the reaction 209^Bi（e, e＇K^＋）209^hPb at the Thomas Jefferson National Laboratory （Jlab）. In the experiment, the performance of the fission fragment detector （FFD） was dramaticlly crashed by the background particles in comparison with that during the test without beam. The scattering of the high intensity （500 nA） primary electrons was the dominant cause. Using the GEANT4 toolkit, this report simulates the experimental situation of the target chamber in which the FFD was located. The simulation results indicate that the background particles were dominantly （~ electrons, and protons and alpha particles were the important heavy background particles. The performance of the multi-wire proportional chambers （MWPCs） depends not only on the background-particle intensity but also the current density, which was also given by the simulation code. Furthermore, the measures to suppress the background particles were also investigated with the simulation code.

Fission Fragment Decay Heat by Using the Most Recent Evaluated Nuclear Data Library ENDF/B-VIII

In this paper, a home-made code was designed to calculate the decay heat emitted by fission fragments as a result of successive radioactive emissions after a fission burst. The nuclear data necessary for the calculations was extracted from the latest version of the Evaluated Nuclear Data Library ENDF/B-VIII.0. The code can calculate the decay heat of thermal and fast neutron-induced fission reactions on the isotopes of Thorium, Protactinium, Uranium, Neptunium, Plutonium, Americium, Curium, California, Einsteinium, and Fermium. A numerical method was used in this work to calculate the decay heat of all fission fragments due to the individual thermal or fast fissions of the isotopes of the previous ten actinides. The most influential nuclei in the decay heat were also identified at different times after the fission event. Moreover, the code showed high capability in calculating the fission fragments inventories and decay heats due to the decay of fission fragments of 31 fissionable nuclei.

New Statistical Methods for Systematizing the Nuclei Fission Fragments: Post-Scission Approach

A new statistical method for systematizing the nuclei fission fragments, investigation of their mass and charge spectra and neutron fission parameters has been suggested. In proposed method, the mass and charge yields of nucleons are determined from the equilibrium conditions of the nuclear fragments post-fission ensemble. Here we consider protons and neutrons of different fragments as statistically non-equivalent. The abilities of the proposed statistical method for explanation of the U, Pa, Th, Ac and Ra post-fission fragments ordering and neutron emission function calculation have been demonstrated.

Sensitivity impacts owing to the variations in the type of zero-range pairing forces on the fission properties using the density functional theory

Using the Skyrme density functional theory,potential energy surfaces of^(240)Pu with constraints on the axial quadrupole and octupole deformations(q_(20)and q_(30))were calculated.The volume-like and surface-like pairing forces,as well as a combination of these two forces,were used for the Hartree–Fock–Bogoliubov approximation.Variations in the least-energy fission path,fission barrier,pairing energy,total kinetic energy,scission line,and mass distribution of the fission fragments based on the different forms of the pairing forces were analyzed and discussed.The fission dynamics were studied based on the timedependent generator coordinate method plus the Gaussian overlap approximation.The results demonstrated a sensitivity of the mass and charge distributions of the fission fragments on the form of the pairing force.Based on the investigation of the neutron-induced fission of^(239)Pu,among the volume,mixed,and surface pairing forces,the mixed pairing force presented a good reproduction of the experimental data.

Position reconstruction in fission fragment detection using the low pressure MWPC technique for the JLab experiment E02-017

When a A hyperon is embedded in a nucleus it can form a hypernucleus. The lifetime and its mass dependence of stable hypernuclei provide information about the AN interaction in the nuclear medium. This work will introduce the Jefferson Lab experiment （E02-017）, which aims to study the lifetime of the heavy hypernuclei using a specially developed fission fragment detection technique： a multi-wire proportional chamber operating under low gas pressure （LPMWPC）. The trajectory of the detected fragment is reconstructed and used to find the fission point on the target foil, the position resolution is less than I ram, which meets the original design, the separation of target materials and events mixture percentage in different regions are verified by Monte Carlo simulation.

Systematics on fission fragment mass distribution of neutron induced ^(235)U fission

Based on the neutron induced fission fragment mass distribution data up to neutron energy 20 MeV measured with the double kinetic energy method （KEM） and the radio active method （RAM）, the systematics of fission fragment mass distribution was investigated by using 5 Gaussian model and the systematics parameters were obtained by fitting the experimental data. With the systematics, the yields of any mass A and at any energy in the region from 0 to 20 MeV of neutron energy can be calculated. The calculated results could well reproduce the experimental data measured with KEM, but show some systematical deviation from the data measured by RAM, which reflects some systematical deviations between the two kinds of measured data. The error of systematics yield was calculated in an exact error transformation way, including from the error of the experimental yield data to the error of the discrete parameters, then to the systematics parameters, and at last to the yield calculated with systematics.

Research on the prompt neutron multiplicity of fission fragments for ^(235)U(n,f)

According to some experimental and evaluated data,the total excitation energy partitioning way between both of the fission fragments was given with a semi-empirical method. With the calculated energy partitioning way,the prompt neutron multiplicity as a function of fragment mass,（A） ,for neutron-induced fission of 235U at En=0.0253 eV,3 MeV,and 5 MeV was calculated. The results are checked with the total average prompt neutron multiplicities and compared with the experimental and evaluated data.

Investigation of fission fragments average spin based on four dimensional Langevin dynamical model

We applied the four dimensional Langevin dynamical model to investigate the average spin of fission fragments. Elongation, neck thickness, asymmetry parameter, and the orientation degree of freedom（K coordinate）are the four dimensions of the dynamical model. We assume that the collective modes depend on the emission angle of the fragments, then different parameters related to the average spin of fission fragments are calculated dynamically.The angle dependence of average spin of fission fragments is investigated by calculating the spin at angles 90？and165？. Also, the obtained results based on the transition state model at scission point are presented. One can obtain better agreement between the results of the dynamical model and experimental data in comparison with the results of the transition state model.

Temperature dependent fission fragment distribution in the Langevin equation

The temperature dependent width of the fission fragment distributions was simulated in the Langevin equation by taking two-parameter exponential form of the fission fragment mass variance at scission point for each fission event. The result can reproduce experimental data well, and it permits to make reliable estimate for unmeasured product yields near symmetry fission.

Apoptosis in immune cells induced by fission fragment ^(147)Pm

Ａｐｏｐｔｏｓｉｓｉｎｉｍｍｕｎｅｃｅｌｓｉｎｄｕｃｅｄｂｙｆｉｓｉｏｎｆｒａｇｍｅｎｔ１４７ＰｍＺｈｕＳｈｏｕＰｅｎｇ，ＺｈａｎｇＬａｎＳｈｅｎｇａｎｄＦｕＱｉａｎｇ（ＳｕｚｈｏｕＭｅｄｉｃａｌＣｏｌｅｇｅ，Ｓｕｚｈｏｕ２１５００７）Ａｂｓｔ...

Systematic study of anomalous fragment anisotropies in subbarrier complete fusion-fission reactions

ＳｙｓｔｅｍａｔｉｃｓｔｕｄｙｏｆａｎｏｍａｌｏｕｓｆｒａｇｍｅｎｔａｎｉｓｏｔｒｏｐｉｅｓｉｎｓｕｂｂａｒｉｅｒｃｏｍｐｌｅｔｅｆｕｓｉｏｎｆｉｓｉｏｎｒｅａｃｔｉｏｎｓＺｈａｎｇＨｕａｎＱｉａｏ，ＬｉｕＺｕＨｕａ，ＸｕＪｉｎＣｈｅｎｇ，...

Effect of Preequilibrium Fission on Fragment Spins

The fission angular distributions and the angular dependence of fragment spins in ter-ms of preequilibrium fission model are calculated.The results show strong effects of preequil-ibrium fission on both angular distributions and angular dependence of fragment spins.

^(252)Cf自发裂变K X射线发射与动能-电荷关系

原子核裂变后多物理量间的关联测量是认识裂变过程直接有效的实验手段,然而由于初级裂变产物准确的电荷鉴别仍面临技术困难,电荷相关的多参数研究相对匮乏.为此,通过高分辨的低能高纯锗探测器和金硅面垒探测器开展了^(252)Cf自发裂变的裂变碎片K X射线和动能的符合测量.利用K X射线可以很好地鉴别电荷数Z=39—62的裂变碎片,电荷分辨ΔZ≈0.7,K X射线产额呈现强烈的电荷相关性.借助K X射线给出了碎片平均动能和平均总动能及其分布宽度随核电荷数的分布,轻碎片动能分布具有鲜明的奇偶效应,偶Z碎片的动能比奇Z碎片的高约0.48 MeV;平均总动能在Z=52—53处达到峰值,总动能分布宽度在Z=56附近呈现凹坑,这反映了形变壳结构对断点形状的显著影响.裂变碎片K X射线发射的信息及动能-电荷关系研究可为裂变独立产额测量和裂变理论模型的检验提供必要的参考数据.

Prediction of the Average Decay Heat per Fission for MOX Nuclear Fuel

MIXED Oxide Nuclear fuel (MOX) contains both uranium and plutonium in oxidized form. It is important to calculate the nuclear decay heat due to the single thermal fission (fission due to 0.0235 eV neutron) for all fissile nuclei in the MOX fuels (U235, Pu239, and Pu241). These fissile nuclei are the main source of the decay heat in MOX fuel. Decay heat calculation of the weighted fissile material content in MOX fuel is also important. A numerical method was used in this work to calculate the concentrations of all fission products due to the individual thermal fission of the three fissile materials as a function of time N(t). The decay heat calculations for the three fissile materials are directly calculated using the summation method by knowing the different concentrations of fission products over time. The average decay heat of the MOX fuel in induced thermal fission is also concluded. The most influential nuclei in the decay heat were also identified. The method used has been validated by several comparisons before, but the new in this work is using the most recent Evaluated Nuclear Data Library ENDF/B-VIII.0. Calculations of decay heat show very common trends for a period of 107 sec after the fission burst of thermal fissions of individual fissile nuclei. Moreover, the code showed high capability in calculating the fission fragments inventories and decay heats due to the decay of fission fragments of 31 fissionable nuclei.

Product yields for the photofission of ^(232)Th,^(234,238)U,^(237)Np,and ^(239,240,242)Pu actinides at various incident photon energies

Photofission fragments mass yield for^(232)Th,^(234;238) U,^(237) Np, and^(239;240;242) Pu isotopes are investigated.The calculations are done using a developed approach based on Gorodisskiy's phenomenological formalism. The Gorodisskiy's method is developed to be applied for the neutron-induced fission. Here we revised it for application to photofission. The effect of emitted neutron prior to fission on the fission fragment mass yields has also been studied. The peak-to-valley ratio is extracted for the240 Pu isotope as a function of energy. Obtained results of the present formalism are compared with the available experimental data. Satisfactory agreement is achieved between the results of present approach and the experimental data.

Interplay Between Scission-Point Model and Experimental Data for Sub-Barrier Fusion-Fission

The fragment angular distributions of fusion-fission reactions for the systemsof 16O+232Th,19F+232Th and 16O+238U at near-and sub-barrier energies were measured.The measured fragment anisotropies obviously deviate from the predictions ofscission-point transition-state model.We also compared the excitation energy of tiltingmode with the statistical assumption.It was found that thermal equilibrium is not estab-lished at scission for the reactions studied.

A precursor of β-delayed fission: ^(230)Ac

The 230Ra has been produced via multinucleon transfer and dissipative fragmentation of heavy target in the 60 MeV/u 18O ion reaction with natural thorium. The radium was radiochemically separated from irradiated thorium targets. 230Ac was obtained by 230Ra β-→230Ac. Thin Ra sources were prepared for observing fission fragments from β-delayed fission of 230Ac. The sources were exposed to the mica fission track detectors and measured by a HPGe γ detector. The two fission events were obtained and could been assigned to the β-delayed fission of 230Ac. The β-delayed fission probability of 230Ac was determined to be (1.19±0.85)×10-8.

通过测量裂变碎片的γ射线研究中子测量技术

描述了通过测量裂变碎片的 γ射线来研究测量中子的方法。2 3 8U薄片的裂变碎片由聚脂膜俘获 ,其γ射线由 Na I(Tl)探测器测量。在不同系统上测量了中子 ,测量结果与用裂变室的测量结果一致。分析和讨论了实验结果。

小型平板铀裂变电离室研制

为了测量特定实验条件下狭小空间内中子注量率分布,研制了小型平板浓缩铀裂变电离室,该裂变室具有体积小、结构材料少等优点。论文叙述了裂变电离室的结构和制作工艺,通过测量自发衰变α粒子谱、裂变碎片谱对裂变电离室的性能进行了测试和评定,并标定了裂变电离室测量裂变碎片的探测效率。从指标上看,裂变电离室能达到设计要求和目的,可用于中子注量率的测量。

235U裂变碎片在PIN探测器中沉积能量的实验研究

利用中子与235U发生裂变反应的截面在裂变中子能区基本不变这一特点,可设计研制裂变靶室探测系统,该系统中子能量响应较平坦,在脉冲中子总数测量中有广阔的应用前景。利用K-400加速器稳态DT中子源,实验标定了235U裂变碎片在PIN探测器中的平均沉积能量,并与理论计算结果进行了比较。裂变靶室系统探测效率可通过数值计算准确给出,与平均沉积能量实验测量值相结合,可得到准确的中子灵敏度数据,进而获得裂变靶室探测系统中子能量响应曲线。