Equivalent properties of single event burnout induced by different sources

The experimental results of single event burnout induced by heavy ions and 252Cf fission fragments in power MOSFET devices have been investigated. It is concluded that the characteristics of single event burnout induced by 252Cf fission fragments is consistent to that in heavy ions. The power MOSFET in the "turn-off" state is more susceptible to single event burnout than it is in the "turn-on" state. The thresholds of the drain-source voltage for single event burnout induced by 173 MeV bromine ions and 252Cf fission fragments are close to each other, and the burnout cross section is sensitive to variation of the drain-source voltage above the threshold of single event burnout. In addition, the current waveforms of single event burnouts induced by different sources are similar. Different power MOSFET devices may have different probabilities for the occurrence of single event burnout.     

Sensitivity of heavy-ion-induced single event burnout in SiC MOSFET

The energy deposition and electrothermal behavior of SiC metal-oxide-semiconductor field-effect transistor(MOSFET)under heavy ion radiation are investigated based on Monte Carlo method and TCAD numerical simulation.The Monte Carlo simulation results show that the density of heavy ion-induced energy deposition is the largest in the center of the heavy ion track.The time for energy deposition in SiC is on the order of picoseconds.The TCAD is used to simulate the single event burnout(SEB)sensitivity of SiC MOSFET at four representative incident positions and four incident depths.When heavy ions strike vertically from SiC MOSFET source electrode,the SiC MOSFET has the shortest SEB time and the lowest SEB voltage with respect to direct strike from the epitaxial layer,strike from the channel,and strike from the body diode region.High current and strong electric field simultaneously appear in the local area of SiC MOSFET,resulting in excessive power dissipation,further leading to excessive high lattice temperature.The gate-source junction area and the substrate-epitaxial layer junction area are both the regions where the SiC lattice temperature first reaches the SEB critical temperature.In the SEB simulation of SiC MOSFET at different incident depths,when the incident depth does not exceed the device's epitaxial layer,the heavy-ion-induced charge deposition is not enough to make lattice temperature reach the SEB critical temperature.     

用12C离子模拟质子引起的单粒子效应

在理论分析的基础上 ,提出了一种利用兰州重离子加速器提供的高能12C离子模拟质子引起单粒子效应的途径 .在保证核反应机制是引起单粒子效应主要机制的前提下,用高能12C离子可以模拟质子在功率金属 -氧化物 -半导体场效应晶体管中引起的单粒子烧毁以及单粒子栅极击穿 ,获得质子单粒子效应的饱和截面 ,定性研究质子单粒子效应的角度效应 ,还可以作为高能质子单粒子效应实验前的预备实验 .该方法拓展了兰州重离子加速器加速的轻的重离子在单粒子效应实验研究方面的应用 ,对现阶段国内开展质子单粒子效应实验研究具有重要意义. The mechanisms for proton and heavy ion induced single event effect (SEE) are discussed and a method to simulate proton induced SSEE (PSEE) with high energy 12 C is proposed in this paper. The experiments which can be done by using this method include single event burnout (SEB) and single event gate rupture in power MOSFET, single event upset (SEU) and single event transient (SET) in less sensitive device and angle effect. The experimets with high energy ...     

Ternary fission within statistical approach

The ternary system with a light nucleus between two heavy fragments is assumed to appear from the binary configuration near scission. The formation of a third light nucleus in the binary system is considered. The calculated charge distributions in spontaneous ternary fission of ²⁵²Cf and in induced ternary fission of ⁵⁶Ni are compared with the available experimental data. The neutron multiplicity from the fission fragments is described. The fine structures of the TKE-mass distribution are predicted.     

252Cf源和重离子加速器对FPGA的单粒子效应

 对10万门基于静态随机存储器的现场可编程门阵列（FPGA）分别在锎-252（²⁵²Cf）源和HI-13串列加速器下进行了单粒子效应试验研究,测试了静态单粒子翻转截面及发生单粒子闩锁的线性能量转移阈值,并对试验结果进行了等效性分析比较。试验结果表明²⁵²Cf源引起的FPGA单粒子翻转截面比重离子加速器引起的约低1个数量级;使用²⁵²Cf源未能观测到该器件的单粒子闩锁现象,而使用重离子加速器可以测出该FPGA发生单粒子闩锁的线性能量转移阈值;在现代集成电路的宇航辐射效应地面模拟单粒子效应试验中²⁵²Cf源不是理想的测试单粒子闩锁的辐射源。     

First principles simulation technique for characterizing single event effects

This paper develops a new simulation technique to characterize single event effects on semiconductor devices. The technique used to calculate the single event effects is developed according to the physical interaction mechanism of a single event effect. An application of the first principles simulation technique is performed to predict the ground-test single event upset effect on field-programmable gate arrays based on 0.25 μm advanced complementary metal-oxide-semiconductor technology. The agreement between the single event upset cross section accessed from a broad-beam heavy ion experiment and simulation shows that the simulation technique could be used to characterize the single event effects induced by heavy ions on a semiconductor device.     

Generation of angular momentum of fission fragments in a cluster model

Based on the dinuclear system concept, the role of bending vibrations in creation of the angular momentum of primary fission fragments is investigated. For ²⁵²Cf spontaneous fission, the angular momenta of the fragments are calculated as a function of the neutron multiplicity and compared with available experimental data. Different cluster compositions of the ²⁵²Cf fission modes at the scission point are considered.     

A multiparameter system for heavy nuclei fission study

A multiparameter system designed to measure as many as six parameters of a single fission event on line with an EC 1010 computer is described. The kinematics of emitted fragments and the calibration of light particle and fragment spectra are discussed. Fragment energy spectra from the thermal neutron induced fission of²³⁵U have been measured. Results of light particle emission from spontaneous fission of²⁵²Cf and from neutron induced fission of²³⁵U are presented.Dedicated to Professor Ivan Úlehla on the occasion of his sixtieth birthday.We would like to thank the following collaborators for their help and support during the course of these experiments: E. Kuli for the improvement of various measuring devices, J. Hoffmann, J. Badura and J. Novotny for the construction of the stabilization system, and J. ech and M. Keller for the construction of the real time interface unit. We are thankful to Z. Kosina for information accorded during the preparation of the data processing codes.     

Investigation of polar emission in 252Cf and 235U + nth fission

The energy distributions and relative intensities of protons, deuterons, tritons and α-particles emitted along the fission axis during spontaneous fission of ²⁵²Cf were measured simultaneously with both fission fragment energies. The absolute intensity of particles, the mass distribution of fragments, the total kinetic energy and total excitation energy of both fragments were subsequently deduced from the experimental data. Statistical model calculations based on a hypothesis that the polar particles are evaporated from fission fragments have been performed for ²⁵²Cf and ²³⁶U fission. Although some experimental results agree remarkably well with the evaporation hypothesis, the considered model cannot describe many features of the polar emission phenomenon.     

Angular momenta of fission fragments in the α-accompanied fission of 252Cf

For the first time, average angular momenta of the ternary fission fragments ^{100, 102}Zr, ¹⁰⁶Mo, ^{144, 146}Ba and ^{138, 140, 142}Xe from the α-accompanied fission of ²⁵²Cf were obtained from relative intensities of prompt γ-ray transitions with the use of the statistical model calculation. Average values of the angular momenta were compared with the corresponding values for the same fission fragments from the binary fission of ²⁵²Cf. Results indicate the presence of a decreasing trend in the average values of angular momenta induced in ternary fission fragments compared to the same binary fission fragments. On the average, the total angular momentum extracted for ternary fission fragments is ∼1.4 ℏ lower than in binary fission. Consequently, results indicate that the mechanism of the ternary α-particles emission may directly effect an induction of angular momenta of fission fragments, and possible scenarios of such mechanisms are discussed. Further, the dependence of the angular momenta of ¹⁰⁶Mo and ¹⁴⁰Xe on the number of emitted neutrons from correlated pairs of primary fragments was obtained also showing a decreasing dependence of average angular momenta with increasing number of emitted neutrons. Consequences are briefly discussed.     

薄壁快脉冲252Cf裂变电离室的研制及性能测试

介绍了用于中子探测器效率刻度的薄壁快脉冲252Cf裂变电离室。 在用飞行时间法测量中子能谱时, 该裂变电离室能够给出252Cf裂变中子发射时刻信号, 输出脉冲上升时间约为5.5 ns, 电离室由厚度为0.15 mm的不锈钢构成。 测试结果表明, 对裂变碎片的探测效率为99.2%, α粒子脉冲幅度和碎片脉冲幅度可清晰分开。A thin wall, fast pulse 252Cf ionization chamber, which was designed for calibrating efficiency of neutron detectors, was described. The ionization chamber can be used as the start detector in time of flight measurements of the 252Cf fission neutron spectrum. The chamber is composed of 0.15 mm thick stainless steel, the rise time of pulse signals is about 5.5 ns. As the test result shows, the detection efficiency of fission fragments is 99.2%, and pulse signals caused by fissions are distinguished clearly from those caused by α decays.     

Role of energy cost in the yield of cold ternary fission of 252 Cf

The energy costs in the cold ternary fission of ²⁵²Cf for various light charged particle emission are calculated by including Wong’s correction for Coulomb potential. Energy cost is found to be higher in cold fission than in normal fission. It is found that energy cost always increases with decrease in experimental yield in all the light charged particle emissions. The higher ground state deformation of the fragments, the odd–even effect and the enhanced yield in the octupole region observed in cold fission are found to be consistent with the concept of energy cost.     

Behaviour of Prompt Gamma-Ray Emission in ColdFission of 252Cf

The behaviour of prompt γ-ray emission in the cold fission of ²⁵²Cf was investigated experimentally using a four-parameter correlation technique. A twin gridded ionization chamber was employed to detect the fission signals and to determine the fragment emission angles, and a φ10cm×10cm NaI(T1) detector was used to record the γ-ray energies. The result shows that the angular distribution coefficient of γ-rays emitted in cold fission is twice as large as that in the normal fission.The fact that in the cold fission the number of γ-rays emitted from the light fragments is approximately three times as large as that from the heavy ones can not be explained satisfactorily so far.     

Orientation windows in the cold synthesis and decay of heavy elements

Due to the multipolar ground state nuclear deformations (β ₂, β ₃, β ₄,...) the cold synthesis of heavy and superheavy elements is dependent on the mutual orientation of target and projectile. When going from lower bombarding energies to higher bombarding energies, windows for orientations are occurring and others are disappearing. The cold fission is also strongly dependent on the deformation but is more selective in respect to orientation of fragments at scission. The measured cold fission yields of ²⁵²Cf show that only one orientation window is active. I propose a qualitative receipt based on the orientation windows of the driving potential which serves as a guidance in understanding the fission and quasifission mass distributions in the synthesis of heavy and superheavy elements.     

Coaxial Fission of Nuclei to Three Commensurate Fragments

Trajectory calculations of the angular distribution of fragments originating from the spontaneous true ternary fission of ²⁵²Cf nuclei are performed with allowance for the rotation of the fissile-nucleus axis. This rotation arises upon scission because of the formation of fragment spins despite the conservation of zero total angular momentum at all fission stages. The calculations in question lead to the conclusion that a collinear tripartition is the most probable in spontaneous true ternary fission of ²⁵²Cf nuclei. This confirms experimental data, thereby creating the basis that is necessary for obtaining deeper insight into them.     

Comparison of the spontaneous fission of 244Cm and 252Cf: (I). Fragment masses and kinetic energies

The energy of both fission fragments of ²⁴⁴Cm and ²⁵²Cf, respectively, was measured in coincidence with the prompt neutrons (see part II). Energy calibration of the surface-barrier detectors was done after the method of Schmitt et al. with the ²⁵²Cf fragments. Mean values and rms widths of the mass and energy distributions of both isotopes are calculated and compared with the results of other authors. The total kinetic energy of ²⁴⁴Cm fragments is at least as high as that of ²⁵²Cf fragments.     

Mass spectrometric investigation of desorbed ions from a valine sample by252Cf fission fragments

Summary Spectra of positive and negative secondary ions desorbed from a valine sample by²⁵²Cf fission fragments were measured in a new time-of-flight mass spectrometer. The outstanding features of the obtained results, including fragmentation, cationization and clustering are discussed. To speed up publication, the authors of this paper have agreed to not receive the proofs for correction.     

Emission properties of fission fragments and their isomeric ratios

The properties of neutron emission from fragments formed in the spontaneous fission of ²⁵²Cf and in the thermal-neutron-induced fission of ²³⁵U are analyzed on the basis of the statistical model of nuclear reactions. Upon extracting the mean excitation energies of fission fragments from experimental data on the mean multiplicities of neutrons, the observables of neutron emission can be described over wide ranges of total kinetic energies and masses. The observed values of mean fragment spins are also reproduced. A method for calculating the isomeric ratios of the independent yields of fission fragments that is based on the cascade-evaporation model of excited-nucleus decay is employed to describe experimental data on ²³⁵U fission induced by thermal neutrons and on ²³⁸U fission induced by alpha particles. The effect exerted on the isomeric ratios for fission fragments by two different assumptions on the spin distributions of primary-fragment populations—the assumption of the distribution associated with rotational degrees of freedom and the assumption of the distribution associated with the internal degrees of freedom of fully accelerated fragments—is investigated.     

Fission Energy Surfaces and Ternary Fission

A three-center phenomenological model, able to explain qualitatively the recently obtained experimental results concerning the quasimolecu-lar stage of a light-particle accompanied fission process is presented. It was derived from the liquid drop model under the assumption that the aligned configuration, with the emitted particle between the light and heavy fragment, is reached by increasing continuously the separation distance, while the radii of the heavy fragment and of the light particle are kept constant. In such a way, a new minimum appears in the deformation energy at a separation distance very close to the touching point. This minimum allows the existence of a short-lived quasi-molecular state, decaying into the three final fragments. The influence of the shell effects is discussed. The half-lives of some quasimolecular states which could be formed in the ¹⁰Be and ¹²C accompanied fission of ²⁵²Cf are roughly estimated to be of the order of 1 ns and 1 ms, respectively.     

用于裂变碎片质量测量的MCP和Au-Si SBD飞行时间探测系统

为了能很好地鉴别碎片质量,建立一个好的飞行时间测量方法是十分必要的。阐述了建立用于裂变碎片质量测量的微通道板（MCP）和金硅面垒探测器（SBD）飞行时间探测系统。对于80 μg/cm2厚的碳膜,241Am的α粒子的探测效率约为39%,252Cf（sf）裂变碎片的探测效率约为98%。在动能为78 MeV条件下,对252Cf（sf）重裂变碎片（138~148 u）得到的时间分辨为（224:1±6:1）ps;在动能为102 MeV条件下,对252Cf（sf）轻裂变碎片（101~111 u）,得到的时间分辨为（154:5±5:8）ps。In order to separate the mass number of fragments in the fission reactions, it is essential to develop a good time-of-flight (TOF) method. The purpose of this article is to set up a TOF detector system including a microchannel plate (MCP) and a Au-Si surface-barrier detector (SBD). The TOF system shows a detection efficiency of 39% for α-particles released from 241Am and 98% for fragments in the spontaneous fission of 252Cf. The experimental results show that the time resolutions of (224:1±6:1) ps for the heavy fragments (Ek=78 MeV, AH=138~148 u) and (154:5±5:8) ps for the light fragments (Ek=102 MeV, AL=101~111 u) can be obtained.