浦项中子装置上~(209)Bi中子全截面测量（英文）

在浦项中子装置(PNF)的100 Me V电子直线加速器上利用透射法和飞行时间法测量了209Bi的0.1～100 e V的中子全截面。文中对于实验装置特点、用吸收片法拟合本底、拟合中子飞行距离和时间零点的处理过程做了较为详细的描述。测量结果与以前发表的实验数据以及评价数据ENDF/B-VII.1做了比较,比较结果符合得较好。     

中高能电子散射全截面测量装置的设计

介绍了中高能电子散射全截面绝对测量装置的设计,采用直线透射技术.因采用了恒温控制作用室,以便较准确测量反应室的绝对气压值;同时采用静电型圆柱能量分析器,并用计数率测量模式代替通常的束流强度测量模式,从而可以大幅度减小接收立体角,抑制零度角的弹性散射贡献.通过以上几项措施,可以有效地提高测量的精度,从而可以对一些有意义的分子的中、高能电子散射全截面进行绝对测量.     

中高能电子散射全截面测量装置的设计

介绍了中高能电子散射全截面绝对测量装置的设计,采用直线透射技术.因采用了恒温控制作用室,以便较准确测量反应室的绝对气压值;同时采用静电型圆柱能量分析器,并用计数率测量模式代替通常的束流强度测量模式,从而可以大幅度减小接收立体角,抑制零度角的弹性散射贡献.通过以上几项措施,可以有效地提高测量的精度,从而可以对一些有意义的分子的中、高能电子散射全截面进行绝对测量.     

中高能电子的散射全截面测量装置

以电子束流光学系统为重点,介绍一台500～4250eV电子的绝对散射全截面测量装置,给出了电子枪和五圆筒透镜的电子光学设计,提供实验对电子光学系统的检验,提出对装置的改进设想。     

16O中子全截面的色散光学模型研究

基于色散关系理论,研究了¹⁶O的光学模型,利用包括色散项在内的光学势计算了¹⁶O的全截面,基本上克服了全截面反常的矛盾.     

基于白光中子源的197Au中子辐射俘获截面测量及共振参数分析

中子辐射俘获反应在反应堆运行、核装置设计及核天体物理研究中起重要的作用. 4πBaF₂探测装置有着高时间分辨能力、低中子灵敏度、高探测效率等优点,适合开展中子辐射俘获反应截面数据的测量.中国原子能科学研究院核数据重点实验室建立了伽马全吸收装置(Gamma total absorption facility, GTAF),该装置用28块六棱BaF₂晶体和12块五棱BaF₂晶体构成了外径25 cm,内径10 cm的球壳,覆盖了95.2%的立体角.利用GTAF在中国散裂中子源Back-n束线上,测量了197Au(n, γ)的反应截面数据.测量数据通过能量筛选、PSD方法、晶体多重性筛选进行了初步本底扣除,随后结合对^natC及空样品的测量数据对本底进行了分析及扣除,获得了197Au俘获反应的产额,利用SAMMY程序拟合得到了¹⁹⁷Au在1—100 e V的共振能量、中子共振宽度和伽马共振宽度参数.实验测量结果与ENDF/B-VIII.0数据库符合良好,其共振参数存在一定差异,分析原因可...     

透射法测量丰中子核8He的去中子截面

利用HIRFL提供的50MeV/u ¹³C束流轰击Be靶, 通过RIBLL选择出丰中子放射性核⁸He. 利用透射法测量了⁸He的去双中子截面和去四中子截面. 利用Ogawa等人的理论结合原有⁸He的反应总截面数据, 得到⁸He的核芯为⁴He的结论.     

8.19 MeV中子与9Be作用的次级中子双微分截面测量

用中国原子能科学研究院HI13串列加速器上的多探测器快中子飞行时间谱仪, 测量了8.19 MeV中子与9Be作用时, 从20°到160°区间26个角度的次级中子双微分截面。测量截面以np散射截面作为标准进行归一。实验结果用Monte Carlo方法进行了中子注量率衰减、多次散射和有限几何修正, 并用MCNP4C程序对所用的Monte Carlo程序进行了验证。测量结果与评价数据以及其它实验室的数据进行了比较。The secondary neutron emission double differential cross section of 9Be induced by 8.19 MeV neutron was measured at 26 different angles from 20°to 150°by using the multi detector fast neutron TOF spectrometer at the HI 13 Tandem Accelerator at China Institute of Atomic Energy(CIAE). The results were normalized to np scattering measurement. A special Monte Carlo code which was validated with the MCNP 4C code was employed to analyze the measured data for the corrections of neutron flux attenuation, multiple scattering and finite geometry. The measured results were compared with the evaluated data and the other measurements.      

14MeV中子引起的核反应截面测量中监督反应的研究

讨论了14MeV中子引起的核反应截面测量中监督反应对测量结果的影响,同时列出了常用的一些监督反应及参数,利用截面的评价值给出了一些监督反应的截面随中子能量变化的关系曲线,并对^27Al（n,p）^27Mg反应做了定性分析,说明了监督反应的选取对反应截面测量的重要性。 It was discussed in this article that the effects of different monitors in the cross section measurements of nuclear reactions induced by 14 MeV neutrons, at the same time some monitors and correlative parameters were listed. The excitation functions of monitors are taken from the evaluatied cross sections, and a qualitative analysis has been performed for ^27Al（n,p） ^27Mg reaction. It indicates that the choice of monitor is very important for cross section measurements     

PGNAA系统中D-T中子管的慢化装置优化设计

为了提高PGNAA系统中D-T中子管的中子慢化效率,获得更高的热中子产额,借助蒙特卡罗模拟,确定了以铅为中子反射层、5个聚乙烯层和铅层相互交替作为中子慢化层、碳化硼含量为3%的含硼聚乙烯作为中子吸收层以及铅作为γ屏蔽层的中子慢化装置模型。针对中子产额为3×107 n/s 的D-T中子管,该慢化装置输出面低于5 eV中子通量可达5.28×106 n/s,占总中子通量的30.8%,有效提高了中子慢化效率。经过验证模拟结果能够满足实验要求。To improve the moderating efficiency of D-T Neutron Generator in PGNAA system, and get higher thermal neutron yield, the Monte Carlo code MCNP was used to optimize the moderation setup. The lead was selected as neutron reflector and gamma absorber, 5 polyethylene layers and 4 lead layers constituted the neutron moderator and 3% boron-doping polyethylene was selected as neutron absorber. For the yield of 3107 n/s D-T Neutron Generator, this moderation setup can provide a yield of lower than 5 eV of 5.28106 n/s, accounting for 30.8% of total neutron yield, dramatically improves the moderating efficiency. It is proved that the simulation results can satisfy the requirement of PGNAA system by preliminary experimental verification.     

Molecular-orbital X-rays from 1 GeV 208Pb + 208Pb and 209Bi + 209Bi collisions

We have measured the spectra of continuum X-rays above the characteristic K lines for 4.5 to 4.8 MeV/N ²⁰⁸₈₂Pb → ²⁰⁸₈₂Pb, Pb → Bi, Bi → Pb and Bi → Bi collisions. Above ≈400 keV X-ray energy the spectral shape and intensity agree roughly with calculations of Kirsch et al. for the 1sσ molecular-orbital (MO) X-ray spectrum from Pb-Pb. Deviations from the theory below ≈400 keV suggest transitions to other MO's.     

Time-dependent Hartree-Fock study of 136Xe + 209Bi collisions

We have performed axially symmetric Skyrme force time-dependent Hartree-Fock calculations for the ¹³⁶Xe + ²⁰⁹Bi system at E(lab) = 940 MeV and 1130 MeV. The evolution of the nuclear geometry is studied in detail. The calculated final fragment kinetic energies, scattering angles, and charges are in good agreement with experiment, but the fragment charge dispersion is greatly underestimated. Studies of head-on collisions for 900 MeV ? E(lab) ? 2000 MeV show no evidence for fusion and indicate a dramatic transparency for E(lab) ? 1500 MeV.     

Scattemng of 14.1 MeV neutrons from 209Bi

Differential cross sections for the elastic and inelastic scattering of 14.1 MeV neutrons from ²⁰⁹Bi have been measured with a time-of-flight system which had an energy resolution of 650 keV. For elastic scattering from ²⁰⁹Bi, an optical-model analysis gave the best-fit potential parameters. The absolute cross sections for excitation of collective (2.66 and 4.36 MeV) states are reproduced by the results of distorted-wave calculations under the assumption of a core (²⁰⁸Pb) excitation model using deformation parameters obtained from (p, p') reactions.     

Distribution of single-particle strengths in the nuclei 207Tl, 207Pb, 209Bi and 209Pb

Within the theory of finite Fermi systems we calculate the distribution of single-particle strengths in the odd mass nuclei surrounding ²⁰⁸Pb. The Dyson equation with an energy dependent mass operator is solved and the resulting single-particle propagator is analysed. It turns out that the concept of quasiparticles used in this theory is very well justified for nearly all the states in the first and the second shells below and above the Fermi surface.     

Extended optical model analyses for the 11B + 209Bi system at near-Coulomb-barrier energies

In the framework of an extended optical model approach in which the polarization potential is decomposed into direct-reaction (DR) and fusion parts, simultaneous c² \chi^{{2}}_{} analyses of elastic scattering and fusion cross-section data for the ¹¹B+ + ²⁰⁹Bi system at near-Coulomb-barrier energies are performed. We show that the DR and fusion potentials extracted from c² \chi^{{2}}_{} analyses separately satisfy the dispersion relation and that the threshold anomaly exhibits in both DR and fusion parts. We find that the analyses using only elastic scattering and fusion data can produce reliable predictions of cross-sections even though the direct reaction cross-section data are not complete. By using the extracted DR potential, we investigate the effects of the projectile breakup on fusion cross-sections.     

On the decay of 201Bi and 199Bi

Level schemes for ²⁰¹Pb and ¹⁹⁹Pb, studied from the radioactive decay of bismuth isobars, are proposed on the basis of γ-ray, electron spectra and γ-γ coincidence measurements. The experimental results are compared mainly with those of two theoretical approaches.     

7 MeV dipole ground state transitions in 207Pb, 208Pb and 209Bi

The Doppler-broadened 7.117 MeV line from the ¹⁹F(p, αγ)¹⁶O reaction has been used to resonantly excite levels in ²⁰⁸Pb at 7071±2 and 7091±2 keV, in ²⁰⁷Pb at 7186±5 and 7206±5 keV and in ²⁰⁹Bi at 7179±5 and 7202±5 keV. On the basis of angular distribution measurements the 7071 and 7091 keV levels of ²⁰⁸Pb are assigned spins of 1 and assuming 100% ground state branching the widths are calculated to be 31±3 and 17±2 eV respectively. It is suggested that the states in ²⁰⁷Pb and ²⁰⁹Bi arise from the weak coupling of a $\text{P}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ neutron hole and an $\text{h}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}$ proton respectively to one or the other of the ²⁰⁸Pb levels. The widths obtained in terms of _gΓ_o²/Γ are 15±4 and 25±5 eV for the 7186 and 7206 keV levels of ²⁰⁷Pb and 24±5 and 30±5 for the levels of ²⁰⁹Bi respectively. These values are consistent with the weak-coupling suggestion.     

Electromagnetic transition probabilities between the low-lying states of 203Tl, 205Tl and 209Bi

A high-accuracy investigation of absolute γ-ray yields and angular distributions after Coulomb excitation of ²⁰³Tl, ²⁰⁵Tl and ²⁰⁹Bi allowed the determination of B(E2) and B(M1) values in these nuclei. Some of the data obtained are compared with direct lifetime measurements and internal conversion data. The influence of deorientation effects on our results is discussed. A comparison is made between the experimental transition matrix elements and shell-model and core-coupling-model calculations. The “l-forbidden” M1 transitions, which are caused by core-polarization effects, have strengths of ≈ 10^?3 W.u. In ²⁰⁹Bi the strength of the $\text{f}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}\text{→}\text{h}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}$. E2 transition is equivalent to a surprisingly large proton polarization charge of (2.8 ± 0.2)e.     

Parity violating effects in the coherent scattering of neutrons by 209Bi

We study the rotation of the spin in the coherent scattering of polarized thermal neutrons by ²⁰⁹Bi. Contributions due to direct weak scattering by the nucleus, parity admixtures into the nuclear wave functions and scattering by the electrons are calculated. We use a parity violating potential derived in the framework of the Salam-Weinberg model and several other semi-empirical potentials. The results show that the direct scattering on nuclei is the dominant contribution and some potentials predict results up to an order of magnitude larger than expected on dimensional grounds. The sign of the effect depends on the isospin properties of the potential and can distinguish between potentials with large isotensor or large isovector contributions.     

12C+13C在库仑位垒以下能区的熔合截面测量

深垒下能区的12C+13C熔合截面测量对检验天体中熔合反应外推模型具有很重要的意义。目前在库仑位垒以下能区存在的各种测量结果,都利用了统计模型来修正得到熔合截面,但对于这些方法间的系统误差仍没有很好地研究。实验采用离线活度测量的方法,在E_c.m.=4.4～5.8 MeV能区内对12C+13C熔合截面进行测量。经Hauser-Feshbach统计模型对分支比的修正后,熔合总截面由24Na活度推导出。通过本实验数据与其它实验方法获得的数据进行比较,确定了统计模型的系统误差为14%。The study of fusion reactions of 12C+13C at the deep sub-barrier energies is very important for the test of predictive power of the extrapolation models for nuclear reactions for astrophysics. Until now, all the measurements below Coulomb barrier energies have to use the statistical model calculations to estimate the branching ratios to deduce the total fusion cross sections. However, the systematic uncertainty induced by the calculated corrections has not been studied well. In this experiment, the fusion cross sections of 12C+13C have been measured using an offline activity measurement in the range of E_c.m.=4.4 to 5.8 MeV. The total fusion cross sections have been deduced from the 24Na activities after correcting the branching ratios estimated with the Hauser-Feshbach statistical model. Through the comparison between our result and other data obtained with other methods, the systematic uncertainty of statistical model has been determined to be 14%.