A microscopic calculation of angular and energy distributions of light fragments in deeply inelastic heavy-ion reactions

A random-matrix model for the form factors connecting channels corresponding to high intrinsic excitation energy of either fragment is used to calculate energy-averaged cross sections in deeply inelastic heavy-ion reactions. The distribution of the form factors is determined microscopically. The calculation yields differential cross sections without any fit parameters. Results for Kr- and Bi-induced reactions are compared with the data.     

Total cross sections for nucleus-nucleus reactions within the Glauber-Sitenko approach for realistic distributions of nuclear matter

The microscopic eikonal phase shifts for nucleus-nucleus collisions and total reaction cross sections are calculated by using the expression previously derived for the profile (thickness) of a realistic distribution of nucleons in the form of a symmetrized Fermi function. If, in addition, the density of the projectile nucleus is approximated by a Gaussian function and if a density profile of arbitrary form is taken for the target nucleus, the phase shift in question reduces to a one-dimensional integral. Questions are considered that are associated with the derivation of density parameters for “pointlike” nucleons in nuclei, with the possibility of approximating realistic densities by Gaussian functions in the region of the nuclear surface, with the dependence of the cross section on the range of nucleon-nucleon interaction and on the nuclear-medium density, and with the role of the distortion of the trajectory. Conclusions on the physics of the process are drawn, and the cross sections calculated on the basis of the present approach without using free parameters are compared with available experimental data.     

Calculation of photoionization cross sections by the absorbing boundary method

A new method for the calculation of quantum state decay rates, the absorbing boundary method (ABM), has recently been developed. In this talk the general form of the ABM will be outlined. The pseudo bound state approach to the calculation of continuum rates such as photoionization cross sections and used by Langhoff and coworkers will be briefly reviewed and shown to lack precision in the absence of information about the line widths and shapes of the pseudo bound states. It will then be noted that the ABM can be used to construct a rigorous new approach to the calculation of photoionization cross sections incorporating the necessary lifetime information for the pseudo bound states while still allowing the computation to be carried out by bound state procedures.     

碳对α的非卢瑟福背散射截面研究

报道了散射角为１７０°±１．５°，α粒子能量在５－９．０ＭｅＶ之间，ｃ的背散射截面的实验测量值；用Ｒ矩阵理论，通过与实验数据拟合，分析、给出了一套能级参数，并计算了能量范围在２－９．０ＭｅＶ，ｃ的背散射截面；讨论了对背散射分析感兴趣的窄而孤立的强共振峰４２５０±１０ＫｅＶ随靶厚、角度的变化关系以及截面变化缓慢的平坦区３．６－４．２０ＭｅＶ，６．４２５－６．７００ＭｅＶ能区的截面值与背散射角度的关系。 关键词：     

Study of form factors for single-proton transfer reactions on152Sm,154Gd and156Gd

The (³He,d) and (α,t) single-proton transfer reactions on targets of¹⁵²Sm,¹⁵⁴Gd and¹⁵⁶Gd were studied at 35MeV incident energy. Differential cross sections of rotational states built upon various single-proton configurations are compared with results of DWBA calculations which employed various radial form factors. The agreement between calculated and measured reaction cross sections is found to improve significantly when the commonly used spherical bound-state potentials are replaced by deformed ones, including deformed Coulomb and spin-orbit wells, and projected form factors are used to calculate DWBA cross sections. Discrepancies in the differential cross sections so large that they cannot be attributed to band mixing phenomena are readily explained by form factor effects.     

M_(αβ) X-ray production cross sections of Pb and B iby 9–40 keV electron impact

The experimental data of Mαβ X-ray production cross sections for Pb and Bi by 9–40 keV electron impact have been given. Thin films with thick carbon substrates are used in the experiment. The effects of target structure on the Mαβ X-ray production cross sections are corrected by using the Monte Carlo method. The corrected experimental data are compared with calculated cross sections in terms of the distorted-wave Born approximation(DWBA) theory. The measured Mαβ X-ray production cross sections for Pb and Bi are lower than the DWBA calculations. The atomic relaxation parameters used in comparing the DWBA values with experimental results affect the degree of difference.     

活性靶技术熔合截面测量极限研究

天体环境中丰中子核素熔合反应率对研究中子星表面超级暴现象的点火机制有重要意义。由于次级束流强过低,无法使用传统固体靶实验技术测量垒下熔合反应截面。活性靶技术的发展为垒下丰中子核素熔合反应截面的测量提供了可行的途径。基于Geant4模拟详细地分析了多重采样电离室（MUSIC）与时间投影室（TPC）两种活性靶探测器中熔合反应与弹性散射的运动学性质,给出了4种熔合反应鉴别判据,并且计算了由这些判据误判引起的熔合截面系统误差。在E_cm=13.6 MeV时,MUSIC与TPC的弹性散射误判截面分别为0.5 mb和2.9×10-3 mb,都远小于此时熔合截面（877 mb）。在垒下,MSUIC的熔合截面系统误差已经超出实验测量要求,而TPC能够进行实验测量的能量可以降低至E_cm=4.7 MeV。Reaction rates of fusion reactions among neutron-rich nuclei in the astrophysical environment are of great significance to understand the ignition of superbursts on neutron stars. Since beam intensity is rather low for radioactive ion beams, it is extremely difficult to operate a direct measurement for cross sections of such fusion reactions below the Coulomb barrier using thick target technique. In this case, a novel technique, active target technique, has been developed recently. To study the energy limit for measurement below Coulomb barrier, the kinematics of elastic scattering and fusion reaction in MUSIC and TPC are discussed with Geant4 simulation. Four identification methods are used and uncertainties of cross sections resulted from misjudgments are calculated. With E_cm=13.6 MeV, the uncertainties of cross sections for MUSIC and TPC are 0.5 mb and 2.9×10-3 mb, respectively. The uncertainties for MUSIC become far beyond measurement when below coulomb barrier, while TPC remains to be a suitable detector for measuring fusion cross sections until E_cm=4.7 MeV.     

Complete fusion and quasi-fission reactions induced by Kr ions on heavy targets

Cross sections for fission (complete fusion) and quasi-fission are measured at a given angle for the systems Kr + Ho, Kr + W, Kr + Bi, Kr + U in the energy range 450–525 MeV. The cross sections for complete fusion are unexpectedly low and the cross sections for quasi-fission are high. The cross section for close collisions (sum of the complete fusion and quasi-fission cross sections) is compared to the value calculated with the critical distance concept. The possibility that complete fusion does not occur for the lowest impact parameters is discussed.     

An optical potential for heavy ion interactions

An optical potential for nucleus-nucleus interactions is evaluated using a density-dependent effective two body force. The resulting interaction potential is then used to discuss elastic scattering cross sections using a quarter-point recipe from Fresnel diffraction theory. Fits to quarter points of cross sectional data are obtained with parameters for the effective interaction which fit properties of nuclear matter and with parameters for target and projectile densities obtained from electron scattering.     

Electron impact total ionisation cross sections for simple bio-molecules: a theoretical approach

In this article, we have reported electron impact total ionisation cross sections for the bio-molecules pyridine, pyrimidine, n-propylamine, urea, formamide and N-methylformamide from ionisation threshold to 2000 eV. The present calculations are based on the spherical complex optical potential formalism and complex scattering potential ionisation contribution method. The results obtained for pyridine and pyrimidine are compared with available theoretical and experimental results and are found to be in excellent agreement with existing data. The ionisation cross sections for other molecules are reported for the first time. An interesting relation between the peak of inelastic and ionisation cross sections with target parameters is also reported. It was found that both the cross sections at their maximum depend linearly with these parameters, confirming the consistency of the values reported here.     

Analysis and optimization of blocks in high-frequency sections of linear accelerators and deflectors of charged particles using an equivalent circuit

Analysis and optimization of blocks in high-frequency sections of linear accelerators and defectors of accelerated particles is performed using an equivalent circuit. This circuit correctly simulates the lowest accelerating mode as well as the first dipole mode of the E-type for various structures consisting of coupled cells. Analytic expressions are derived for parameters of individual cells of sections for which traveling waves with a preset form of oscillations propagate at a given frequency; optimization of the parameters of the input and output wave-type transformers is carried out. Simple analytic expressions are considered for calculating the complex reflection coefficient of a section in a certain cross section of the lead-in waveguide. The sections may contain identical cells as well as different cells.     

类氦氪离子双电子复合的相对论计算

本文采用相对论性的Flexible Atomic Code (FAC)程序计算类氦氪离子的双电子复合截面及速率系数。其中自电离速率的计算采用相对论扭曲波近似，并考虑了组态相互作用的影响。文中还将所得的自电离和总辐射速率与采用MCDF和HULLAC计算得到的结果作了比较。我们检验了n-3标度律的有效性并用它对速率系数做了外推。文中还讨论了辐射分支比随不同共振峰和原子序数的变化以及级联辐射的影响。     

A barrier-penetration model for heavy-ion fusion,valid at all energies

We present a barrier-penetration model for heavy-ion fusion valid from the lowest energies available up to the largest energies for which the critical-radius picture is realistic. The parameters of the model are a critical radius and the parameters of a nucleus-nucleus interaction, whose form factor can be chosen freely. Fusion cross sections for a large number of systems, for which low-energy data exist, are fitted with a Woods-Saxon potential. Realistic parameters are obtained for the Coulomb barrier. Different applications and some limitations of the model are discussed.     

Differential cross section and related integrals for the molière potential

The Molière potential is widely used in radiation damage simulation studies. It is not much used in analytical transport theory calculations because of the awkward expression for the differential cross section corresponding to the potential. We follow a two step process to obtain a useful cross section: adopting the Lindhard, Nielsen and Scharff (LNS) approximations in order to generate a simpler form of the Molière cross section and then creating a simple, easy-to-use, fit to that approximate form. Within the framework of the LNS treatment of atomic cross sections, our fit is accurate to 6%. Simple forms for the total cross section and several related quantities are presented.     

Diffractive jet production in deep-inelastic e^+p collisions at HERA

A measurement is presented of dijet and 3-jet cross sections in low- diffractive deep-inelastic scattering interactions of the type , where the system X is separated by a large rapidity gap from a low-mass baryonic system Y. Data taken with the H1 detector at HERA, corresponding to an integrated luminosity of 18.0 pb, are used to measure hadron level single and double differential cross sections for and . The energy flow not attributed to jets is also investigated. The measurements are consistent with a factorising diffractive exchange with trajectory intercept close to 1.2 and tightly constrain the dominating diffractive gluon distribution. Viewed in terms of the diffractive scattering of partonic fluctuations of the photon, the data require the dominance of over states. Soft colour neutralisation models in their present form cannot simultaneously reproduce the shapes and the normalisations of the differential cross sections. Models based on 2-gluon exchange are able to reproduce the shapes of the cross sections at low values. Received: 21 December 2000 / Published online: 6 April 2001     

1.30-2.21MeV质子在硅上的160°散射截面测量

采用薄靶对能量 1.30 - 2 .2 1MeV质子在纯度为 99.99%硅上的非卢瑟福弹性背散射截面(16 0°背散射角 )进行了测量 .质子束由 2× 1.7MV串列加速器提供 ,测量仪器采用金硅面垒探测能谱仪 .实验中最低能区进入卢瑟福弹性散射能区 ,测量结果与以前发表的结果进行了比较 .所测量数据可供从事背散射分析技术的有关人员参考 . The elastic backscattering cross sections of H + from silicon for a wide energy range are very useful parameters in the proton backscattering analysis for investigating silicon content and distribution profiles in the films. It is necessary to measure the scattering cross sections with good accuracy at a large scattering angle for the applications of proton backscattering analysis. The present paper reports our measured results of differential elastic backscattering cross sections of 1.30-2.21 MeV...     

Electron-impact ionization cross sections and rates for ions of argon

A distorted-wave Born exchange (DWBE) approximation including relativistic correction is used to calculate the electron-impact ionization cross sections and rate coefficients for the highly charged ions Ar⁷⁺,…,Ar¹⁷⁺. The comparison of the calculated results with the experimental data and other theoretical calculations shows that the DWBE method is valid for these ions of argon. The calculated results for direct ionization cross sections and excitation autoionization were fitted by empirical formulas to meet the requirements of applications. A set of improved empirical formulas are used for the fast and accurate calculations of rate coefficients from the fit parameters of cross sections.     

Charged particle reaction cross sections and nucleosynthesis

The role of proton and α-particle induced reactions in carbon, neon, oxygen and silicon burning in massive stars is surveyed. The problems associated with determining thermonuclear reaction rates for reactions with widely spaced resonances and with closely spaced or overlapping resonances are discussed and the associated experimental approaches are reviewed. Experimental techniques which have been used in the measurement of reaction cross sections are discussed and their strengths and weaknesses are identified. Recent developments in attempts to establish reliable statistical-model codes for calculation of reaction cross sections are presented and discussed. Finally, the results of experimental tests of statistical model codes are summarised and evaluated.     

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The total Born cross sections summed over the orbital quantum numbers, as well as the corresponding excitation rates for transitions between highly excited states induced by electron impact, are calculated. The calculations were made for the following principal quantum numbers: 10≤n≤100, Δn/n≤0·3 (Δn=n|n?n′|). The results are presented in a form convenient for interpolations (see Tables 1 and 2).The calculations were performed by using an asymptotic expansion in powers of 1/n and 1/n′, for the exact analytical expression of the total generalized oscillator strength. Comparison of the exact results with the asymptotic ones shows that an accuracy of about 10 percent is achieved for n?2 (see Figs. 1 and 2).For high electron energies, analytical expressions are obtained for the cross sections and the excitation rates. The approximation used is analogous to that of Kramers for the oscillator strenght, the errors do not exceed ～30 percent.