质子滴线核~(12)N在~(28)Si靶上的核反应总截面测量

描述了50.4 MeV/u的12N和42.3MeV/u的13N次级放射性束在28Si靶上引起的核反应总截面σr实验研究,结果发现12N的反应总截面σr比其相邻同位素核13N有着异常的增大. 这可能是核形变及核子对效应造成的,试验中的测量误差也不可忽视. 利用微观Glauber模型计算了12N在28Si靶上的核反应总截面,并与实验结果做了比较,发现理论计算与实验结果拟合较好.     

35MeV/u40Ar+197Au中的熵产生

根据量子统计模型(QSM)的计算分析,找到了一个提取核反应过程中熵产生的新的可观测量.核反应过程中约化d的产额d/(d+t+³He+⁴He)和熵有单调的函数关系,并且和体系的碎裂密度(ρ/ρ₀)及体系的N/Z都无关,可以作为提取核反应过程中熵产生的一个观测量.和目前已经有的其他方法相比,约化d产额这一提取熵方法可以用于较低能量的重离子核反应中,并且数据处理分析简单.对于35MeV/u⁴⁰Ar+¹⁹⁷Au的核反应过程所提取的熵和利用约化带电粒子多重性提取的熵结果一致.结合后角类靶热核发射体系实验提取的同位素核温度为4.7±1.2MeV及S/A=2.5±0.5,根据熵和核温度的关联关系,可以确定其Break up密度接近但小于0.1(ρ/ρ₀) 关键词： 熵 约化d产额 核温度 统计发射     

中能8B和9C与Si反应总截面的测量

能量为75MeV/u的¹²C初级束轰击2mm厚的初级Be靶,并利用RIBLL从弹核碎片中分离出54.2MeV/u质子滴线核束8B和61.1MeV/u的⁹C,再轰击Si靶,用透射法测量了它们与Si的反应总截面σ_R.并应用Glauber模型进行理论计算,分析结果表明⁸B和⁹C都可能具有质子晕结构.     

12N直接碎裂反应研究

描述了在兰州放射性束流线(RIBLL)上用78.6MeV/u的¹⁴N束流轰击Be靶产生出34.9MeV/u的¹²N次级束流. 利用¹²N轰击Si靶作为次级靶, 利用直接碎裂反应测量它的反应总截面. 利用理论模型进行了计算, 理论计算和实验结果符合的很好. 发现¹²N的质子密度分布相对于中子而言, 有一个很大的弥散.     

46.7MeV/u 12C引起的弹核碎裂反应

测量了46.7MeV/u ¹²C束流轰击不同靶核的核反应中前方向出射的类弹碎片,发现弹核碎裂产物的最可几能量可用Abrasion图象来解释.它们的平行动量分布宽度满足Goldhaber关系式,实验中提取的约化平行动量分布宽度σ₀=80±10MeV/c,接近于相对论情形下的值,并且σ₀对于不同的反应系统有相近的值.     

6Li与核弹性散射的微观光学势

从基本的Dirac-Brueckner-Hartree-Fock微观理论出发,得到同时包含实部和虚部的核子-核散射的微观光学势,并利用折叠模型直接获得了核-核散射参数无关的整体微观光学势.考虑到核-核散射去弹过程高级项的贡献和⁶Li的碎裂效应,在微观光学势的实部和虚部中引入了修正因子N_R,N_I.系统研究了入射粒子⁶Li与靶核¹²C,²⁸Si,关键词： 弹性散射 Dirac-Brueckner-Hartree-Fock方法 折叠模型 微观光学势     

中性硅3s23P2 3P2,1D2→3s3p3 3D3o跃迁能量,超精细结构常数与同位素移动的MCDHF计算

本文使用多组态Dirac-Hartree-Fock方法计算了²⁹Si的3s²3p^{2 3}P₂,¹D₂→3s3p³D₃⁰跃迁能量和³P₂,³D₃⁰超精细结构A常数以及Si同位素²⁹Si,³⁰Si和³¹Si相对于²⁸Si在3s²3p^{2 3}P₂→3s3p^{3 3}D₃⁰跃迁的同位素移动.通过尝试双电子激发（SD）和三电子激发（SDT）,分别考虑VV相关,CV相关和CC相关产生各种不同的扩展组态波函数得到的计算结果和实验值的比较,推测了对于中性硅原子这两个组态,内壳层2p2s,1s电子活动到外壳层的概率较小,而3s3p壳层中的电子都比较活跃,但主要是在n=3,4的壳层内活动,活动到更高n壳层的概率则比较小.     

丰中子奇异核17B的实验研究

在兰州重离子加速器国家实验室(HIRFL)放射性次级束流线(RIBLL)上,用束流透射法测量了丰中子奇异核¹⁷B与C靶反应的总截面.假定¹⁷B具有¹⁵B(核芯)＋2n结构,采用Gauss＋HO形式的密度分布和零力程Glauber模型进行计算的结果可以很好地拟合实验数据,并得出¹⁷B的密度分布有一个很大的弥散,表明¹⁷B是双中子晕核. 关键词： 丰中子奇异核 反应总截面 Glauber模型 密度分布     

用阻塞效应测量28Si 13.095MeV激发态能级寿命

改进Al单晶样品的处理方法,得到了高质量的样品。进行了Al单晶辐照损伤实验,直接测量了E_p=1565keV时²⁷Al(p,α)²⁴Mg共振所形成的²⁸Si 13.095MeV激发态能级寿命。采用MonteCarlo模拟和“分析”方法计算得到其寿命值τ=16.3±2.4as,对应的能级宽度Γ=40±6eV,与文献报道的共振产额法结果符合得较好。 关键词：     

46.7MeV/u 12C引起的核反应中碎裂与转移的竞争

本文讨论了46.7MeV/u ¹²C引起的核反应中弹核碎裂与转移反应的共存及相互竞争,实验中提取的转移部分的约化平行动量分布宽度为44±10MeV/c,这比弹核碎裂部分的σ₀=80±10MeV/c要窄.弹核碎裂及转移反应发生的几率都与被转移结团的结构有关.     

Reliable cross sections of partial photoneutron reactions on 188,189Os isotopes free of neutron multiplicity sorting problems

Experimental data on the cross sections of partial photoneutron reactions, obtained for ^188,189Os isotopes using quasimonoenergetic annihilation photon beams and neutron multiplicity sorting method, are analyzed. Using special criteria (transition multiplicity functions F _i = σ(γ, in)/σ(γ, xn), the ratios of the cross section of the corresponding partial reaction to the total neutron yield reaction’s cross section σ(γ, xn) = σ(γ, 1n)+ 2σ(γ, 2n) + 3σ(γ, 3n) free of the problems associated with experimental neutron multiplicity sorting), it is demonstrated that the data contain significant systematic errors. New data are evaluated for cross sections of partial photoneutron reactions (γ, 1n), (γ, 2n), (γ, 3n) and total photoneutron reaction (γ, sn) for ^188,189Os isotopes within an experimental-theoretical approach proposed earlier. It is shown that the significant systematic errors in the experimental cross sections of partial reactions can be attributed to the ambiguity of the relation between the photoneutrons’ multiplicity and their kinetic energy.     

The energy dependence of nuclear reaction cross sections

The reaction cross section σ_R^pA(E) for proton-nucleus collisions varies with energy as the total cross section σ_t^pN(E) does for proton-nucleon scattering in the energy regime 100 MeV ? E ?400 GeV. We propose several empirical relations, and test them by a χ² analysis of various data. Within the framework of Glauber theory, the parameters in the relations can be linked to the cross section for a single inelastic collision.     

The shape of the giant dipole resonance for light nuclei

A complete spectrum of the giant dipole resonance is calculated taking into account the finite depth of the single particle potential. The mixing of the one particle-one hole excitations because of residual interactions is treated in the time-dependent Hartree-Fock approximation. If the interaction is approximated by a separable potential a general formula can be derived, which gives the total dipole excitation cross section σ(E) in terms of the simple shell-model cross section σ₀(E). Numerical results are given for O¹⁶ and C¹² by evaluating σ₀(E) in a square well potential.     

Absolute photofission cross section of 209Bi in the energy range from 40 to 65 MeV

The absolute photofission cross section of ²⁰⁹Bi has been measured with monoenergetic γ-radiation between 40 and 65 MeV photon energy. Cross-section data have been obtained with an accuracy between 9 and 20%. The experimental result is compared with the excitation function calculated on the basis of the statistical model. In order to reproduce the measured data on σ_γf, the (γ, n) cross section must decrease with increasing photon energy faster than the experimental total (γ, n) cross section. This behaviour can possibly be explained by the assumption that after photon absorption a compound nucleus is formed only for a small, and with photon energy decreasing, fraction of all decays.     

The reactions of 12C with 12C AT 293 MeV

Energy spectra, angular distributions, and elemental yield distributions have been measured for products Z = 1?9 produced in the reactions of ¹²C on ¹²C. A total reaction cross section 1170_?100⁺¹⁷⁰ mb was determined from the measured elemental cross sections and the principle of charge conservation. This total reaction cross section is about 250 mb less than the geometric cross section and agrees with the Glauber-model calculations of DeVries and Peng. The experimental energy spectra, angular distributions, and yield distributions were compared with those from model calculations for the statistical decay of the products of fusion and of incomplete fusion reactions. For both types of calculations, a modified version of the code LILITA was used. By comparing the data to model calculations, an upper limit of 75 mb for the fusion cross section was determined. That limit corresponds to an upper limit of L_crit for fusion of 10? in the sharp-cutoff approximation. The dominant reaction mechanisms appear to be incomplete fusion processes.     

Isomeric cross sections for the (n, 2n) reaction on 82Se, 81Br,and 45Sc at 15.1 MeV

Activation techniques have been used to measure the cross sections at 15.1 MeV neutron energy for the following reactions: ⁸²Se(n, 2n)^81m+gSe, ⁸¹Br(n, 2n)^80m+gBr, and ⁴⁵Sc(n, 2n) ^44m+gSc. Isomeric cross-section ratios were evaluated by applying the method of least squares to the time behavior of γ-ray activity following the ground-state decay of each isomeric pair. The absolute cross section σ_m for the formation of the metastable state was measured by the mixed-powder method with the ²⁷Al(n, α)²⁴Na reaction as the monitor. The cross section σ_g for the formation of the ground state was then determined by using the isomeric cross-section ratio. The sum of σ_m and σ_g for each reaction is compared with the theoretical value obtained from calculations based on the statistical model for the formation of a compound nucleus and its subsequent emission of neutrons.     

The ππ total cross section: Its scale and massless pion limit

The question of the scale of the ππ total cross section is considered. We first give a simple intuitive argument for expecting cross sections in the massless chiral world to be finite. Assuming the universality of P-f Regge couplings, we give a simple dispersion theoretic evaluation of the asymptotic ππ total cross section, σ^ππ. We deduce an algebraic expression for σ^ππ and find that its scale is determined by 1/m_?² or, equivalently, 1/f_π² — just as Pagels conjectured. This relation has a smooth, finite limit as m_π tends to zero. Numerically, we obtain σ^ππ = 17 ± 4mb for physical mass pions and 14 ± 3mb for massless pions.     

The total photon deuteron hadronic cross section in the energy range 0.265–4.215 GeV

The total cross section for photoproduction of hadrons on the deutron, σ_T^d, has been measured for photon energies in the range 0.265–40215 GeV. From this, using results for the photon total cross section, obtained previously with the same apparatus, the neutron total cross section has been determined in the resonance region. The resonant structure is found to be quite different from that for the proton. Thereafter the neutron cross section falls off steadily with energy, and the values obtained are consistently lower than those for the proton. Forward scattering amplitudes have been evaluated for the deuteron.     

Absorption of massless scalar wave from Schwarzschild black hole surrounded by quintessence

By using the partial wave method, we investigate the absorption of massless scalar wave from Schwarzschild black hole surrounded by the quintessence. We obtained the expression of absorption cross section
080402
Then we numerically carry out the absorption cross section and we find that the larger angular momentum quantum number l is, the smaller the corresponding maximum value of partial absorption cross section is, and that the total absorption cross section tends to geometric-optical limit σ_abs^hf≈ π b_c². We also find that higher value of ω_q (state parameter of the quintessence) corresponds the higher value of absorption cross section σ_abs.