能损法测平均电离激发能

采用电子透过金属箔后的最可几能损测量法，由兰多公式经实验反推Ａｌ，Ｔｉ，Ｆｅ，Ｃｕ及Ｔａ平均电离激发能之实验值，所得结果与已有文献值比较有很好的一致性。实验结果表明这是一种测平均电离激发能的简便、易行且具有较高准确性的方法。     

Pressure dependence of the mean excitation energy of atomic systems

Changes in the mean ionization energy of atoms in compressed matter are estimated through cage models of atomic confinement whereby pressure is obtained in terms of the rate of change of total atomic energy with volume. Resort is taken to a recently implemented shellwise Thomas–Fermi–Dirac–Weizsacker theory for confined atoms to construct the atomic energy functional, which is self-consistently optimized for different confinement conditions. The resulting modified atomic orbital densities are then used within the Local Plasma Approximation to evaluate the corresponding orbital and total mean excitation energies. Good agreement is obtained with accurate calculations for free atoms. For compressed atoms agreement is found with a previously derived universal expression [J.M. Peek, Phys. Rev. A 36 (1987) 5429] for total mean excitation energies suggesting its adequacy for this class of studies.     

Mean excitation energies extracted from stopping power measurements of protons in polymers by using the modified Bethe–Bloch formula

Recent stopping power measurements in thin polymeric films have been performed for protons of 0.4–3.5 MeV energies using the indirect transmission technique [H. Ammi, S. Mammeri, M. Chekirine, B. Bouzid, M. Allab, Nucl. Instr. and Meth. B 198 (2002) 5]. Experimental stopping data have been analyzed with the modified Bethe–Bloch formula and the mean excitation energies I have been then extracted from the data. Resulting values for each thin film are 76 ± 1 eV in Mylar, 70.8 ± 1 eV in Makrofol, 82.2 ± 1.2 eV in LR-115 and 55.4 ± 1 eV in Polypropylene. The I-extracted values are compared to those I_B calculated by using the Bragg’s rule.     

高能136Xe离子辐照聚酰亚胺化学改性的电子能损效应

用1．755GeV^136Xe离子在真空室温环境下辐照叠层聚酰亚胺薄膜,通过红外和紫外光谱测量研究了高电子能损离子辐照引起的化学降解及炔基产生效应。红外测量结果表明,典型官能团随辐照注量的增加指数降解,且径迹芯中所有官能团均遭到破坏;对应8．8(最小能损,第一层)和11．5keV／nm(最大能损,第五层)电子能损,^136Xe辐照聚酰亚胺的平均降解半径分别为3．6和4．1nm。而相应能损条件下炔基的生成截面分别为5．6和5．9nm大于官能团的降解截面。紫外结果表明辐照引起的吸光度的改变随辐照注量线性增加,发色团的产生效率随电子能损的增大而增加。     

快电子能量损失谱仪的一种新的多道测量方法

介绍了一维位置灵敏探测器在高分辨快电子能量损失谱仪上的应用。系统地讨论了在定点测量模式和扫描测量模式下的针对此谱仪的数据处理方法,并提出了一种新的数据处理方法,可以在扫描模式下通过离线分析得到更细致的能谱。     

Comparison between Monte Carlo and experimental aluminum and silicon electron energy loss spectra

A Monte Carlo (MC) simulation is described and used to calculate the energy distribution spectra of backscattered electrons from Al and Si. For the simulations, elastic scattering cross sections are calculated by numerically solving the Dirac equation in a central field. Inelastic scattering cross sections are computed within the dielectric response theory developed by Ritchie, and by Tung et al. Extension from the optical case to non-zero momentum transfer is done according to Ritchie and Howie. To evaluate surface and bulk contributions to the spectra, the Monte Carlo model treats the surface excitations according to the Werner differential surface and volume excitation probability theory. The Monte Carlo calculations are compared with the experimental reflection electron energy loss (REEL) spectra acquired in our laboratory.     

电子能量损失符合谱仪前端电子学和数据获取系统

介绍了用于原子分子实验的能量损失符合谱仪的前端电子学和数据获取系统。考虑到谱仪的高计数率的特点,设计了适应高计数率的反堆积放大器和无延迟线恒比定时甄别器。该系统现已用于原子分子实验室,并取得了令人满意的实验结果。     

电子能量损失符合谱仪的一维位置灵敏探测器的读出系统

介绍了用于电子能量损失符合谱仪的一维位置灵敏探测器的读出系统。一维位置灵敏探测器可以大大提高谱仪的探测效率。其读出系统包括电荷灵敏前置放大器、主放大器、位置信号采集板和接口电路。使用自己设计的信号源对系统进行了测试,取得了较好结果。     

Monte Carlo calculation of energy loss of hydrogen and helium ions transmitted under channelling conditions in silicon single crystal

In this work, we report on calculations of the electronic channelling energy loss of hydrogen and helium ions along Si〈1 0 0〉 and Si〈1 1 0〉 axial directions for the low energy range by using the Monte Carlo simulation code. Simulated and experimental data are compared for protons and He ions in the 〈1 0 0〉 and 〈1 1 0〉 axis of silicon. A reasonable agreement was found.Computer simulation was also employed to study the angular dependence of energy loss for 0.5, 0.8, 1, and 2 MeV channelled ⁴He ions transmitted through a silicon crystal of 3 μm thickness along the 〈1 0 0〉 axis.     

Measurement of α particle energy loss in biological tissue below 2 MeV

The energy loss of α particles crossing biological tissue at energies between 0.8 and 2.2 MeV has been measured. This energy range is very important for boron neutron capture therapy, based on the ¹⁰B(n,α)⁷Li reaction, which emits α particles with energies of 1.78 and 1.47 MeV. One of the methods used for the measurement of the boron concentration in tissue is based on the deconvolution of the α spectra obtained from neutron irradiation of thin (70 μm) tissue samples. For this technique, a knowledge of the behaviour of the energy loss of the particles in the irradiated tissue is of critical importance. In particular, the curve of the residual energy as a function of the distance travelled in the tissue must be known. In this paper, the results of an experiment carried out with an ²⁴¹Am source and a series of cryostatic sections of rat-lung tissue are presented. The experimental measurements are compared with the results of Monte Carlo calculations performed with the MCNPX code.     

背散射法测定低能氩离子对金的溅射率

本文用背散射方法测定了300—1200eV不同能量的氩离子对金的溅射率。实验测得的背散射能谱用两种不同的方法(能量损失和面积法)处理,结果表明,用背散射法测得金的溅射率与G.K.Wehner用称重法测定的数据很接近,其与入射离子能量的关系为Y∝E~(0.4)。     

Transtarget residue products of 47MeV／u 12C ions on ^133Cs targets

Ｔｒａｎｓｔａｒｇｅｔｒｅｓｉｄｕｅｐｒｏｄｕｃｔｓｏｆ４７ＭｅＶ／ｕ１２Ｃｉｏｎｓｏｎ１３３ＣｓｔａｒｇｅｔｓＬｉＺｏｎｇＷｅｉ，ＹａｎｇＷｅｉＦａｎａｎｄＺｈａｏＺｈｉＺｈｅｎｇ（ＩｎｓｔｉｔｕｔｅｏｆＭｏｄｅｒｎＰｈｙｓｉｃｓ，ｔｈｅＣ...     

Influence on electron energy loss spectroscopy of the niobium-substituted uranium atom: A density functional theory study

We present the electronic structure and electron energy loss spectroscopy (EELS) for uranium, niobium and U3Nb in which uranium is substituted by niobium. Comparing the electronic structures and optical properties for uranium, niobium and U3Nb, we found that when niobium atom replaces uranium atom in the center lattice, density of state (DOS) of U3Nb shifts downward to low energy. Niobium affects DOS forfand d electrons more than that for p and s electrons. U3Nb is similar to uranium for the electronic energy loss spectra.     

Impact-parameter dependence of the electronic energy loss of fast cluster projectiles

Electronic energy loss of molecular clusters as a function of impact-parameter is less understood than atomic energy loss. Vicinage effects due to mutual interference between cluster fragments play a key role in the determination of the cluster electronic energy loss. In this work, we describe a molecular extension of the perturbative convolution approximation (PCA) energy loss model, namely MPCA (molecular PCA), which yields remarkable agreement with first-order Born semiclassical approximation (SCA) results. The physical inputs of the model are the oscillators strengths of the target atoms and the projectile electron density. A very good agreement is obtained with time consuming full first-order calculations for bare incident molecular clusters for several angles between cluster axis and velocity direction.     

螺线管磁场旋转束流法测量Mini-LIA电子束能量

介绍了螺线管磁场旋转束流法的能量测量原理和在Mini-uA上开展的单脉冲电子束能量测量实验.通过测量束流在螺线管磁场中的旋转角度,得到Mini-LIA出口处电子束能量,与加速器总的加速电压符合得很好.分析了旋束法的测量误差和应用特点,给出了旋束法测量的适用范围.     

Calculation of Fast Neutron Spectrum in a Homogeneous Medium by Direct Operational Method

A new formalism based on the direct operational method5 has been developed for numerically calculating the fast neutron spectrum in an infinite homogeneous medium. By this method the fine structures of nuclear data such as the anisotropy of scattering cross sections in the high energy region can be easily taken into account. Application of this method to light water system has yielded the conclusion that: (1) the effect of anisotropic scattering in the center-of-mass system becomes significant near the source energy and near scattering resonance peaks, (2) the errors introduced by the G.G.-approximation are also significant under similar circumstances and (3) the contribution from inelastic scattering is negligible (>0.2%) in the case of fission neutron source in light water system.     

Measuring energy loss of alpha particles in different vacuum conditions

In this paper,energy loss of alpha particles in different vacuum levels is studied experimentally and via theoretical analysis.A better understanding of energy loss of a particle in vacuum will help detect more exact numbers of alpha particles.Two ²³⁹Pu sources are used to measure the energy loss of a particle crossing different vacuum levels （different air pressures）.The experimental data are obtained from an instrument-PAM-100 developed by authors. The experimental results have shown that increasing vacuum levels will lead to more alpha residual energy but less energy loss.When the vacuum level reaches 0.04 MPa,alpha particles(²³⁹Pu,5.115 MeV)will lose the energy of about 0.175 MeV with traversing 5 mm distance.Theoretical calculations have shown a good agreement with experimental results.This implies that the instrument has a high accuracy and could be applied in field work.     

Energy deposition of y-ray in different instances and its influence on energy detection

In this paper, we simulate y-ray energy deposition for different incident energies with four different models using the tool GEANT4 ( Geant4.7.0, 2005 ) developed by CERN (the Center of European Research of Nucleus).The results we obtained indicate that there are different peak values for different incident energies. That is, we can differentiate the incident energy accurately if the detector can determine the peak value accurately. This is meaningful for the geometrical configuration of the detector to get the most probable distribution (MPD) of energy deposition for different incident energies. According to the simulation, we can insert certain slices with large absorption coefficient to obtain a better MPD of energy deposition which will not alter the shape of the energy deposition.     

Evaluations of proton inelastic mean free paths for 12 elemental solids over the energy range from 0.05 to 10 MeV

The systematical calculations of the inelastic mean free paths (MFPs) of 0.05-10 MeV protons in 12 elemental solids (Al, Si, Ni, Cu, Mo, Rh, Ag, W, Os, Ir, Pt, Au) have been performed. The calculations are based on the algorithm derived from Ashley’s optical-data model including the higher-order corrections to stopping power (SP) for protons. The prominence and necessity of the higher-order corrections are demonstrated by calculating the proton SPs for the 12 solids using Ashley’s optical-data model and by comparing the calculated SPs with the experimental results, the tabulated values and other corresponding theoretical evaluations. The algorithm of evaluating the proton inelastic MFP is described. In this algorithm, the Barkas-effect correction and the Bloch correction are taken into account, the minimum impact parameter from Lindhard is used in the Barkas-effect correction, and an empirical estimation of a free parameter involved in the Bloch correction to the inelastic MFP is proposed. The evaluated inelastic MFPs of 0.05-10 MeV protons for the 12 solids under two different cases, i.e. the higher-order corrections not being considered and the Barkas-effect correction and the Bloch correction being included, are presented in the tabulated form and are first results for these solids. These numerical results provide an alternative basic data for the Monte Carlo studies on low-energy proton transport in these 12 solids.