The effect of temperature on the diffusion length and the scattering cross section of thermal neutrons in graphite

The effect of heating graphite on the diffusion length and effective scattering cross section of thermal neutrons was investigated. It was established that in the 15–350 °C range the diffusion length changes mainly in accordance with the law 1/v for the absorption cross section. The slight deviation from this law is due to the increase of 0.5 mb/deg in the scattering cross section with an increase in temperature.     

The effect of temperature and microstructure of sintered beryllium oxide on the scattering cross section of thermal neutrons

The total effective neutron cross section _t for sintered beryllium oxide in the 0.0025–10 ev neutron energy range was measured by means of a mechanical selector at four temperatures of the scattering sample: 290, 800, 1300 and 1500 °K. Measurements of _t for beryllium oxide samples of different microstructure were also carried out at room temperature. Slight anisotropy of scattering, due to texture, and a marked influence of the size of the crystal grain on _t, due to the extinction effect, were noted.     

Evaluation of non-Rutherford proton elastic scattering cross section for nitrogen

The available experimental information on the proton elastic scattering from ¹⁴N in the energy range up to 5 MeV was compiled. The critical analysis of the revealed discrepancies was performed taking into account the applied experimental technique and possible error sources. Based on this, the apparently reliable experimental points were selected. Model calculations with comparison and fitting to the experimental data were used for parameterization of the cross section. The R-matrix theory was employed in the calculations, the phase shifts calculated for Saxon-Woods potential well being substituted for commonly used hard-sphere ones in order to take into account direct potential scattering. The result of the evaluation is that the required excitation functions for proton elastic scattering from nitrogen may be calculated for any scattering angle with reliability exceeding that for any individual measurement. The evaluated cross sections are provided by the SigmaCalc web site at www-nds.iaea.org/sigmacalc/.     

Status of the problem of nuclear cross section data for IBA

The progress achieved in an IAEA Coordinated Research Project (CRP) to improve the cross section data for IBA is reported. The objective of the CRP, started in 2005, is to create a nuclear cross section database for IBA that contains reliable and usable data freely available to the entire IBA community. The major results achieved so far by the CRP participants are discussed. The results include compilation and assessment of the existing cross sections, new experimental data and evaluation of the most wanted cross sections. The experimental results are incorporated into the IBANDL database (www-nds.iaea.org/ibandl/) and evaluated data are presented at the SigmaCalc cross section calculator (www-nds.iaea.org/sigmacalc/).     

Evaluation of non-Rutherford proton elastic scattering cross section for silicon

The experimental data available for silicon (p,p) elastic scattering cross section have been reviewed. The analysis of the data was made using the theoretical model approach. The obtained results provide the evaluated differential cross sections for silicon (p,p) elastic scattering in the energy region up to 3.0 MeV.     

Influence of screening length modification on the scattering cross section in LEIS

Scattering cross sections for He⁺ ions in the energy range of 100 eV to 100 keV and for Al, Cu and Au target atoms were calculated. Employing the Thomas-Fermi-Molière model the potential strength was tuned by variation of the screening length. The resulting change in scattering cross section was analyzed and the absolute value is compared to cross sections obtained from potentials commonly employed in the medium-energy ion scattering (MEIS) regime. A large influence on the scattering cross section is observed for targets with large atomic number in the very low energy range. For instance, the scattering cross section for 100 eV He⁺-ions scattered from Au by 129° changes by a factor of 2.5 between different potential strengths claimed in the literature to be suitable for low-energy ion scattering (LEIS) energies. An experiment to determine electronic energy loss of very slow ions in metals is presented. It shows how uncertainties in the scattering potential strength can lead to systematically wrong results, although perfect agreement between experimental data and simulations is found. The impact of these results on quantitative surface structure and composition analysis is discussed.     

一套用于激光多步共振电离截面测量的多定标数据获取系统

本文主要介绍了一套应用于激光多步共振电离截面测量的CAMAC多定标数据获取系统.它可以实现严格同步采集多个实验参数,并能灵活适应实验条件的宽范围变化.CAMAC前端的定标器数目可通过更改数据读出表文件来任意增减;获取方式分为自动重复获取和手动单次获取;获取时间单位可在1ms-800s范围内调节.经过测试得到,本数据获取系统的获取时间单位选择100s时长时间工作的稳定性(△t/t)好于±0.01%,充分证实了该套数据获取系统长时间在线采集实验数据的可靠性.最后利用这套系统同步测量了三台热电偶激光功率探头的功率-响应时间曲线.     

用于剂量计算的核反应总截面经验公式

在核物理及核物理应用研究中，利用核反应总截面经验公式进行理论计算具有现实意义。这方面的计算公式很多，本文以中能区应用的Kox经验公式为基础，结合重离子治疗肿瘤计算剂量深度模型的需要，对Kox经验公式的参数进行了修正，使其具有更广泛的应用价值，同时对修正参数的物理意义进行了探讨。     

Measurement of the effective cross section in Th232 for thermal neutrons and the resonance integral for neutron absorption

The effective cross section in thorium for thermal neutrons (_ther = 7.31 ± 0.10 barns) and the resonance integral for thorium have been-measured in a heavy water reactor. The measurements were made by the activation method. Gold, indium, and uranium were used as comparison standards. The precise value of the effective cross section for indium for thermal neutrons is (_ther = 162 ± 10 barns) and the resonance integral in indium is (RI=2340 ± 200 barns).