Half lives of the 482.2 keV and 615.3 keV levels in181Ta

The half lives of the excited levels at 482.2 keV and 615.3 keV in¹⁸¹Ta have been measured by the delayed coincidence technique. In the nanosecond time range (482.2 keV level) the most serious sources of errors are jitter, walk and drift phenomena. To minimize those the time pick-off has been defined carefully by means of modern fast timing detectors and electronics. In the microsecond time range (615.3 keV level) the ratio of true delayed coincidences to chance coincidences influences considerably the final accuracy of the half-life measurements. It has been reduced as much as possible. From a series of independent measurements half lives ofT _1/2=(10.67±0.05) ns andT _1/2=(17.64±0.14) μs have been deduced for the 482.2 keV and 615.3 keV levels, respectively. The results have been compared with other values published before.     

15～600 keV脉冲硬X射线能谱测量

介绍了基于吸收法的脉冲硬X射线能谱测量的基本原理及设计思路,完成了探测器及吸收片的选型,设计了射线准直系统,研究了散射对测量的影响,以12路PIN探测器阵列及铜、铝吸收片为测量核心部件研制了脉冲硬X射线能谱测量系统。实验测量了真空环境下"闪光二号"加速器串级二极管产生的脉冲硬X射线强度,获得了不同衰减程度的实验波形,通过解谱获得了脉冲硬X射线的能谱,光子最高能量约600 keV,平均能量约89.1 keV,与理论计算的结果比较符合。     

4.75 keV能点四通道Kirkpatrick-Baez显微镜

基于CH柱形靶压缩实验的时间分幅诊断需求,研制了4.75 keV能点四通道Kirkpatrick-Baez(KB)显微镜。进行了四通道KB系统的光学设计、像质模拟和分析。采用支撑锥芯的方式解决了四通道KB物镜的集成装配问题,并通过4.75 keV+8 keV双能点多层膜完成了实验室内的KB系统装调。该套系统在神光Ⅱ装置成功进行了像质考核实验,获得了高分辨的四象限网格图像,成像间距符合设计要求,具备了开展时间分幅惯性约束聚变物理实验的条件。     

Lattice disorder produced in GaAs by 60 keV Cd ions and 70 keV Zn ions

Abstract

We have used the standard channeling technique with a 1.0 MeV He⁺ analyzing beam to investigate the lattice disorder produced in GaAs by 60 keV Cd and 70 keV Zn ion implantations made at room temperature. The amount of disorder produced increases linearly with dose and saturates at a dose of approximately 1–2 × 10¹³ Cd ions/cm². The disorder present in low dose implants (～5 × 10¹² Cd ions/cm²) anneals appreciably by 150 °C. With increasing doses of Cd or Zn the samples show a continuous increase in the anneal temperature required to remove a substantial amount of lattice disorder. There is no apparent difference between the anneal of Zn and Cd implants. The rate at which lattice disorder is produced in GaAs by heavy ion implantations and the doses of heavy ions required to saturate the lattice disorder observed are significantly different from the values of the corresponding quantities for Si and Ge.     

能量范围从20ke到34kev的锆元素K壳层电离截面

用20～34keV能量的电子束轰击锆靶,从而测得锆元素的K壳层电离截面。这些数据是国际上首次报道。在实验中采用电子输运双群模型修正了由厚衬底产生的反射电子对计数的影响。同时用蒙特-卡罗EGS4程序计算了电子在质量厚度为24.3μg cm     

能量范围从20keV到34keV的锆元素K壳层电离截面

 用20~34keV能量的电子束轰击锆靶,从而测得锆元素的K壳层电离截面。这些数据是国际上首次报道。在实验中采用电子输运双群模型修正了由厚衬底产生的反射电子对计数的影响。同时用蒙特卡罗EGS4程序计算了电子在质量厚度为24.3mg/cm²的锆靶中的平均路径长度。     

Theoretical cross sections for keV antiprotons

Partial and total close-coupled semiclassical (impact parameter) cross sections and total classical Monte-Carlo cross sections for interactions in and , p+H collisions are computed in the intermediate keV range for antiprotons, , up to 100 keV lab. Total cross sections for antihydrogen, , formation are found to be large, 10−20×10⁻¹⁶ cm² in a wider energy range than was anticipated earlier, up to some 20 keV lab. New estimates of cross sections for ionisation of atomic hydrogen by antiproton impact are reported for the low-energy range 1–30 keV lab where they are 10−20×10⁻¹⁷ cm², being much larger than the corresponding cross sections for ionisation of hydrogen by proton impact. Data for excitation of H by impact is also presented.     

Effective attenuation length dependence on photoelectron kinetic energy for Au from 1 keV to 15 keV

Hard X-ray PhotoElectron Spectroscopy (HAXPES) is an extremely powerful tool for the electronic, compositional, and chemical characterization of bulk materials and buried interfaces. Its success is based on the dramatic increase of the electron effective attenuation length (EAL) with increasing photoelectron kinetic energy. EALs are well established for electrons with kinetic energies up to several keV (below 3 keV). However, few data are available for kinetic energies up to 15 keV. In the present study we have determined the EAL dependency on kinetic energy for gold from 1 keV up to 15 keV. Two different approaches have been used. The first approach consists of following the signal rate from a core level for a fixed kinetic energy as a function of overlayer thickness (overlayer method). The second approach consists of following the signal rate from a core level as a function of the incident photon energy, i.e., electron kinetic energy, for a fixed overlayer thickness (depth profile method). An EAL dependency of EAL (nm) = 0.022 × E_kin (eV)^0.627 has been obtained from both methods. Hence, the EAL, for gold, is 4.7, 7.3 and 9.4 nm for 5 keV, 10 keV and 15 keV electron kinetic energies, respectively. A comparison between the experimental data and the EALs predicted by practical expressions available in the literature is also performed.     

Research with Trapped keV Ion Beams

Hyperfine Interactions - The motion of an ion bunch trapped between two electrostatic mirrors in an ion trap resonator has been studied. Under certain conditions the ion motion becomes correlated...     

Relic keV sterile neutrinos and reionization

A sterile neutrino with a mass of several keV can account for cosmological dark matter, as well as explain the observed velocities of pulsars. We show that x rays produced by the decays of these relic sterile neutrinos can boost the production of molecular hydrogen, which can speed up the cooling of gas and the early star formation, which can, in turn, lead to a reionization of the Universe at a high enough redshift to be consistent with the Wilkinson Microwave Anisotropy Probe results.     

Calculation of free-free Gaunt factors for 1 keV electrons in a 1 keV normal density Ce plasma

We compare numerical results for free-free Gaunt factors in a hot dense cesium plasma, obtained in the average atom approximation either with a simple approximate analytic potential or with the finite temperature Thomas-Fermi model. We obtain results (for the spectrum of radiation from a 1 keV electron incident on a cesium ion in a 1 keV plasma) from an exact numerical calculation in partial waves of the relativistic electron Bremsstrahlung cross section treated as a single electron transition within these potentials. Comparison shows that Born approximation results in the same potentials fail by large factors, especially at the soft photon end of the spectrum.     

Half-life measurements of the 86.6 keV level in233Pa and 59.6 keV level in237Np

The half-lives of the 86.6 keV level in²³³Pa and the 59.6 keV level in²³⁷Np have been measured. A silicon surface barrier alpha detector and a NaI(Tl) gammadetector were used. The decay time spectrum of alpha-gamma coincidences obtained from a start-stop type of time-to-pulse height converter was recorded on a 2048-channel analyser. Analysis of the data gave the following half-life values: $$\begin{gathered} T_{\frac{1}{2}} :^{233} Pa (86.6 keV level) = (37.4 \pm 0.4) ns \hfill \\ T_{\frac{1}{2}} :^{237} Np (59.6 keV level) = (66.7 \pm 0.7) ns \hfill \\ \end{gathered}$$ . Using the experimental levelT _1/2's, partial gamma-ray half-lives have been calculated for the 86.6- and the 29.6-keV transitions (from the 86.6 keV level) in²³³Pa and the 59.6- and the 26.36-keV transitions (from the 59.6 keV level) in²³⁷Np. The results are compared with the single particle and the Nilsson estimates.     

Cross sections for K-shell ionization of Si and Ar by 4 keV to 10 keV electron impact

K-Auger electron emission of Si and Ar produced by 4 keV to 10 keV electrons was measured. Absolute yields were obtained by normalizing to the elastically scattered primary electrons. From the yields cross sections for K-shell ionization were deduced. The cross sections are in good agreement with the results of a fit formula for K-shell excitation in the whole range measured, while they agree with results of PWBA calculations including electron exchange in the Ochkur approximation only for the higher impact energies.     

Modulation of A 10 keV ion beam

Density modulation of a 10 keV - 1 mA - He⁺-ion beam at frequencies up to MHz has been achieved by deflecting the beam ions across an aperture. The modulation mechanism depends mainly on the periodical disturbance of the beam space charge neutrality.     

Improved energies for the 5.2 keV M1 and 42.0 keV M2 nuclear transitions in 83Rb

The European Physical Journal A - The low-energy electron spectrum following the decay of 83Sr was analysed at high instrumental resolution by an electrostatic spectrometer. Significantly improved...     

Sputtering of solid argon by keV electrons

Thermochemical maskless etching of compound semiconductors (GaAs, InP, InSb, and GaP) has been performed by focused Ar-laser irradiation in chloride gas atmospheres. A controlled minimum linewidth of down to 0.6 m with a maximum etching rate of up to 13 m/s has been obtained. Minimum laser powers necessary for thermochemical etching in each of compound semiconductors were found to be 0.24, 0.56, and 0.06 W, corresponding to minimum local temperature rises of 190, 515, and 110°C for GaAs, InP, and InSb, respectively. Etching rates exhibited Arrhenius behavior with activation energies of 3.6–3.9 kcal/mole. Etching at excessively higher laser powers than those minimum powers was found, by microprobe photoluminescence measurements, to degrade the optical quality of the etched substrate.     

511 keV photons from superconducting cosmic strings

We show that a tangle of light superconducting strings in the Milky Way could be the source of the observed 511 keV emission from electron-positron annihilation in the Galactic bulge. The scenario predicts a flux that is in agreement with observations if the strings are at the approximately 1 TeV scale, making the particle physics within reach of planned accelerator experiments. The emission is directly proportional to the galactic magnetic field, and future observations should be able to differentiate the superconducting string scenario from other proposals.