强流高电荷态全永磁ECR离子源LAPECR2的初步调试

研制成功了一台强流高电荷态全永磁ECR（Electron Cyclotron Resonance）离子源LAPECR2（Lanzhou All Permanent Magnet ECR Ion Source No．2）。该离子源在完成磁体装配后已成功在近代物理研究所320kV高压平台上安装就位,与后束运线完成对接组装。离子源于2005年7月在14．5GHz实现了第一次成功起弧,并引出较强的混合束流。目前离子源已与后束线以及部分实验终端完成了联调,在实验终端能够获得强流较高电荷态的离子束流。本文将着重论述该全永磁源的结构技术特点和主要参数指标。本文还着重论述了LAPECR2离子源在14．5GHz微波功率馈入条件下的初步调试结果,在此基础上对束流向实验终端联调的实验结果进行了讨论,着重分析了影响束流引出与传输效率的主要因素。     

Study of a new cusp field for an 18 GHz ECR ion source

A feasibility study was performed to generate new sufficient mirror cusp magnetic field (CMF) by using the coils of the existing room temperature traditional 18 GHz electron cyclotron resonance ion source (ECRIS) at RIKEN. The CMF configuration was chosen because it contains plasma superbly and no multipole magnet is needed to make the contained plasma quiescent with no magneto-hydrodynamic (MHD) instability and to make the system cost-effective. The least magnetic field, 13 kG is achieved at the interior wall of the plasma chamber including the point cusps (PC) on the central axis and the ring cusp (RC) on the mid-plane. The mirror ratio calculation and electron simulation were done in the computed CMF. It was found to contain the electrons for longer time than in traditional field. It is proposed that a powerful CMF ECRIS can be constructed, which is capable of producing intense highly charged ion (HCI) beam for light and heavy elements.     

Design of an ion extractor system for a prototype ion source experiment for SST-1 neutral beam injector

An ion extractor system has been designed for the steady state superconducting tokamak (SST-1) neutral beam injector (NBI) for an experiment using a prototype ion source with fully integrated regulated high voltage power supply (RHVPS) and data acquisition and control system (DACS) developed at Institute for Plasma Research (IPR) to obtain experience of NB operation. The extractor system is capable of extracting positive hydrogen ion beam of ∼10 A current at ∼20 kV. This paper presents the beam optics study for detailed design of an ion extraction system which could meet this requirement. It consists of 3 grid accel-decel system, each of the grid has 217 straight cylindrical holes of 8 mm diameter. Grids are placed on a specially designed G-10 block; a fiber reinforc plastic (FRP) isolator of outer diameter of 820 mm and 50 mm thickness. Provisions are made for supplying high voltage to the grid system through the embedded feed-throughs. Extractor system has been fabricated, mounted on the SST-1 neutral beam injector and has extracted positive hydrogen ion beam of 4 A at 20 kV till now.     

2.45GHz单电荷态电子回旋共振离子源

描述了一台2．45GHz单电荷态电子回旋共振（ECR）离子源的原理、结构与应用。介绍了其微波系统与磁场结构。在微波输入功率约600W,引出高压22kV,引出孔径为φ6mm时,该离子源的总束流I（H1^ H2^ H3^ )可达90mA。     

Be AMS measurements at low energies (E < 1 MeV)

The longlived isotope ¹⁰Be is of great importance in earth sciences for dating applications, reconstruction of the solar activity or in climate research. Routine AMS measurements with BeO samples are performed on accelerators with a terminal voltage above 2 MV. Applying the degrader foil technique for boron suppression, first tests with BeO samples on the 0.6 MV ETH/PSI machine were limited by background to a ¹⁰Be/⁹Be ratio of 10⁻¹³. The background was identified as ⁹Be which reaches the detector by scattering processes. By applying an additional magnetic mass filter to the high energy mass spectrometer the background was effectively removed. A ¹⁰Be/⁹Be background ratio of <5 × 10⁻¹⁵ was achieved. The overall efficiency (detected ¹⁰Be compared to BeO⁻ injected into the accelerator) was 7-8%.     

Study of low work function materials for hot cavity resonance ionization laser ion sources

The selectivity of a hot cavity resonance ionization laser ion source (RILIS) is most often limited by contributions from competing surface ionization of the hot walls of the ionization cavity. In this article we present investigations on the properties of designated high temperature, low work function materials regarding their performance and suitability as cavity material for RILIS. Tungsten test cavities, impregnated with a mixture of barium oxide and strontium oxide (BaOSrO on W), or alternatively gadolinium hexaboride (GdB₆) were studied in comparison to a standard tungsten RILIS cavity as being routinely used for hot cavity laser ionization at ISOLDE. Measurement campaigns took place at the off-line mass separators at ISOLDE/CERN, Geneva and RISIKO/University of Mainz.     

Excitation functions for some W, Ta and Hf radionuclides obtained by deuteron irradiation of Ta up to 40 MeV

Experimental excitation functions for deuteron induced reactions up to 40 MeV on mono-isotopic Ta (¹⁸¹Ta) were measured with the activation method using a stacked foil irradiation technique. From high resolution gamma spectrometry and X-ray analysis cross-section data for the production of ¹⁸¹W, ^{177,178g,180g,182m+g}Ta, and ^179m2,180mHf were determined. Comparison with the scarce earlier published data are presented and results for values predicted by different theoretical codes, adapted for more reliable calculations for d-induced reactions, are included. Thick target yields for ^{182m+g,180g,178g}Ta and ¹⁸¹W were calculated from a fit to our experimental excitation curves. Using dose conversion factors and irradiation scenarios, possible occupational doses to maintenance or scientific personnel around high power accelerators where Ta based structural elements (collimators, beam stoppers, shielding) are present could be derived.     

Study of the excitation functions for K, Sc and Ti by proton irradiation on Sc up to 37 MeV

The excitation functions of proton induced reactions on Sc targets (100% ⁴⁵Sc), leading to the formation isotopes ⁴³K, ⁴³Sc, ^44mSc, ^44gSc and ⁴⁴Ti were studied by the stacked foil activation technique up to 37 MeV. High-resolution gamma-spectrometry measurements were performed on an HPGe detector in order to determine the activity of the irradiated Sc₂O₃ pellets and Ti monitor foils. The reaction cross-sections were measured from their respective thresholds up to E_p = 36.4 MeV and were compared with previous values reported in literature. Possible batch yields and optimal irradiation parameters for generator ⁴⁴Ti -^44gSc in high current accelerators are discussed.     

Alkali ion scattering from Ag(0 0 1) and Ag thin films at low and hyperthermal energies

We have investigated the scattering of K⁺ and Cs⁺ ions from a single crystal Ag(0 0 1) surface and from a Ag-Si(1 0 0) Schottky diode structure. For the K⁺ ions, incident energies of 25 eV to 1 keV were used to obtain energy-resolved spectra of scattered ions at θ_i = θ_f = 45°. These results are compared to the classical trajectory simulation safari and show features indicative of light atom-surface scattering where sequential binary collisions can describe the observed energy loss spectra. Energy-resolved spectra obtained for Cs⁺ ions at incident energies of 75 eV and 200 eV also show features consistent with binary collisions. However, for this heavy atom-surface scattering system, the dominant trajectory type involves at least two surface atoms, as large angular deflections are not classically allowed for any single scattering event. In addition, a significant deviation from the classical double-collision prediction is observed for incident energies around 100 eV, and molecular dynamics studies are proposed to investigate the role of collective lattice effects. Data are also presented for the scattering of K⁺ ions from a Schottky diode structure, which is a prototype device for the development of active targets to probe energy loss at a surface.     

Energy dependence of electron stopping powers in elemental solids over the 100 eV to 30 keV energy range

We analyzed the energy dependence of electron stopping powers (SPs) calculated for 41 elemental solids from experimental optical data for electron energies between 100 eV and 30 keV. Our analysis was performed with the Hill equation to represent a series of steps in plots of the slopes of Fano plots. The average root-mean-square difference between SPs from fits with an equation derived from the Hill equation and the calculated SPs was 1.0%. The new equation can provide SPs over a wide energy range for Monte Carlo simulations of electron transport with the continuous slowing-down approximation.     

Computer simulation of CAICISS spectra of clean Cu(1 0 0) surface and Cu(1 0 0) surface by Pt deposition

The clean Cu(1 0 0) surface and Pt/Cu(1 0 0) surface by Pt deposition at room temperature have been investigated using the computer simulation of coaxial impact-collision ion scattering spectroscopy (CAICISS). The computer simulations employing the ACOCT program code, which treats the atomic collisions three-dimensionally and is based on the binary collision approximation (BCA), were carried out for the case of 3 keV He⁺ ions incident along the 〈1 0 0〉 and 〈1 1 0〉 azimuths of the clean Cu(1 0 0) and Pt/Cu(1 0 0) surfaces. The comparisons between ACOCT results and experimental CAICISS data show that the experimental results on the clean Cu(1 0 0) surface are relatively well reproduced by the ACOCT simulations including the inward relaxation of 1.2% in the first interlayer spacing and the outward relaxation of 1.6% in the second interlayer spacing, and that the ACOCT simulations for the Pt deposition with coverages of 2.35 ML and 2.75 ML on the Cu(1 0 0) surface appear the concentrations of 0.24 ML of Pt sitting 2.3 Å and 0.25 ML of Pt sitting 2.5 Å above the outermost atomic layer, respectively.     

K-shell X-ray fluorescence cross-sections and intensity ratios for some pure metals at 59.5 and 123.6 keV

K-shell X-ray fluorescence cross-sections for some pure metals such as Cr, Fe, Co, Cu, Zn, Ga, Se, Y, Mo, Cd, In, Sn, Te, Ba, Ta, W and Bi have been theoretically and experimentally determined. The Cr, Fe, Co, Cu, Zn, Ga, Se, Y, Mo, Cd, In, Sn, Te and Ba metals were excited by 59.5 keV γ-ray from 50 mCi ²⁴¹Am radioactive source and the Ta, W and Bi targets were excited by 123.6 keV γ-ray from 25 mCi ⁵⁷Co radioactive source. The characteristic K X-rays emitted by samples were detected by using a super Si(Li) detector having a resolution of 150 eV at 5.9 keV. In addition, the I_Kβ/I_Kα intensity ratios for these metals were studied. The obtained experimental values of the K-shell X-ray fluorescence cross-sections and the I_Kβ/I_Kα intensity ratios have been compared with theoretical values. The measured values were in good agreement with theoretical values.     

Investigation of the Zn(p, 2p)Cu nuclear reaction: New measurements up to 40 MeV and compilation up to 100 MeV

The excitation function was measured for the ⁶⁸Zn(p, 2p)⁶⁷Cu nuclear reaction from its threshold energy up to 40 MeV. Nine pieces of highly enriched ⁶⁸Zn (>98%) metal foils were irradiated to obtain reliable cross-sections using the usual stacked-foil technique. All foils were subjected to high efficiency radiochemical separation before the activity measurements. A critical compilation of the available experimental cross-section results was also performed. Thick target yields of ⁶⁷Cu and the longer-lived copper radio-contaminants (⁶¹Cu and ⁶⁴Cu) were calculated using the reliable literature results up to 100 MeV. Additionally, EOB (End Of Bombardment) contamination levels as a function of bombarding energy and irradiation time were deduced.     

A sextupole ion beam guide to improve the efficiency and beam quality at IGISOL

The laser ion source project at the IGISOL facility, Jyväskylä, has motivated the development and construction of an rf sextupole ion beam guide (SPIG) to replace the original skimmer electrode. The SPIG has been tested both off-line and on-line in proton-induced fission, light-ion and heavy-ion induced fusion-evaporation reactions and, in each case, has been directly compared to the skimmer system. For both fission and light-ion induced fusion, the SPIG has improved the mass-separated ion yields by a factor of typically 4-8. Correspondingly, the transmission efficiency of both systems has been studied in simulations with and without space charge effects. The transport capacity of the SPIG has been experimentally determined to be ∼10¹² ions s⁻¹ before space charge effects start to take effect. A direct comparison with the simulation has been made using data obtained via light-ion fusion evaporation. Both experiment and simulation show an encouraging agreement as a function of current extracted from the ion guide.     

A detailed study of the d + B system for nuclear reaction analysis - Part A: The B(d,p)B reaction in the energy region Ed,lab = 900-2000 keV

The differential cross-sections of the ¹⁰B(d,p_{0,1,2,3,4-5,6}) reactions for the determination of the depth distribution of boron in near-surface layers of materials have been determined in the projectile energy region E_d,lab = 900-2000 keV. The experiment was carried out in energy steps of 25 keV and for eight detector angles between 135° and 170° (in steps of 5°). The obtained experimental data are suitable for nuclear reaction analysis (NRA) studies. A qualitative discussion of the observed cross-section variations through the strong influence of overlapping resonances in the d + ¹⁰B system is also presented.     

Experimental study of the Ho(d, 2n) and Ho(d, p) nuclear reactions up to 20 MeV for production of the therapeutic radioisotopes Er and Ho

The radioisotope ¹⁶⁵Er (T_1/2 = 10.36 h) is a candidate for Auger-electron therapy. The β⁻-emitting ^166gHo (T_1/2 = 26.83 h) is now being explored for various therapeutic applications. In the frame of our systematic study of charged particle production routes of therapeutic radionuclides the excitation functions of the ¹⁶⁵Ho(d, 2n)¹⁶⁵Er and ¹⁶⁵Ho(d, p)^166gHo reactions were measured up to 20 MeV by using a stacked foil irradiation technique and X/γ-ray spectroscopy. The excitation function of the ¹⁶⁵Ho(d, 2n)¹⁶⁵Er reaction was measured for the first time while for the ¹⁶⁵Ho(d, p)^166gHo reaction only a single dataset of earlier measured cross-sections was found. The measured excitation functions were compared to the results of different nuclear reaction model codes. The calculated thick target yield of the ¹⁶⁵Ho(d, 2n) reaction is significantly higher over the optimal energy range than that for the ¹⁶⁵Ho(p, n) reaction investigated earlier by us. The integral yield of the ¹⁶⁵Ho(d, p)^166gHo reaction is rather low compared to the established ¹⁶⁵Ho(n, γ)¹⁶⁶Ho reaction in a nuclear reactor.     

Calculation and evaluation of cross-sections for p+Fe reactions up to 250 MeV

All cross-sections of proton-induced reactions, angular distributions and the energy spectra of neutron, proton, deuteron, triton, helium and alpha-particle emission are consistent calculated and analyzed for p+^{54,56,57,58,nat}Fe at incident proton energies below 250 MeV by using nuclear theoretical models which integrate the optical model, the intra-nuclear cascade model, direct, preequilibrium and equilibrium reaction theories. Especially, the cross-sections of the light composite particle (d, t, ³He and α) emissions are improved based on the exciton model including the pick-up mechanism. Theoretical calculated results are compared with existing experimental data.     

Effect of spin polarization of Ni(1 1 0) surface on Auger neutralization for grazing scattering of He ions

The survival of ions during grazing scattering of keV He⁺ ions from a clean Ni(1 1 0) surface is studied as function of target temperature. We observe ion fractions in the scattered beams of typically 10⁻³ which show a slight increase with temperature of the target surface. From computer simulations of projectile trajectories we attribute this enhancement for ion fractions to effects of thermal vibrations of lattice atoms on the survival of ions in their initial charge state. Based on concepts of Auger neutralization, we discuss the role of the spin polarization of target electrons on charge transfer. We do not find corresponding signatures in our data and conclude that in the present case of Ni(1 1 0) the spin polarization has to be small.