BRISOL钠同位素放射性核束的产生

北京放射性核束装置在线同位素分离器（BRISOL）采用100 MeV、200 μA回旋加速器提供的质子束打靶产生中、短寿命放射性核束,在线分析后供物理用户使用,其质量分辨率好于20 000。为开展²⁰Na核的奇异衰变特性研究,研制了氧化镁靶,并采用100 MeV质子束轰击氧化镁靶在线产生了^20～26Na⁺的钠同位素放射性核束。当质子束流强为8 μA时,²⁰Na⁺离子束的最大产额为2×10⁵ s^-1,²¹Na⁺离子束的最大产额为4×10⁸ s^-1。完成了北京放射性核束装置首个放射性核束物理实验,累计供束近200 h。     

An ion trap for nuclear laser spectroscopy at Tohoku ISOL

An on-line ion trap directly connected to the Tohoku ISOL has been constructed. The trap is aimed at the study of nuclear magnetic properties through precision measurements of ionic ground-state hyperfine structures of unstable nuclei. As a first step to a systematic study, the hyperfine splitting of the ground state of ⁸⁷Sr⁺ ions was measured by laser microwave double-resonance spectroscopy.     

Very high sensitivity in collinear laser spectroscopy: resonance detection by particle counting techniques

Fast-beam collinear laser spectroscopy with resonance detection by counting of fluorescence photons provides a versatile tool for precise determinations of nuclear ground-state properties. The intrinsic high sensitivity of this method can be further increased by almost three orders of magnitude if measuring schemes based on ion or atom counting are introduced. The optical pumping from one atomic state to another at an appreciably different excitation energy is detected via state-selective collisional charge exchange processes and charge-state separated atom or ion counting. Applications of these techniques on alkaline earth, noble gas, mercury and thallium beams is examined.     

Selective detection of C by laser photodetachment mass spectrometry

In this paper, we demonstrate how laser photodetachment mass spectrometry (LPMS) can be used to selectively detect ¹³C⁻ ions in the presence of ¹²C⁻ ions in a low energy ion beam. An isotopically enriched beam of carbon ions consisting of equal amounts of ¹³C⁻ and ¹²C⁻ ions was extracted from an ion source. The ions interacted with a laser beam in a collinear geometry over a distance of 70 cm. Residual atoms produced in the photodetachment process were detected in a neutral particle detector placed downstream of the collinear interaction region. By making use of the Doppler effect we were able to selectively photodetach ¹³C⁻ ions. The number of detected ¹³C atoms was 13 times larger than the number of detected ¹²C atoms. The population of the excited, weakly bound ²D excited state of the C⁻ ion was depleted by the use of a second laser. This significantly reduced the background accompanying the signal arising from the photodetachment of the ⁴S ground state C⁻ ion. Different applications of the LPMS method will be discussed in the paper.     

BRISOL钾同位素放射性核束的产生

北京放射性核束装置在线同位素分离器（BRISOL）采用一台100 MeV回旋加速器提供的最大200 μA的质子束打靶在线产生放射性核束,其最高质量分辨率好于20 000。2015年,BRISOL装置建成并使用05 μA质子束轰击氧化钙靶产生了37K+、38K+放射性核束,其中38K+的产额为1×106 pps。为了提高氧化钙靶产生钾放射性核束的产额以满足物理用户需求,BRISOL于近期开展了氧化钙靶的在线实验。实验中使用氧化钙靶产生了36～38K+、43K+、45～47K+等多种放射性核束,同时将38K+的最大产额提高到了112×1010 pps。本文详细介绍氧化钙靶的研制及在线实验结果。     

Nanosecond laser preheating effect on ablation morphology and plasma emission in collinear dual-pulse laser-induced breakdown spectroscopy

Focus-offset collinear dual-pulse laser-induced breakdown spectroscopy is designed and used to investigate the laser ablation and spectral intensity with an aluminum alloy sample. The laser crater morphologies and ablation volumes were measured. An inter-pulse time delay dependent ablation efficiency on a nanosecond laser-heated sample was observed, which was similar to the trend of spectral intensity versus inter-pulse time delay in the delay time less than 3 μs. Based on the observation, the nanosecond pulse laser preheating effect on subsequent second laser ablation and signal enhancement is discussed, which will be helpful for understanding the ablation and signal enhancement mechanism in the standard collinear DP-LIBS technique.     

The Laser Ion Source Trap (LIST) coupled to a gas cell catcher

The proof of principle of the Laser Ion Source Trap (LIST) coupled to a gas cell catcher system has been demonstrated at the Leuven Isotope Separator On Line (LISOL). The experiments were carried out by using the modified gas cell-based laser ion source and the SextuPole Ion Guide (SPIG). Element-selective resonance laser ionization of neutral atoms was taking place inside the cold jet expanding out of the gas cell catcher. The laser path was oriented in longitudinal as well as transverse geometries with respect to the atoms flow. The enhancement of beam purity and the feasibility for in-source laser spectroscopy were investigated in off-line and on-line conditions.     

Status report of the JAERI on-line isotope separator

A mass separator has been connected on line to the 20 MV tandem accelerator at JAERI/Tokai. Using a thermal ion source, decay spectroscopic studies have been carried out for neutron-deficient isotopes in the mass 120–130 region. A study with collinear laser spectroscopy has begun recently. The present paper describes the status of the mass separator facility together with some experimental results.     

CSR ns级重离子束动力学研究

采用束团在纵向相空间快速旋转的非绝热压缩方法研究了在兰州重离子加速器冷却储存环(HIRFL-CSR)上获取高能ns量级短脉冲重离子束的可行性,利用K-V包络方程对能量为250MeV/u、初始纵向束团长度为200ns、初始动量分散为5×10-4的238U72+离子束团的非绝热压缩过程进行了束流动力学模拟,给出了在束团压缩过程中束流相关参数的变化。结果表明,在CSR上可取得最短为16ns长度的238U72+离子束团,可满足用于高能量密度物理研究的50ns束团长度的要求。     

Cu and Y ion beams by a new LIS generator

In this work, we present the experimental results of a laser ion source (LIS) implemented for ion accelerators. A KrF excimer laser beam operating at 248 nm was focused on a solid target mounted inside a vacuum chamber in order to obtain the plasma. The laser energy was fixed at 11.5 mJ/pulse. The ion components of the plasma were extracted and accelerated up to 160 keV per charge state by a double gap system formed in two different stages. The beam cross section was circular, 1.5 cm in diameter. Using Cu and Y disks, as laser targets, we produced ion beams containing 1.2 × 10¹¹ ions/pulse (0.7 × 10¹¹ ions/cm²). Applying a total accelerating voltage of 60 kV we obtained an increase in ion dose up to 3.4 × 10¹¹ ions/pulse, (2 × 10¹¹ ions/cm²) for the Cu target and up to 6.3 × 10¹¹ ions/pulse (3.5 × 10¹¹ ions/cm²) for the Y target. The characterization of the plasma was performed using a Faraday cup for the electromagnetic properties, and a pepper pot system for the geometric ones. At 60 kV accelerating voltage and 5.5 mA output current the normalized beam emittance resulted in 0.22 π mm mrad for the Cu target, while under the same accelerating voltage, but with 7.4 mA output current, the normalized beam emittance resulted in 0.14 π mm mrad for the Y target.     

Selective isobar suppression for accelerator mass spectrometry and radioactive ion-beam science

A new method of selective isobar suppression by photodetachment in a radio-frequency quadrupole ion cooler is being developed at HRIBF with a twofold purpose: (1) increasing the AMS sensitivity for certain isotopes of interest and (2) purifying radioactive ion beams for nuclear science. The potential of suppressing the ³⁶S contaminants in a ³⁶Cl beam using this method has been explored with stable S^? and Cl^? ions and a Nd:YLF laser. In the study, the laser beam was directed along the experiment’s beam line and through a RF quadrupole ion cooler. Negative ³²S and ³⁵Cl ions produced by a Cs sputter ion source were focused into the ion cooler where they were slowed by collisions with He buffer gas; this increased the interaction time between the negative-ion beam and the laser beam. As a result, suppression of S^? by a factor of 3000 was obtained with about 2.5 W average laser power in the cooler while no reduction in Cl^? current was observed.     

Beam test results of high Q CBPM prototype for SXFEL

In pursuit of high-precision beam position measurements at micrometers or submicrometers for the Shanghai soft X-ray free-electron laser (SXFEL) facility which is under construction in the vicinity of the Shanghai Synchrotron Radiation Facility,a high Q cavity beam position monitor (CBPM) with a resonant frequency of 4.7 GHz is developed by the Shanghai Institute of Applied Physics,and the relevant BPM electronics with a dedicated RF front end,and a digital BPM,are completed.The cavity design,cold test,system architecture,and first beam test are performed at the Shanghai deep ultraviolet free-electron laser (Zhao et al.in Nucl Instrum Meth A 528(1-2):591-594,2004.doi:10.1016/j.nima.2004.04.108) facility.Results of the beam experiment show that the performance of the CBPM is consistent with basic expectations,and the beam position resolution can fulfill the requirements for the SXFEL project if the beam conditions are optimized.     

改进的激光多步共振电离实验技术

描述了一套改进了的利用于激光多步共振电离谱学研究的实验装置和技术.在此技术中,利用加热蒸发的方式产生高温难熔元素的原子流;对激光功率和中性原子流进行实时监测,对测量结果作归一化处理;采用V-F变换器对堆积了的光信号和离子信号作瞬时变换,企图得到堆积的事件个数; CAMAC多道定标获取系统与其联合操作实现原子流强度、共振电离生成的离子数和激光功率等参数的同步获取.通过离线数据分析,能够得到更精确的实验数据.     

Laser-induced plasma generated by a 532nm pulsed laser in bulk water:unexpected line-intensity variation with water temperature and the possible underlying physics

The effect of the matrix temperature on laser-induced plasma generated in bulk water by using a532 nm pulsed laser beam has been studied.Ca Ⅰ and Ⅱ emission line intensities were recorded for an aqueous solution of CaCl_2 in the temperature range of 7℃-70℃.The emission line intensities did not follow the matrix temperature in our experiments.Maximum intensities were observed at ～18℃ for both lines.Herein,a possible mechanism responsible for the observed variation in intensity is suggested,in which laser-produced bubbles play important roles.Bubble formation is essential to ignite plasma in the liquid and more feasible at the higher liquid temperature.However,the abundant bubbles at the higher temperature can scatter the incident laser beam more effectively to decrease the energy delivered for the laser-induced plasma.Thus,these two roles have effects on the optical emission intensities in opposite ways.The validity of the suggested mechanism is discussed based on the plasma temperature,temperature dependence of the refractive index of water,plasma electron density,scattered light intensity,and plasma ignition threshold energy.Our result indicates that the temperature of the liquid is also an important parameter to be considered in the laser-induced breakdown spectroscopy analysis of bulk liquid samples and its application in deep-sea exploration.     

Synchrotron micro-XRF study of metal inclusions distribution and variation in fused silica induced by ultraviolet laser pulses

Metal inclusions play critical roles in laser-induced damage for large fused silica optics. Here, the spatial distribution of sodium, aluminum, iron and copper in as-prepared samples is analyzed by synchrotron based X-ray fluorescence spectrometry microprobe system at the BL15U1 beam line at the Shanghai Synchrotron Radiation Facility. The as-prepared fused silica samples are induced by 355 nm laser pulses with no, or low, or high fluences. The spatial resolution of the obtained elemental maps is up to 50 μm. Analysis of the elemental maps indicates that the distribution of metals has a close association with the laser fluence and pulses. The normalized fluorescence signal attenuation for metal inclusions corresponds to the laser fluence. The decrement of metals depends chiefly upon the fluence other than pulses of the incidence laser, which is most pronounced for iron and least for copper. The decrement is evident for high fluence laser irradiation, while the amount is negligible for low fluence laser irradiation. Among the four metals, iron concentration is suggested as the most destructive factor for optics lifetime, especially under high fluence irradiation. The quasi-periodic feature of elemental distribution is partly ascribed to laser intensity modulation induced by Fresnel diffraction.     

Formation of secondary radiation fields at NICA

The crucial points of a radiation shielding design for a relativistic heavy ion accelerator are the source term problem, neutron fluence and dose attenuation characteristics of the shielding. Simulations of the radiation shielding for JINR’s Nuclotron-Based Ion Facility (NICA) project were carried out using the GEANT4 code. Some regularities in the secondary neutron field generation at the 4.5 GeV/n uranium beam interaction with thick targets are discussed. Neutron attenuation by the ordinary concrete shielding of NICA was considered as well.     

Performance of a New Ion Source for KSTAR Tokamak Plasma Heating

In the experimental campaign of 2010 and 2011 on KSTAR, the NBI-1 system was equipped with one prototype ion source and operated successfully, providing a neutral beam power of 0.7-1.6 MW to the tokamak plasma. The new ion source planned for the 2012 KSTAR campaign had a much more advanced performance compared with the previous one. The target performance of the new ion source was to provide a neutral deuterium beam of 2 MW to the tokamak plasma. The ion source was newly designed, fabricated, and assembled in 2011. The new ion source was then conditioned up to 64 A/100 keV over a 2-hour beam extraction and performance tested at the NB test stand （NBTS） at the Korea Atomic Energy Research Institute （KAERI） in 2012. The measured optimum perveance at which the beam divergence is a minimum was about 2.5μP, and the minimum beam divergent angle was under 1.0° at 60 keV. These results indicate that the 2.0 MW neutral beam power at 100 keV required for the heating of plasma in KSTAR can be delivered by the installation of the new ion source in the KSTAR NBI-1 system.     

基于大科学装置的放射性新核素产生进展

放射性新核素的产生是核物理研究的热点,它对于扩展核素版图、研究奇异核结构和性质、理解核天体物理中的快中子俘获过程都非常重要.目前,人们有关原子核的认识主要集中在稳定线附近长寿命的核素,并建立了多套模型用以解释其基本性质,但对于远离稳定线的核素,特别是重区丰中子核的研究还很缺乏.本文结合国内外产生放射性同位素大科学装置的...     

Enhancement of optical emission generated from femtosecond double-pulse laser-induced glass plasma at different sample temperatures in air

In double-pulse laser-induced breakdown spectroscopy(DP-LIBS), the collinear femtosecond double-pulse laser configuration is experimentally investigated with different initial sample temperatures using a Ti:sapphire laser. The glass sample is ablated to produce the plasma spectroscopy. During the experiment, the detected spectral lines include two Na(I) lines(589.0 nm and 589.6 nm) and one Ca(I) line at the wavelength of 585.7 nm. The emission lines are measured at room temperature(22 ℃) and three higher initial sample temperatures(T_s?=?100 ℃, 200 ℃, and 250 ℃). The inter-pulse delay time ranges from-250 ps to 250 ps.The inter-pulse delay time and the sample temperature strongly influence the spectral intensity,and the spectral intensity can be significantly enhanced by increasing the sample temperature and selecting the optimized inter-pulse time. For the same inter-pulse time of 0 ps(single-pulse LIBS), the enhancement ratio is approximately 2.5 at T_s?=?200 ℃ compared with that obtained at T_s?=?22 ℃. For the same inter-pulse time of 150 ps, the enhancement ratio can be up to 4 at T_s?=?200 ℃ compared with that obtained at T_s?=?22 ℃. The combined enhancement effects of the different initial sample temperatures and the double-pulse configuration in femtosecond LIBS are much stronger than that of the different initial sample temperatures or the double-pulse configuration only.     

Isomer separation of Cu and Cu with a resonance ionization laser ion source

Radioactive copper isotopes were ionized with the resonance ionization laser ion source (RILIS) at the on-line isotope separator ISOLDE (CERN). Using the different hyperfine structure in the 3d¹⁰ 4s  ²S_1/2 – 3d¹⁰ 4p  ²P⁰_1/2 transition the low- and high-spin isomers of ⁷⁰Cu were selectively enhanced by tuning the laser wavelength. The light was provided by a narrow-bandwidth dye laser pumped by copper vapor lasers (CVL) and frequency doubled in a BBO crystal. The ground state to isomeric state intensity ratio could be varied by a factor of 30, allowing to assign gamma transitions unambiguously to the decay of the individual isomers. It is shown that the method can also be used to determine magnetic moments. In a first experiment for the 1⁺ ground state of ⁷⁰Cu a magnetic moment of (+)1.8(3) μ_N and for the high-spin isomer of ⁷⁰Cu a magnetic moment of (±)1.2(3) μ_N could be deduced.