15 TW激光与氮气作用产生稳定电子束的实验研究

利用15 TW激光脉冲,系统研究了基于电离化注入的激光尾波场加速。实验中,研究了等离子体密度、相互作用位置、激光脉宽以及激光能量对电子束的电荷量、发散角、指向性、能量以及产生概率的影响。将约400 mJ、25 fs的激光脉冲聚焦在喷嘴前沿,等离子体密度约9×10¹⁸ cm^-3时,电子的产生概率高达100%,获得了水平（竖直）发散角（6.5±0.5） mrad（（5.3±0.3） mrad）、水平（竖直）指向稳定性±1.2 mrad （±0.7 mrad）、峰值能量（135±8） MeV和电荷量（13.5±2.0） pC（＞50 MeV）的稳定电子束,为其应用奠定了基础。     

High density γ-ray emission and dense positron production via multi-laser driven circular target

A diamond-like carbon circular target is proposed to improve γ-ray emission and pair production with a laser intensity of 8×10²² Wcm⁻² by using 2D particle-in-cell simulations with quantum electrodynamics. It is found that the circular target can enhance the density of γ-photons significantly more than a plane target, when two colliding circularly polarized lasers irradiate the target. By multi-laser irradiating the circular target, the optical trap of lasers can prevent the high energy electrons accelerated by laser radiation pressure from escaping. Hence, γ-photons with a high density of beyond 5000n_c are obtained through nonlinear Compton backscattering. Meanwhile, 2.7×10¹¹ positrons with an average energy of 230 MeV are achieved via the multiphoton Breit–Wheeler process. Such an ultrabright γ-ray source and dense positron source can be useful in many applications. The optimal target radius and laser mismatching deviation parameters are also discussed in detail.     

Time-Resolved Optical Emission Spectroscopy Diagnosis of CO2 Laser-Produced SnO2 Plasma

The spectral emission and plasma parameters of SnO_2 plasmas have been investigated.A planar ceramic SnO_2 target was irradiated by a CO2 laser with a full width at half maximum of 80 ns.The temporal behavior of the specific emission lines from the SnO_2 plasma was characterized.The intensities of Sn I and Sn II lines first increased,and then decreased with the delay time.The results also showed a faster decay of Sn I atoms than that of Sn II ionic species.The temporal evolutions of the SnO_2 plasma parameters(electron temperature and density) were deduced.The measured temperature and density of SnO_2 plasma are 4.38 eV to0.5 eV and 11.38×10~(17) cm~(-3) to 1.1×10~(17) cm~(-3),for delay times between 0.1 μs and 2.2 μs.We also investigated the effect of the laser pulse energy on SnO_2 plasma.     

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。     

Development of a helicon-wave excited plasma facility with high magnetic field for plasma-wall interactions studies

The high magnetic field helicon experiment system is a helicon wave plasma(HWP)source device in a high axial magnetic field(B_0)developed for plasma–wall interactions studies for fusion reactors.This HWP was realized at low pressure(5?×?10~(-3)?-?10 Pa)and a RF(radio frequency,13.56 MHz)power(maximum power of 2 k W)using an internal right helical antenna(5 cm in diameter by 18 cm long)with a maximum B_0of 6300 G.Ar HWP with electron density~10~(18)–10~(20)m~(-3)and electron temperature~4–7 e V was produced at high B_0 of 5100 G,with an RF power of 1500 W.Maximum Ar~+ion flux of 7.8?×?10~(23)m~(-2)s~(-1)with a bright blue core plasma was obtained at a high B_0 of 2700 G and an RF power of 1500 W without bias.Plasma energy and mass spectrometer studies indicate that Ar~+ion-beams of 40.1 eV are formed,which are supersonic(~3.1c_s).The effect of Ar HWP discharge cleaning on the wall conditioning are investigated by using the mass spectrometry.And the consequent plasma parameters will result in favorable wall conditioning with a removal rate of 1.1?×?10~(24)N_2/m~2 h.     

Scintillation properties of RbGd2Br7:Ce.Advantages and limitations

The scintillation properties of RbGd₂Br₇ crystals, doped with Ce³⁺ concentrations of 0.02, 0.11, 0.88, 2.05, 4.1, and 9.8%, are studied under X-ray and γ-quanta excitations. For the RbGd₂Br₇ sample doped with 9.8% Ce, the authors measured a light yield of 56000±6000 photons per MeV of absorbed γ-ray energy with a main decay time of 43±1 ns, using a Hamamatsu R1791 photomultiplier (PMT), a ¹³⁷Cs radioactive source, and a shaping time of 10 μs. A time resolution of 790±10 ps was measured for the RbGd₂Br₇:9.8% Ce compound, using BaF₂ as second scintillator, two XP2020Q PMTs, a ²²Na source, and an energy threshold set at E⩾511 keV. With the R1791 PMT, an energy resolution of 4.1% (FWHM over peak position) for the 662-keV full absorption peak has been observed for two crystals of 7×4×2 mm³ and 15×5×1 mm³ with 4.1 and 9.8% Ce content, respectively. Moreover, the nonproportional responses of three RbGd₂Br₇:Ce compounds with different concentrations (0.11, 2.05, and 9.8%) were studied revealing an almost-constant light output response from 17.4 keV to 1 MeV. These properties are compared to three other well-known scintillators: NaI:Tl, CsI:Tl, and Lu₂SiO₅:Ce     

22Na次级束的产生与应用

在日本东京大学核研究中心的放射性离子束分离器上,利用逆运动学反应¹H(²²Ne,²²Na)n产生了²²Na次级束。经分离器电磁系统的分离提纯后,获得了能量为（78.3±1.0） MeV的²²Na次级束。实验靶站处次级束的强度达2.5×10⁵ s^-1,其中²²Na的纯度好于90%。²²Na次级束已应用于与核天体物理Ne丰度异常问题相关的²²Na+α共振散射实验研究。     

Effect of Foil Target Thickness in Proton Acceleration Driven by an Ultra-Short Laser

Proton acceleration experiments were carried out by a 1.2 x 101s W/cm2 ultra-short laser interaction with solid foil targets.The peak proton energy observed from an optimum target thickness of 7μm in our experiments was 2.1 MeV.Peak proton energy and proton yield were investigated for different foil target thicknesses.It was shown that proton energy and conversion efficiency increased as the target became thinner,on one condition that the preplasma generated by the laser prepulse did not have enough shock energy and time to influence or destroy the target rear-surface.The existence of optimum foil thickness is due to the effect of the prepulse and hot electron transportation behavior on the foil target.     

Bright γ-ray source with large orbital angular momentum from the laser near-critical-plasma interaction

We propose a new laser-plasma-based method to generate bright γ-rays carrying large orbital angular momentum by interacting a circularly polarized Laguerre–Gaussian laser pulse with a near-critical hydrogen plasma confined in an over-dense solid tube. In the first stage of the interaction, it is found via fully relativistic three-dimensional particle-in-cell simulations that high-energy helical electron beams with large orbital angular momentum are generated. In the second stage, this electron beam interacts with the laser pulse reflected from the plasma disc behind the solid tube, and helical γ beams are generated with the same topological structure as the electron beams. The results show that the electrons receive angular momentum from the drive laser, which can be further transferred to the γ photons during the interaction. The γ beam orbital angular momentum is strongly dependent on the laser topological charge l and laser intensity a0, which scales as ${L}_{\gamma }\propto {a}_{0}^{4}$. A short (duration of 5 fs) isolated helical γ beam with an angular momentum of −3.3 × 10⁻¹⁴ kg m² s⁻¹ is generated using the Laguerre–Gaussian laser pulse with l = 2. The peak brightness of the helical γ beam reaches 1.22 × 10²⁴ photons s⁻¹ mm⁻² mrad⁻² per 0.1% BW (at 10 MeV), and the laser-to-γ-ray angular momentum conversion rate is approximately 2.1%.     

AB-BNCT中子靶物理设计分析

质子加速器适用于为硼中子俘获治疗提供中子源,其中子源强及能谱较反应堆中子源更具可调性。中子靶物理计算分析是加速器中子源设计的基础,为其提供粒子能量、流强等参数需求分析,并为靶体结构尺寸设计、中子慢化和屏蔽分析等提供前端参数。本文利用MCNPX蒙特卡罗程序,通过对质子打靶的中子产额和能谱、靶体能量沉积、打靶后靶材放射性活度和中子出射空间角分布等进行研究,提出能量2.5 MeV质子轰击100～200 μm锂靶的设计,并用模拟计算数据论证其合理性。该设计中子源在1 mA流强质子轰击下,源强可达9.74×10¹¹ s^-1;拟设计15 mA、2.5 MeV质子束产生的中子源,在治疗过程中靶材放射性活度累积最大值约为1.44×10¹³ Bq。     

Spectral Characteristics of Laser-Induced Graphite Plasma in Ambient Air

An experimental setup of laser-induced graphite plasma was built and the spectral characteristics and properties of graphite plasma were studied. From the temporal behavior of graphite plasma, the duration of CN partials(B~2∑~+→X~2∑~+) emission was two times longer than that of atomic carbon, and all intensities reached the maximum during the early stage from0.2 μs to 0.8 μs. The electron temperature decreased from 11807 K to 8755 K, the vibration temperature decreased from 8973 K to 6472 K, and the rotational temperature decreased from7288 K to 4491 K with the delay time, respectively. The effect of the laser energy was also studied, and it was found that the thresholds and spectral characteristics of CN molecular and C atomic spectroscopy presented great differences. At lower laser energies, the electron excited temperature, the electron density, the vibrational temperature and rotational temperature of CN partials increased rapidly. At higher laser energies, the increasing of electron excited temperature and electron density slow down, and the vibrational temperature and rotational temperature even trend to saturation due to plasma shielding and dissociation of CN molecules. The relationship among the three kinds of temperatures was T_(elec)T_(vib)T_(rot) at the same time. The electron density of the graphite plasma was in the order of 10~(17)cm~(-3) and 10~(18)cm~(-3).     

Estimation of plasma density perturbation from dusty plasma injection by laser irradiation on tungsten target in DiPS

To investigate the interaction of dusty plasma with magnetized plasmas at divertor plasma simulator, radial profiles of plasma density(ne) and electron temperature were measured in terms of plasma discharge currents and magnetic flux intensity by using a fast scanning probes system with triple tips. Dusty plasma with dusts(a generation rate of 3 μg s~(-1) and a size of 1–10 μm)was produced via interactions between a high-power laser beam and a full tungsten target. As ne increases, the scale of the effects of dusty plasma injection on magnetized plasmas was decreased. Also, the duration of transient fluctuation was reduced. For numerical estimation of plasma density perturbation due to dusty plasma injection, the result was ~10% at a core region of the magnetized plasma with n_e of(2–5)×10~(11) cm~(-3) at steady state condition.     

Experimental study of density pump-out on EAST

In the experimental advanced superconducting tokamak,density pump-out phenomena were observed by using a multi-channel polarimeter-interferometer system under different heating schemes of ion cyclotron resonant heating,electron cyclotron resonance heating,and neutral beam injection.The density pump-out was also induced with application of resonant magnetic perturbation,accompanied with a degradation of particle confinement.For the comparison analysis in all heating schemes,the typical plasma parameters are plasma current 400 k A,toroidal field 2 T,and line average density 2?×?10~(19)m~(-3).The experimental results show that the degree of pump-out is concerned with electron density and heating power.Low density deuterium low confinement(L-mode) plasmas(3.5?×?10~(19)m~(-3)) show strong pump-out effects.The density pump-out correlated with a significant drop of particle confinement.     

加速器质谱测量岩石样品中41Ca的初步研

⁴¹Ca在核天体物理及地质年代学方面可能具有较高的应用价值。为测量天然岩石样品中⁴¹Ca的本底水平,探讨了⁴¹Ca-AMS测量中岩石样品的CaF₂制备,提出了二次氟化的制备方法。在此基础上,通过对导电介质与靶锥的改进,设计了一种提高CaF^-₃束流引出强度的方案。该方案可有效提高CaF^-₃束流引出强度。实验结果表明,天然岩石样品中⁴¹Ca/⁴⁰Ca（⁴¹Ca、⁴⁰Ca原子个数比）的本底水平低于8×10^-14。     

LiH和LiT与H2O反应机理研究

氢材料在微量H₂O、CO₂、O₂和N₂存在下可能发生物理化学反应,使材料的物理品位下降。由于反应过程十分复杂,很难从实验上准确获取这类反应的最佳通道和具体产物信息,因此,从理论上研究氢材料分子的物理化学性质及其化学反应机制,了解化学反应过程具有十分重要的意义。本文使用Gaussian03软件包和Gaussview工具软件,在6-311G(d)全电子基函数水平上,应用二阶微扰理论优化得到了⁶LiH、⁶LiT与H₂O反应的中间体、过渡态及产物的结构,总能量,振动频率和零点能等。通过计算发现⁶LiH、⁶LiT均只有1个反应通道,⁶LiH与H₂O反应的焓变、活化能和反应速率常数分别为-156.99 kJ/mol、8.95 kJ/mol和3.75×10¹⁰(mol•dm^-3)^-1/s,⁶LiT与H₂O反应的焓变、活化能和反应速率常数分别为-159.02 kJ/mol、9.92 kJ/mol和1.72×10¹⁰ (mol•dm^-3)^-1/s。     

Measurement ofHe2* density with an auxiliary measuring electrode in atmospheric pressure plasma jet

In this study, the density of metastable He₂* in an atmospheric-pressure plasma jet operating in helium with 0.001% nitrogen has been measured using an auxiliary measuring electrode technique. In the glow discharge mode, waveforms from two grounding electrodes, including one main discharge electrode and one auxiliary electrode, are captured. The isolated current peak formed by Penning ionization in waveforms from the auxiliary measuring electrode is identified to calculate the density of metastable He₂*. In our discharge environment, the helium metastable densities along the jet axis direction are between 2.26× 10¹³ and 1.74× 10¹³ cm^-3, which is in good agreement with the results measured by other techniques. This measurement technique can be conveniently applied to the diagnosis of metastableHe₂* in an atmospheric-pressure plasma jet array.     

Preparation of High Specific Activity Strontium-89 Solution in High Flux Engineering Test Reactor

⁸⁹SrCl₂ is an important radioactive drug for the bone metastasis. It is included in the new pharmacopoeia in 2015 and has a promising future in the market. Depending on the high flux engineering test reactor(HFETR), the process of preparation of high specific activity⁸⁹SrCl₂ solution by nuclear reaction ⁸⁸Sr(n, γ)⁸⁹Sr was studied. High purity enriched⁸⁸SrCO₃ was used as target material and irradiated for 56 days under the condition of thermal neutron fluence rate about 2×10¹⁴ n•cm^-2•s^-1. After dissolution and filtration, the colorless⁸⁹SrCl2 solution was obtained. The specific activity of⁸⁹SrCl₂ solution was 7.77×10⁹-1.08×10¹⁰ Bq•g^-1, the activity concentration was 3.59×10⁸-1.21×10⁹ Bq•mL^-1, the gamma impurity content was 0.11%-0.14%, the Al impurity content was much lower than 2 μg•mL^-1(activity concentration 7.4×10⁷ Bq• mL^-1).⁸⁹SrCl₂ solution had been tested to meet the requirements of the industry and could be used as raw material for the production of injection. The development of single 7.4×10¹⁰ Bq level preparation device of high purity and high specific activity of ⁸⁹Sr had been finished. This research is important for localization of isotope products.     

Measurement of the H2-D mass difference with a nuclear microprobe

A 1.24 MeV deuteron (D) beam mixed with a H₂ molecular beam was separated with a microslit system of a nuclear microprobe consisting of a 100 μm diameter object and a 1 mm diameter aperture diaphragm. D was distinguished from H₂ by Rutherford backscattering (RBS) on a thin Au film. By slightly changing the magnetic field strength of the beam steerer installed in front of the object diaphragm, the maximum and the minimum RBS D/H₂ ratios were found to be 50.3 and 1.5, respectively. M/ΔM = 3.9 × 10³ was obtained as the mass resolution of the nuclear microprobe. The transmission of this system was 2 × 10⁻³.     

用0.5 MV端电压的串列AMS装置开展10Be测量方法研究

本文通过对¹⁰Be离子在加速器质谱计（CAMS）高能端束流传输进行模拟计算,确定了¹⁰Be离子束流传输的优化设计。设计安装了测量⁹Be束流的法拉第筒、能量吸收膜（SiN膜）装置、ΔE-E_res气体探测器等,结果表明,改进后的CAMS可进行¹⁰Be测量,¹⁰Be测量总传输效率约为2%,测量本底约为4×10^-14。