紫外超短激光驱动铜薄膜靶产生质子的实验研究

在中国原子能科学研究院的放电泵浦的紫外KrF超短脉冲激光放大装置上,开展了紫外超短脉冲激光与铜薄膜靶相互作用加速产生质子束的实验研究。紫外超短脉冲激光输出能量为30 mJ、波长为248 nm、脉冲宽度为500 fs,采用离轴抛物面镜聚焦获得激光聚焦功率密度为1.2×10¹⁷ W/cm²。激光以45°入射5 μm厚的铜薄膜靶,质子最大能量超过300 keV。紫外超短脉冲激光的高对比度和高吸收效率是紫外激光加速的优点。     

超短超强激光与薄膜铝靶作用加速产生质子的实验研究

实验研究了功率密度6×1016W/cm2、脉宽120fs的激光与5μm铝靶的相互作用,观测到了高能质子的产生。设计加工了用于测量质子能谱的Thomson质谱仪,用于快质子的测量。测得其能谱和产生的最高质子能量为180keV,同时测得质子发散全角为38°。     

用CR-39固体径迹探测器测量激光加速产生的100 keV以下的质子能谱

本文通过实验验证CR-39临界角是其不能探测到100 keV以下质子能谱的原因。并据此改进探测方案,利用CR-39和Thomson谱仪测得超强激光与5 μm厚Al靶作用产生的100 keV以下的质子能谱。探讨了利用单粒子模拟法处理Thomson谱仪的数据,该方法规避了谱仪中磁场边缘场对测量的影响,提高了谱仪测量精度。     

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。     

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。     

氮化镓材料中质子输运过程的模拟

对入射能量为50keV~3MeV的质子在氮化镓(GaN)材料中的输运过程进行了Monte-Carlo模拟,得到垂直入射质子在GaN材料中的输运情况、质子与晶格原子作用产生的空位分布特征。模拟结果表明：在厚度固定（3.5μm）的GaN材料中,当入射能量小于300keV时,质子束横向扩展明显,入射离子全部被阻止在材料中;随着入射能量增大,质子束横向扩展减弱,离子穿透几率增大,当能量大于500keV时,入射离子几乎全部从材料中穿出。     

150 keV质子辐照对GaAs子电池性能的影响

低能质子辐射会使电池产生较大的非电离能量损失，导致少数载流子寿命降低从而破坏GaInP/GaAs/Ge电池的电性能，其中尤以中间的GaAs子电池的衰减最严重。本文以卫星用主流GaInP/GaAs/Ge三结电池为研究对象，制备与三结电池中GaAs子电池相同尺寸结构和工艺的单结GaAs电池，以150 keV质子辐照后对其性能进行测试。测试结果表明，150 keV质子辐照后电池的量子效率衰减，且基区衰减最严重。光致发光测试结果显示，在3×10¹⁰、1×10¹¹、5×10¹¹ cm^-2辐照注量下，非辐射复合少数载流子寿命分别为2.22、0.67、0.13 ns。基于上述结果，利用多物理场仿真软件COMSOL建立了GaAs的物理模型，对GaAs子电池衰减进行仿真，将实验结果与模拟结果进行对比，两者电学参数的最大相对偏差为7%。仿真结果表明：中国空间站中电池的辐射衰减主要源于内辐射带中的质子，空间站轨道太阳能电池运行5 a，在太阳活动极大时，最大功率衰减约为7.6%，太阳活动极小时，最大功率衰减约为13.7%。     

长脉冲KrF激光驱动高速飞片实验研究

利用侧向阴影成像技术开展了激光驱动高速金属飞片实验研究,并介绍了飞片实验系统与条纹相机时空标定结果。实验在辐照激光波长248 nm、脉宽28 ns、能量100 J、功率密度1.8×10¹²W/cm²的条件下加速带有50 μm烧蚀层的5 μm铝飞片至10 km/s左右。讨论了不同条件下加速过程的区别,分析了冲击波对飞片加速过程的影响,并从铝、钽飞片实验对比中发现激光烧蚀不同材料的能量转化效率是不同的。     

超短脉冲激光与固体靶相互作用的硬X射线能谱

本实验使用高纯锗探测器，运用单光子法，对超短脉冲激光与固体铜靶相互作用产生的硬X射线能谱进行测量。实验结果表明：在激光强度I≈8×10¹⁶W/cm²的P极化光以45°入射角照射5 mm铜靶、探测立体角为4.5×10^－6的实验条件下，产生的硬X射线的能量主要集中在低于100keV能量范围内，超热电子温度分别为(7.4±0.7)keV和(19.5±1.6)keV。     

RBS法测量重元素衬底上轻元素薄靶厚度的方法研究

在核反应实验中,靶厚的精度往往会直接影响实验结果的可靠性。为精确测量重元素衬底上轻元素薄靶的厚度,本文通过卢瑟福背散射(RBS)法,使用能量1.5 MeV的质子束对蒸镀在300 μm厚¹⁸¹Ta衬底上薄⁷⁴Ge靶的厚度进行了测量。RBS法测量结果与称重法相差较小,但信噪比从1∶2 000提升到1∶12,靶厚相对不确定度由10%减少到5%左右。同时采用SIMNRA软件对测量结果进行了模拟验证,模拟能谱与实验能谱符合较好。通过RBS法测量重元素衬底上轻元素薄靶的厚度,尤其当重元素衬底的质量远大于靶物质时,可有效提高测量结果的信噪比及不确定度,为核反应实验的分析提供了较好的依据。     

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.     

Reduction of light elements loss in polymer foils during MeV-proton irradiation by application of an aluminum coating

Backscattering and forward-scattering spectrometry with 2.2 MeV-protons have been applied to detect light elements including H, C, N and O in polymer foils of aromatic polyimide (PI), polyethylene telephthalate (PET) and polyethylene naphthalate (PEN). In the case of PI, no significant loss of H, C, N and O was observed during proton irradiation. In the case of PET and PEN, on the other hand, all the light elements gradually decreased as irradiation fluence increased and the contents of 15%-H, 14%-C, 47%-O in PET and 7%-H, 5%-C 31%-O in PEN were eventually released up to a fluence of 2.1 × 10¹⁶ protons/cm². An aluminum thin film (thickness ∼0.1 μm) was sputter-deposited on the upper surface of 4 μm thick PET and PEN foils to prevent the release of light elements. In Al coated PEN foil, for example, the losses of H, C and O were 2%, 0.5% and 22% of the starting contents, respectively, considerably smaller than those found for uncoated PEN. Thus the Al coating was found to be an effective method to suppress the loss of constituent elements.     

Energy calibration of the 500 kV heavy ion implanter ionas

Gamma ray yield functions of (p, αγ) and (p, γ) resonance reactions on semi-thick ¹⁹F, ²³Na, ^24,26Mg and ²⁷Al targets were measured and used to calibrate the accelerating voltage and energy resolution of the new 500 kV heavy ion implanter at Göttingen. The energy spread of the proton beam was found to vary linearly with the accelerating voltage from ΔE(200 keV) = 55 eV fwhm to ΔE(500 keV) = 105 eV; it is made up by a 0.012% high voltage ripple and the Doppler broadening of the resonances due to the thermal motion of the target nuclei. A long term stability of the proton energy of < 5 eV/h at 300 keV was achieved with new resistors in the voltage regulating system.Applications of the accelerator for the remeasurement of some resonance energies and widths and for depth profiling of light implanted ions in metals by the resonance broadening method will be briefly discussed.     

Ion-implanted S targets for astrophysics studies

The fabrication of isotopically pure 10.4 μg/cm² targets of ³²S by the implantation of 60-100 keV negative ions into a 61 μg/cm² pure ¹²C thin foil is described. The process has been accomplished in rather shorter times than has been achieved previously by implanting the as-prepared carbon foil while still mounted on the underlying glass slide, thereby allowing for the use of much larger beam current intensities. The target has been assayed for absolute composition as a function of depth using Rutherford backscattering spectrometry and excellent agreement between the measured and nominal ³²S fluences was observed. The implanted targets exhibit excellent stability with regard to subsequent 34.5 MeV proton beam irradiation.     

The influence of the charged back side on the transmission of highly charged ions through PC nanocapillaries

We have measured the fraction of the ions transmitted through nanocapillaries with their initial charge state for 200 keV Xe⁷⁺ ions impact on a polycarbonate (PC) foil with a thickness of 30 μm and a diameter of 150 nm. An Au film was evaporated on both the front and back side. It is found that more than 97% of the transmitted ions remain in their initial charge state. Then, the transmitted ion fraction and the characteristic tilt angle of 40 keV Xe⁷⁺ ions through this foil and another one with the same thickness and diameter, but evaporated by Au only on the front side, were measured. By comparing the results of these two foils, the influence of the ions deposited in the capillary exit region on the transmitted ion fraction and the characteristic tilt angle is studied. In comparison with the foil evaporated by Au on both sides, the maximum transmitted ion fraction of the foil evaporated by Au on the front side only is nearly 4 times smaller. Also, the characteristic tilt angle is slightly decreased. These results are discussed within the models for the guiding effect.     

The PTB single ion microbeam for irradiation of living cells

At the PTB's ion accelerators, a new microbeam facility is now in operation that is capable of delivering single ions, for example, to the nuclei of individual living cells. The wide range of proton and ⁴He²⁺ ion energies affords LET-values between 3 and 200 keV/μm. A beam diameter of less than 2 μm outside the vacuum system has been measured and a targeting accuracy of better than 2 μm has been determined. In contrast to other microbeam facilities operated for radiobiological research using mechanical collimators in front of the target to define the beam, the PTB facility utilises beam focusing by quadrupole magnets. The microbeam has a unique ion optical design that incorporates a 90° bending magnet in the beam transport system. This design has the advantage of providing a microbeam basically without scattered particles. Every ion reaching the target is detected by a thin scintillating foil and a photomultiplier tube with efficiency close to 100%. Presently up to 1500 single cells per hour can be automatically irradiated with a chosen number of particles. Procedures and results of first cell irradiations are described as an example.     

An absolute determination of the U fission cross section at 964 keV

An absolute measurement of the ²³⁵U fission cross section has been carried out using a ²⁴Na---Be photoneutron source with median neutron energy of 964 keV. A symmetric two-foil experiment was set up to measure the fission rate in a low-albedo laboratory, and variations in the source-to-foil spacing used to determine the room background. Fission fragments passing through a limited solid angle aperture were recorded from each foil by solid state tracketch techniques. The photoneutron source was calibrated after each run using the manganese bath method and the secondary national standard source NBS-II. A computed neutron source spectrum with 32 keV FWHM was derived by the Monte Carlo method and used in reducing the data to a cross section at 964 keV. The final value of 1.21 ± 0.025 barns is absolute in that, except for small corrections, its determination was independent of any other cross section data.