北京放射性核束装置在线同位素分离器的研制

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,进行在线分析后供物理用户使用,其质量分辨率好于20 000。BRISOL装置现已建成,并开展了氧化镁、氧化钙靶的在线实验,在线产生了³⁷K⁺、³⁸K⁺、²⁰Na⁺、²¹Na⁺等多种放射性核束。本文详细介绍该装置的研制及运行情况。     

Charged-particle activation methods for the analysis of carbon and oxygen in high-purity gallium

Methods for the instrumental analysis of C and O at trace level in high-purity gallium were developed. The ¹²C (d, n)¹³N and ¹⁶O(t, n)¹⁸F reactions were used between 2.5 and 3.5 MeV, allowing analyses down to tens of ppb/weight. The ¹⁶O(p, )¹³N reaction at 15 MeV was also used; in this case ¹³N has to be separated radiochemically.     

低本底高分辨测量技术在16N衰变的出射α粒子测量中的应用

¹⁶N的β延迟α衰变能谱在Ec.m.≈12 MeV处有一低能峰,该α峰的形状和高度可用于约束12C(α,γ)16O反应截面的E1部分,对其进行测量具有重要意义。本工作尝试采用重离子注入法对其进行测量,在兰州重离子加速器国家实验室RIBLL1放射性束流线上产生了16N放射性束流并将其注入到双面硅微条探测器(DSSD)中,利用DSSD对其β延迟α能谱进行了测量。通过选用薄的DSSD探测器、DSSD正反面能量符合关系以及DSSD点火数约束等方法,显著减小了16N衰变产生的电子对α能谱测量的干扰,将α能谱的测量阈值降低到800 keV左右,成功观测到了Ec.m.≈12 MeV处的低能峰。该方法为间接研究12C(α,γ)16O反应率开辟了一条新的实验方法。     

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。     

恒星中子源~(13)C(α,n)~(16)O反应的研究

13 C(α,n)16 O是渐进巨星支(AGB)星中慢速中子俘获(s)过程的主中子源反应,而17 O 6.356 MeV1/2+阈下共振对13 C(α,n)16 O反应影响很大。本文使用HI-13串列加速器和Q3D磁谱仪,首次测量了13C(11B,7Li)17 O转移反应角分布,确定了影响13C(α,n)16 O反应最关键、最不确定的17 O(Ex=6.356MeV)阈下共振态的α宽度,从而得出天体物理能区13 C(α,n)16 O反应的天体物理S因子和反应率,澄清了国际上已有S因子数据间高达25倍的巨大分歧。AGB星s过程核合成网络计算表明:新反应率数据导致恒星中铅的丰度增加了25%。     

Production, acceleration and use of radioactive ion beams at Louvain-la-Neuve

The production and acceleration of radioactive beams using two cyclotrons coupled by an electron cyclotron resonance ion source is described. Pure beams of ¹³N(T1/2 = 9.96 min) and ¹⁹Ne(T1/2 = 17 s) with an energy around 1 MeV/amu are obtained with intensities larger than 50 ppA. As an example, cross section measurements using a ¹³N beam on hydrogen and deuteron targets are presented. Finally, the ARENAS³ project, a future plan for the production of radioactive beams in Belgium, is described.     

A new concept kinetic-ejection negative-ion source for rib generation

Chemically active radioactive species are often released from target-materials in a variety of molecular forms. For example, ¹⁷F, is principally released from Al₂O₃ target-material as Al¹⁷F. Because of the low probability of simultaneously dissociating such molecular carriers and efficiently ionizing their atomic constituents with conventional hot-cathode, electron-impact ion sources, species of interest are often distributed in several mass channels in the form of molecular side-band beams. Consequently, beam intensities of the desired radioactive species are diluted. The sputter negative-ion beam generation technique is particularly effective for simultaneously dissociating molecular carriers and efficiently ionizing highly electronegative atomic constituents. Therefore, a new concept kinetic-ejection negative-ion source (KENIS), based on this principle, was conceived to address this problem. The source has proven to be highly efficient for simultaneously dissociating and negatively ionizing sputter-ejected atomic fluorine from cesiated surfaces. The source has been successfully employed on-line to generate high intensity ¹⁷F⁻ beams for use in the astrophysics research program at the Holifield Radioactive Ion Beam Facility (HRIBF) using the ¹⁶O(d,n)¹⁷F reaction. The mechanical design features, principles of operation, operational parameters, beam quality information (emittance data) and efficiencies for forming intense beams of ¹⁷F⁻ during off-line and on-line operation of the source are presented in this report.     

Radiation damage factor for ion-implanted silicon detectorsirradiated with heavy ions

Ion-implanted silicon detectors were irradiated with 18-150 MeV ¹⁶O, 20 MeV ⁴⁰Ar, and 53 MeV ¹¹⁰Xe. A linear increase of the leakage current was observed as a function of the particle fluence up to 2.2×10⁸ cm^-2. Extracted damage factors are proportional to the averaged nuclear stopping power over five orders of magnitude covering heavy ions studied in the present work and also protons of 25-800 MeV energies     

Analysis of Cu and O in high-Tc superconductors by 7–9 MeV protons

The use of proton-induced γ-ray emission for the simultaneous analysis of Cu and O in high-T_c superconductors is demonstrated. Utilizing 7–9 MeV protons, the ratio of O relative to Cu can be determined reliably to a few percent accuracy in homogeneous bulk samples and films thicker than 130 μm using standard bulk samples of O and Cu. Results of the present method are compared with those of the analysis of YBa₂Cu₃O_7xdone by the Rutherford scattering of particles and the non-Rutherford scattering through the ¹⁶O(p,p₀)¹⁶O reaction.     

Determination of O concentrations in musamples of biological fluids

The ¹⁸O(p, )¹⁵N reaction has been developed for the analysis of musamples of biological fluids containing ¹⁸O-enriched water. Samples as small as 50 μl have been used. Well characterized Ta₂O₅ targets were prepared from these fluids and irradiated with several hundred nA of protons from the 3 MV Van de Graaff at Lucas Heights. The broad (47 keV) 846 kV resonance in this reaction was used to measure ¹⁸O concentrations down to natural backgrounds (0.2 at.%) in a few minutes of accelerator running time. Concentrations of ¹⁸O from 0 to 5 at.% were measured in body fluids in small Australian lizards directly after doping with ¹⁸O-enriched water and then again after several days of roaming around in their natural desert environments. The changes in these levels were related to the metabolic rates of these animals.     

The cross section for the K(n,p)Ar reaction between 14.2 and 17.2 MeV

Activation techniques have been used to measure the cross section for the ⁴¹K(n,p)⁴¹Ar reaction between 14.2 and 17.2 MeV. Neutrons were produced by the ³H(d,n)⁴He reaction, and the mixed-power method was used to measure the neutron flux through the ²⁷Al(n,)²⁴Na reaction. The activated samples were counted for the 1294 keV, 1.827 h γ-activity of ⁴¹Ar and the 1369 keV, 15.03 h γ-activity of ²⁴Na using a 16% Ge(Li) detector and a 4096-channel analyzer. The cross sections for the ⁴¹K(n,p)⁴¹Ar reaction using the mixed-power method were found to be 53 ± 3 mbarn at 14.2 ± 0.2 MeV, 47 ± 3 mbarn at 15.2 ± 0.2 MeV, 41 ± 3 mbarn at 16.2 ± 0.2 MeV and 36 ± 4 mbarn at 17.2 ± 0.2 MeV. The associated-particle method was also used for measuring the neutron flux in order to check the mixed-powder result at 14.2 MeV. The average cross section for three associated-particle runs at 14.2 MeV was found to be 50 ± 3 mbarn which, within experimental error, agrees with the mixed-powder value.     

北京大学4.5 MV静电加速器核反应分析系统

为满足对聚变堆面向等离子体材料中氘氚滞留问题的研究,北京大学4.5 MV静电加速器在原束线基础上新增核反应分析系统,该系统使用能量0.8～3.6 MeV的H⁺、D⁺、³He⁺和⁴He⁺粒子束流,可对核反应微分截面和样品中元素浓度的深度分布进行测量分析。本文对核反应分析原理、核反应分析系统的设备布局和实验方法进行了讨论,并以D(³He,p)⁴He核反应为例,分析了微分截面计算和样品中氘元素浓度深度分布的数据结果,其深度分辨小于1.5 μm,实验误差约为7.5%。     

水平衡法与高温转化法在矿泉水氢氧稳定同位素测定中的应用

为了鉴别不同品牌矿泉水标注水源地信息真伪,对11种不同品牌饮用水的氢氧稳定同位素(δD和δ18 O)进行测定。结果表明,水平衡法(GasBench-IRMS)和高温转化法(TC/EA-IRMS)的测定结果一致性较好,两种方法测定6种不同饮用水的δD和δ18 O的平均差异分别为(0.6±1.59)‰和(0.02±0.13)‰。水平衡法需要较长的制备和测定时间,但δD和δ18 O的测定精度明显优于高温转化法。11种饮用水δD和δ18 O变化范围较大,其δD和δ18 O受不同品牌饮用水的水源地降水影响形成明显的地域性。虽然无法区分矿泉水是否由其他类别饮用水伪造,但δD和δ18 O可以为特定区域(如高海拔与沿海地区)以及产地相近的矿泉水水源地鉴别提供依据。     

快中子活化法对声空化核效应的验证

采用纯铜作为阈探测器检测声致核聚变产生的14 MeV中子。根据14 MeV中子与Cu的核反应,选择合适的放射性核素及其特征γ峰作为测量依据。中子辐照时间为50 min,经30 min和198 min冷却,NaI探测器分别测量了超声和非超声下活化铜片的511 keV特征γ峰计数,测量结果显示,采用短冷却时间可测得⁶²Cu的511 keV γ特征峰,γ峰净面积计数增量ΔC均为正值,具有统计意义,在声空化条件下核反应液体中D-T反应产生的14 MeV中子发生率大于在非声空化条件下的;采用长冷却时间可测得⁶⁴Cu的511 keV γ特征峰,ΔC均为正值,具有统计意义,在声空化条件下核反应液体中D-D反应产生的2.45 MeV中子发生率大于在非声空化条件下的。由此验证了声空化核效应（NEAC）,并初步分析了中子成核声空化核效应的机制。     

Heavy ion linear energy transfer measurements during single eventupset testing of electronic devices

A heavy ion beam diagnostic system installed at the Brookhaven Single Event Upset Test Facility is described. Calibration of the system with the help of a-particles, essential for linear energy transfer (LET) measurements, is discussed. Measured LET values for 20 different ions, including ⁷Li, ⁹B, ¹²C, ¹⁶O, ¹⁹F, ²⁸Si, ³²S, ³⁵Cl, ⁴⁰Ca, ⁴⁵Sc, ⁴⁸Ti, ⁵⁶Fe, ⁵⁸Ni, ⁶³Cu, ⁷⁴Ge, ⁷⁹Br, ¹⁰⁷Ag, ¹²⁷I, ¹⁹⁷Au, and ²³⁵U, with energies between 0.5 and 8.5 MeV/AMU but not exceeding 400 MeV for the heaviest ions, are presented in both graphical and numerical forms. Results are compared to predictions of the TRIM-90 simulation program, with an average difference between the measured and calculated values of 2±6%     

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。     

The development of a time of flight spectrometer for LARN

An elastic recoil detection time of flight system to depth profile light elements has been developed on ALTAÏS, the new Tandetron accelerator at LARN. The detector mounted at 45° from the beam axis consists of two isochronous electron detectors for the timing signal (START and STOP) and a 450 mm² heavy ion PIPS detector that detects the energy of the recoil atoms. The 2MV Tandem accelerator provides heavy ion beams with a maximum energy of 16 MeV depending on the charge transfer efficiency of the gas exchange canal located in the middle of the machine. A large variety of primary ion beams like ²⁸Si, ³⁵Cl, ⁶³Cu, ¹²⁷I or ¹⁹⁷Au can be produced with the SINIX heavy ion source and accelerated on the target. Typical current around 1 nA can be obtained. The energy transfer to the recoil atoms is typically in the MeV range and depends on the mass and the energy of the projectile. Some secondary effects like the energy loss in the carbon foils of the timing detector but also in the entrance window of the energy detector should not be neglected if we try to depth profile light elements with this technique. Time resolution of about 1 ns for the electrons detectors is suitable to obtain 1 amu mass resolution. Some examples of applications will be developed in this paper.     

用转移反应研究6He奇特核体系的光学势

由于受到放射性束强度弱、品质差的限制,奇特核体系的光学势性质一直是亟待解决的国际难题。本工作利用稳定束的转移反应作为探针,深入研究了反应出射道奇特核体系的光学势性质。利用中国原子能科学研究院的HI-13串列加速器在近库仑位垒能区高精度测量了⁷Li+⁶³Cu、²⁰⁸Pb的弹性散射以及单质子转移反应角分布,并利用扭曲波玻恩近似（DWBA）和耦合反应道（CRC）方法对实验数据进行了拟合,抽取了出射道⁶He+⁶⁴Zn、²⁰⁹Bi晕核体系的光学势参数。所得参数可重现文献中已有的6He体系的弹性散射角分布,验证了这种方法的可靠性。对所得势参数的能量相依性的分析表明,在重体系⁶He+²⁰⁹Bi中,基于因果律的色散关系并不适用,其潜在的物理原因还需进一步深入研究。     

Determination of sulphur and copper depth distribution in patina layers using nuclear reaction techniques

A method for Cu and S profiling in patina layers was developed by applying a combination of nuclear reaction analysis (NRA) and Rutherford backscattering spectroscopy (RBS). The copper profiling was performed by using the 1327 keV γ-ray deexciting the third excited state to the ground state of ⁶³Cu produced by the reaction ⁶³Cu(p,p^′γ)⁶³Cu. For the determination of sulphur the 2230 keV γ-ray was used deexciting the first excited state to the ground state of ³²S formed through the reaction ³²S(p,p^′γ)³²S, which exhibits three sharp resonances at projectile energies 3.094, 3.195 and 3.379 MeV. The relevant cross-sections were measured in the energy range between 3.0 and 3.7 MeV in steps of 20 keV at 125° to the incident proton beam direction. The technique was tested using artificially produced and natural copper patina layers. Supporting information on the depth distribution of the constituent elements of the patina samples was obtained by p-RBS (E_p: 1.5 MeV, θ: 160°).     

Cobalt cross sections for 14 MeV neutrons

14 MeV cross sections for the reactions ⁵⁹Co(n,2n) ^58m+gCo, ⁵⁹Co(n,p) ⁵⁹Fe and ⁵⁹Co(n,) ⁵⁶Mn were measured relative to the ⁵⁶Fe(n,p) ⁵⁶Mn reaction employing the activation technique. Accuracies of about 1% were achieved for the (n,) reaction and 2% for the others. The isomeric cross section ratio was measured for the ⁵⁹Co(n,2n) reactions.

Nuclear reactions – ⁵⁹Co(n,2n) ^58m+gCo, ⁵⁹Co(n,p) ⁵⁹Fe, ⁵⁹Co(n,) ⁵⁶Mn, E_n = 14.3, 14.7 MeV: measured activation cross sections relative to ⁵⁶Fe(n,p) ⁵⁶Mn.

⁵⁹Co(n,2n) ^58m,gCo, E_n = 14.3 MeV; measured isomeric cross section ratio. Natural targets. Ge, NaI and 4πβ detectors.