背角无齿蚌对放射性核素富集作用的γ能谱分析

利用HPGe多道γ能谱仪对背角无齿蚌蚌肉、蚌壳及其天然生存环境样品中的238U、225Ra、223Ra、232Th、40K、137Cs、134Cs、210pb、103Ru、131I 10种放射性核素进行了测试分析.环境样品中检出238U、226Ra、232Th、210Pb、40K、137Cs;蚌肉中检出226Ra、232Th、210Pb、40K;蚌壳只中检出226Ra、232Th.结果表明,在天然本底环境下,蚌肉对226Ra的富集作用最强,对232Th、210pb的富集作用相对较强.对40K的富集作用相对较弱,富集系数由大到小的顺序为:226Ra＞232Th＞210pb＞40K;蚌壳对226Ra、232Th的富集作用较强,富集系数的大小顺序为:226Ra＞232Th,蚌壳对210Pb、40K的富集作用均非常弱;蚌肉对226Ra、232Th、210pb、40K的富集作用均强于蚌壳.本工作为合理开发利用河蚌这一自然资源提供了参考数据和科学依据.     

进口锆英砂放射性γ能谱分析

利用γ能谱分析技术对2个产地共17个进口锆英砂样品中的放射性核素226Ra、232Th和40K进行了定量分析,并提出了一种新的样品自吸收修正方法。结果:产地1样品中226Ra的比活度均值为2399.75Bq/kg,232Th的比活度均值为422.72Bq/kg;产地2样品中226Ra的比活度均值为1852.91Bq/kg,232Th的比活度均值为455.45Bq/kg;2个产地样品中40K的比活度均很低。研究表明,锆英砂样品中放射性主要来源是226Ra、232Th。两产地样品中232Th的放射性比活度相差较小,而226Ra的放射性比活度差别明显。同一产地样品中放射性核素比活度也存在较大差异。样品自吸收对分析结果的影响可达10%—30%,须进行自吸收修正。     

中国散裂中子源反角白光中子源束内伽马射线研究

在基于白光中子源的中子核反应测量中,伴随中子束的伽马射线是重要的实验本底之一.本文对中国散裂中子源反角白光中子源的束内伽马射线进行了研究.通过蒙特卡罗模拟,得到了伽马射线的能量分布和时间结构.通过直接测量和间接测量两种方法测得低能中子区的束内伽马射线的时间结构.直接测量实验中,将载6Li的ZnS(Ag)闪烁体探测器置于束流线上,通过飞行时间法直接测量束内的中子和伽马射线的时间结构,并利用波形甄别技术进行粒子鉴别.间接测量法是将铅样品置于束流线上,利用C6D6闪烁体探测器测量样品上的散射伽马射线,从而得到入射伽马射线的时间结构.实验测量结果与模拟结果在12μs—2.0 ms的时间区间内具有较好的一致性.     

石笋中放射性核素高纯锗分析方法

石笋是一种在地下溶洞中形成的碳酸钙沉积物,其生长过程中会吸收并固定周围环境中的各种核素,因此被广泛用作古气候和古环境的代用指标。然而,石笋中的放射性核素,如铀、钍等,对石笋的地球化学性质和环境指示意义有重要影响。因此,对石笋中的放射性核素进行准确测定,对于理解石笋的形成机制和环境指示意义具有重要意义。为了测出当中所包含的核素,通常利用γ谱学的内容,确定石笋中放射性核素的能量,从而找出对应的核素。高纯锗(HPGe)γ谱仪因其优越的性能,通过γ射线与谱仪上的高纯锗相互作用,可对石笋中放射性射线进行测量。对由中国计量科学研究院提供的¹³³Ba、²⁴¹Am、¹⁵²Eu三个标准点源在轴向距离探测器0 cm、5 cm处进行实验测量,通过Gamma Vision32软件进行能量刻度,获得能量与全能峰道址之间的关系,利用放射性核素总表找出能量所对应的核素,从而确定石笋中放射性核素。     

西藏ASγ实验首次发现PeV能量宇宙线源存在于银河系的证据

2021年4月2日,中国科学院高能物理研究所在京召开新闻发布会,宣布中日合作西藏ASγ实验观测到迄今为止最高能量的弥散伽马射线辐射,最高能量达957TeV,接近1 PeV.这些超高能伽马射线弥漫分布在银盘上,这是国际上首次发现拍电子伏特宇宙线加速器(PeVatron)在银河系中存在的证据.在同一天,日方合作组和美国物理...     

光谱和能谱法测定磷矿渣中放射性元素的含量和比活度

本文用红外光谱和X－射线衍射法研究了磷矿渣的基本成分,其主要相组成为玻璃体。用偶氮胂Ⅲ光度法测定了矿渣中铀和钍的含量,并用γ谱测定了放射性核素^226Ra,^232Th和^40K的比活度,为了解磷矿渣对环境的污染程度及其综合利用提供理论依据。     

D-T中子与平板型聚乙烯材料作用的次级中子角度谱实验研究

基于反冲质子法建立了一种测量D-T中子与平板型宏观样品作用的次级中子角度谱的实验方法.为保证探测器的能量线性并在较低的中子有效测量下阈(0.5 MeV)情况下获得好的中子-伽马射线甄别性能,采用高、低能段分别测量的方法.采用事件记录法,同时记录了次级中子和伴随伽马射线的脉冲形状甄别和脉冲幅度二维信息,利用基于ROOT数据分析平台编写的离线数据分析程序,完成了伴随伽马射线的挑选和扣除,以及高、低两能段反冲质子谱的拼接,并成功的将神经网络技术应用于中子能谱的解谱,获得了D-T中子与9和18 cm厚平板型聚乙烯材料作用的0.5-15 MeV的次级中子角度谱实验结果.实验模型的MC模拟由MCNP5完成,数据库采用ENDF-VI,实验结果和MC计算结果在实验不确定度范围内一致. 关键词： D-T中子 积分中子学 反冲质子法 次级中子能谱     

封底照片说明

 2004年11月20日,被命名为"雨燕"的伽马射线探测器,搭乘"德尔塔2"火箭升空,它将用于搜寻宇宙中的伽马射线暴,并揭开伽马射线暴与黑洞诞生的关系之谜。     

掺少量La、Ce薄铜膜的弱局域性及磁电导

本文报道了100(?)铜膜及加少量 La,Ce 后在1.5K 和40K 之间的电阻随温度的变化以及在固定温度4.2K 和1.5K 的磁电导.铜膜结果和文献一致.La,Ce 的加入对电子的自旋轨道散射有相近的影响.少量 Ce 的加入明显影响到电子的非弹性散射.加 Ce 样品电导随温度关系中的对数反常及磁散射行为难于用现有的弱局域理论解释.     

强激光驱动高能极化正负电子束与偏振伽马射线的研究进展

高能自旋极化正负电子束与偏振伽马射线在高能物理、实验室天体物理与核物理等领域有十分重要的应用.近年来随着超短超强激光脉冲技术的快速发展,利用强激光与物质相互作用的非线性康普顿散射和多光子Breit-Wheeler过程为制备高极化度、高束流密度的高能极化粒子束提供了新的可能.本文对基于强激光产生高能极化正负电子束与偏振伽马射线的研究成果进行简要回顾,并介绍了这些方法的基本物理原理和主要结果.     

利用强流ISOL束研究20Na的奇异衰变模式(英文)

北京放射性离子束装置（Beijing Radioactive Ion-beam Facility,BRIF）是基于在线同位素分离器技术的国家大科学平台。在BRIF装置上利用100 MeV的质子束轰击较厚的反应靶产生放射性核素;反应产物经离子源电离和在线分离,在线同位素分离段可引出100~300 keV的放射性核束,质量分辨率达20 000。在基金委科学仪器基础研究专项的支持下,建成了多用途的衰变实验终端,包括束流传输管道、通用靶室、带电粒子和γ探测器、集成电子学和数据获取系统等。利用100 MeV的质子束轰击MgO厚靶产生了流强高达1×105 pps的20Na放射性核束。通过高效率地同时测量β,γ和α,第一次直接观测到20Na非常稀有的β-γ-α衰变模式。Beijing Radioactive Ion-beam Facility(BRIF) has been commissioned as the national Radioactive Ion Beam(RIB) facility based on the Isotope Separator On Line(ISOL) technique since 2016. At BRIF, the radioactive nuclides are produced by the proton beam of 100 MeV bombarding a thick-target, the reaction products diffusing out of the target are ionized by an ion source and delivered to the online mass separator. In addition to the post-accelerated radioactive ion beams, BRIF can provide low-energy ISOL beams of 100 to 300 keV with a mass resolution of 20 000. A general-purpose decay station has been built including the ISOL beam transport line, a conventional reaction chamber, charge-particle and γ detectors with integrated electronics and data acquisition system. An intense 20Na ISOL beam up to 1×105 pps was produced by using the 100 MeV proton beam bombarding a MgO thick target. With high-efficiency measurements of β, γ and α simultaneously, very rare β-γ-α decay mode in 20Na has been directly observed for the first time in the present work.     

利用18O(6Li,d)22Ne反应研究22Ne Eα=470 keV共振态的性质

慢速中子俘获过程（s过程）是合成比铁重元素的重要途径之一。22Ne（α,n）25Mg反应是大质量AGB星中s过程主要的中子源,其中的22Ne主要通过14N（α,γ）18F（β+）18O（α,γ）22Ne反应链合成。该反应链中关键反应18O（α,γ）22Ne在天体物理感兴趣能区的截面非常低,其天体反应率主要来自于22Ne α分离阈附近低能共振态的贡献,但目前相关能级的共振参数严重缺失。在HI-13串列加速器的Q3D磁谱仪上,通过测量18O（6Li,d）22Ne反应的角分布,利用DWBA分析确定了22Ne分离阈附近共振能级E_α=470 keV的自旋宇称为0+,为后续计算18O（α,γ）22Ne的天体反应率打下了基础。About a half of the abundances of elements heavier than iron comes from the so-called slowneutron capture process (s-process) in Asymptotic Giant Branch (AGB) stars, with the 22Ne(α, n)25Mg reaction as one of the main neutron sources. In the beginning phase of AGB thermal pulse, 22Ne is produced by the 14N(α, γ)18F(β+)18O(α, γ)22Ne reaction sequence, in which the 18O(α, γ)22Ne reaction plays a key role. While the reaction rate of the 18O(α, γ)22Ne is mainly affected by several resonant states lying closely to the α threshold in 22Ne, up to now, the relevant 22Ne parameters are fragmentary in the energy region corresponding to the typical temperatures of s-process. The direct measurement of the 18O(α, γ)22Ne reaction rate is extremely difficult due to the very low cross section. In this work, we investigated the 22Ne resonant states via the 18O(6Li, d)22Ne reaction at the Beijing HI-13 tandem accelerator of China Institute of Atomic Energy. Based on the DWBA analysis, preliminary results showed that the spin-parity of 22Ne E_α=470 keV resonant states was assigned as 0+, which would make contributions to subsequent calculation for the reaction rate of the 18O(α, γ)22Ne.     

高准确度的钙离子光频标

近年来,冷原子技术和激光技术促进了高精度光频标的发展,有望在建立时间基准、推动基础研究和满足国家需求等方面发挥重要的作用.本文介绍了中国科学院武汉物理与数学研究所近年来在高准确度钙离子(~(40)Ca~+)光频标研究方面的进展:采用新的ULE腔系统,实现了729 nm钟跃迁激光器1—100 s的频率稳定度均优于2×10~(-15),通过对外场和环境效应的控制及克服,特别是囚禁离子运动效应的抑制,获得单个钙离子光频标的不确定度优于5.5×10~(-17);通过两台光频标的比对,测得20000 s的稳定度也进入10~(-17)量级;基于高精度钙离子光频标平台,进行了相关精密测量的工作,包括:基于全球定位系统的超高精度远程光频绝对值测量方案,第二次测量了钙离子的光频跃迁绝对值,该测量结果再次被国际时间频率咨询委员会采纳,更新了钙离子的频率推荐值;精确测量了钙离子的钟跃迁魔幻波长,由此提出新型的全光囚禁离子光频标的方法;精密测量了钙离子的亚稳态寿命等参数.以上工作推动了基于冷原子的精密测量工作.     

Achieving ultracold Bose-Fermi mixture of 87Rb and 40K with dual dark magnetic-optical-trap

We demonstrate that dual dark magnetic-optical-traps (MOTs) have great importance in the two-species ⁸⁷Rb and ⁴⁰K mixture compared with dual bright MOTs. The dark MOT has a little improvement in the trapping of single-species ⁸⁷Rb or ⁴⁰K gases compared with bright MOT. For the case of loading two-species ⁸⁷Rb and ⁴⁰K simultaneously, the improvement of ⁴⁰K in the dual dark MOTs is mainly from the reduction of light-assisted collision losses. The dual dark MOTs employ a pair of conical lenses to produce the hollow beam for repump laser with high efficiency. The number and density of ⁸⁷Rb and ⁴⁰K atoms after evaporative cooling in the hybrid magnetic trap with dark MOT loading are compared with those in bright MOT. The atoms with large number and high density make it easier to realize the quantum degenerate of Bose-Fermi mixture.     

Natural activities of U, Th and K in some Indian building materials

The activity concentrations of ²²⁶Ra, ²³²Th and ⁴⁰K have been determined by gamma-ray spectrometry. The measured activity in the selected building materials ranges from (3.2 to 151.7 Bq/kg), 14 to 63.7 Bq/kg and 24.3 to 121.5 Bq/kg for ²²⁶Ra, ²³²Th and ⁴⁰K respectively. The activity concentration of ²³⁸U has been determined using fission track technique and the value ranges from 0.11 to 3.85 ppm. The concentrations for these natural radionuclides are compared with the reported data from other countries. Radium-equivalent activities (Ra_eq) are calculated for the measured samples to assess the radiation hazards arising due to the use of these materials in the construction of dwellings. All building materials have shown Ra_eq activities lower than the limit set in the Organization for Economic Cooperation and Development (OECD) report (370 Bq/kg), equivalent to external gamma dose of 1.5 mSvyr⁻¹. A good correlation has been observed between ²³⁸U and ²²⁶Ra in these materials.     

238U（9Be,5n）242Cm熔合蒸发反应激发函数测量（英文）

第一次测量到238U（9Be,5n）242Cm熔合蒸发反应的激发函数。通过使用叠层靶,在不改变束流能量的条件下,在线获得20个能量点下的实验数据。利用蒸发余核242Cm的半衰期较长,且衰变模式是α衰变的特点,用离线测量α放射性的方法得到目标核产额。实验最大截面约1 mb,激发函数曲线的形态和峰值所在的能量位置与现有的理论模型的计算结果一致。激发函数的实验数据对选择和优化理论模型,推动超铀核区核物理研究具有重要的意义。The excitation function of the 238U(9Be, 5n) reaction was obtained for the first time. By using a stack of uranium targets, 20 experimental data were obtained by the on-line irradiation without changing beam energy. Taking the advantage of the long lifetime and α decay mode of the residue nucleus 242Cm, the off-line measurement of the α radioactive was performed to obtain its yields. The maximum cross section is about 1 mb. The curve's shape and the maximum's position agree with the present model. The value of the cross section will help us to develop the ralated models, and push the nuclear studies in the transuranium region.     

Gamma decay of K levels

Electromagnetic transition rates between states in ⁴⁰K up to 2.6 MeV excitation were investigated. The reaction ³⁷Cl(, nγ)⁴⁰K was used for lifetime measurements with the DSAM, and the reaction ⁴⁰Ar(p, nγ)⁴⁰K for the derivation of spins and mixing ratios from angular distributions. The transition strengths between states of predominant particle-hole character are well described by a rather simple shell-model structure with empirical effective charges and moments.     

恒星氦燃烧关键反应12C(α,γ)16O天体物理S因子及其反应率

恒星氦燃烧阶段3α反应和12C（α,γ）16O反应相互竞争,两者的反应率共同决定了氦燃烧结束后12C与16O的丰度比,该比值是大质量恒星后继演化以及伴随的元素核合成过程的初始条件。目前,氦燃烧12C（α,γ）16O反应起始T₉=0.2处,天体物理模型要求的反应率的精确度要低于10%,然而尚未有实验或理论给出满足要求的结果。最为直接和可靠地获取12C（α,γ）16O反应率的方法,就是尽可能往低能区测量其天体物理S因子,然后通过理论外推到感兴趣的能区。为此基于经典的R-矩阵理论,建立了适用于低能核反应的多道、多能级的约化R-矩阵理论来拟合几乎所有可用的16O系统的实验数据。配合使用协方差统计和误差传播理论,拟合外推得到了客观的、内部自恰的和唯一性好的12C（α,γ）16O反应天体物理S因子。总的外推S因子STOT（0.3 MeV）=162.7±7.3 keV·b,理论上首次给出达到恒星演化与元素核合成模型的最低要求的S因子。基于计算给出的全能区的S因子,数值积分给出了温度位于0.04 6 T₉ 6 10的12C（α,γ）16O天体物理反应率。在T₉=0.2处,推荐的反应率为（7.83 ±0.35）×10-15 cm3mol-1s-1。During stellar helium burning, the rates of 3α and the 12C(α,γ)16O reaction, in competition with one another, determine the relative abundances of 12C and 16O in a massive star. The abundance ratio is the beginning condition of the following nucleosynthesis and star evolution of massive stars, which are extremely sensitive to the rate of 12C(α,γ)16O reaction at T₉=0.2. The most direct and trustworthy way to obtain the reaction rate of the 12C(α,γ)16O reaction is to measure the S factor for that reaction to as low energy as possible, and to extrapolate to energies of astrophysical interest. Based on a new multilevel and multichannel reduced R-matrix theory for applications in nuclear astrophysics, we have obtained an accurate and self-consistent astrophysical S factor of 12C(α,γ)16O, by a global fitting for almost all available experimental data of 16O system, with the coordination of covariance statistics and error-propagation theory. The extrapolated S factor of 12C(α,γ)16O was obtained with a recommended value STOT (0.3 MeV)=162.7±7.3 keV·b. And the reaction rates of 12C(α,γ)16O for stellar temperatures between 0.04 6 T₉ 6 10 are provided. At T₉=0.2, the reaction rate is (7.83 ±0.35)×10-15 cm3mol-1s-1, where stellar helium burning occurs.     

全剥离离子94mRu44+的衰变研究

在兰州重离子加速器冷却储存环（HIRFL-CSR）上,用等时性质量谱仪首次研究了百微秒量级全剥离离子94mRu44+的衰变。94mRu44+由初级束流112Sn轰击Be靶产生,经过放射性束流线RIBLL2的筛选后注入到等时性设置的实验环CSRe中,并利用安装在实验环中的飞行时间探测器测量离子在CSRe中的循环周期。94mRu44+退激引起的质量改变会带来其循环周期的变化,由此直接观测到了94mRu44+退激到基态的过程。确定了本次实验中衰变事例探测的灵敏区间,并讨论了衰变发生时刻的测量精度。同时,测量了短寿命核素94mRu44+的质量,其半衰期约为100 μs,这是目前储存环质量谱仪测量的最短寿命核素的质量。The decay of the fully stripped ion 94mRu44+ in the order of one hundred microseconds has been studied for the first time by using the Isochronous Mass Spectrometry (IMS) at the HIRFL-CSR facility in Lanzhou. 94mRu44+ was produced via projectile fragmentation of a 112Sn primary beam bombarding on a 9Be production target. After the in-flight separation with RIBLL2, the ions were injected into the experimental ring (CSRe) and then stored there. The revolution times of the stored ions were measured by a Time-of-Flight (TOF) detector. Due to the mass change of a 94mRu44+ ion caused by its de-excitation to the ground state, hence the revolution time change, the decay process of 94mRu44+ could be directly observed in the CSRe. The sensitive window for detection of the decay events and the measurement precision of the decay time have been determined in this work. At the same time, we measured the mass of short-lived 94mRu44+ with the half-life about one hundred microseconds, which is the shortest among nuclides that have been studied by using storage-ring mass-spectrometry.     

Measurement of natural radioactivity in Jordanian sand

Sand samples were collected from Adasiah (near Amman), Jerash and Ghor As-Safi (near Karak). ²²⁶Ra, ²³²Th and ⁴⁰K activities, present in these samples, were measured using a gamma ray spectroscopy technique. The average values of the radium equivalent activities were calculated and were found to be 41.06 Bq kg⁻¹, 54.7 Bq kg⁻¹ and 85.53 Bq kg⁻¹ in samples collected from Adasiah, Jerash and Ghor As-Safi, respectively. These values are within the limit (i.e. less than 370 Bq kg⁻¹) recommended for the safe use of construction materials for dwellingsby OECD.