γ射线和PET用晶体单元相互作用特性的研究

γ射线与晶体单元的相互作用特性对于PET探测器的研制有着重要的参考意义. 通过实验测得了不同能量的γ射线在BGO, CsI, NaI 3种闪烁晶体中的探测效率、 能量分辨率等相互作用特性参数, 并与蒙特卡洛模拟结果进行了比较. 结果给出了最适合PET探测器的晶体单元. It’s important for development of PET detector that the interaction effect of γ rays and scintillator units are studied. The detection efficiencies and energy resolutions of γ rays for BGO, CsI and NaI crystal detector units are measured. Geant4 Monte Carlo simulations are compared with the experimental results. The results of the best detection units for PET detector are presented.     

液体闪烁体探测器γ射线测量研究

利用几种单能γ源对BC501A型液体闪烁体探测器进行能量刻度, 以得到探测器对电子的光输出响应函数。 介绍了用蒙特卡罗模拟法确定康普顿边缘所对应的电子能量的方法, 得到的结果与用半高点确定康普顿边缘方法所得的结果做了比较。 利用德国PTB开发的PHRESP蒙特卡罗程序计算出液体闪烁体探测器对各种单能γ射线的光响应矩阵, 阐述了利用γ射线响应函数矩阵和γ射线的反冲电子谱求解待测γ能谱的原理, 对解谱的误差来源也进行了简要的分析。 The light output of the BC501A liquid scintillation detector for γ rays was calibrated by serial monoenergetic γ ray sources. The Monte Carlo simulation method to confirm Compton edge was described briefly. The result was compared with that obtained by the semi height method. The γ ray response matrix of BC501A liquid scintillation detector was calculated by the Monte Carlo code PHRESP from PTB. The method of using response function matrix and recoil electron spectrum to unfold γ ray energy spectrum was introduced and the error of unfolding spectrum was also briefly discussed.     

上海激光电子γ源

激光具有高强度、 高极化度等优异的性能。 用激光束轰击高能电子束就可以产生高强度、 高极化度的γ射线束。 上海激光电子γ源就是上海同步辐射装置上的这样一条束线站。 预计可以获得能量范围为1—22 MeV的准单色、 高强度（109—1011 s-1）和高极化度（线极化或圆极化）的γ射线束。 介绍了这条束线站目前的进展情况。 Shanghai Laser Electron Gamma Source (SLEGS) is a high intensity,short pulse and compact γ ray source which is based on inverse Compton scattering via interaction between pulsed high power laser beams and picosecond relativistic electron bunches. One of the attractive features of the laser Compton scattering is the easy control of polarization of the produced high energy photons that duplicates polarization of the applied laser beam. The γ ray with energy up to 22 MeV and intensity of 109—1011s 1 are expected to be produced by Compton backscattering of CO2 laser photons on the 3.5 GeV electrons bunches in the Shanghai Synchrotron Radiation Facility (SSRF). In this communication, we report same simulation results and the progressing status of SLEGS.     

208Hg β衰变新γ射线的初步观察

利用８．４ＭｅＶ／ｕ的１８Ｏ束轰击天然铅靶，分离出汞元素产物，并以此研究２０８Ｈｇβ衰变的新γ射线．除已报道的γ射线以外，观察到对应于２０８Ｔｌ已知能级间跃迁的９条新γ射线.The Hg products produced in the bombardment of natural lead targets by 18 O beam of 8.4 MeV/u were separated by means of an off line gas thermochromategraphic device. The coincident gamma spectra and time successive single γ ray spectra were measured. Except the already known γ rays, nine new γ rays assigned to the transitions between the known levels of 208 Tl were observed.     

D-D 中子发生器n-γ 密度测井的蒙特卡罗模拟研究

根据D-D 反应中子的能谱和角分布数据,建立了中子源模型;根据石灰岩地层标准刻度井群数据,建立了井模型。采用MCNP 程序模拟了井中中子和γ 射线的输运,得到了不同地层密度和不同源距处NaI 探测器中的混合γ 射线能谱和非弹γ 射线能谱。在混合γ 射线能谱2.5~5.0 MeV 能区开窗,研究了开窗区混合γ 射线相对计数随源距的变化关系,确定源距应选择在30~80 cm 范围,给出了密度与混合γ 射线计数之间的非线性关系。研究表明,可以利用D-D中子源的混合γ 射线能谱来实现n-γ 密度测井。A D-D neutron source model was developed according to the neutron spectrum and the neutron angular distribution of D-D reaction. A standard calibration well model was built. The transports of the D-D neutrons and γ-rays in the well were simulated using MCNP code. The mixed γ-spectra and inelastic γ-spectra in the NaI detector were obtained for both different distances from a neutron source and different densities. Mixed γ count in the energy range of 2.5 to 5.0 MeV as a function of distance shows that the NaI detector should be located at a distance of 3080 cm from the neutron source. The nonlinear relationships between the density and the mixed γ count were presented in this paper.It was demonstrated that the energy spectrum of mixed γ rays can realize the n-γ density logging.     

用MC方法计算铅玻璃对核材料γ射线的屏蔽作用(已撤稿)

核材料辐射出的γ射线对人体有很强的辐射损伤, 实际工作中多用铅玻璃对其进行屏蔽。 以甲状腺为研究对象, 应用蒙特卡罗方法通用软件MCNP4B程序建立模型, 模拟计算了操作人员在操作核弹头时, 弹头中产生的γ射线透过各种厚度的铅玻璃时人体甲状腺吸收剂量率。 结果表明, 铅玻璃确有良好的降低γ射线吸收剂量率的作用。
The γ ray which is radiated from a nuclear material can cause serious radiation damage to human organs, so lead glass are often used as a shielding material. In this paper, thyroid was the subject investigated. A mathematical model was established by using the general software code MCNP4B. We have calculated a series of thyroid’s absorbed dose rate when the γ ray which was generated from the warhead penetrated the various depths of the lead glass via the model. The results indicate that lead glass work well as a protector against γ rays.     

176，178Os新低位激发态的识别

利用在束实验产生具有β^＋/EC衰变性质核素^176，178Ir，分析了在柬实验条件下获得的γ—γ符合数据，识别出了^176Os的4条新能级和13条新γ跃迁、^178Os的5条新能级和14条新γ跃迁。籍助氨喷嘴快速带传输系统，进一步对^176Ir的β’/EC衰变进行了测量，在确认在束测量新γ射线的同时建议了^176Ir的一个低自旋同核异能态。通过两准粒子耦舍的半经验计算，建议了^176，178Ir基态及同核异能态的组态。The γ rays following the β^＋/EC decay of ^176. 178Ir nuclei have been investigated using in-beam γ- ray experiment. A total of 4 new levels, 13 new γ transitions of ^176Os and 5 new levels, 14 new γ transitions of ^178Os were identified. In addition, with the aid of a helium-jet recoil fast tape transport system, the β^＋/EC decay of ^176Ir was further studied, the above new γ rays were proved and an isomer was proposed in ^176Ir. By the semiempirical calculations of two-quasiparticle intrinsic states of odd-odd nuclei, the configurations of ground states and isomeric states were also proposed for ^176, 178Ir     

First-principles calculations for the elastic properties of Ni-base model superalloys: Ni/Ni3Al multilayers

A model system consisting of Ni[001](100)/Ni3Al[001](100) multi-layers are studied using the density functional theory in order to explore the elastic properties of single crystal Ni-based superalloys. Simulation results are consistent with the experimental observation that rafted Ni-base superalloys virtually possess a cubic symmetry. The convergence of the elastic properties with respect to the thickness of the multilayers are tested by a series of multilayers from 2γ′+2γ to 10γ′+10γ atomic layers. The elastic properties are found to vary little with the increase of the multilayer’s thickness. A Ni/Ni3Al multilayer with 10γ′+10γ atomic layers (3.54 nm) can be used to simulate the mechanical properties of Ni-base model superalloys. Our calculated elastic constants, bulk modulus, orientation-dependent shear modulus and Young’s modulus, as well as the Zener anisotropy factor are all compatible with the measured results of Ni-base model superalloys R1 and the advanced commercial superalloys TMS-26, CMSX-4 at a low temperature. The mechanical properties as a function of the γ′ phase volume fraction are calculated by varying the proportion of the γ and γ′ phase in the multilayers. Besides, the mechanical properties of two-phase Ni/Ni3Al multilayer can be well predicted by the Voigt-Reuss-Hill rule of mixtures.     

一种基于阶梯阈值的射线违禁品探测方法

在γ射线违禁品探测技术中,快速准确的γ射线康普顿散射信号平滑具有非常重要的意义。现有的多项式平滑法和小波分析方法不仅运算速度慢,且易受噪声干扰,容易出现弱峰、谱峰错位等问题。为解决上述问题,提出一种新的基于阶梯阈值的散射信号分析方法。首先通过数据预处理,计算康普顿散射信号的基底变量,然后根据自适应阶梯阈值和测量差值,依次迭代更新背散射数据,进行信号滤波,最后自动检测峰位,实现可疑物识别。实验结果表明,相比现有的信号分析方法,阶梯阈值算法能够降低噪声干扰,保留康普顿散射信号的峰值和峰位,运算速度快,满足便携式探测设备的实时性要求。Fast and accurate Compton scattering signal smoothing plays an important part for γ-ray-based contraband identification.Traditional methods based on polynomial averaging or wavelet analysis are not only slow but also sensitive to noise,which makes them suffer from issues such as peak amplitude decrease and peak dislocation.A new method based on step threshold is proposed for scattering signal analysis,which can overcome aforementioned issues.Firstly,the base value for Compton scattering signal is computed via data pre-processing.Secondly,the scattering data is iteratively updated using adaptive threshold and system measurement,thus producing smoothed signal data.At last,the peak is localized from the filtered signal data and abnormality is identified.Experimental results show that our method is robust against noise compared to existing methods.The amplitude and location of the peak can be accurately perceived and identified.The method is efficient and can be deployed on portable contraband detection devices.     

NaI探测器对23.8 MeVγ射线的效率刻度方法

低能D(d,γ)4He辐射俘获反应截面的研究在聚变领域和天体物理等领域中起到非常重要的作用。由于受到标准γ源能量的制约,在研究D(d,γ)4He反应高能γ射线产额实验过程中不能用标准源进行效率刻度。采用实验测量与计算相结合的方法实现NaI探测器对23.8 MeV γ射线的效率刻度,先对6.13MeVγ射线效率进行实验刻度,然后用蒙卡程序MCNP－4C模拟计算出NaI探测器的效率曲线,再用实验数据与模拟结果进行对比校正,计算出NaI探测器在23.8MeV能量点对γ射线的探测效率。该方法对高能γ射线效率刻度给出了一种参考依据。In the study of D(d,γ)4He radiative capture reactions research, which is very important for fusion and astrophysics, the efficiency calibration of the detector is necessary. Due to the restriction on energy of the standard gamma source, the efficiency calibration of high-energy gamma-rays can not be calibrated by a standard source. In this paper, the method combining the experimental measurements and calculations for the efficiency calibrations of high energy gamma rays is given in the experiment of 6.13MeV gamma rays efficiency calibration using NaI detector, the efficiency curve of which is calculated by MCNP-4C and corrected experimentally. In this case, the detection efficiency of 23.8MeV gamma ray is known. The method provides a reference to high energy gamma ray efficiency calibration.     

MIRD体模肺部γ内污染探测效率分布的蒙特卡罗模拟

运用MCNP5程序,建立了基于MIRD数字体模的肺部γ内污染模型以及NaI(Tl)探测器模型,模拟计算了NaI(Tl)探测器对基于MIRD数字体模的肺部γ内污染的探测效率,获得了在多种空间位置上对沉积在肺部的9 种能量 射线的探测效率。模拟结果表明,在不同位置的探测效率并不完全符合人体肺部的解剖学结构,在右下肺位置可获得最高的探测效率,左下肺次之,左上肺最低。在探测器位置固定的情况下,探测效率随能量的增加,有先增高后降低的现象。In order to obtain detection efficiencies of nine kinds of gamma rays emitted by isotopes deposited in lungs at various measurement geometry, Monte Carlo N-Particle Transport Code 5 (MCNP5) has been employed to for calculation. The results show that the detection efficiency in different locations of lung is not completely accord with human body’s anatomy structure. The efficiency decreases gradually from lower-right lung, to lowerleft lung, and then to upper-left lung. When the location of detector is fixed, with the increase of energy, thedetection efficiency rises up firstly and then falls down.     

Preliminary experimental study and simulation of an energy-tunable quasi-monochromatic laser-Compton X/γ-ray source

We propose a slanting collision scheme for Compton scattering of a laser light against a relativistic electron beam. This scheme is suitable to generate an energy-tunable X/γ-ray source. In this paper, we present theoretical study and simulation of the spectral, spatial and temporal characteristics of such a source. We also describe two terms laser-Compton scattering (LCS) experiments at the 100 MeV Linac of Shanghai Institute of Applied Physics, where quasi-monochromatic LCS X-ray energy spectra with peak energies of ～30 keV are observed successfully. These preliminary investigations are carried out to understand the feasibility of developing an energy-tunable quasi-monochromatic X/γ-ray source, the future Shanghai Laser Electron Gamma Source.     

三级GEM探测器的增益一致性实验研究

随着二维GEM气体探测器在X射线成像探测领域的应用, 三级GEM的探测结构和电场均匀性带来的增益一致性修正问题, 成为需要深入研究的课题内容。 介绍了有效探测面积为100 mm×100 mm的三级倍增GEM探测器, 共采用100路阵列读出, 每路读出Pad面积为9.5 mm×9.5 mm。 测量了55Fe放射源准直入射的全能峰谱。 实验表明, 随着时间的变化, 探测器的增益基本上保持稳定; 随气流的增大, 增益由变化明显到变化不大。 GEM探测器各个阵列单元的增益一致性良好（>80%）; 能量分辨率在0.18～0.22之间, 运用最小二乘法拟合给出增益一致性的修正结果, 修正后相差约0.1, 为GEM气体探测器的增益一致性修正方法提供了参考方案。 With the application of the two dimensional GEM gaseous detector in X ray imaging, the correction method of gain uniformity caused by triple GEM avalanche structures and electric field uniformity should be studied. The paper reported the study of the triple GEM detector with effective area 100 mm×100 mm used the Pad’s size of 9.5 mm×9.5 mm. In the test, 100 readout channels were designed. Results showed that gain remained stable over time; as air flow increases, gain from increases obviously to changes very little. Particularly, triple GEM’s gain uniformity was very good (more than 80%) and the range of energy resolution was from 0.18 to 0.22. To improve gain consistency of results, the difference value revised was obtained to be about 0.1 by the least square method. It provided a better method to improve gain uniformity of GEM detector.     

Are operators describing b→sγ？

The operators of b→sγ, b→sl⁺l^- are usually regarded as being sufficient to describe b→sγγ, b→sl⁺l^-γ with the statement that contributions from diagrams without an effective vertex b→sγ to processes b→sγγ and b→sl⁺l^-γ are negligible. In this work we present a comprehensive analysis of the transition b→sγγ and find that 1) Effects due to off-shell quarks in vertex b→sγ on b→sγγ are large; 2) Contributions from diagrams without an effective vertex b→sγ to b→sγγ are not negligible compared with others; 3) These effects cancel each other out exactly, so the operators of b→sγ can safely be used to describe b→sγγ.     

康普顿背散射技术对贮存环电子束诊断及其应用-II贮存环电子束的极化度测量

简单介绍以激光 电子康普顿背散射原理为基础建立的康普顿背散射极化仪, 采用它能实时、 非破坏性地监测电子束的极化. 该项工作可作为上海激光电子γ源（SLEGS）低能γ束应用研究的内容之一. The Compton backscattering polarimeter is described briefly on the basis of the principle of Compton backscattering in this paper. The polarization of the electron beam can be measured and monitored on time and nondestructively. The project will be one of applications of low energy γ ray beam of SLEGS.     

Effect of size polydispersity on the structural and vibrational characteristics of two-dimensional granular assemblies

Two-dimensional disordered granular assemblies composed of 2048 polydispersed frictionless disks are simulated using the discrete element method. The height of the first peak of the pair correlation function, g1, the local and global gbond orientational parameters lψ6and ψ6, and the fluctuations of these parameters decrease with increasing polydispersity s,implying the transition from a polycrystalline state to an amorphous state in the system. As s increases, the peak position of the boson peak ωBP shifts towards a lower frequency and the intensity of the boson peak D(ωBP)/ωBP increases, indicating that the position and the strength of the boson peak are controlled by the polydispersity of the system. Moreover, the inverse of the boson peak intensity ωBP/D(ωBP), the shear modulus G, and the basin curvature SIS all have a similar dependence on s, implying that the s dependence of the vibrational density of states at low frequencies likely originates from the s dependence of the basin curvature.     

The geometrical acoustic method for calculating the echo of targets submerged in a shallow water waveguide

A geometrical acoustic method based on image-source method and physical acoustic method was developed to calculate the echo of targets submerged in the shallow water waveguide.The incident rays and the scattering rays are reflected by two boundaries for many times,and then the back rays become countless.The total backscattering field is obtained through summing up the scattering field produced by each combination of incident rays and back rays.The echo of the 10m-radius pressure release sphere in Pekeris waveguide with the range is calculated by the geometrical acoustic method.Compared with the results calculated by the wave acoustic method in the available literature,it shows that both are in accordance on average value and descend trend.The following results indicate that the difference between Effective Target Strength(ETS) in shallow water and the Target Strength(TS) in free space for spheres and certain other rounded objects is small.However,the ETS of some targets such as cone-shaped is quite different from TS in free space,which can lead to large errors in estimating a target’s scattering property using traditional sonar equation.Compared with the method of wave acoustics,the geometrical acoustic method not only has the definite physical meaning but also can calculate the echo of complex objects in shallow water waveguide.     

Study of n-γ discrimination for 0.4-1 MeV neutrons using the zero-crossing method with a BC501A liquid scintillation detector

An experimental system aimed at n-γ discrimination using the zero-crossing method with a φ3’’×2’’ BC501A liquid scintillation detector was established and tested with an Am-Be neutron source. Two-dimensional plots of energy versus zero-crossing time were obtained. The quality of n-γ discrimination was checked by the figure-of-merit (FOM), the neutron peak-to-valley ratio, and the proportion of leaked neutrons over all neutron events. The performance of n-γ discrimination in terms of FOM was compared with previous work done by other groups. The n-γ discrimination in four different energy regions with an interval of 0.1 MeV between 0.3 MeV and 0.7 MeV was studied, and the results indicate that the n-γ discrimination threshold can go down to 0.4 MeV.     

辐照诱变对小麦生理学效应的影响

以小麦品种小偃81为材料, 利用低能N+离子, 60Co-γ射线以及紫外线UV-C等为诱变源, 对种子胚部进行辐照处理。 研究其对小麦发芽势、 发芽率、 根长及苗高等生理指标的影响。 以辐照后的幼苗为材料研究了低能N+注入对过氧化氢酶（CAT）、 过氧化物酶（POD）、 超氧化物歧化酶（SOD）活性及还原型谷胱甘肽（GSH）含量的影响。 研究结果表明: N+注入后种子活力先升高后降低, 苗高在5×1017 N+/cm2时显著低于对照; 60Co和紫外线辐照对种子活力有较显著的影响, 辐照后的根长和苗高均显著低于对照; N+束辐照后的幼苗CAT酶活随剂量的变化规律性不明显, POD和SOD酶活总体趋势随剂量的增加先升高后降低, GSH含量随剂量的增大先降低后升高。 由此可知, 辐照诱变可以诱导小麦一系列的生理变化。60Co-γ射线和紫外线UV C对小麦胚根的伤害较大, 导致幼苗在后期大量死亡。N+注入对小麦的损伤效应较60Co和紫外线γ射线和紫外线UV-C小, 一定注量的N+注入处理可促进小麦生长。 In this paper, the biological effects,such as germination percentage, germination index and the length of seedlings and roots were investigated by using low energy N+, 60Co- γ rays and ultraviolet UV C to irradiate the embryos of wheat seeds （Xiaoyan81）. The anti oxidative enzyme system (CAT,POD, SOD) and GSH content were studied as well. The results show that the vitality of seed increased and then reduced with increasing the dosage of N+ ion implantation. The length of roots and seedlings were significantly higher than control. The seed vigor was significant effected after irradiated by 60Co-γ rays and ultraviolet UV-C, but the length of roots and seedlings were significantly lower than control. After N+ implantation, the changing pattern of CAT was not obviously. The enzymatic activity of POD and SOD were increased at low dosage and reduced at high dosage. The content of GSH was reduced and then raised. The results proved that the damage induced by γ ray and UV C to the radicle of wheat was severe that result in a large number of seedling died. However the damage induced by N+ implantation was lower than that by rays and UV C irradiation. Certain dosage of ion implantation can promote the growth of wheat.     

137Eu衰变的在线测量

使用在线同位素分离器及快带传输系统研究了缺中子稀土核137Eu的衰变性质,测量了A＝137核的γ、X单谱及γ-X、γ-γ符合谱,得到了137Eu核的半衰期为9．8s,并观测到了137Eu的一条能量为209．0keV的衰变γ线． The decay properties of neutron-deficient rare earth nucleus 137Eu have been studied by means of on-line isotope separator combined with rapid tape transport system.The products were produced by 190 MeV 36Ar bombarding on Pd target via natPd (36Ar, pxn)137Eu reactions. γ, X singles and γ-X, γ-γ coincidence spectra of the nuclei with A=137 were measured. The half-life of 137Eu is obtained to be 9. 8 s. A γ-ray with energy of 209. 0 keV for 137Eu was observed.