The Low Energy X-ray telescope (LE) onboard the Insight-HXMT astronomy satellite

The Low Energy X-ray telescope(LE) is one of the three main instruments of the Insight-Hard X-ray Modulation Telescope(Insight-HXMT). It is equipped with Swept Charge Device(SCD) sensor arrays with a total geometrical area of 384 cm^2 and an energy band from 0.7 to 13 ke V. In order to evaluate the particle induced X-ray background and the cosmic X-ray background simultaneously, LE adopts collimators to define four types of Field Of Views(FOVs), i.e., 1.6°×6°, 4°×6°, 50°-60°×2°-6 oand the blocked ones which block the X-ray by an aluminum cover. LE is constituted of three detector boxes(LEDs) and an electric control box(LEB) and achieves a good energy resolution of 140 e V@5.9 ke V, an excellent time resolution of 0.98 ms, as well as an extremely low pileup(<1%@18000 cts/s). Detailed performance tests and calibration on the ground have been performed,including energy-channel relation, energy response, detection efficiency and time response.     

The beta branching ratio and conversion coefficients in the137Cs decay

The decay of¹³⁷Cs has been reinvestigated using several precision counting methods. The emission rate ofβ-particles plus internal conversion electrons was measured by the 4π-proportional counter method using vacuum evaporated sources free of self-absorption and checked by the liquid scintillation method. TheK-conversion coefficient was determined by the electron X-ray coincidence method using a magnetic spectrometer and a high resolution Si(Li) detector. TheK/(L+M+...) conversion ratio and a second less accurate value for the β-branching ratio were obtained from the recorded electron spectra. Theγ-ray emission rate of all sources was determined to within ±0.14%, on the average, with a calibrated NaI(Tl) crystal detector. As results the intensity of theβ-decay to the ground state of¹³⁷Ba could be determined to (5.4±0.3)% of the¹³⁷Cs decays, theK-conversion coefficient to 0.0916±0.0004, and theK/(L+M+...) conversion ratio to 4.41±0.04. From these values the γ-ray emission intensity is (85.1±0.4)% of the¹³⁷Cs decays and theK X-ray emission intensity is (8.13±0.10)% of the emittedγ-rays. All errors are discussed in detail.     

The levels of144Pr from the decay of144Ce

The level scheme of¹⁴⁴Pr has been studied from the decay of¹⁴⁴Ce. The intensities and energies of gamma rays have been determined with a X-ray Ge(Li) detector. TheK-shell internal conversion coefficients for γ-rays have been measured with theK X-ray/γ-ray ratio method using NaI(Tl)—X-ray Ge(Li) coincidence techniques.     

THE INVESTIGATION OF THE HIGH DENSITY MULTIWIRE PROPORTIONAL CHAMBER AS A DETECTOR FOR NEUTRAL PARTICLES

This paper describes a position sensitive multiwire proportional chamber with effective area of 200×200mm². The chamber combining with multi-layer lead γ-ray converter form a high density multiwire proportional chamber γ-ray detector. The lead converter is made in auniformly arranged matrix of 0.9mm diameter holes on a 1.1mm pitch. For 511keV photons the detection efficiency is 5.6%, and the spatial resolution is 1mm. The detector has been used in the investigation of positron camera, it also offers possibility for X-ray detection.     

Full-Energy peak efficiency of an NaI(Tl) detector with coincidence summing correction showing the effect of the source-to-detector distance

The coincidence summing effect is considered to be one of the most important problems in γ-ray spectrometry. It has played an important role in the detector calibration process, especially at low source-to-detector distances, which are the typical conditions when the environmental samples have to be measured. In this work, the γ–γ coincidence summing correction factors (CSCF) for a 3″×?3″ NaI(Tl) γ-ray detector have been calculated at different distances from the detector end cap. These factors with NaI(Tl) γ-ray detectors have rarely been discussed in the previous literature, due to the lack of the separation process of the close gamma energy lines in the scintillation detector spectrum. The γ–γ CSCF were calculated for ⁶⁰Co, ¹³³Ba and ¹⁵²Eu radioactive point sources, which show the simple and the complex decay scheme of several radionuclides. In order to obtain the CSCF, the following parameters must be estimated by the numerical simulation method (NSM): the total efficiency (ε_T), the full-energy peak efficiency (ε_P) and the effective solid angle (Ω_eff). These parameters were calculated numerically depending on the direct mathematical method and efficiency transfer method. The obtained CSCF was used to correct the measured efficiency curves, which were measured at different distances, then compared to the ETNA and EFFTRAN programs, as well as the CSCF. The results show a good agreement, especially at large source-to-detector distances.     

BaF2 Scintillator Coupling with a Low-pressure Multistep Avalanche Chamber

We studied the properties of a UV light sensitive low-pressure multistep avalanche chamber containing pure TMAE vapour.The gain of two chambers with different constructure at various temperatures is measured.With pure TMAE vapour at 40°C the gain of one chamber was 4×10⁵,the time resolution was 4.1ns.Coupling the chamber with a 2×2×2.4cm³ BaF₂ scintillator we successfully observed the signal of ¹³⁷Cs γ-ray of 0.661MeV.     

二羟基丙二酸根乙二胺合铂的分子结构及晶体结构

用SYNTEX P3/R3四圆衍射仪收集到1672个独立衍射点,晶体属三斜晶系,空间群为P1,α=4526(15)?,b=6.0947(8)?,c=10.1854(15)?,α=106.48(I),β=103.65(I),γ=79.12(I),z=2,用Patterson法得到重原子铂的坐标参数,用Fourier法得到全部非氢原子的坐标参数,用块矩阵最小二乘法修正,最后的R因子为0.055,铂采取d²sp³杂化轨函成键及六配位八面体构型。 关键词：     

A new configuration of the Moxon–Rae detector based on Si detector

A new Moxon–Rae detector configuration based on Si semiconductor detector was proposed in this paper. Three γ-ray sources, ¹³⁷Cs, ⁶⁰Co, and ²⁴Na, were employed to make actual measurements using the new Moxon–Rae detector. The measured pulse height spectra and detection efficiencies were compared with the EGS4 simulated values. The results revealed that the proposed new configuration is indeed a successful method and specially a useful technique for higher energy γ-ray measurement.     

Low-lying 134Cs excited states from the (n, γ) reaction

Low-energy γ-ray and conversion electron spectra from the ¹³³Cs(n,γ)¹³⁴Cs reaction have been investigated with a bent cyrstal spectrometer, β-speetrometer, Ge(Li) and Si(Li) detectors. Gamma-gamma coincidence measurements were made with the Ge(Li)-Ge(Li) arrangement. Gamma-gamma delayed coincidences have been studied with the use of the Ge(Li)-NaI(Tl) coincidence set-up. The decay of 2.9 h ^134mCs has been investigated with the prism β-spectrometer and Ge(Li) detector. The half-lives of the 176.403 and 257.112 keV levels have been measured to be 49.7 ± 0.8ns and 12.3 ± 1.1 ns respectively. The neutron binding energy B_n have been calculated to be 6891.4 ± 1.3 keV. Spin and parity assignments have been made for almost all the levels. The possible structure of the levels deduced is discussed.     

基于微通道板的中子探测器γ射线灵敏度

研制了一种基于微通道板的超快脉冲中子探测器,对其γ射线灵敏度进行了理论和实验研究。建立了探测器的γ射线灵敏度理论计算模型,利用蒙特卡罗方法模拟计算了不同能量γ射线在不同厚度聚乙烯靶中产生的出射电子能谱和出射角度分布,并结合经验公式计算了单个电子在微通道板(MCP)孔道中产生的二次电子产额,最后得到了探测器的γ射线灵敏度,结果表明当聚乙烯靶厚度大于某一值时,γ射线灵敏度基本相同。利用西北核技术研究所的标准γ射线放射源对探测器的γ射线灵敏度进行了实验标定,实验结果与理论计算结果一致。     

Studying the radiation protection properties of materials via γ-ray attenuation over a wide range of γ-quanta

A setup for investigating the radiation protection properties of materials used in the manufacture of special protective clothing is described. The setup contains a collimated γ-ray source, a detector based on NaI (Tl) crystal, a movable platform for examining large areas of a material, and a data acquisition system based on a digital signal processor. A procedure for measuring the surface density of all absorbing elements in a material from the attenuation of γ-rays over a wide range of energies is described.     

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.     

An updated search of steady TeV γ-ray point sources in northern hemisphere using the Tibet air shower array

Using the data taken from Tibet Ⅱ High Density (HD) Array (1997 February--1999 September) and Tibet-Ⅲ array (1999 November--2005 November), our previous northern sky survey for TeV γ-ray point sources has now been updated by a factor of 2.8 improved statistics. From 0.0° to 60.0° in declination (Dec) range, no new TeV γ-ray point sources with sufficiently high significance were identified while the well-known Crab Nebula and Mrk421 remain to be the brightest TeV T-ray sources within the field of view of the Tibet air shower array. Based on the currently available data and at the 90% confidence level (C.L.), the flux upper limits for different power law index assumption are re-derived, which are approximately improved by 1.7 times as compared with our previous reported limits.     

HXMT卫星地面样机成像实验

硬X射线调制望远镜(HXMT)致力于实现硬X射线能段的高灵敏度巡天.HXMT地面样机已在中国科学院高能物理研究所粒子天体物理重点实验室建成.它包括18个栅条准直的NaI(Tl)/CsI(Na)复合晶体探测器,总有效探测面积为5000cm². 探测器工作在20—250keV,视场范围5.7°×5.7°通过近距离放射源成像实验和直接解调成像方法的使用,地面样机能够达到2'点源定位精度和5'角分辨率(FWHM).     

The effect of gamma de-excitation competition on the (α, n) and (α, 2n) reactions on gold and antimony

Absolute cross sections for P¹⁹⁷Au(α, n)²⁰⁰Tl ¹⁹⁷Au(α, 2n)¹⁹⁹Tl, ¹²¹Sb(α, n)¹²⁴I and ¹²¹Sb(α, 2n)¹²³I are measured in the energy range from threshold to 27 Me V.The experimental results are interpreted in terms of evaporation statistical theory, including gamma de-excitation. The values of the level density parameters and of the average γ-ray strength for the compound systems are extracted.     

碘化钠NaI(Tl)单晶闪烁探测器的应用

碘化钠NaI(Tl)单晶闪烁探测器由射线探测器、计算机多道、高压电源及线性放大器、计算机多道脉冲幅度分析器等部分组成。当放射源发出的γ射线进入闪烁体时,γ光子即与闪烁体中的原子、分子及晶体系统发生相互作用(如光电效应,康普顿散射和电子对效应等)。     

Performance assessment of Cs I(T1) screens on various substrates for X-ray imaging

Thallium-doped cesium iodide(Cs I(Tl)) screens are widely used in X-ray imaging devices because of the columnar structure of the Cs I(Tl) layer, but few reports focus on the optical role of the substrate in the screen system.In this paper, four substrates including fused silica(Si O2), silver-film coated Si O2, graphite(C) and fiber optic plate(FOP) are used to fabricate Cs I(Tl) screens by thermal evaporation. Their imaging performance is evaluated by relative light output(RLO), modulation transfer function(MTF), normalized noise power spectrum(NNPS) and noise equivalent quanta(NEQ). The results reveal that although Cs I(Tl) film on graphite plate yields images with the lowest light output, it presents relatively higher spatial resolution and better signal-to-noise characteristics.However, films on Si O2 plate obtain low MTF but high NNPS curves, whether they are coated with silver film or not.Furthermore, scintillation screens on FOP have bright images with low NNPS and high NEQ, but have the lowest MTF. By controlling the substrate optical features, Cs I(Tl) films can be tailored to suit a given application.     

Behaviour of Prompt Gamma-Ray Emission in ColdFission of 252Cf

The behaviour of prompt γ-ray emission in the cold fission of ²⁵²Cf was investigated experimentally using a four-parameter correlation technique. A twin gridded ionization chamber was employed to detect the fission signals and to determine the fragment emission angles, and a φ10cm×10cm NaI(T1) detector was used to record the γ-ray energies. The result shows that the angular distribution coefficient of γ-rays emitted in cold fission is twice as large as that in the normal fission.The fact that in the cold fission the number of γ-rays emitted from the light fragments is approximately three times as large as that from the heavy ones can not be explained satisfactorily so far.     

激光主动探测拼接光学系统的装调设计

介绍由两组视场为8°×6°的光学系统在水平方向拼接为视场不小于15°×6°的探测接收系统。为保证其在整个探测视场范围内的视场拼接质量和角定位精度，对该探测接收系统的装调方法及流程进行了详细设计，对各装调步骤的精度指标进行了分配。重点针对折转光路的光轴平行性、分辨率以及视场拼接的装调方法及要点进行阐述。通过对各装调步骤的精度进行严格控制，最终探测接收系统的测试结果为:焦距f ′=52.7 mm、视场15.2°×6.2°，达到设计指标要求。     

The decay scheme of 127Ba and half-lives of some low-lying excited states in 123, 125, 127, 129Cs

Radioactive sources of ^{123, 125, 127, 129}Ba obtained in the spallation reaction have been studied with Ge(Li), Si(Li), NaI(Tl) and plastic detectors. On the basis of γ-ray energies, intensities, energy sums and coincidence information, the decay scheme has been proposed for ¹²⁷Ba. No high-spin isomer of ¹²⁷Ba has been observed. The lifetimes of $\text{5}\text{2}$⁺ → $\text{1}\text{2}$⁺ transitions in ^{123, 125, 127, 129}Cs have been measured. No evidence for the shape isomerism in ¹²⁷Cs has been found.