Imaging Properties of a Positron Tomograph with 280 Bgo Crystals

The basic imaging properties of the Donner 280-BGO-Crystal positron tomograph were measured and compared with the same system when it was equipped with 280 NaI(T1) crystals. The NaI(T1) crystals were 8 mm × 30 mm × 50 mm deep, sealed in 10 mm wide stainless steel cans. The BGO crystals are 9.5 mm wide × 32 mm × 32 mm deep and as they are not hygroscopic do not require sealed cans. With a shielding gap of 3 cm (section thickness 1.7 cm FWHM) the sensitivity of the BGO system is 55,000 events per sec for 1 ?Ci per cm3 in a 20 cm cylinder of water, which is 2.3 times higher than the NaI(T1) system. For a 200 ?Ci/cm line source on the ring axis in a 20 cm diameter water cylinder, the BGO system records 86% of the scatter fraction and 66% of the accidental fraction of the NaI(T1) system. The lower light yield and poorer time resolution of BGO requires a wider coincidence timing window than NaI(T1); however, the ability to use full-energy pulse height selection with a 2.3-fold improvement in sensitivity results in an overall reduction in the fraction of accidental events recorded. The in-plane resolution of the BGO system is 9-10 mm FWHM within the central 30 cm diameter field, and the radial elongation at the edge of the field in the NaI(T1) system has been nearly eliminated.     

Positologica: A Positron ECT Device with a Continuously Rotating Detector Ring

A rotary positron emission computed tomography device is developed for human brain and animal studies. The device utilizes 64 rectangular BGO detectors arranged at unequal spacing on a circular ring. The detector ring is continuously rotated at a constant speed of 60 rpm or less. This single continuous motion of the ring with the detector array provides excellent sampling characteristics and high detector redundancy. The device has a field of view 24 cm in diameter with a slice thickness adjustable from 1 cm to 2 cm. Measured width of system response to a 2 mm diameter line source is 5.8 mm FWHM at the center and less than 9 mm FWHM within a circle 16 cm in diameter. Measured sensitivity including scattered coincidence events is about 17 kcps/pCi/ml for a 20 cm diameter water phantom and 2 cm thick slice.     

Measurement of HETP of SUS Dixon Ring and Porcelain Packing in Small-Scale Water Distillation Column for H2O-HTO Isotope Separation

Series of water distillations in a total reflux mode have been performed in a 100cm height column of 1.6cm I. D. in order to measure values of HETP for various packings, that is, one brass or three SUS Dixon rings and three porcelain packings. The HETP were measured by changing the vapor flow rate within the column. The SUS Dixon ring of 1.5 mm diameter and the porcelain packing of 1.2 mm O. D. had a small HETP (～5cm), but could not meet a large vapor flow rate because of a large pressure drop. The SUS Dixon ring of 6.0 mm diameter had a small HETP (～6cm) in the vapor flow rate under 2g/min, but the HETP value increased with increasing the vapor flow rate. The pressure drop for the ring, however, was almost constant in the range of these measurements.     

强激光与固体靶相互作用所致硬X射线剂量和能谱的实验测量

为了研究强激光与固体靶相互作用产生的电离辐射危害,本文在星光Ⅲ300TW强激光装置上开展了一系列激光打靶实验。实验使用的激光功率密度为5×10~(18)~4×10~(19)W/cm~2,激光脉冲能量为60~153J,靶为直径1mm、厚度1mm的Ta圆柱,本文分别对X射线剂量、X射线能谱和超热电子能谱进行了测量。实验结果表明,测量到的单发最大X射线剂量约为16.8mSv,靠近激光传播方向(0°),距靶50cm处;激光0°方向的X射线剂量随激光功率密度的增加而显著增加,激光90°方向的X射线剂量随激光功率密度的变化相对较小;测量到的X射线能谱可大致用含有两个X射线温度的指数分布函数描述,其中0°方向测量到的X射线温度为0.4~1.15 MeV,90°方向测量到的X射线温度为0.25~0.54 MeV;实测超热电子温度与Wilks定标率符合较好。     

Optimization Design of Crystal Thickness Combination for Dual-layer-offset DOI Detector for Brain PET

Dual-layer-offset crystal array is a low cost and simple scheme for positron emission tomography (PET) system to achieve depth of interaction (DOI) information. Different thickness combinations of two layer crystals influence system performances. Monte Carlo simulations using GATE toolkit were implemented to optimize the design by evaluating the performances of the system with different thickness combinations in this study. Eleven magnetic resonance imaging (MRI) compatible brain PET inserted systems with an inner diameter of 345 mm, dual layer LYSO of 20 mm total thickness and inner layer thickness varied from 0 mm to 10 mm with a step size of 1 mm were built. Six point sources in the x-axis of the center slice from x=0 cm to x=10 cm with an interval of 2 cm were simulated. The sensitivity at the center was calculated and the radial resolutions were evaluated using the reconstructed points by the filtered back projection algorithm. The results show that dual-layer crystal design has a slight sensitivity decrease, but can significantly improve the radial spatial resolution and the resolution uniformity compared with the single-layer design. With the thickness increase of the inner crystal, the average radial spatial resolution decreases and then increases, and achieves minimal at inner layer with a thickness of 8 mm. In conclusion, 8 mm in the inner layer and 12 mm in the outer layer is the optimal design for the brain PET system with 20 mm dual-layer-offset crystal proposed in this study.     

双层错位DOI脑PET探测器晶体厚度组合优化设计

双层错位晶体阵列是正电子发射断层成像（PET）仪获取作用深度（DOI）信息的一种低成本且简便的方案。为获得晶体厚度最优组合方案,本文使用GATE软件进行蒙特卡罗仿真研究。模拟兼容核磁共振成像（MRI）的嵌入式脑PET,环内径345 mm,使用硅酸钇镥（LYSO）晶体,2层晶体总厚度20 mm,内层晶体从0 mm到10 mm共11种厚度（间隔1 mm）;进行点源模拟实验,点源位于中心断层x轴上,偏移从x=0 cm到x=10 cm共6种情况（间隔2 cm）。计算中心点灵敏度;采用滤波反投影算法重建图像,评估径向空间分辨率。结果显示,双层晶体的设计相比于单层晶体灵敏度略有下降,但系统径向空间分辨率显著提高且其均匀性得到改善。随着内层晶体厚度的增大,视野平均径向空间分辨率先减小后增大,在内层晶体厚度为8 mm时达到最小。综上所述,所设计的双层错位DOI脑PET探测器晶体厚度最优组合方案为内层晶体厚度8 mm、外层晶体厚度12 mm。     

Line-Scanning Proportional Counter Camera

A new method was developed for imaging spatial distributions of photons, charged particles, or neutrons over large areas by a line-scanning camera. This camera uses a linear position-sensitive proportional counter (PSPC) based on resistance-capacitance (RC) position encoding. 1-6 Applications of this camera include low-dose, medium-resolution radiography of large objects (>2 by 2 m); and, in nuclear medicine, low-dose, whole-body radionuclide imaging and radiography with low energy photons (<150keV). A prototypic camera was built and tested to scan an area of 60 by 100 cm. The spatial resolution is 1 by 1 mm fwhm for radiography with 60-keV photons and 3 by 3 mm fwhm for radionuclide imaging with 50-keV photons (limited by collimator resolution). Compared to point-by-point scanning, the line-scanning method reduces the mechanical complexity of the camera and eliminates problems encountered in construction of large-area, high pressure PSPCs. This method is superior to the area PSPC for imaging objects >60 by 60cm.     

Longitudinal Drift and Fine dE/dx Sampling in Various Gas Mixtures

Results of measurements realized at 15 GeV/c in a tagged e/?/p beam are presented. A longitudinal drift detector of 88 cm total length consisting of 16 stages of 4.7 cm drift each was used. Fast shaped signals from the detector were processed in a set of Flash ADC's with 25 ns sampling interval, corresponding to 0.3 - 2.6 mm distance in the drift space. Resolution and particle separation efficiency obtained in mixtures of Ne + 10% C3H8, Ar + 5% C3H8, Ar + 20% CO2, C3H8 + 20% C2H6 and in pure CH4 are compared to the performance of a classical method of charge integration over large samples.     

D-T中子照射下贫化铀球、钒球介质内中子能谱和伴生γ能谱测量

为获得介质内中子能谱及伴生γ能谱的实验数据，在中心D-T中子照射下，用18mm×20mm的茋闪烁体探测器，测量了与D+束成45°角的水平方向距球心7、10、13、16、19、22cm位置处贫化铀球介质内的中子能谱和伴生γ能谱，以及钒球内与D+束成0°角、距离球心1.8、4.8和8.3cm处的中子能谱和伴生γ能谱。用MCNP/4B程序和ENDF/B-VI库数据对实验模型进行模拟计算，并与实验结果进行了比较。     

Dryout Heat Flux for Core Debris Bed, (III)

Mixture of cylindrical steel pellets and Al₂O₃ balls, which simulated the intact fuel pellets and fragmented claddings, respectively, was inductively heated in a 50 mm I.D. pyrex glass cylinder filled with water, to investigate the coolability of TMI-2 type degraded core debris bed. The size of steel pellets was 11 mm dia. × 11 mm for BWR, 8 mm dia. × 12 mm for PWR and 5.5 mm dia. × 9 mm for FBR and Al₂O₃ balls were about 2 mm in diameter. The height of the debris bed was 25 cm or lower.

The dryout heat flux does not level off up to a bed height of 25 cm or over for the TMI-2 type bed while 8 cm or so in the bed of only steel balls. The dependence of dryout heat flux on the system pressure agrees with the Lipinski's 0-D model by adopting a proper equivalent diameter. When a simple number-weighted average is used as the equivalent diameter, the prediction gives a fairly good agreement with the experiment for FBR type bed but underestimations for the PWR and BWR type beds. It should be noted, that the small balls of less fraction, not the large pellets, substantially govern the dryout. When the coolant flow is allowed from the bottom, however, the dryout heat flux is enhanced up to the level for the complete vaporization of coolant, and small amount of mass flux or circulation head can greatly improve the coolability.     

Quantification in positron emission mammography (PEM) with planardetectors: contrast resolution measurements using a custom breastphantom and novel spherical hot-spots

The authors have previously demonstrated that their Positron Emission Mammography-1 (PEM-1) system can successfully detect small (<2 cm diameter) tumors. Images in the current system are judged qualitatively for the presence of focal uptake of ¹⁸F-FDG. The authors are presently taking steps toward quantifying the emission images. To this end they have constructed a breast phantom and developed a novel technique for fabricating very small wall-less radioactive hot-spots. The hot-spots are made by adding ¹⁸F-FDG to a 25 mg/cc solution of Agarose in water. The heated solution is poured into spherical molds which are separated upon congealing to yield robust wall-less radioactive hot-spots. The hot-spots were uniform to within 1-5 parts in 100. Less than 0.1% of the total hot-spot activity leaked into the background in 30 minutes. Contrast resolution experiments have been performed with 12 mm and 16 mm diameter hot-spots in the breast phantom containing water with various amounts of background activity. In both cases, the observed contrast values agree well with the ideal values. In the case of the 12 mm hot-spot with a 350-650 keV energy window, image contrast differed from the ideal by an average of 11%. The image contrast for 12 mm hot-spot improved by 40% and the number of detected events decreased by 35% when the low energy threshold was increased from 300 keV to 450 keV     

薄型较大面积THGEM气体探测器的研制

为满足环形正负电子对撞机项目配置的需要,研制了薄型较大面积THGEM气体探测器。该探测器工作时不需要额外的腔室,并且其厚度能达到8 mm,较原来的11 mm有明显减少。其有效面积为20 cm×20 cm,其增益在Ar/iC_4H_(10)(97/3)工作气体中能达到10~4倍,最好能量分辨为30%,增益均匀性能达到88.5%,探测器增益也呈现出较好的长期稳定性。     

克量粉末样品中低比活度放射性核素的γ能谱分析

报道了缺少小直径圆盘状体标准源条件下,快速简便地测定固体粉末样品中多种人工放射性核素比活度的γ能谱分析方法。取1g左右样品,装在特制的塑料盒中,形成Φ26mm×3mm的小圆盘状。由于样品的比活度较低,采用低源距(1cm,记为H1)测量。由于没有与样品圆盒相同形式的体标准源,利用直径26mm的60Co平面标准源在高源距(25cm,记为H25)测定若干放射性核素平面源的活度及峰效率,再测定H1的平面源峰效率。然后源距在H1基础上逐次增加1mm以测量平面源的峰效率,拟合峰效率随距离变化的函数,模拟得到厚度为3mm圆盘体标准源的峰效率。最终测定了样品比活度(包含自吸收校正)。与样品中两种核素的放化分析结果比对,测定结果偏差≤4%。     

背光成像技术测量冷冻靶参数研究进展

建立了可见光背光成像装置,测量距离实现了4~30 cm可调,对应分辨率为0.7 ~4.6 μm,并可对样品仓内的冷冻靶进行有效的中心定位,定位精度达0.1 mm,获得了不同分辨率下的塑料靶球与玻璃靶球的背光影像。通过获得背光图像的能量密度图及靶球的光路追踪模型,建立了靶球内部DD/DT冰层厚度的精确测量及计算方法。研究发现,将背光成像技术与干涉条纹法相结合可获得一种无损测量透明聚变靶丸材料折射率的方法。结果表明,背光成像技术是透明冷冻靶有效的诊断方法。     

Monte-Carlo simulation of pinhole collimator of a small field of view gamma camera for small animal imaging

Needs in scintimammography applications,especially for small animal cardiac imaging,lead to develop a small field of view,high spatial resolution gamma camera with a pinhole collimator.However the ideal pinhole collimator must keep a compromise between spatial resolution and sensitivity.In order to design a pinhole collimator with an optimized sensitivity and spatial resolution,the spatial resolution and the geometric sensitivity response as a function of the source to collimator distance has been obtained by means of Monte-Carlo simulation for a small field of view gamma camera with a pinhole collimator of various-hole diameters.The results show that the camera with pinhole of 1 mm,1.5 mm and 2 mm diameter has respectively spatial resolution of 1.5 mm,2.25 mm and 3 mm and geometric sensitivity of 0.016%,0.022% and 0.036%,while the source to collimator distance is 3 cm.We chose the pinhole collimator with hole diameter size of 1.2 mm for our the gamma camera designed based on the wade-off between sensitivity and resolution.     

基于GATE的双平板正电子发射乳腺断层成像系统的仿真研究

采用Monte Carlo法仿真软件GATE,构建专用于乳腺成像的双平板正电子发射断层成像系统PEM并研究其性能。参考NEMA NU 4–2008标准,并在试验中略作改动。研究了PEM(positron emission mammography)的灵敏度、散射分数、晶体散射、计数率、固有空间分辨率等参数。结果表明,在350–650 keV能窗、6 cm平板间距下,系统灵敏度达14.17%,固有空间分辨率约1.2 mm;乳腺仿体活度为29.6 MBq时,噪声等效计数率NECR为1.508×105/s,满足PEM系统所需。     

氚示踪剂在土壤包气层实验中的应用

测定了土壤包气层中氚在天然条件和人工喷淋条件下的扩散系数,研究了氚示踪剂在黄土包气层中的迁移规律。实验结果表明,在华北地区黄土高原天然条件下,包气带中氚示踪剂以０．０３ｃｍ／ｄ速度迁移,纵向扩散系数Ｄｘ为０．１０ｃｍ＾２／ｄ;在２ｍ＾２实验坑中,以５ｍｍ／ｈ喷淋强度每天喷淋３ｈ的条件下,氚示踪剂以２．２７ｃｍ／ｄ的速度向下迁移,Ｄｘ为７．７５ｃｍ＾２／ｄ。     

X(γ)刀吸收剂量测量方法研究

利用自制的直径f160mm有机玻璃球形模体和能够插入球形模体中心的PTW31006型0.015cm3尖点电离室测量了3种X(g)刀的等中心处不同辐射野的吸收剂量,并与半导体探测器(灵敏体积为1mm2?.5mm)的测量数据进行了比对,对电离室和半导体探测器的不同适用范围进行了分析,给出了一种适合X(g)刀的吸收剂量测量方法。     

Optical Design of ECEI Diagnostic System for HT-T Tokamak

Electron cyclotron emission imaging system in the frequency range of 95 GHz -125 GHz is going to be constructed for a two-dimensional diagnosis of the electron temperature profiles and fluctuations on the HT-7 Tokamak. The optical design for the ECEI diagnostic system is completed. Because of the superconducting technology used in HT-7, the vacuum chamber is rather thick (630 mm), the height of the horizontal windows is limited (maximum 450 mm), which constrains greatly the ECE imaging Gaussian beam that passing through the windows. We here comes to make a design compromise between the number of the beams that can pass through the windows and the spatial resolution (around 1.1 cm). We also find that due to the field curvature of the optical system, the gaussian beams of edge channels are always overlapped. To flatten the field curvature, it is needed to insert a concave made of a material with a low refractive index (compared with the one used in the convex). But the suitable material has not been avail     

Submersion-Subcritical Safe Space (S) reactor

The Submersion-Subcritical Safe Space (S⁴) reactor, developed for future space power applications and avoidance of single point failures, is presented. The S⁴ reactor has a Mo–14% Re solid core, loaded with uranium nitride fuel, cooled by He–30% Xe and sized to provide 550 kWth for 7 years of equivalent full power operation. The beryllium oxide reflector of the S⁴ reactor is designed to completely disassemble upon impact on water or soil. The potential of using Spectral Shift Absorber (SSA) materials in different forms to ensure that the reactor remains subcritical in the worst-case submersion accident is investigated. Nine potential SSAs are considered in terms of their effect on the thickness of the radial reflector and on the combined mass of the reactor and the radiation shadow shield. The SSA materials are incorporated as a thin (0.1 mm) coating on the outside surface of the reactor core and as core additions in three possible forms: 2.0 mm diameter pins in the interstices of the core block, 0.25 mm thick sleeves around the fuel stacks and/or additions to the uranium nitride fuel. Results show that with a boron carbide coating and 0.25 mm iridium sleeves around the fuel stacks the S⁴ reactor has a reflector outer diameter of 43.5 cm with a combined reactor and shadow shield mass of 935.1 kg. The S⁴ reactor with 12.5 at.% gadolinium-155 added to the fuel, 2.0 mm diameter gadolinium-155 sesquioxide interstitial pins, and a 0.1 mm thick gadolinium-155 sesquioxide coating has a slightly smaller reflector outer diameter of 43.0 cm, resulting in a smaller total reactor and shield mass of 901.7 kg. With 8.0 at.% europium-151 added to the fuel, along with europium-151 sesquioxide for the pins and coating, the reflector's outer diameter and the total reactor and shield mass are further reduced to 41.5 cm and 869.2 kg, respectively.