超宽浓度放射性参考气DT制备装置设计及性能研究

为了满足流气式氚电离室测试和校准需求,须制备不同活度浓度的放射性参考气DT。借助秦山第三核电有限公司CANDU6堆中的含氚重水慢化剂和树脂净化系统,利用液体闪烁计数测量-电解法获得慢化剂活度浓度,质谱法分析电解气氢同位素丰度,并基于PVT指数稀释法,研制了超宽浓度放射性参考气DT制备装置。装置设计有催化-氧化-液体闪烁计数法验证单元,尾气收集-再利用处理单元,同时,样品制备时采用同位素浸润、内壁电镀等措施降低装置壁吸附-记忆效应。装置具有体积小、活度浓度范围宽、低浓度DT壁吸附-记忆效应小、交叉污染小、不确定度小等优点。制备的放射性参考气DT在标准状态下的活度浓度范围为4.0×10⁴～1.0×10¹⁴Bq/m³,放射性参考气DT可满足国内不同类型不同用途的流气式氚电离室测试、校准等需求。     

60Coγ射线空气比释动能绝对测量

为解决⁶⁰Coγ射线空气比释动能量值溯源与传递的问题以及进一步提升量值溯源与传递能力,中国测试技术研究院采用石墨空腔电离室以布拉格-格雷理论为基础测量光子辐射空气比释动能的方法建立⁶⁰Coγ射线空气比释动能绝对测量装置,复现⁶⁰Coγ射线空气比释动能,其量值复现的相对标准不确定度为0.2%。文中阐述和研究石墨空腔电离室结构和⁶⁰Coγ射线空气比释动能量值复现的影响因子。为进一步验证⁶⁰Coγ射线空气比释动能量值复现结果的准确性与一致性,中国测试技术研究院与加拿大国家实验室NRC (National Recerche Coucil),就⁶⁰Coγ射线空气比释动能量值复现进行测量比对,比对结果在相对标准不确定度0.52%以内一致,E_n值为–0.07。     

两种符合计数方法测定131I核素活度

采用4πβ(LS)-γ与4πβ(PC)-γ 2种数字符合计数法对放射性核素¹³¹I进行了活度测量，并对这2种方法得到的测量结果进行了不确定度评定。β道分别采用了以氩甲烷为工作气体的流气式正比计数器(PC)和制样简单的液体闪烁计数器(LSC)探测β射线。同时，运用可实现短寿命核素活度测量的数字符合计数法对β、γ脉冲序列文件进行离线处理，经过死时间修正和符合分辨时间修正后，给出用于效率外推的符合计数。结果表明，2种测量方法得到的¹³¹I核素的比活度在不确定度范围内一致，相对标准偏差为0.27%。     

氡子体体积活度的液体闪烁计数方法研究

基于液体闪烁计数原理和滤膜采样技术,建立了一种氡（²²²Rn）子体体积活度和α潜能浓度的测量方法。应用该方法对氡室中处于放射性平衡状态的氡子体体积活度进行了取样测量,氡子体α潜能浓度测量结果的扩展不确定度小于1.5%（k=2）;用α能谱法对氡子体液体闪烁计数测量方法进行了旁证,两种方法的测量结果在不确定度范围内一致。     

常温黑体光谱发射率校准技术研究

为了能够实现常温状态下的黑体光谱发射率的准确测量,基于连续可调激光器,搭建了一套中红外波段黑体光谱发射率测量装置。采用自行设计10 mA恒流源对MCT探测器进行驱动,测量结果的动态范围从7.29×10⁴提高到4.32×10⁵,有效提升了探测系统的动态范围。该装置实现了覆盖光谱范围7.5～10.6μm,发射率测量量值范围0.01～0.999 9的高精度测量,最优不确定度为4.0×10^-5(k=2)。     

富集10B的Ce:Li6Lu(10BO3)3晶体生长及其闪烁性能

为了提高中子探测效率, 以富集¹⁰B的H₃¹⁰BO₃为原料, 通过提拉法生长了富集¹⁰B的Ce:Li₆Lu(¹⁰BO₃)₃晶体。X射线激发发射光谱测试表明: 其发光峰位于360~480 nm, 属于Ce³⁺离子典型的5d - 4f跃迁发光, 其闪烁发光效率为BGO晶体的3.9倍。在350 nm紫外光和¹³⁷Cs所发出的662 keV的γ射线激发下测得的衰减时间分别为21.0 ns 和31.7 ns, 在¹³⁷Cs辐射源激发下所测得的相对光输出是CsI(Tl)晶体的20%, 能量分辨率为9.7%。在慢化²⁵²Cf中子源激发下可以观测到明显的中子全能峰, 其能量分辨率为33%。上述研究结果表明, Ce:Li₆Lu(¹⁰BO₃)₃晶体具有较高的闪烁效率、快的衰减时间和良好的中子探测效率, 是一种具有应用前景的中子探测用闪烁晶体。     

北湖污水处理厂深隧泵站水泵装置安装及调试

武汉北湖污水处理厂近期设计规模为80×10⁴m³/d,远期达到150×10⁴m³/d,是国内一次性建成规模最大的污水处理厂。首次在污水处理厂设置深度达46m、直径达43m的深隧泵站,用于提升大东湖深隧系统来水。本文介绍了深隧泵站大型水泵装置的选型、安装及调试过程,在水泵装置选型正确,安装精度满足要求,按步骤调试的情况下,确保了水泵装置正常运行。     

微小音速喷嘴临界背压比测试装置

音速喷嘴工作时的背压比小于临界背压比是实现并保持临界流的关键。现行国际标准建议,对于喉部雷诺数Red小于2×10⁵的音速喷嘴,需保持0.25的临界背压比或进行临界背压比的实际测量。基于此,建立了一套微小音速喷嘴临界背压比测试装置,该装置能够实现喉径为0.3~3mm,流量范围为0.05~5m³/h音速喷嘴临界背压比的测量,测量结果的扩展不确定度为0.56%(k=2)。     

90Sr/90Y放射源及外推电离室蒙特卡罗模型建立与实验验证

针对β射线次级标准装置(BSS2)中的⁹⁰Sr/⁹⁰Y放射源以及PTW23392型外推电离室进行蒙特卡罗(MC)建模。使用BEAMnrc计算⁹⁰Sr/⁹⁰Y放射源在不同校准位置处产生的组织深度剂量曲线,并与实验结果进行比较。根据模拟结果与实验结果的差异,修正放射源MC模型。此外,对外推电离室的外推曲线、校准位置处的组织透射因子和组织吸收剂量率进行模拟计算。在距离放射源30 cm和使用展平过滤的条件下,外推曲线的计算结果和实验结果基本吻合。组织透射因子和组织吸收剂量率的模拟结果与校准证书值相差分别在1.43%和2.11%之内。最终建立了较为准确的⁹⁰Sr/⁹⁰Y放射源和外推电离室的MC模型,研究结果可以为计算β参考辐射场中的注量谱、剂量转换系数和外推电离室相关的修正因子等提供参考。     

一种陶瓷砖吸水率检测装置的研究与设计

煮沸法检测陶瓷砖的吸水率时,现有的检测装置最少需将陶瓷砖搬运两次,且搬运过程中,陶瓷砖吸收的水容易蒸发或渗出,导致结果不准确^[1]。本文拟通过设计一种陶瓷砖吸水率检测装置,使样品在检测过程中无需多次搬运,且操作简便、节约人力,提高了检测工作的效率和精度。     

Three-detector setup for positron-lifetime spectroscopy of solids containing Co radionuclide

A three-detector BaF₂ positron-lifetime spectrometer is described. The spectrometer is suited for investigations of the neutron-irradiated reactor pressure vessel steels with a high content of ⁶⁰Co. Both timing and energy information about annihilation γ-rays is used for selection of coincidence events. In the triple-coincidence mode, the time resolution of around 220 ps FWHM and the coincidence count rate of 15 s⁻¹ for a 4 MBq ²²Na positron source are simultaneously achieved. Test measurements performed have shown that in this mode the ⁶⁰Co prompt-peak contribution in the positron-lifetime spectrum is suppressed to be below 1% when ⁶⁰Co activity of a pair of specimens studied does not exceed the level of 4 MBq.     

Excited levels in Po and Pb fed by β-decays of Bi (T1/2 = 45.6 min) and Tl (T1/2 = 2.2 min)

The γ-decay of radiochemically separated ²¹³Bi sources (T_1/2 = 45.6 min), in equilibrium with ²⁰⁹Tl (T_1/2 = 2.2 min) and ²¹³Po (T_1/2 = 4.2 μs), has been reinvestigated using coaxial HPGe detectors, a LEPS detector and the γ-γ coincidence method. The energies and intensities of 20 γ-lines were measured, of which 11 are reported for the first time. Of the ten γ-rays attributed to ²¹³Bi β-decay, five are new. All of them were interpreted in a ²¹³Po level scheme using γ-γ coincidence data. New levels at 292.8, 1003.6 and 1119.5 keV are proposed in ²¹³Po. In the ²⁰⁹Tl β-decay, five γ-lines were measured, two of which are new. On the basis of γ-γ coincidence, we suggest that two new levels of 3069.6 and 3388.9 keV are fed into the ²⁰⁹Pb magic nucleus.     

A coincidence system for radionuclide standardization using surface barrier detectors

A system for the standardization of alpha-gamma or electron-X radionuclide emitters is described. The system consists of one or two surface barrier detectors for alpha or electron detection which are coupled to thin-window NaI(Tl) crystals suitable for low-energy X- or gamma-ray detection. The performance of the system has been verified by the standardization of ²⁴¹Am, ¹³⁷Cs and ¹⁰⁹Cd solutions. The activity has been obtained using the extrapolation method applied to the 4π -γ and 2π e-X coincidence techniques. The surface barrier detection efficiency was varied by placing absorbers over the radioactive source or by changing the source-to-detector distance. The results were compared to those obtained using conventional absolute systems based on gas-flow and pressurized 4π proportional counters, or using radioactive solutions standardized in international comparisons sponsored by the Bureau International des Poids et Mesures, France. The expected and measured activities agreed within the experimental uncertainties, which were: 0.2% for ²⁴¹Am, 0.7% for ¹³⁷Cs and 0.6% for ¹⁰⁹Cd.     

Emission probability measurement of γ-ray of Rh

¹⁰⁵Rh becomes a stable ¹⁰⁵Pd after β⁻-decay with a half-life of 35.36 h. The energies of especially strong γ-rays emitted from ¹⁰⁵Rh are 306.1 and 318.9 keV, and the emission probabilities are evaluated to be 5.1±0.3% and 19.1±0.6% by de Frenne et al. To improve the certainty, the γ-ray emission probabilities were determined from the disintegration rate and absolute γ-ray intensities measured using a 4πβ(ppc)-γ(HPGe) coincidence apparatus with two-dimensional data-acquisition system. The results for the 306.1 and 318.9 keV γ-rays were 4.76±0.05% and 16.99±0.17%, respectively.     

A tritium gas-handling system for muon catalyzed fusion research at the RIKEN-RAL Muon Facility

A tritium gas-handling system has been constructed to produce a high-purity D–T target gas for precise measurements of the -sticking probability in the muon catalyzed fusion cycle at the RIKEN-RAL Muon Facility in the UK. At the experiment site, the system enables us to purify the D–T target gas by removing the ³He component, to adjust the D/T gas mixing ratio and to measure the hydrogen isotope components. The system is designed to handle D–T gas with a negative pressure; the total volume is 1.1 liter. The whole performance has been confirmed, and tritium gas with an inventory of 56 TBq (1500 Ci) has been operated in the system. We have completed a series of muon catalyzed fusion experiments at tritium concentrations of 99%, 70%, 60%, 50%, 40%, 28%, 20% and 10%, allowing a more precise determination of the -sticking probability.     

Measurement of fluorine total concentration in dental enamel using fast-neutron activation

Fluorine which is present in dental enamel, at the level of a few tens to a few hundred ppm, plays an important role in the behaviour of this tissue. Therefore its quantitative determination is of interest for particular studies of the dental system. We present a nuclear nondestructive method to determine the total fluorine content in dental enamel by cyclotron-produced fast-neutron activation. The ¹⁹F(n, 2n) reaction leads to ¹⁸F which is a β⁺ emitter with a 109.8 min half-life. The irradiated sample activity is measured by detecting in coincidence the annihilation photons. A fluorine standard is used for calibration. The detection limit is of the order of 1 ppm, while the reproducibility is better than 95%.     

Preliminary calibration of the ACP safeguards neutron counter

The Advanced Spent Fuel Conditioning Process (ACP), a kind of pyroprocess, has been developed at the Korea Atomic Energy Research Institute (KAERI). Since there is no IAEA safeguards criteria for this process, KAERI has developed a neutron coincidence counter to make it possible to perform a material control and accounting (MC&A) for its ACP materials for the purpose of a transparency in the peaceful uses of nuclear materials at KAERI. The test results of the ACP Safeguards Neutron Counter (ASNC) show a satisfactory performance for the Doubles count measurement with a low measurement error for its cylindrical sample cavity. The neutron detection efficiency is about 21% with an error of ±1.32% along the axial direction of the cavity. Using two ²⁵²Cf neutron sources, we obtained various parameters for the Singles and Doubles rates for the ASNC. The Singles, Doubles, and Triples rates for a ²⁵²Cf point source were obtained by using the MCNPX code and the results for the ft8 cap multiplicity tally option with the values of ε, f_d, and f_t measured with a strong source most closely match the measurement results to within a 1% error. A preliminary calibration curve for the ASNC was generated by using the point model equation relationship between ²⁴⁴Cm and ²⁵²Cf and the calibration coefficient for the non-multiplying sample is 2.78×10⁵ (Doubles counts/s/g ²⁴⁴Cm). The preliminary calibration curves for the ACP samples were also obtained by using an MCNPX simulation. A neutron multiplication influence on an increase of the Doubles rate for a metal ingot and UO2 powder is clearly observed. These calibration curves will be modified and complemented, when hot calibration samples become available. To verify the validity of this calibration curve, a measurement of spent fuel standards for a known ²⁴⁴Cm mass will be performed in the near future.     

A personal discriminating monitor for tritiated water vapor

A personal monitor for tritiated vapor in air based on scintillation is being developed by the Polytechnic of Milan and JRC of Ispra. A thin hygroscopic salt layer has been laid on the flat surface of a solid scintillator mounted inside the monitor. A small pump continuously supplies the monitor with filtered air samples taken from the room. The tritium oxide (HTO) in the air flow is reversibly trapped on the hygroscopic surface. A fraction of the beta particles emitted by tritium produces scintillation light in the solid scintillator which is detected by a miniaturized photomultiplier tube. The monitor can reveal HTO air contamination as low as 8×10⁵ Bq m⁻³–which is one-tenth of the limit for workers – in a short time (150 s). Several tests have been performed to check instrument response linearity and delay, the sensitivity to tritium and gamma-rays and the influence of other parameters such as air flow rate, relative humidity, vibrations and shocks.     

TRASMA, a detector for γ-charged particle coincidences

An apparatus for detecting light and heavy fragments, in coincidence with γ-rays is described. Its use is foreseen for studying heavy ion complete and incomplete fusion reactions at low and intermediate energy.

The ΔE-E and TOF techniques are used for charged particle identification at small angles using a combination of Si strip detectors and CsI(Tl) crystals. The γ-ray detection is performed by using a coverage of 9 clusters, each consisting of 7 BaF₂ crystals, similar to the TAPS configuration, resulting in a large solid angle and a high granularity. We report on recent results about the charged particle discrimination and the time and energy resolution for the whole detector. Initial tests were performed using ¹²C, ¹⁹F and ²⁸Si beams accelerated by the 15 MV tandem of the Laboratorio Nazionale del Sud in Catania.     

Production of 11C in Fullerene Cages: Short Half-Life Tracers

¹¹C “raditfullerenes” C_n1¹¹C (n = 60, 70, 76 to 84) have been produced, purified by high performance liquid chromatography, and characterized using optical absorption spectroscopy and an ultrasensitive coincidence counting technique for radioactivity measurement. The first successful direct labelling of the higher fullerenes C_n-1¹¹C (n = 76 to 84), in addition to C₅₉¹¹C and C₆₉¹¹C, suggests that well characterized ¹¹C radiofullerenes of various sizes could find possible applications as tracers in fluid flow systems (both biological and physical) and in porosity characterization of nanoscale membranes.