快速测定磷尾矿中14个稀土元素

矿物中稀土元素的含量是研究矿物形成和发展的科学依据。 中子活化分析具有灵敏度高,多元素同时测定,无试剂空白等优点,已广泛用于地质样品中稀土元素的分析。 地质样品成份复杂,干扰元素多,用仪器中子活化分析直接测定全部稀土元素是困难的,故必须采用放化分离。目前报道化学分离测定稀土元素的文章很多,但一般分离步骤都很复杂,且耗费时间。本法是将辐照后的样品用混合酸溶解,加适量的掩蔽剂,在pH=2.5     

NH-A型中子土基含水量测定仪的研制

本文介绍研制的NH-A型中子土基含水量测定仪,这是一种用来测量土基含水量的快速、精确、非破坏性的测量仪器。仪器测量误差≤±0.012g/Cm~3。     

在特定实验条件下的散射中子本底研究

研究了d-T中子源与探测器距离较近时,扣除实验大厅散射中子本底的方法。实验上采用屏蔽法,用了铀裂变电离室。用MCNP/4A程序和FENDL2库数据计算了实验大厅散射中子本底曲线。采用实验和计算相结合的方法扣除了在特定实验条件下的散射中子本底,方法是可行的。     

Design of the thermal neutron beam for neutron radiography at the Syrian MNSR

Neutron beam design was studied at the Syrian reactor (MNSR, 30 kW) with a view to generating thermal neutron beam in the vertical irradiation sites for neutron radiography. The design of the neutron collimator was performed using MCNP4C and the ENDF/B-V cross-section library. Thermal, epithermal and fast neutron energy ranges were selected as <0.4 eV, 0.4 eV–10 keV, >10 keV, respectively. To produce a good neutron beam quality, bismuth was used as photon filter. In this design, the L/D ratio of this facility had the value of 125. The thermal neutron flux at the beam exit was about 2.548 × 10⁵ n/cm² s. If such neutron beam were built into the Syrian MNSR many scientific applications would be available using the neutron radiography.     

岩石中多元素仪器中子活化分析及其在地学中的应用

采用仪器中子活化分析法测定了各种地质样品中20多个元素的含量。为了检验方法的准确度和精密度,分析了美国国家地质局的标准物质USGS-AGV-Ⅰ、USGS-BCR-1及美国国家标准局的NBS-1632煤粉,准确度和精密度的误差均小于15％。 用仪器中子活化分析法测定了日喀则蛇绿岩中稀土元素含量,通过对稀土元素地球化学特征的分析,我们认为日喀则蛇绿岩在地球化学性质方面相似于大洋中脊拉斑玄武岩,它们可能是形成于特提斯洋脊。     

辐照前富集微型堆中子活化法测定地质样品中稀土元素的研究

介绍了一种过氧化钠熔样、稀土元素、过氧化物共沉淀、阳离子交换树脂富集后，用ＩＮＡＡ分析方法在微型堆上完成１４个稀土元素的测定程序。该方法的探测下限各元素不等．最低Ｅｕ为８．４ｎｇ，最高Ｐｒ为３．９２μｇ，可满足土壤、水系沉积物和某些岩石样品的稀土元素分析。与纯仪器方法相比，不仅可完成Ｅｒ、Ｐｒ、Ｔｍ、Ｎｄ、Ｈｏ的测试．补充纯仪器法的不足，而且其它元素如Ｌａ、Ｃｅ、Ｓｍ、Ｇｄ、Ｌｕ、Ｄｙ、Ｅｕ、Ｙｂ、Ｔｂ等元素的测试灵敏度也得到很大程度的改善。     

CMRR中子自旋回波谱仪引束导管模拟研究

中国绵阳研究堆(China Mianyang Research Reactor,CMRR)采用由弯导管和直导管组成的引束导管偏转第三条冷中子管(C3)冷中子束第二端口(C32)上部区域内的中子束流,为自旋回波谱仪提供中子束。应用中子射线追踪程序McStas 2.5对引束导管进行蒙特卡罗模拟,从弯导管通道个数、曲率半径以及超镜因子三个方面,考察引束导管设计方案以验证其设计可行性。结果表明:1)弯导管通道个数设计值合理;2)弯导管曲率半径取值在谱仪与屏蔽体安装空间可接受情况下,应尽量大;3)弯导管超镜因子取2.5时,引束导管出口与样品处中子通量可达到最大强度。根据模拟计算结果,弯导管超镜因子设计值偏大,引束导管设计方案总体具有可行性。     

复杂环境条件下脉冲中子散射本底测量方法

介绍了在复杂环境条件下脉冲中子散射本底测量方法和计算公式,并在实验室进行了实验测量,分析了影响实验结果的因素。     

Measurement of the neutron total cross section of carbon at the Back-n white neutron beam of CSNS

To verify the performance of the neutron total cross-sectional spectrometer, the neutron total cross section of carbon is initially measured in the energy range of 1 eV to 20 Me V using the time-of-flight method. The measurement is performed at the Back-n white neutron source with a 76-m time-of-flight path using the China Spallation Neutron Source. A multilayer fast fission chamber with ~(235)U and ~(238)U is employed as the neutron detector. The diameter and thickness of the natural graphite sample are70 mm and 40 mm, respectively. Signal waveforms are collected using a data acquisition system. Off-line data processing was used to obtain the neutron time-of-flight spectra and transmissions. The uncertainty of the counting statistics is generally approximately 3% for each bin in the energy range of 1–20 Me V. It is determined that the results for the neutron total cross section of carbon obtained using ~(235)U cells are in good agreement with the results obtained using ~(238)U cells within limits of statistical uncertainty.Moreover, the measured total cross sections show good agreement with the broadening evaluated data.     

Supermirror neutron guide system for neutron resonance spin echo spectrometers at a pulsed neutron source

A neutron guide system for neutron resonance spin echo spectrometers has been constructed at BL06 of the Japan Proton Accelerator Research Complex, Materials and Life Science Experimental Facility. The spectrometers consist of two types of neutron spin echo instruments, a modulated intensity by zero effort instrument (MIEZE) and a neutron resonance spin echo instrument (NRSE), to cover a wide energy range for various sample environments. A neutron beam from the moderator is deflected by supermirror neutron guides, split, and separately guided into the MIEZE and NRSE. The characteristic wavelengths of the neutron guide tube for the MIEZE and NRSE are 2.9 and 4.9 Å, respectively. The cross sections of the exit of the MIEZE and NRSE guides are 15 mm × 50 mm and 30 mm × 50 mm, respectively. The neutronics and shielding design were optimized by using the heavy ion transport code system (PHITS), and the absolute average neutron fluxes at the exits of the MIEZE and NRSE guides are estimated to be 2.7 × 10⁸ and 6.9 × 10⁸ n/cm²/s/MW, respectively. The measured fluxes of the MIEZE and NRSE neutron guides are 0.56 and 0.95 times the calculated values, respectively.     

中子源屏蔽体尺寸和源室结构对本底的影响

采用蒙特卡罗粒子输运计算程序(Monte Carlo N-partical transport code,MCNP),就中子源屏蔽体和中子源室结构对屏蔽体不同探测位置的中子透射和反射情况进行了计算机模拟计算.计算采用的入射粒子分别为14 MeV和5 MeV的单能中子以及252 Cf自发裂变中子.从计算结果看,屏蔽体的尺寸和结构对中子透射的影响都比较明显;源室的结构和地坑也对本底产生较大影响.通过理论计算可以了解屏蔽体结构和源室情况对测量本底的影响,可为源室设计以及中子实验研究提供重要参考.     

罕见的地表低辐射水平区域:珊瑚礁区

相对于陆地辐射水平研究,珊瑚礁区的研究较为匮乏。利用高纯锗γ谱仪测量南海岸礁和环礁的珊瑚礁区沉积物中的放射性核素,得到:²³⁸U比活度均值为28.96 Bq/kg,²²⁸Ra为5.08 Bq/kg,²²⁶Ra为3.34 Bq/kg,⁴⁰K为24.36 Bq/kg。研究发现南海珊瑚礁区沉积物的辐射环境质量评价指数显著低于国际推荐值,南海珊瑚礁区沉积物的等当量镭指数为其它中国海区、中国均值、世界均值的等当量镭指数的10%左右,是高辐射本底区域的等当量镭指数的1‰,是地表环境中罕见的低辐射水平区域。     

D-D中子源产额的大角度伴随质子监测技术研究

利用伴随质子法对D-D源中子产额进行了监测,选择了双叉管靶室和三叉管靶室,在与入射D 束成90°、135°和178.2°的三个方向上,获得了伴随质子谱和中子产额,确定了进行准确的产额监测的实验条件,实验表明在大角度方向(178.2°)进行产额监测是可行性的.对实验结果及其不确定度进行了分析和讨论.     

Cold neutron source at KAERI, Korea

The HANARO (High-flux Advance Neutron Application ReactOr), an open tank in a pool type multi-purpose research reactor, generating a high neutron flux (fast: 2.1 × 10¹⁴ n/cm²/s, thermal flux: 5 × 10¹⁴ n/cm²/s) has been operating at 30 MWth since its first criticality in February 1995. The HANARO provides neutrons to various utilization and research groups for global competition. Based on the world-wide trend for an availability of cold neutrons and the national demand for taking full advantage of such a strong neutron source, Korean government decided to commence with the cold neutron source (CNS) project at the HANARO on 2003. The HANARO will be equipped with a vertical liquid hydrogen-moderated CNS within the next 3 years. A moderator cell, made of 1 mm thickness of aluminium 6061-T6, whose shape is a double cylinder type and is connected to a heat exchanger, establishing two phase flow by a natural convection. These components are contained in the vacuum chamber. The cold neutron flux will be 3.9 × 10⁹ n/cm²/s at the reactor face and approximately 8.4 × 10⁸ n/cm²/s at the location of the instruments. This paper presents the current status and future prospect of the CNS project driven by KAERI, Korea.     

Total cross-section of chromium at low neutron energies

The total neutron cross-section of chromium has been measured in the range 1.3 × 10^?4 to 30 eV by the transmission method with pulsed neutron time of flight techniques. A theoretical fit was performed giving a value of (3.25 ± 0.15) b for σ_abs at 0.0253 eV.