利用12C+96Zr弹性散射角分布研究96Zr的中子皮

中子皮是原子核的关键物理参数之一,对非对称核物质状态方程有重要的约束作用。本工作主要利用¹²C+⁹⁶Zr弹性散射角分布研究⁹⁶Zr的中子皮,首先采用Woods-Saxon势,通过改变实部势参数得到与实验数据拟合最优的1组光学势参数,然后利用双折叠势模型（DFM）计算⁹⁶Zr在不同中子密度分布下与¹²C的相互作用势,通过比较两组相互作用势,找出与最佳光学势对应的⁹⁶Zr核的中子分布均方根半径,从而得到⁹⁶Zr的中子皮厚度为0.087 fm,此结果与其他研究结果在误差范围内符合很好。     

兰州大学的中子发生器研制及应用展望

1988年兰州大学成功研制了3×10¹² s^-1的ZF-300强流中子发生器,主要用于核数据测量、材料辐照损伤等研究。为进一步开展活化法中子核数据测量、裂变物理等研究,兰州大学启动了基于倍压加速器的ZF-400强流中子发生器研制工程,该中子发生器的设计指标为D束流能量400 keV、D束流强度大于30 mA、D-D中子产额大于5×10¹⁰ s^-1,D-T中子产额大于5×10¹² s^-1。在裂变物理研究方面,已成功发展了描述裂变核断点裂变势的势驱动模型（potential-driving model）,并开展了中子诱发典型锕系核素裂变发射中子前裂变产物的质量分布计算研究;将potential-driving model植入Geant4程序,发展了用于裂变发射中子后裂变产物质量分布、动能分布、裂变中子能谱等模拟的蒙特卡罗方法,并开展了可靠性评估研究;研制了一套用于裂变产物实验测量的双屏栅电离室（TFGIC）,并完成了初步实验测试。在中子应用技术方面,为满足小型化中子应用技术系统的研发需求,兰州大学成功研制了长度984 mm、直径234 mm的紧凑型中子发生器,通过在引出加速电极和靶之间加电阻的方式产生偏置电场,实现对靶上二次电子的抑制。在自注入靶条件和150 keV氘束流能量下,D-D中子产额可大于5×10⁸ s^-1,该中子发生器已具备产生D-T中子产额大于10¹⁰ s^-1量级的潜力。完成了基于紧凑型D-T中子发生器的快中子准直屏蔽体的设计,并研发了基于微通道板的快中子成像探测器,初步D-T快中成像测试显示,图像空间分辨率约为500 μm。开展了基于紧凑型D-D中子发生器的核燃料棒²³⁵U富集度及均匀性检测系统研发,仿真研究表明,在D-D中子产额5×10⁸ s^-1条件下,对核燃料棒中10%范围内的²³⁵U富集度相对变化的检测置信度可达到99%。     

Investigation of neutron converters for production of optically stimulated luminescence (OSL) neutron dosimeters using Al2O3:C

This paper presents the optically stimulated luminescence (OSL) properties of neutron dosimeters in powder and in the form of pellets prepared with a mixture of Al₂O₃:C and neutron converters. The neutron converters investigated were high density polyethylene (HDPE), lithium fluoride (LiF), lithium fluoride 95% enriched with ⁶Li (⁶LiF), lithium carbonate 95% enriched with ⁶Li (⁶Li₂CO₃), boric acid enriched with 99% of ¹⁰B and gadolinium oxide (Gd₂O₃). The proportion of Al₂O₃:C and neutron converter in the mixture was varied to optimize the total OSL signal and neutron sensitivity. The neutron sensitivity and dose-response were determined for the OSL dosimeters using a bare ²⁵²Cf source and compared to the response of Harshaw TLD-600 and TLD-700 dosimeters (⁶LiF:Mg,Ti and ⁷LiF:Mg,Ti). The results demonstrate the possibility of developing an OSL dosimeter made of Al₂O₃:C powder and neutron converter with a neutron sensitivity (defined as the ratio between the ⁶⁰Co equivalent gamma dose and the reference neutron absorbed dose) and neutron–gamma discrimination comparable to the TLD-600/TLD-700 combination. It was shown that the shape of the OSL decay curves varied with the type of the neutron converter, demonstrating the influence of the energy deposition mechanism and ionization density on the OSL process in Al₂O₃:C.     

TEPC中子和γ分辨技术研究

混合辐射场中子剂量、剂量当量的测量需进行中子、γ分辨。依据各种辐射沉积线能的不同,组织等效正比计数器（TEPC）具有一定的中子、γ分辨能力。本文采用自制的圆柱形TEPC在5SDH-2加速器单能中子辐射场进行了微剂量谱测量,对其中子、γ分辨技术进行了探讨分析。采用¹³⁷Cs纯γ辐射微剂量谱匹配法,在²⁵²Cf、²⁴¹Am-Be中子辐射场进行了中子、γ分辨研究。分辨后的中子剂量当量与约定真值一致性较好,表明TEPC用于中子、γ混合辐射场的吸收剂量、剂量当量测量是可行的。     

医院中子照射器中子束流出口处热中子注量率的测量

医院中子照射器是基于微型反应堆而设计的专门用于硼中子俘获治疗（BNCT）的核反应堆装置,其额定功率为30 kW。在堆芯相对两侧分别设有一条热中子束流和超热中子束流用于病人照射,在热中子束流内引出一条实验用热中子束流,用于瞬发γ法测量病人血硼浓度。本工作利用²³⁵U裂变靶和白云母探测片测量了热、超热和实验用热中子束流出口处的热中子绝对注量率。结果显示,在30 kW额定功率运行时,热、超热和实验用热中子束流出口处的热中子注量率分别为1.67×10⁹、2.44×10⁷和3.03×10⁶ cm^-2•s^-1。以上结果达到了BNCT设计要求,并能满足瞬发γ测量血硼浓度的要求。     

缓发中子计数法定量235U、239Pu初步研究

利用缓发中子计数法对²³⁵U-²³⁹Pu混合物中²³⁵U和²³⁹Pu含量的快速测定进行了初步研究。在中国原子能科学研究院30 kW微型反应堆(简称微堆)垂直孔道辐照²³⁵U、²³⁹Pu以及²³⁵U-²³⁹Pu混合物样品30 s,冷却2 s,用缓发中子探测器测量100 s,得出²³⁵U和²³⁹Pu的探测限分别为0.14和0.18 μg;探测器效率为0.015 0±0.001 0;当²³⁵U和²³⁹Pu质量比m(²³⁵U)/m(²³⁹Pu)=1.2时,²³⁵U、²³⁹Pu含量计算值与标称值的相对偏差分别为0.8%和6.9%。     

利用HFETR制备有载体177Lu

¹⁷⁷Lu是一种优良的诊疗一体化医用放射性核素,其标记的放射性药物被广泛用于多种癌症的诊断和治疗。其中,有载体¹⁷⁷Lu的制备具有放射化学处理简单、¹⁷⁷Lu产量高等优点。为此,在高通量工程试验堆(HFETR)中利用热中子辐照¹⁷⁶Lu,开展有载体¹⁷⁷Lu的制备研究。本研究分别辐照天然Lu和富集¹⁷⁶Lu进行热实验验证,结果表明：天然Lu在2×10¹⁴ n·cm^-2·s^-1热中子通量下辐照13 d,生成¹⁷⁷Lu比活度约为0.87 Ci/mg,^177mLu杂质含量为0.009%;富集(86.5%)¹⁷⁶Lu在热中子注量率为1×10¹⁴ n·cm^-2·s^-1条件下辐照28 d,生成¹⁷⁷Lu比活度约为24.9 Ci/mg,^177m...     

Fusion-driven transmutation of selected long-lived fission products

The long-term radiological burden associated with nuclear power production is usually attributed to long-lived fission products (LLFP). Their lifetime and large equilibrium mass and hence radioactivity accumulated in the course of fission energy generation make their storage a rather formidable task to solve. Therefore the idea of artificial incineration of LLFP through their transmutation has been quite naturally incorporated into the concept of self-consistent nuclear energy system (SCNES) based primarily on fast breeder reactor technologies. However it is now acknowledged that neutron environment of fission facilities including fast breeder reactors does not seem most appropriate for LLFP transmutation. The issue has been then extensively developed within the framework of multi-component self-consistent nuclear energy system (MC-SCNES). Neutrons of specific quality required for LLFP transmutation are proposed there to be of non-fission origin. Given neutron excess available and neutron quality, a fusion neutron source (FNS) is appearing as the candidate No. 1 to consider for LLFP transmutation. Research on LLFP transmutation by means of FNS has very long history and has received an additional boost during the decade passed. In the present study, potential of thermal flux blanket of FNS is exemplified by transmutation of ⁹³Zr and ¹²⁶Sn, the most difficult LLFP to transmute. It is shown that transmutation of ⁹³Zr is effective even with a rather modest neutron loading of 1 MWt·m⁻², typical for ITER project. Transmutation of ¹²⁶Sn, however, requires neutron loading of as high as 3 MWt·m⁻² for DD fusion and is quite unattractive for DT fusion. In the latter case, transmutation through the threshold (n,2n) reaction may be preferable.     

用于医用核素钼-99的制备方法

⁹⁹Mo的衰变子体核素^99mTc是核医学中应用最为广泛的放射性同位素,其使用量约占所有放射性同位素的70%。基于对目前国内外⁹⁹Mo制备方法的文献调研,阐述了医用⁹⁹Mo的主要制备方法,包括反应堆生产⁹⁹Mo、加速器制备⁹⁹Mo和中子发生器制备⁹⁹Mo。从靶件形式与化学提取等方面重点分析了以高浓铀（HEU）或低浓铀（LEU）为靶材料,利用反应堆生产裂变⁹⁹Mo的方法。鉴于近年来使用加速器与中子发生器制备⁹⁹Mo的方法已取得了较大进展,本文亦对此进行了较详细的阐述,并对进一步的研究工作提出建议。     

CARR堆冷中子瞬发伽玛活化分析系统及实验研究

利用中国先进研究堆（CARR）在国内首次开展了冷中子瞬发伽玛活化分析（CNPGAA）实验,采用定制加长的电制冷高纯锗（HPGe）探测器和先进的数字多道谱仪DSPEC®-502进行测量,获得了NH₄Cl样品中元素冷中子瞬发伽玛谱和本底谱等数据,同时利用伽玛放射源¹⁵²Eu、¹³⁷Cs、⁶⁰Co以及NH₄Cl产生的瞬发伽玛射线对探测器在宽能区0.1~8 MeV进行能量刻度。为降低环境辐射本底,HPGe探测器外围采用环形锗酸铋（BGO）康普顿谱仪,10 cm铅以及含⁶Li和¹⁰B材料对中子束流准直屏蔽。此外,利用金片活化法测量了CARR堆运行功率为15 MW时有无冷源情况下冷中子导管B(CNGB)末端1 m处的中子注量率,结果显示有冷源时中子注量率可提高一个量级。     

恒星中子源~(13)C(α,n)~(16)O反应的研究

13 C(α,n)16 O是渐进巨星支(AGB)星中慢速中子俘获(s)过程的主中子源反应,而17 O 6.356 MeV1/2+阈下共振对13 C(α,n)16 O反应影响很大。本文使用HI-13串列加速器和Q3D磁谱仪,首次测量了13C(11B,7Li)17 O转移反应角分布,确定了影响13C(α,n)16 O反应最关键、最不确定的17 O(Ex=6.356MeV)阈下共振态的α宽度,从而得出天体物理能区13 C(α,n)16 O反应的天体物理S因子和反应率,澄清了国际上已有S因子数据间高达25倍的巨大分歧。AGB星s过程核合成网络计算表明:新反应率数据导致恒星中铅的丰度增加了25%。     

中子能谱对压水堆慢化剂温度系数的影响分析

在压水堆中,水铀比和²³⁵U富集度是影响中子能谱分布的重要参数。本工作在不同水铀比、²³⁵U富集度下分析两群中子能谱随燃耗的变化。利用中子能谱分布对慢化剂温度系数的变化进行分析,结果表明：在给定²³⁵U富集度条件下,随着水铀比的变化,堆芯存在一慢化剂温度系数绝对值最大值;²³⁵U富集度的增加、燃耗的加深,不一定导致慢化剂温度系数绝对值增大。     

Nondestructive high-sensitivity measurement method for activation estimation in accelerator room concrete

This study established a method for easily and quickly estimating the specific activity produced in the concrete walls and floors of accelerator rooms during long-term operation of accelerator,for advanced zoning of activated/non-activated areas in planning the decommissioning of an accelerator.We propose a new,highly sensitive method for nondestructively estimating the specific activity in concrete that can be applied to activation zoning.In this method,instead of direct determination of the specific activities of important long-half-life radionuclides for decommissioning,such as ¹⁵²Eu and ⁶⁰Co,we determine the specific activities of short-half-life radionuclides,²⁴Na and ⁵⁶Mn,in situ to obtain neutron flux.The obtained neutron flux and accelerator operation history yield the specific activities of ¹⁵²Eu and ⁶⁰Co for the advance zoning of activated/non-activated concrete.This method is a powerful long-term prediction tool for concrete activation.     

Low temperature fast-neutron and gamma irradiation of glass fiber-epoxy composite. Part 2: Structure and chemistry

Structure and chemistry of S2-glass fiber-epoxy composite to fast-neutron and gamma irradiation at 4.2 K have been studied. Fast-neutron fluence ranged from 0.9 × 10²² to 1 × 10²³ n/m². At the neutron fluence of 3.1 × 10²² n/m², ordering of the amorphous S2-glass structure intervened. Ordering was followed by partial crystallization at the neutron fluence of 1 × 10²³ n/m². Although the epoxy matrix retained its amorphous structure, reactor irradiation induced crosslink formation and hydrogen evolution. These processes became significant at neutron fluences equal to or higher than 1.8 × 10²² n/m². No evidence has been found for hydrogen bubble or void nucleation at the glass-epoxy interface at the neutron fluence of 3.1 × 10²² n/m². Futhermore, sharp compositional changes measured at the glass-epoxy interface preclude an extended irradiation-induced atom mixing at this neutron fluence.     

252Cf生产关键技术及展望

²⁵²Cf是一种重要的超钚元素,可用于核反应堆启动、中子照相、中子活化分析、地质勘探等核技术应用及基础科研,目前世界上只有美国和俄罗斯具备²⁵²Cf生产能力。本研究对²⁵²Cf基本性质、国外²⁵²Cf生产现状进行介绍,提出²⁵²Cf生产需攻克的关键技术。     

利用测热技术测量核反应堆中子通量密度

一种新型中子探测器被研究,其原理是利用带电离子在矿物中沉积的能量退火时会以热量的方式释放出来,通过测量释放的热量而确定中子通量密度。对新型中子探测器进行刻度,在反应堆内某位置测量的热中子通量密度为5.108×10¹¹ cm^-2•s^-1,与标定的热中子通量密度(5.000×10¹¹ cm^-2•s^-1)在2%内符合,说明该探测器可测量中子通量密度。本文方法制作的探测器体积小,可制作成不同形状,便于反应堆不同环境下的中子通量密度测量。选取相应中子能量反应截面较大的元素,该探测器还可测量不同中子能量的通量密度。     

Prediction of (n,3He) cross-sections around 14 MeV

A comprehensive review of the neutron-induced cross-sections for (n,³He) reactions has been made for the interval of 14⩽Z⩽84 around 14 MeV neutron energy. For practical purposes, an empirical expression has been found by using the experimental (n,³ He) cross section values as a function of (N-Z) and (E_n-E_th) where (N-Z) is the neutron excess of the target nucleus, E_n and E_th are the incident neutron energy and the (n,³He) threshold energy, respectively. The derived empirical relation gives a good fit with the experimental values     

The simultaneous neutron and photon interrogation method for fissile and non-fissile element separation in radioactive waste drums

Measuring -emitters such as (^{234,235,236,238}U, ^{238,239,240,242,244}Pu, ²³⁷Np, ^241,243Am, …), in solid radioactive waste allows us to quantify the -activity in a drum and then to classify it. The simultaneous photon and neutron interrogation experiment (SIMPHONIE) method dealt with in this paper, combines both active neutron interrogation and induced photofission interrogation techniques simultaneously. Its purpose is to quantify fissile (²³⁵U, ^239,241Pu, …) and non-fissile (^236,238U, ^238,240Pu, …) elements separately in only one measurement. This paper presents the principle of the method, the experimental setup, and the first experimental results obtained using the DGA/ETCA Linac and MiniLinatron pulsed linear electron accelerators located at Arcueil, France. First studies were carried out with U and Pu bare samples.     

Neutron economy and nuclear data for transmutation of long-lived fission products

In the study of Self-Consistent Nuclear Energy System, the following 29 long-lived fission products (LLFPs) have been selected to be transmuted into stable or short-lived nuclides: ¹⁰⁶Ru, ¹⁰²Rh, ¹⁰⁹Cd, ¹²⁵Sb, ¹³⁴Cs, ^146,147Pm, ^154,155Eu, ¹⁷¹Tm, ⁸⁵Kr, ⁹⁰Sr, ^93mNb, ^113mCd, ^121mSn, ¹³⁷Cs, ¹⁵¹Sm, ¹⁵²Eu, ^108mAg, ¹⁵⁸Tb, ^166mHo, ⁷⁹Se, ⁹³Zr, ⁹⁴Nb, ⁹⁹Tc, ¹⁰⁷Pd, ¹²⁶Sn, ¹²⁹I, ¹³⁵Cs. In the present study, the number of neutrons necessary for the transmutation of the 29 LLFPs with an FBR was evaluated, and the present status of the (n, γ) and (n,2n) cross section data of the 29 LLFPs in JENDL-3.2 and ENDF/B-VI was investigated. The main results of the present study are as follows: (1)only 0.25 neutron per fission is necessary for the transmutation of the 29 LLFPs with isotopic separation, whereas 6.8 neutrons are necessary with chemical separation, (2)the accuracy of the cross sections is 30 to 100% except for the (n, γ) cross sections of limited nuclides in limited incident neutron energy regions.     

Fast neutron radiation effects in silicon detectors fabricated bydifferent thermal oxidation processes

High resistivity silicon detectors along with MOS capacitors made on five silicon dioxides with different thermal conditions (975°C to 1200°C) have been exposed to fast neutron irradiation up to the fluence of a few times 10¹⁴ n/cm². New measurement techniques such as capacitance-voltage of MOS capacitors and current-voltage and back-to-back diodes (p⁺-n^--p ⁺ if n^- is not inverted to p) or resistors (p⁺-p-p⁺ if inverted) have been introduced in this study in monitoring the possible type-inversion (n→p) under high neutron fluence. No type-inversion in the material underneath SiO₂ and the p⁺ contact has been observed for detectors made on the five oxides up to the neutron fluence of a few times 10¹³ n/cm². However, it has been found that detectors made on higher temperature oxides (⩾1100°C) exhibited less leakage current increase at high neutron fluence