多种β射线阻挡层及X射线产额精度对BIXS技术的影响

氚分析在聚变堆与核技术的研究中有着广泛的应用。BIXS 技术(β 衰变诱发X射线谱技术)是一项无损的氚分析技术,该技术的分析深度对于高原子序数的材料能达到100 m,对低原子序数的材料能达到1 mm。在BIXS 技术中,采用金属薄膜作为β射线阻挡层具有排除极化韧致辐射干扰、减少探测器信号堆积等优点。为了研究多种β射线阻挡层材料对BIXS 技术的影响,利用Monte Carlo 方法PENELOPE 并行模拟程序分别模拟了采用Al、Au 金属薄膜和Ar 气作为β射线阻挡层的BIXS 技术,并使用GENEREG 反演程序对模拟结果进行反演计算及比较。还讨论了韧致辐射与特征X射线产额计算精度、韧致辐射谱倾斜对BIXS 技术的影响。研究表明Al 金属薄膜最适合用作BIXS 技术的β射线阻挡层。Tritium analysis has an extensive application in the study of fusion reactor and nuclear technology. β-decay induced X-ray spectroscopy (BIXS) is a nondestructive tritium analysis technique, and it can detect deeper tritium distributions (~0.1 mm and ~1 mm for high-Z materials and low-Z materials, respectively). In the BIXS method, a metal film as β-ray stopping layer has advantages of eliminating the interference of polarizational bremsstrahlung and reducing the detector’s signal pile-up. In order to study the effect of several β-ray stopping layers on the BIXS method, in this paper, we use the Monte Carlo code PENELOPE to simulate the BIXS experiments using Al, Au metal films and Ar gas as the β-ray stopping layers, and then use the regularization method to calculate and compare the results. In this paper, we also discuss the effects of accuracy of X-ray yield and bremsstrahlung spectrum incline on the BIXS method. The study in this paper indicates that the Al film is the best β-ray stopping layer in the BIXS method.     

卵石材料在中子场下的次级放射性分析

由中国科学院近代物理研究所负责设计和建设的加速器驱动嬗变研究装置（CiADS）将建于广东省惠州市。作为一个核装置,CiADS在运行过程中会对环境造成次级放射性影响,因此评估CiADS对环境造成的次级放射性影响水平不仅对公众健康有重要意义,对屏蔽设计也具有一定的指导作用。利用241Am-Be中子源对兰州重离子加速器研究装置（HIRFL）附近的卵石材料进行了辐照实验,测量和分析了辐照后卵石样品内产生的24Na,54Mn,56Mn和27Mg的比活度等相关信息。通过对实验数据与利用蒙特卡罗程序Geant4模拟得到的各放射性核素比活度的比较,验证了Geant4模拟分析中子场下环境介质次级放射性这一方法的可靠性。进而利用Geant4模拟研究了CiADS质子加速器HEBT隧道底部屏蔽层外的中子能谱以及隧道底部屏蔽层外卵石层因中子活化产生的主要放射性核素的饱和比活度。分析结果表明,在合理的屏蔽设计条件下,CiADS运行期间泄露到屏蔽层外的中子活化环境中卵石材料造成的环境影响几乎可以忽略。The China initiative Accelerator Driven System (CiADS) is the first integrated ADS facility designed to study the safety disposal of nuclear waste. As a nuclear facility, it will cause radiological impact on the environment. Therefore, the assessment of radiological impact on the environment around this facility will not only meaningful to the public health, but also offers significant guides to the shielding design of CiADS. Pebble samplings were collected around the campus of the Heavy Ion Research Facility in Lanzhou (HIRFL) and irradiated by a 241Am-Be neutron source. Based on the γ-spectrum measured by a HPGe detector before and after the neutron irradiation, the specific activities of induced radionuclides 24Na,54Mn,56Mn and 27Mg in these samples were analyzed and compared with the Monte-Carlo simulation values obtained with the Geant4 toolkit. The comparison between the experimental and simulated results indicates that Geant4 toolkit is feasible for radiation impact assessment of nuclear facilities, such as CiADS. Then the neutron spectrum outside the concrete shielding of HEBT tunnel of the CiADS have been simulated by the Geant4 toolkit, and the saturation activities of the induced nuclides in the first 10 cm pebble layer have been predicted. The results show that the saturation activities of induced radionuclides in pebbles outside the CiADS shielding are much lower than their exemption values and their radiation impacts to the environment could be ignored.     

加速器驱动嬗变研究装置中关键材料的辐照损伤分析

反应堆中各结构部件的抗辐照性能,对整个系统的使用寿命及安全性有较大的影响。本工作通过MCNPx2.70蒙特卡罗软件建立CiADS散裂靶次临界反应堆模型,结合NJOY2016核数据截面处理软件制作的材料原子离位截面,在堆芯组件数分别为30,42,72盒的情况下分别计算和分析了316L、15-15Ti、SIMP 3种不锈钢材料和ZTA陶瓷作为候选结构材料的中子辐照损伤情况。当用作CiADS燃料包壳时,3种不锈钢材料中SIMP制成的包壳的R_dpa值最小,在燃料组件数为30,42,72盒的情况下其年辐照损伤量分别约为1.16,1.61和12.0 dpa/a。而ZTA制成的燃料包壳的R_dpa值均大于不锈钢材料的辐照损伤。在散裂靶次临界反应堆耦合区域,轴向上CiADS中心管在束靶作用面附近所受到的辐照损伤最大。燃料组件数为30盒时,由316L制成的中心管的辐照损伤率峰值约为2.7 dpa/a。