核部件缓发γ能谱时间演化行为模拟

在分析无外中子源照射条件下核部件中裂变产物的来源及其释放缓发γ射线机理基础上,提出了应用CINDER90程序计算核部件中裂变产物活度的方法,计算并分析了裂变产物的种类、活度及其随辐照时间和冷却时间的变化规律,继而根据裂变产物β~-衰变释放的特征γ射线的能量与分支比数据,计算得到了核部件中裂变产物缓发γ射线源项,并应用蒙特卡罗方法计算了核部件释放的缓发γ能谱随辐照时间和冷却时间的变化,分析了缓发γ能谱的时间演化行为。结果表明:核部件缓发γ能谱中强度最大的γ射线是裂变核素~(140)Laβ~-衰变发射的1 596 keV射线,且该γ射线的强度在部件组装一定时间后保持稳定,该结果与文献结果符合一致。本文提出的裂变产物缓发γ能谱模拟计算方法和结果可为核部件γ能谱的测量与分析提供参考。     

HPGe γ谱仪测量级联γ辐射152Eu、133Ba、60Co核素活度的方法

给出了HPGe γ谱仪测量级联γ辐射核素活度的一种实用方法,在探测器与样品之间放置一定厚度的水吸收层,能够很好降低探测效率,显著降低级联γ符合效应和偶然符合效应的影响。实验表明,TC-45样品中¹⁵²Eu、¹³³Ba、⁶⁰Co核素活度的探测效率和测量活度相对偏差随水吸收层厚度增加遵循指数衰减规律,当厚度增加到70 mm以上,其测量活度相对偏差小于4%。     

特征峰干扰判据K值法解析γ能谱

本文采用γ谱分析软件对土壤样品核素进行分析,针对分析时采用两条及以上特征γ射线给出样品核素活度值的情况提出了特征峰干扰判据K.得出:(1)对同一核素,若判据K近似为一个常数,则判定γ特征峰没有受到其他射线干扰,反之存在干扰.(2)判据K值不是常数时,要对样品中核素活度重新分析,给出校正值.     

γ能谱法分析放射性核素时对γ射线全能峰干扰的修正

针对在中核集团公司核电厂和“两厂两院”环境监测实验室比对中γ能谱分析存在的γ射线全能峰干扰问题,开展土壤中铀、钍、镭、钾、铯等γ核素测量实验。天然土壤标准源对谱仪进行效率刻度时,分析γ射线特征峰是否受到其它射线干扰,对受到干扰的γ射线通过修正代入效率计算的核素活度值以实现效率的拟合。由谱仪分析软件分析样品核素活度时,当利用不同特征γ射线计算的核素活度相差较大时,应进行活度修正。分析用于核素活度计算的γ特征峰(如²³⁵U 185.7 keV,²³⁸U 92.6 keV)受到的干扰峰,计算干扰峰对测量能谱峰(重峰)活度贡献,扣除干扰峰活度,即为γ特征峰贡献,由此给出样品核素活度值。这种方法在中核集团土壤样品比对中报出的²³⁸U、²²⁶Ra、²³²Th、⁴⁰K和¹³⁷Cs数据全部合格。     

总剂量和重离子协同作用下浮栅单元错误的退火特性研究

针对25 nm商用Flash存储器,利用中国科学院新疆理化技术研究所的60Coγ射线源和兰州重离子加速器先后进行了总剂量效应和单粒子效应实验。实验中器件先辐照30 krad(Si)的γ射线,然后再辐照不同线性能量转移(Linear Energy Transfer,LET)的重离子,得到了不同条件下Flash存储器浮栅单元错误的退火特性。实验结果表明与只进行重离子辐照相比,总剂量和重离子协同作用下器件浮栅单元错误消失的比例会发生变化,且在不同LET离子的辐照下表现出相异的趋势。分析认为辐照总剂量会引起浮栅单元电荷丢失和电荷俘获,影响浮栅单元的错误退火特性。     

直接测量~(109)Cd活度

~(100)Cd是一个重要的低能γ射线源和X射线源,其半衰期为462.6d。广泛地用于刻度半导体谱仪的效率和X射线荧光分析中作为X射线源。本文介绍了利用4πβ(PPC),4πβ(L,S)和4πe-γ符合法测量~(109)Cd活度的原理,并对几朴方法作了比较和讨论。     

辐射交联超高分子量聚乙烯热稳定性及蠕变性能

本文研究了γ射线对超高分子量聚乙烯(UHMWPE)热稳定性和抗蠕变性能的影响规律.首先,将常规UHMWPE粉末通过硫化成型机热压成1 mm厚的板材,采用γ射线对板材样品进行辐照处理,研究辐照后样品的化学结构、热稳定性、微观形貌以及拉伸和蠕变性能的变化.结果表明:γ射线辐照后,熔点和结晶度增加,热稳定性提升,凝胶含量最高...     

准单能6—7MeV γ射线参考辐射场的建立和对6.13MeV能点γ探测效率的绝对刻度

建立了准单能6—7 MeVγ射线参考辐射场并介绍了有关特性;重点描述在E_γ=6.13 MeV能点对NaI(Tl)γ探测器的探测效率的绝对刻度方法;给出了实验结果并对实验误差进行了讨论。     

钍样品放射性平衡判断方法

天然样品中~(232)Th的含量或活度通常可采用γ能谱法测量其子体~(212)Pb来计算,其测定准确度取决于~(232)Th系列的放射性是否平衡。然而,很多实际样品中~(232)Th系列并不一定处于平衡状态,这就使得γ能谱法测定此类样品具有测定结果偏离真值的风险。通过研究总α放射性比活度和各个γ核素放射性比活度的理论关系,来判断样品钍系列是否处于放射性平衡状态,并通过硫酸浸泡打破天然平衡体系,实验验证了该判断方法的可行性。     

典型VDMOSFET单粒子效应及电离总剂量效应研究

利用252Cf源和60Coγ射线源对典型VDMOSFET进行单粒子效应和电离总剂量效应模拟试验,给出典型VDMOSFET的单粒子烧毁(SEB)、单粒子栅穿(SEGR)效应测量结果以及不同偏置条件下漏源击穿电压随辐照剂量的变化情况。结果表明,VDMOSFET对SEB和SEGR效应以及VDMOSFET漏源击穿电压对电离总剂量效应比较敏感,空间应用时需重点考虑VDMOSFET的抗SEB和SEGR能力;考核VDMOSFET的抗电离总剂量效应能力时对阈值电压和击穿电压等敏感参数应重点关注。     

辐照加工宝石的放射性测量研究

利用辐照进行天然宝石改色,能显著提升宝石的观赏价值和商业价值。但经反应堆辐照后的宝石含有人工放射性核素,会对相关人员产生照射。本文利用γ能谱分析方法对辐照宝石进行了直接放射性测量。采用实验和蒙特卡罗模拟相结合的方法分析了辐照宝石的几何结构、密度对其γ能谱测量准确性的影响,得到探测效率与能量、样品质量的修正公式,从而实现了无需磨制过程的辐照宝石放射性的γ能谱准确测量。     

~(238)Pu低能光子源衰变γ能谱识别

利用同轴P型高纯锗探测器,对X荧光分析的~(238)Pu低能光子源进行γ能谱分析,并对~(233)Pa、~(224)Ra、~(212)Pb、~(212)Bi及~(208)Tl的特征γ射线进行分析,确定上述核素的来源。其中,~(233)Pa是生产~(238)Pu的原料237 Np的衰变产物,~(224)Ra、~(212)Pb、~(212)Bi及~(208)Tl均为生产~(238)Pu的副产物~(236)Pu的衰变子核。能量为350、440、844、1 014、1 130、1 266、1 368、1 454keV的γ射线是α粒子轰击源封装材料引起原子核库伦激发或γ射线照射周边环境引起核激发产生。进行效率刻度后,使用γ能谱法计算各放射性核素的活度,并根据放射性平衡计算各放射性核素的质量。通过对~(238)Pu源γ能谱的分析,建立计算放射性同位素活度与质量的方法。     

Modifications in structural, cation distribution and magnetic properties of Co gamma irradiated Li-ferrite

Polycrystalline samples of Li_0.5Fe_2.5O₄ ferrite precursor were prepared by conventional standard double sintering ceramic technique and then irradiated with three different doses of ⁶⁰Co gamma rays. The crystal structure and phase orientation of the irradiated and unirradiated samples of Li_0.5Fe_2.5O₄ ferrite was done by using X-ray diffraction technique at room temperature. The lattice parameter of the studied samples increased due to the formation of Fe²⁺ ions under the ionizing effect of gamma radiation. The strain in the materials due to the irradiation was calculated from XRD data. Scanning electron microscope (SEM) studies indicate that the irradiation causes amorphization, especially at the grain boundaries. The cation distribution was calculated from XRD data analysis. By using cation distribution structural parameters such as theoretical lattice constant, ionic radii of available sites and the oxygen parameter ‘u’ have been calculated. The estimated cation distribution and other structural parameters shows strong influence of gamma rays on polycrystalline Li-ferrite. The magnetic properties of irradiated and unirradiated lithium ferrite were performed by using pulse field hysteresis loop technique at room temperature. Electrical properties such as diffusion coefficient and dielectric properties were carried out with the influence of gamma irradiation. Activation energy of diffusion process decreased after irradiation. The increase of diffusion coefficient with increasing dose rate of gamma irradiation was reinforced by the increase of Fe²⁺ ions and the displacement of metal ions from its original sites under the effect of gamma irradiation.     

重离子和γ辐照硼硅酸盐玻璃的辐照效应对比

为研究玻璃固化体在不同辐照方式下的宏观和微观结果及其对应关系,使用重离子和γ辐照硼硅酸盐玻璃,分别测量了辐照后硼硅酸盐玻璃的硬度和模量变化。发现在γ辐照条件下,直到吸收剂量达到6×10⁶ Gy,硼硅酸盐玻璃的宏观性质（硬度和模量）均未发生明显改变。在Xe离子辐照条件下,当辐照剂量达到0.1 dpa时,硬度和模量减少达饱和值。此外,测量了γ辐照后的硼硅酸盐玻璃的吸收光谱,得到了辐照后硼硅酸盐玻璃带隙随吸收剂量的变化规律,讨论了辐照产生的微观缺陷来源和产生机理。发现重离子辐照产生的硬度和模量的下降主要来源于玻璃网络结构的断裂,而重离子的核能量沉积是造成网络体结构断裂的主要原因。结合γ辐照样品的吸收光谱结果,通过对比γ射线和重离子辐照后的样品硬度和模量变化不同趋势可发现：γ辐照会在硼硅酸盐玻璃中产生微观缺陷（非桥氧空位色心等）,这些缺陷主要来源于网络体末端与钠相连的键的断裂。而网络体末端的断裂不影响硼硅酸盐玻璃的网络体结构,所以γ辐照产生的缺陷不会引起硼硅酸盐玻璃的硬度和模量变化。     

放射源壁厚被动识别的可行性分析

放射源壁厚是强γ辐射环境γ定量测量和军控核查中所关注的一个重要参数。本工作根据γ全能谱中同一放射核素的不同能量γ射线出射强度比与源壁厚的关联性研究了源壁厚的被动γ测量方法。实验测量的源壁厚与真值基本吻合,表明通过被动γ法测量源壁厚是可行的。     

ST401闪烁探测器γ能量响应的实验研究

对脉冲γ射线束测量中常用的一种由塑料闪烁体ST401组成的电流型闪烁探测器的γ能量响应进行了实验研究。利用反应堆、加速器等多种手段产生一系列准单能的γ射线,实验标定了包括¹³⁷Cs、⁶⁰Co在内的13个能量点,得到了ST401闪烁体相对灵敏度随入射γ射线能量的变化曲线。实验值与理论计算结果进行了比较,二者在不确定度范围内基本一致。     

含纤维素辐照食品的ESR法研究

60Co发出的γ射线于0,0.5,1.0,3.0,5.0,10.0kGy剂量范围对干燥的红辣椒粉、花生和提取出的草莓籽进行了辐照处理,用电子自旋共振(Electron spin resonance,ESR)来分析研究信号强度与辐照剂量的关系以及相关性R2.结果表明,三种样品的ESR信号与剂量正相关,其中草莓的ESR信号随剂量增长最慢,红辣椒粉的计算最为精确,花生的次之.含纤维素辐照食品的剂量与ESR信号关系清晰,可作为建立ESR方法检测辐照食品的方法.     

Development of a dose-adjustable α-particle irradiation facility for radiobiological studies

Bystander effects induced by low-dose or low dose-rate radiation have put a great challenge to the traditional model for radiation protection. In order to get a better assessment of the adverse effects of radiation, especially the low-dose radiation risk in environment, a radioactive irradiation facility, by which the dose and dose-rate to the biological targets can be controlled by rotating the sample bracket and changing the space between the radioactive source and the targets, was developed. The energy of our α-radioactive source (241Am) is measured averagely 3.5MeV at the position of the irradiated sample. The dose rate was measured by using a silicon surface barrier detector and a CR39 particle track detector. A dose rate ranging from 0.045 cGy/s to 1.07 cGy/s can be obtained by changing the space length from the radioactive source to the sample dish.     

Effect of oxygen on gamma irradiation of polypropylenes studied by positron annihilation spectroscopy

The aim of this paper is to study the effect of oxygen on the microstructure of PP irradiated by gamma ray. The released gases from the sample in irradiation process were measured by gas chromatography. The results showed that the hydrogen release from the irradiated PP is independent on the irradiation atmosphere. It is only dependent on the irradiation dose that could be interpreted by a simple model. The microstructure of PP samples irradiated under different atmospheres is studied by positron annihilation spectroscopy. It is found that there are two sub-peaks in free volume distribution of PP irradiated under helium, while only one peak in the distribution of PP irradiated under air. It is the direct evidence to the argument that the new voids are formed in the irradiation process under inert gas and the oxygen may induce the voids to merge together. The influence of oxygen on the crystalline of PP irradiated by gamma is also discussed.     

Enhancement of the electrical performance of poly(vinyl) alcohol by doping with chlorophyll and gamma irradiation

The electrical properties of poly(vinyl) alcohol (PVA) have been improved pronouncedly by doping with chlorophyll (Chl) and gamma irradiation. PVA/Chl films have been prepared and irradiated with γ-rays at dose levels of 10, 20, 30, 50, 70, 100, 150, 200 and 250 kGy. The crystalline and chemical structures of the samples have been studied using XRD and FTIR techniques. Also, the direct current electrical conductivity and the dielectric constant and loss have been determined for the proposed samples before and after gamma exposure. It is clearly shown that the electrical conductivity of PVA films was increased two orders of magnitude due to chlorophyll doping and about fifteen times due to gamma irradiation. Considering the dielectric constant and loss, their values were shown to increase significantly due to PVA doping with chlorophyll. The obtained results can be attributed to the existence of the conducting Mg atom, as well as, the conjugated double bonds in the chlorophyll. Moreover, the gamma irradiation of PVA/Chl, over 50 kGy, improves also this electrical performance. Therefore, the study suggests the possibility of the utilization of the gamma irradiated PVA/Chl films in different electronic applications.