Koster-Ammerlaan M J J, Bode P, Winkelman A J M
Reactor Institute Delft, Delft University of Technology, Mekelweg 15, 2629 JB Delft, The Netherlands.
J Radioanal Nucl Chem. 2012;291(2):569-572. doi: 10.1007/s10967-011-1241-5. Epub 2011 Jun 18.
The assumption that the shape of the epithermal neutron spectrum can be described, in any research reactor, by the 1/ function is a fundamental starting point of the standardization. This assumption may be questioned from a reactor physics viewpoint. The type of moderator, the existence of neutron reflectors, the additional production of (γ, ) neutrons and resonance capture by construction materials may be different for each reactor, with consequences for the shape of the neutron spectrum. This dependency may explain that various practitioners reported contradicting experiences with the use of Zr-Au flux monitors for the determination of the α-parameter. An objective view on the influence of the design of the reactor and irradiation facility on the shape of the neutron spectrum can be obtained by modeling. This has been applied in the Reactor Institute Delft for reactor configurations in which the irradiation facilities face the fuel elements with the presence of beryllium reflector elements. The Monte Carlo calculations indicate a distortion of the 1/ relationship at the higher energy edge of the epithermal neutron spectrum. This distortion is attributed to the formation and thermalisation of both photoneutrons and (, 2) produced fast neutrons in the beryllium, and has a direct impact on the resonance activation of Zr, other than represented by the 1/ function. The obtained relationship between neutron flux and neutron energy was also used for estimating the -value and compared with the value obtained by the Delft Cr-Mo-Au flux monitor.
在任何研究堆中，超热中子能谱形状都能用1/v函数描述这一假设是标准化的基本出发点。从反应堆物理角度来看，这一假设可能受到质疑。每个反应堆的慢化剂类型、中子反射层的存在、（γ，n）中子的额外产生以及结构材料的共振俘获情况可能不同，这会对中子能谱形状产生影响。这种依赖性或许可以解释为何不同从业者在使用锆 - 金通量监测器测定α参数时报告了相互矛盾的经验。通过建模可以客观地了解反应堆和辐照设施设计对中子能谱形状的影响。代尔夫特反应堆研究所已将此应用于辐照设施面对带有铍反射层元件的燃料元件的反应堆配置。蒙特卡罗计算表明，在超热中子能谱的较高能量边缘，1/v关系存在畸变。这种畸变归因于铍中光中子和（n，2n）产生的快中子的形成与热化，并且除了由1/v函数表示的情况外，对锆的共振活化有直接影响。所获得的中子通量与中子能量之间的关系也用于估算α值，并与代尔夫特铬 - 钼 - 金通量监测器获得的值进行比较。
