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本文提出了三种可能的物理因素,企图解释热中子对U235,Pu239的裂变中子谱中,在2-3兆电子伏附近出现的结构现象。首先讨论了核温度分布可能产生的影响,结果表明,连续的核温度分布是不会在能谱上出现有结构现象的;而在两个孤立的核温度情况,发现要在相当不合理的温度比,即T1/T2 ≥3 时才会在能谱上出现有结构现象。其次,考虑到在能谱的“蒸发”公式中应该用光学模型的吸收截面。在裂变的情况下,光学模型吸收截面在轻重碎片不同的能量位置出现巨共振,计算结果表明,目前裂变中子谱中2-3兆电于伏出现的结构现象,很可能是重碎片吸收截面中d波巨共振所引起。在考虑了一定的核温度分布以后,用光学模型吸收截面所计算的裂变中子谱在结构的大小和位置上,和实验符合得很好。再其次,我们考虑了中子从碎片中发射可能存在各向异性,发现它也可能在裂变中子谱上出现一定的结构现象,但是很为微弱。最后,作者提出了进一步澄清这些物理因素可能做的一些实验。An attempt is made to explain the observed structure phenomenon in the 2-3 Mev region of the spectra of the neutrons from the fission of U235 or Pu239 by the thermal neutron. Three possible causes for the effect are proposed and investigated. Firstly, . the effect of distribution of the nuclear temperature is studied. It is found that a continuous distribution of the nuclear temperature is unable to cause formation of any structure in the spectra, while two distinct nuclear temperatures would bring about such an effect; however, the value of the ratio of the two temperatures, i.e. T1/T2≥ 3 seems rather unreasonable. Next, in the "evaporation" formula of the energy spectra, the absorption cross section of the optical model is employed. In the case of fission, giant resonances of the absorption cross-section occur at various energies both for the light and for the heavy fragment. The calculation suggests that the structure phenomenon in the 2-3 Mev region of the spectra of the fission neutrons could very possibly be caused by the d-ware giant resonance in the absorption cross-section of the heavy fragments. By using the optical model absorption cross-section and taking a certain temperature distribution, the calculated spectra of the fission neutrons agree well with the experiment in magnitude as well as in position of the structure of the neutron spectra. Thirdly, the fact that the neutrons emitted by the fragments may be anisotopic, would also cause a structure phenomenon in fission neutron spectra; the effect is, however, rather small. Finally, some experiments for further clarification of the problem are proposed.
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