α+209Bi反应激发函数及厚靶产额计算

Calculation of Excitation Function and Thick Target Yield for α+209 Bi Reaction

  • 摘要: 211At是理想的靶向α治疗核素,209Bi(α,2n)211At是产生该放射性核素的重要核反应,精确可靠的核反应数据对于211At核素生产具有重要意义。209Bi(α,3n)210At反应产物210At核素会衰变为剧毒的210Po核素,掌握该反应信息也有助于安全有效提取211At产物。为获得上述反应相关信息,对国际核反应实验数据库(EXFOR)中相关实验测量数据进行了收集分析,使用EMPIRE程序,基于选取的合理光学模型势与能级密度参数对上述反应的激发函数进行了计算。通过理论计算结果与实验数据的比对,得到了209Bi(α,2n)211At、209Bi(α,3n)210At反应激发函数。在此基础上,计算了211At核素和210At核素的厚靶产额。最后得到了入射能量小于50 MeV能区范围内209Bi(α,2n)211At、209Bi(α,3n)210At反应激发函数推荐值及211At(医用放射性同位素)和210At(衰变子体为长寿命极毒性核素210Po)的厚靶产额推荐评价结果。210At核素厚靶产额计算结果表明,生产211At核素过程中,入射α粒子能量需低于29 MeV。此条件下210At与211At厚靶产额比小于10-5,满足国际放射防护委员会规定的职业摄入量,符合211At后续标记的要求。

     

    Abstract: The excitation function of the charged particle-induced reaction plays an important role in basic nuclear physics research, nuclear engineering design and nuclear technology applications, and which is also essential input information required in areas such as accelerator shielding and fusion reactor design, space radiation effects, radiation therapy and biomedical radioisotope production. In the field of tumor therapy, 211At is ideal targeted therapeutic nuclide for generating α-rays, which is prepared by α-particle bombardment of a bismuth target, and therefore the large-scale production of 211At nuclide relies on the information related to the data of 209Bi(α,2n)211At reaction excitation function and the thick target yield of the 211At nuclide. The production of 211At nuclide is accompanied with the production of 210At nuclide (the decaying substrates are highly toxic 210Po nuclides), and it is also necessary to analyze the data of excitation function for the 209Bi(α,3n)210At reaction and the thick target yield of the 210At nuclide for determining whether the prepared 211At product meets the requirements of the subsequent drug labelling. Based on the above background, the experimental data of 209Bi(α,2n)211At and 209Bi(α,3n)210At reaction excitation function in the Experimental Nuclear Reaction Database (EXFOR) were compiled and analyzed. However, there are still divergency in the experimental data of the reaction excitation functions, especially for the 209Bi(α,3n)210At reaction, and the analyzed available experimental data are discontinuous in some energy region. For providing the reasonable and continuous data of the above two reactions, the relevant theoretical calculations were carried out based on the EMPIRE code. Through the comparison between the experimental data and the EMPIRE calculation results, the reasonable forms of optical potential parameters and level density parameters are chosen. With the enhanced generalized superuid model (EGSM) for level density in the EMPIRE code, the evolution data of the excitation functions of the above two reactions are obtained, and both of them are in general agreement with the analyzed experimental data. Based on the evolution data of 209Bi(α,2n)211At reaction excitation function, the thick target yield of the medical radioisotope 211At was calculated, and it is in good agreement with the related experimental data. Besides, the thick target yield of 210At (the parent nucleus of the highly toxic nuclide 210Po) was also studied. And the results show that the thick target yield ratio of 210At to 211At is less than 10-5 at Eα<29.0 MeV, which is lower than the prescribed occupational intake and meets the requirements for 211At subsequent labelling.

     

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