^(211)At干馏装置研制及分离工艺研究

Development of Dry Distillation Equipment and Separation Process for Production of^(211)At

^(211)At是一种α核素,其半衰期为7.2 h,不仅适用于α靶向内放射治疗,也可替代长半衰期核素用于α辐解的研究。为解决现有^(211)At干馏工艺产额低、稳定性差的问题,本研究优化设计了^(211)At干馏生产工艺,集成了一套半自动化^(211)At干馏分离装置。采用碘干馏模拟实验确定了影响干馏分离的主要影响因素,改进得到了简便可行的^(211)At干馏分离工艺步骤。^(211)At干馏分离结果表明:当加速器α束流强度为20μA、能量为28.5 MeV时,轰击Bi靶4 h后,^(211)At的3次平均产额为17.87 mCi(6.61×10^(8) Bq),产品核纯度>99.9%,无Bi、Cu等杂质。^(211)At收率达98%以上,分离耗时45~60 min。本研究不仅为各类^(211)At应用工作的开展垫定了良好的基础,也可为后续^(211)At干馏自动化装置的研制提供参考。

With a half-life of 7.2 h,the decay of^(211)At producesαparticles that have a limited range in tissues(55-80μm),equivalent to approximately 6-8 cell widths.Its LET value of 98.84 keV/μm is very close to the optimal LET value(100 keV/μm)for effective internal radiation therapy,exhibiting strong cytotoxicity.Consequently,^(211)At is considered the most suitableαemitting isotope for targeted internal radiation therapy.It is also used as an alternative internal radiation source forαirradiation studies involving extractants and similar substances,replacing long-lived nuclides such as 238/239 Pu and 241 Am.However,due to the limitations in^(211)At yield,the maximum irradiation dose is difficult to increase,imposing constraints on irradiation dosage.Hence,it becomes crucial to enhance the radiochemical separation yield of^(211)At,whether for tumor-targeted therapy orαirradiation investigations.The production of^(211)At is typically accomplished using a cyclotron through the 209 Bi(α,2n)^(211)At reaction.And the radiochemical separation techniques employed for purification^(211)At primarily involve wet and dry distillation methods.Nonetheless,the current dry distillation methods have certain drawbacks,including unstable yield and the requirement for physically stripping irradiated bismuth from the target substrate,which poses a risk of nuclide escape.To solve these issues,a dry distillation process for production of^(211)At with an integrated semi-automatic dry distillation separation equipment was designed and optimized in this paper.The main influencing factors on dry distillation separation were determined using iodine as a simulation for astatine due to their similar chemical character,and feasible steps for the^(211)At dry distillation separation process were improved.It is found that once the furnace temperature is capable of vaporizing the target product,the key factors influencing the dry distillation process revolve around carrier gas velocity,holding time,and vacuum conditions.The results of^(211)At dry distillation separation show that when theαbeam intensity of accelerator is 20μA,αenergy is 28.5 MeV,and the Bi target is bombarded for 4 h,the^(211)At yield of separated by the equipment for single run can reach more than 17.87 mCi(6.61×10^(8) Bq).The nuclear purity of the prepared^(211)At is more than 99.9%,and free of impurities such as Bi and Cu.The integrated semi-automatic equipment has a recovery rate of over 98%for^(211)At in a separation time of 45-60 min.