从裂变产物中快速萃取分离^(94)Sr的研究

Research on Fast Extraction Separation of ^(94)Sr from Fission Products

为提高短寿命裂变产物核素^(94)Sr核参数的测量精度,需要快速从裂变靶中分离出较高活度的放化纯样品。本工作研究了SISAK系统快速分离Sr的工艺,建立了SISAK系统从裂变产物中快化分离^(94)Sr的流程。经热实验验证,靶量14μg的235U辐照20 s,可在100 s内获得^(94)Sr样品,并可测得明显且无干扰特征峰,流程对Sr的化学回收率大于80%,对主要干扰核素的去污因子均大于10~2。本研究采用“堆辐照+跑兔送样+SISAK分离”联用的技术,获得了可用于测量的^(94)Sr样品,对半衰期为分钟量级的裂变产物的核参数测定与衰变特性研究具有重要参考价值。

The measurement of nuclear parameters(especially fission yield)of short-lived fission products plays an important role in studying nuclear structure models,or fission reaction theory and determining nuclear fuel burnup.Its accuracy mainly depends on the separation ability of fission products and the measuring precision of instruments.When using off-line method to measure the yield,it is hard to implement as the life-time of some fission products are too short or too long,and consequently the yield of about a quarter of the mass chain could not achieved.In order to improve the measurement accuracy of nuclear parameters of short-lived nuclides in neutron-induced fission of uranium,it demands to separate high-activity and radiochemical-purity samples from fission targets rapidly.SISAK system is a fast chemical separation system for short-lived nuclides based on AKUFVE.Under a certain suitable chemical separation system,the extraction equilibrium time can be obviously improved and the phase separation can be completed quickly.And that means SISAK has a positive effect on the rapid separation of short-lived fission products.In this work,two stages of centrifugal extraction unit were applied to form the SISAK system,and solenoid valves were installed in the liquid flow path.The opening and closing time of these solenoid valves was matched with the result extraction kinetics through the program.Consequently,the automatic operation of the separation procedure was fulfilled.^(94)Sr,one of the neutron induced uranium fission products,has a short half-life(75 s)and a high independent yield(4.3%),which was the suitable nuclide to verify the fast separation ability of SISAK system.The optimum extraction efficiency was obtained using 0.1 mol/L dicyclohexyl-18-crown-6-tetrachloroethane to extract strontium from aqueous phase of 1.0 mol/L nitric acid medium and back-extracting with 0.1 mol/L sodium citrate solution.In addition,the high speed stirring(65%to 70%of full revolution speed of 1400 r/min)made the two phases reaching extraction equilibrium in 10 s.A completely automated fast chemical separation procedure of strontium was established based on SISAK system.The target solution obtained by irradiating 14μg 235U for 20 s through the reactor could get the sample within 100 s,and the characteristic peak of ^(94)Sr can be detected obviously without interference by HPGeγspectrometer.The chemical recovery of Sr is better than 80%.This research used the“batch irradiation plus fast chemical separation”technique to obtain fission product samples with half-life of minutes,which is of great significance for the determination of nuclear parameters and the study of decay characteristics of fission products with half-life of minutes.