BRISOL钾同位素放射性核束的产生

Production of Potassium Isotope Radioactive Ion Beam at BRISOL Facility

北京放射性核束装置在线同位素分离器(BRISOL)采用一台100 MeV回旋加速器提供的最大200μA的质子束打靶在线产生放射性核束,其最高质量分辨率好于20000。2015年,BRISOL装置建成并使用0.5μA质子束轰击氧化钙靶产生了^(37)K^(+)、^(38)K^(+)放射性核束,其中^(38)K^(+)的产额为1×10^(6) pps。为了提高氧化钙靶产生钾放射性核束的产额以满足物理用户需求,BRISOL于近期开展了氧化钙靶的在线实验。实验中使用氧化钙靶产生了^(36~38)K^(+)、43 K^(+)、^(45~47)K^(+)等多种放射性核束,同时将^(38)K^(+)的最大产额提高到了1.12×10^(10) pps。本文详细介绍氧化钙靶的研制及在线实验结果。

The Beijing radioactive ion beam facility isotope separator on-line(BRISOL)is a radioactive ion beam facility based on a 100 MeV@200μA proton cyclotron.The radioactive ion beams are produced by bombarding the thick target with proton beam provided by cyclotron.The mass resolving power of the BRISOL is better than 20000.The first radioactive beams of ^(37)K^(+)and ^(38)K^(+)were generated at BRISOL with CaO targets in 2015,and the maximum current of the ^(38)K^(+)beam is only 1×10^(6) pps when the current of proton beam is 0.5μA.The collinear laser spectroscopy experiments using ^(37-43)K^(+)beams will be carried out on BRISOL.The yields of ^(37-43)K^(+)would not be less than 1×10^(6) pps in the experiment.In order to fulfill the requirements,it is necessary to increase the yield of radioactive ion beams.So a series of studies were carried out.The first step is the targets preparation.According to the requirements of the ISOL targets,CaO was selected as the targets material for the generation of radioactive ion beams.The CaO targets were prepared by cold pressing methods with Ca(OH)2,carboxymethyl cellulose(CMC)and deionized water.CMC was added as a binder and pore-forming agent.Those materials were mixed in proportion and were cold pressed into desired shape.The thermal treatment was performed in a graphite furnace.After sintering,the targets were porous and then loaded into the targets container.The ion source with the ability of dual ionization mode,including surface ionization mode and FEBIAD ionization mode,was applied in the study.In order to improve the surface ionization efficiency for K,a 0.1 mm thick rhenium metal lining was installed on the inner wall of the cathode.Then an off-line experiment was conducted and the spectra of CaO targets were measured.The experimental results show that Ca^(+)is ionized when the cathode current is high enough.Therefore,it is necessary to optimize the cathode currents for larger yield of K^(+).After that,an on-line experiment at BRISOL was carried out.The experiment results show that the ^(36-38,43,45-47)K beams are produced successfully.The yield of ^(38)K^(+)is increased to 1.12×10^(10) pps when the proton beam is 10μA,the much larger yields are achieved through increasing proton intensities,optimizing both the structure of ion source and the targets working temperature.The development of CaO targets and the results of on-line experiment will be presented in this paper.